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Group III-Nitrides: fundamental research, optoelectronic devices and sensors

III-Nitrides are the basis of modern optoelectronics due to their successful technological implementation. This Symposium will review the challenges related to their extension towards UV and longer wavelengths (green, yellow, IR). Nanostructures and surface phenomena have opened new opportunities for sensorics, which will also be considered.


The symposium will be devoted to the new challenges associated to the extension of the III-nitride optoelectronic technology towards the ultraviolet, green/yellow, or infrared spectral regions, as well as the new opportunities in fields like sensorics opened by research on nanostructures and surface-related phenomena. In III-nitrde optoelectronics, difficulties appear associated to substrate availability (bulk AlN/GaN or silicon), strain engineering, alloy inhomogenities, strain pulling effects, and segregation. The polarization management has become an important issue for device design, and alternative crystallographic orientations are explored as a potential solution. Furthermore, new and more demanding applications have led to the reconsideration of the doping methods, turning back to Ge and Be for a deeper evaluation as alternative dopants. The incorporation of nanostructures (quantum dots, nanowires) promises performance improvement, but requires efforts to understand strain and doping in three-dimensional objects, and the now dominant role of surface states and surface-related phenomena, such as the effect of adsorbates (hydrogen, water, oxygen, nitrogen, ammonia). A new family of sensors based on III-nitride nanostructures aims at exploiting the effect of adsorbates on nanostructures, taking advantage of the internal electric fields, optical emission properties, and intrinsic robustness of III-nitrides. Other issue directly related to surface states is the contact behavior, since surface states and metal induced gap states (MIGS) can dominate the Schottky barrier height and complicate tunneling transport.

Hot topics to be covered by the symposium:

  • Recombination in nitride devices& material characterization: polarization, electric fields, segregation, mechanism of optical emission…
  • Dopants and defects: Mg, Be, Ge, DX formation, other point defects…
  • Nanostructures: nanowires, nanorods, quantum dots…
  • UV devices: emitters, photodetectors & FETs
  • Long wavelength emission - green, yellow and red LEDs and LDs
  • Substrates & strain relaxation
  • Optoelectronic devices
  • Surface properties: growth mechanism, surface states & sensor applications
  • Non-polar & semi-polar structures & devices

List of invited speakers:

  • Oana Malis (Purdue University, USA). III-nitrides for infrared intersubband optoelectronics
  • Valentin Jmerik (IOFFE Institute, St.Petersburg, Russia). AlGaN solar-blind UV photodetectors and high-efficiency mid-UV emitters grown by plasma-assisted molecular beam epitaxy
  • Martin Strassburg (OSRAM, Germany). GaN-based optoelectronics –state of the art
  • Moritz Brendel (Ferdinand Braun Institut, Berlin, Germany). Development of highly efficient AlGaN metal-semiconductor-metal photodetectors for the UVB and UVC spectral region
  • François Julien (Université Paris Sud, France). Flexible nitride nanowire optoelectronic devices
  • Yasuhiko Arakawa (The University of Tokyo, Japan). Advances in III-Nitride quantum dots for single photon emitters
  • Pawel Kempisty (Nagoya University, Nagoya, Japan). First-principles and thermodynamic analysis of the molecular processes at polar surfaces during GaN growth by HVPE/MOVPE
  • Chris Van de Walle (UCSB, Santa Barbara, USA). Impact of point defects on efficiency of nitride light emitters
  • Shigefusa Chichibu (Tohoku University, Sendai, Japan). Periodic compositional undulation in the m-plane AlInN epilayers grown by metalorganic vapor phase epitaxy on a GaN substrate
  • John L. Lyons (NRL, Washington, USA). Characterizing acceptor impurities in wide-band-gap III-nitrides
  • Lorenzo Rigutti (Université de Rouen, Saint Etienne du Rouvray, France). Correlating structural and optical properties in III-N nanoscale systems by atom probe-based multi-microscopy
  • Jürgen Christen (Otto-von-Guericke-University, Magbdeburg, Germany). Ultra High resolution TEM-CL nanostructures characterization
  • Robert Kudrawiec (Wrocław University of Technology, Poland). Contactless electroreflectance spectroscopy of III-N heterostructures: The built-in electric field and Fermi level position
  • Hideki Hirayama (RIKEN, Japan). Recent Progress in High-Efficiency Deep UV LED
  • Ian M. Watson (University of Strathclyde, Glasgow UK). III-nitride micro-LEDs for visible light communication at multi-Gb/s rates
  • Motoaki Iwaya (Meijo University, Japan). Characterizations of AlGaN/GaN based electron beam pumped laser
  • Michal Bockowski (Nagoya University, Nagoya, Japan). Growth and Characterization of Bulk HVPE-GaN. Pathway to Highly Conductive and Semi-Insulating GaN Substrates
  • James S. Speck (UCSB, USA). Role of MBE in the Development of GaN Optoelectronics
  • Hutomo S. Wasisto (Braunschweig University, Germany). High-aspect-ratio 3D GaN nanostructures for optoelectronic sensor platforms and vertical transistors
  • Ramon Collazo (North Carolina State University, Raleigh, USA ). Alternatives for point defect reduction in MOCVD Al/GaN
  • Klaus Thonke (Universität Ulm, Germany). Optical transitions in AlN and GaN involving deep levels
  • Robert Taylor (University of Oxford, UK). Non-polar Nitride Single Photon Sources
  • Tao Wang (University of Sheffield, UK). Development of overgrown non-polar and semi-polar GaN for photonics and electronics
  • Dabing Li (Chinese Academy of Sciences, Changchun China). AlGaN-Based Deep Ultraviolet  Detectors
  • Detlef Hommel (Wroclaw Research Center EIT+, Wroclaw, Poland). Deep UV emitter based on AlGaN: State of art and challenges
  • Tadeusz Suski (Institute of High Pressure Physics, Warsaw, Poland). Pecularities of InGaN/GaN Structures with Extremly Thin Wells and/or Barriers
  • Benjamin Damilano (CRHEA-CNRS Valbonne, France). Yellow-red emission with InGaN/(Al)GaN quantum wells, impact of Auger effect

List of scientific committee members:

  • Nicolas Grandjean (EPFL, Switzerland)
  • Enrique Calleja (Universidad Politecnica de Madrid, Spain)
  • Martin Stutzmann (TU München, Germany)
  • Philomela Komninou (Aristotle University of Thessaloniki, Grece)
  • Rachel Oliver (University of Cambridge, UK)
  • Izabella Grzegory (IHPP PAS, Warsaw, Poland)
  • Hiroshi Amano (Nagoya University, Nagoya, Japan)
  • Zlatko Sitar (NCSU, Raleigh, USA)
  • Marek Godlewski (IP PAS, Warsaw, Poland)


Selected papers will be published in Physica Status Solidi (Wiley-VCH)

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Session 1: Long wavelength emission - green, yellow and red LEDs and LDs : Agata Kaminska
Authors : B. Damilano
Affiliations : Université Côte d'Azur, CNRS, CRHEA, France

Resume : The efficiency of light emitters based on InGaN quantum wells (QWs) is very high for blue emission. Extending the wavelength emission to yellow or red while keeping a high efficiency is challenging due to the difficulty to obtain InGaN alloys with a large composition and a good quality. A fine control of the QW parameters (thickness, In composition) is mandatory. Some strategies relying on polarization and strain engineering can be used to improve the quality of these structures. We will discuss the impact of Auger effect on the carrier recombination of yellow and red -emiting InGaN QWs and compare this behavior with blue emitting QWs. Finally, we will show that by combining different InGaN QWs in a same LED structure, white light emission can be obtained without the help of phosphor conversion.

Authors : Ian M . Watson
Affiliations : Institute of Photonics, Department of Physics, University of Strathclyde, G1 1RD, UK

Resume : Visible light communication (VLC) is of growing importance in areas including free-space indoor applications (including LiFi), short-range plastic fibre links, and underwater asset management. Micro-pixellated LEDs based on conventional III-nitride epistructures offer great potential and versatility as VLC sources. The dimensions of individual emitting elements, with diameters in the 10-100 micron range, enable intrinsically high modulation bandwidths of several hundred MHz. Data streams are encoded by applying a small modulation to a dc background, meaning that the relation between mean carrier lifetime and current density can be exploited to obtain fast dynamics. The use of advanced digital encoding schemes is also critical in achieving data transmission rates in the multi-Gb/s regime, which can be further enhanced by multiplexing schemes employing different wavelengths and/or spatial dimensions. The micro-pixellated LEDs for VLC are fabricated as dense 2D arrays, and designs can be customised and optimised for various modes of operation and electronic control. Driving schemes successfully demonstrated include direct flip-chip bonding of backside-emitting LED arrays to custom silicon CMOS drive chips.

Authors : M. H. Kim1, K. Nokimura1, Y. Kurisaki1, M. Takebayashi1, H. Shibuya1, K. Sasai1, S. Kamiyama1, T. Takeuchi1, M. Iwaya1, and I. Akasaki1,2
Affiliations : ;1Department of Materials Sciences and Engineering, Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468-8502, Japan. ;2Graduate School of Engineering, Akasaki Research Center, Nagoya University, Nagoya 464-8601, Japan.

Resume : We demonstrated 450 nm multi-quantum-shell (MQS) three-dimension (3D) light-emitting diodes (LEDs) fabricated on high-quality n-Al0.03Ga0.97N templates using metalorganic chemical vapor deposition (MOCVD) and selective area growth (SAG) method. The growth and characterization of GaN nanowires (NWs) on the hole-shaped-patterned n-Al0.03Ga0.97N templates have been investigated. We focus on that to study n-GaN nanostructure formation and growth behavior by manipulating the growth temperature, and the growth pressure. We investigated the change in the NW profile evolution in relation to the reactor pressure from 200 mbar to 380 mbar and the growth temperature from 950 °C to 1100 °C. We have found that as the growth pressure increases, the vertical-to-lateral growth rate of NWs becomes larger, the NW array uniformity improves and the amount of parasitic growth is reduced as well. Additionally, a lower growth rate of {11(_)01} m-plane is observed at a higher growth temperature. We clearly observed that most dislocations were filtered by the SiO2 mask and defect-free penetrated the inner core of the n-GaN NWs. Experiments are also performed to support the proposed mechanism. We have also found that the suppression of lateral growth while maintaining vertical growth is necessary for NW formation. Furthermore, the crystalline and optical properties of the MQS 3D 450nm LEDs are demonstrated in detail. Therefore, the results of this study are considered to contribute to understanding of the emission properties of the 3D LEDs, thereby helping to achieve highly efficient devices through further control of the growth and fabrication.

10:15 Coffee break    
Session 2: UV devices: emitters, photodetectors & FETs I : Motoaki Iwaya
Authors : V.N.Jmerik, D.V. Nechaev, A.A. Toropov, E.A.Evropeitsev, S.V. Ivanov
Affiliations : IOFFE Institute, Politekhnicheskaya, 26, Saint-Petersburg, Russia

Resume : We consider plasma-assisted molecular beam epitaxy (PA MBE) as a promising epitaxial technology for the implementation of solar-blind photodetectors and UV emitters of spontaneous and stimulated emissions within wavelengths less than 300nm. First, the main features of growth kinetics of bulk AlGaN layers and quantum well (QW) heterostructures by PA MBE at the metal-rich stoichiometric conditions are analysed taking into account of relatively low growth temperatures (<700C) and possibility to control the Al content in AlGaN by means of rapid variation of Al/N2-activated flux ratio. Unrivalled possibilities of this technology on controlled fabrication of QW structures with the well thickness varied from several to fractional monolayer (MLs) that efficiently emit in mid-UV range down to wavelengths of 236 nm under optical and electron-beam pumping are demonstrated. The optimum design of the AlGaN QWs and technological parameters of their growth are discussed to ensure maximum internal quantum efficiency of QW structures. Various approaches used in PA MBE of (Al,Ga)N heterostructures grown on c-Al2O3 substrates for lowering the threading dislocation densities down to ~108 -109cm-2 are discussed. The problems of p-type doping of AlxGa1-xN layers with high Al-content are considered and the effectiveness of the polarization doping for realization of solar-blind p-i-n photodiodes and photocathodes with a responsivity at wavelengths less than 260-280 nm is demonstrated.

Authors : Dabing Li, Xiaojuan Sun, Ke Jiang
Affiliations : State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China; University of Chinese Academy of Sciences, Beijing 100039, People's Republic of China

Resume : AlGaN-based deep ultraviolet (DUV) detectors have attracted much attention due to its great potentials for many applications. However, the performances of AlGaN based DUV detectors are far from the expectation. The basic problem is the quality of AlGaN based materials. The structure of the DUV detectors also should be optimized. In our previous work, we proposed the two-step growth method to grow AlN/Sapphire templates. To further improve the quality of AlN templates, regrowth of HVPE AlN/sapphire template via MOCVD and high temperature annealing processing on AlN had been studied. Meanwhile, we also did some efforts on optimizing the structure of AlGaN based DUV detectors. Surface plasmon was introduced into AlGaN detectors and the performance of the detectors were enhanced greatly. The physical origin of this enhancement was revealed by Kelvin Probe Force Microscopy (KPFM). The detail of the work will be presented at the conference. This work was supported by the National Key R&D Program of China (2016YFB0400101, 2016YFB0400900), the National Natural Science Foundation of China (grant nos 61574142, 61322406).

Authors : H. K. Cho 1, I. Ostermay 1, U. Zeimer 1, J. Enslin 2, M. Guttman 2, T. Kolbe 1 A. Knauer 1, T. Wernicke 2, S. Einfeldt 1, M. Weyers 1, M. Kneissel 1,2
Affiliations : 1 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany 2 Technische Universität Berlin, Institute of Solid State Physics, Hardenbergstr. 36, EW 6-1, 10623 Berlin, Germany

Resume : AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) are promising devices that could replace fluorescent lamps in various applications, including sterilization, water purification, medical diagnostics, phototherapy and UV curing. One approach to improve the performance of DUV LEDs is to increase the light extraction efficiency (LEE) by using highly UV-reflective contacts on the p-side of the bottom-emitting LEDs. In this study, we propose a new highly reflective p-contact for DUV LEDs. It combines Al as a UV-reflector with a contact material such as Pd as the ohmic contact material to p-GaN. The contact is formed spontaneously from a layer structure by annealing which results in spatially separated areas one with a high UV-reflectivity and the other one with a reasonable contact resistivity. The contact was tested in flip-chip mounted DUV LEDs emitting at 305 nm. Different Pd-Al metal stacks were annealed and a reflectivity of 82 % was obtained in the UV-B range (280~320nm) which is about two times of the value measured for standard Pd contacts (43%). The high reflectivity is attributed to the formation of an Al phase and a Pd4Al phase in the annealed contact. Incorporating of the reflective contact in a DUV LED allowed to increase the optical power at a current of 20 mA by 30 %. At the same time, however, the operation voltage of the LEDs increased significantly which is attributed to the diffusion of Al towards the GaN surface which is known to be detrimental for a low-resistance p-contact. To suppress the diffusion of Al interlayers such as Pt and alternative ohmic contact materials such as ITO have been studied to achieve an UV-reflective and a low-resistance p-contact, simultaneously.

Authors : Akhil S. Kumar, Dolar Khachariya, Kuldeep Takhar,Swaroop Ganguly, Dipankar Saha
Affiliations : Applied Quantum Mechanics Laboratory, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India

Resume : We have demonstrated lateral 1-D nanowire transistor controlled by a non-contacting side gate with air as dielectric. The nanowire is fabricated on AlGaN/GaN heterostructure by a top down approach using a combination of dry and anisotropic wet etching. The nanowires are site-controlled with high aspect ratio (20 µm/10 nm), thickness controllable and discrete. The gate is lithographically defined parallel to the nanowire on either sides and is electrostatically coupled to the channel from three sides similar to the Ω-gate. The effective control can be increased by placing the gate closer to the channel, increasing the height of the metal stack and a dielectric encapsulation of nanowire. Room temperature quantum effects is observed since the channel can be narrowed down to less than 10 nm so as inter sub-band separation becomes more than the thermal energy. The transfer characteristics shows rise in current with interleaved plateaus as the gate voltage changes. Oscillations are observed in the transconductance which is attributed to the quantum capacitance which dominates over geometric capacitance in 1-D systems. The output characteristic shows a non-linear and non-square law dependence of the saturation current with the gate voltage typical of a 1-D transistor. The gate leakage is found in pico-ampere (pA) range for positive gate bias and sub-threshold slope of 125 mV/decade is observed.

12:30 Lunch break    
Session 3: UV devices: emitters, photodetectors & FETs II : Tao Wang
Authors : D. Hommel
Affiliations : Wroclaw Research Center EIT+ Sp. Z o.o., Wroclaw, Poland

Resume : To be announced

Authors : Hideki Hirayama1, Yukio Kashima1,2, Eriko Matsuura1,2, Hideki Takagi3, Noritoshi Maeda1, Masafumi Jo1, Takeshi Iwai4, Toshiro Morita4, Mitsunori Kokubo5, Takaharu Tashiro5, Ryuichiro Kamimura6, Yamato Osada6
Affiliations : 1-RIKEN, 2-1 Hirosawa Wako, Saitama, 351-0198 Japan; 2-Marubun Corporation, 8-1 Oodenma-cho, Nihonbashi, Chuo Ward, Tokyo, 109-8577 Japan; 3-AIST, Tsukuba-East, 1-2-1 Namiki, Tsukuba, Ibaraki, 305-8564 Japan; 4-Tokyo Ohka Kogyo Co., Ltd. 150 Nakamaruko, Nakahara, Kawasaki, Kanagawa, 211-0012 Japan; 5-Toshiba Machine Co., Ltd. 2068-3, Ohoka, Numadu, Shizuoka, 410-8510 Japan; 6-ULVAC, Inc. 2500, Hagizono, Chigasaki, Kanagawa, 253-8543 Japan

Resume : AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) are attracting much attention due to their wide area application fields such as water purification, sterilization, skin cure, resin courting, printing, and so on. However, the external quantum efficiency (EQE) of DUV LED is still much lower than that of InGaN-based blue LEDs. One of the targets for commercially available DUV LED is to achieve higher efficiency than that of mercury lamp (20%). It is required to improve poor light-extraction efficiency (LEE) to realize efficient DUV LED. In this work, in order to improve LEE, we introduced transparent p-AlGaN contact layer and highly-reflective electrode, and also integrated lens with flip-chip (FC) DUV LED. We prepared FC DUV LEDs with p-AlGaN transparent contact layer and highly-reflective (70%) Rh electrode, those were supplied by DOWA ELECTRONICS MATERIALS CO., LTD. We observed drastic increase of EQE from 4 to 15.5% by taking place p-GaN by transparent p-AlGaN contact layer and by using highly reflective Rh electrode. Although the forward voltage was increased by about 4V by introducing p-AlGaN contact layer, wall-plug efficiency was increased from 3 to 6.5 %. Then, we bonded sapphire lens (D=3 mm) on the backside of sapphire of the FC. By integrating sapphire lens, we achieved maximum EQE of 20.1% and WPE of 9.6 % for 285 nm FC DUV LEDs. We also demonstrated that LEE of UVC LED was significantly enhanced by introducing highly-reflective photonic-crystal (PhC) fabricated on p-AlGaN contact layer and obtained maximum EQE of 10% under bare wafer measurement.

Authors : Christian Kuhn(1), Tolga Teke(1), Martin Guttmann(1), Arne Knauer(2), Konrad Bellmann(1), Carsten Hartmann(3), Andrea Dittmar(3), Jürgen Wollweber(3), Tim Wernicke(1), Matthias Bickermann(3), Markus Weyers(2), and Michael Kneissl(1,2)
Affiliations : 1) Technische Universität Berlin, Institute of Solid State Physics, Hardenbergstr. 36, EW 6-1, 10623 Berlin, Germany 2) Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany 3) Leibniz-Institut für Kristallzüchtung, Max-Born-Str. 2, 12489 Berlin, Germany

Resume : AlGaN-based light emitting diodes (LEDs) in the UVC spectral region can enable applications such as water treatment, bioanalysis, and gas sensing. In this paper we compare AlGaN heterostructures grown by metalorganic vapor phase epitaxy (MOVPE) on bulk AlN and sapphire substrates. Each substrate provides certain advantages and challenges, e.g., low threading dislocation density, but relatively poor UVC transparency for bulk AlN. In this study, the effect of the off-axis orientation α of the (0001) AlN on the surface morphology of MOVPE-grown AlN layers is investigated. It is dominated by multilayer step bunching for α > 0.35° and a transition to monolayer steps for α < 0.15°. By controlling the offcut of the substrates smooth epitaxial AlN layers with monolayer steps can be obtained enabling the realization of highly efficient UVC LEDs. The LED heterostructures consist of n-AlGaN current spreading layers, an AlGaN MQW active region, followed by a p-AlGaN superlattice and a p-GaN cap layer. The morphology of the LEDs as well as their strain state depends on the choice of substrate which may influence epitaxial growth and lead to slightly different AlN lattice constants. On-wafer electroluminescence measurements show a single emission peak at 270 nm and an output power of 0.5 mW at 20 mA for the transparent sapphire substrate. On the AlN substrate the LEDs reach an emission power of 0.08 mW at 20 mA measured through the 650 µm thick partially absorbing substrate.

Authors : Maria Spies 1, Jonas Lähnemann 2,3, Martien I. den Hertog 1, Pascal Hille 4,5, Jörg Schörmann 4, Jakub Polaczyński 1, Bruno Gayral 2, Martin Eickhoff 4,5, and Eva Monroy 2
Affiliations : 1 University Grenoble-Alpes, CNRS-Institut Néel, 25 av. des Martyrs, 38000 Grenoble, France 2 University Grenoble-Alpes, CEA-INAC-PHELIQS, 17 av. des Martyrs, 38000 Grenoble, France 3 Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, 10117 Berlin, Germany 4 I. Physikalisches Institut, Justus Liebig Universität Giessen, Heinrich-Buff-Ring 16, 35390 Giessen, Germany 5 Institut für Festkörperphysik, Universität Bremen, 28359 Bremen, Germany

Resume : Nanowire photodetectors attract scientific and industrial interests due to their low dimensionality, small electrical cross-section, and ultrahigh photocurrent gain. With the physically and chemically robust material GaN, single-nanowire ultraviolet (UV) photodetectors present a visible rejection as high as six orders of magnitude. In this study, we introduce a single GaN nanowire UV photodetector whose efficiency is improved by the insertion of a GaN/AlN superlattice within an asymmetric n/n+ doping profile. The application of negative bias leads to carrier collection from the nanowire stem in the UV-A range (330-360 nm), with the structure behaving as a standard nanowire photodetector. In contrast, positive bias results in an enhancement of carrier collection from the superlattice in the UV-B range (280-330 nm) and the responsivity is increased by about two orders of magnitude. The pronounced sub-linearity of the photocurrent response with illumination power is reduced, while the UV/visible contrast of more than six orders of magnitude is maintained. These findings have been confirmed by correlating electron beam induced current and photocurrent measurements, as well as transmission electron microscopy images on the same single nanowire, with three-dimensional simulations of the strain and band structure.

15:30 Coffee break    
Session 4: Optoelectronic devices : Shigefusa F. Chichibu
Authors : F. H. Julien, M. Tchernycheva, N. Guan, X. Dai, H. Zhang, V. Piazza, L. Mancini, A. Kapoor, J. Eymery, C. Durand
Affiliations : F. H. Julien; M. Tchernycheva; N. Guan; X. Dai; H. Zhang; V. Piazza; L. Mancini C2N-Orsay, UMR 9001 CNRS, University Paris Sud, Univ. Paris-Saclay, 91405 Orsay, France. A. Kapoor; J. Eymery; C. Durand CEA/CNRS/University Joseph Fourier, CEA, INAC, SP2M, 17 rue des Martyrs, 38054 Grenoble, France

Resume : Flexible electronics, flexible light sources, displays and solar cells are key emerging technologies with a high expected growth of the market share. Indeed, flexible devices offer new functionalities inaccessible with conventional technologies (e.g., rollable screens, bendable or implantable light sources, energy harvesters integrated in clothing, etc.). The conventionally used technology for flexible devices relies on organic materials. Despite their low cost, organic devices present significant drawbacks related to their short lifetime and relatively low efficiency in comparison with inorganic devices. There is a strong research effort to fabricate mechanically flexible devices based on inorganic semiconductors. In this talk I will present our recent progress towards flexible nitride nanowire devices: we propose a method to combine the high flexibility of polymer films with the high quantum efficiency provided by nitride nanowires. The lift-off and transfer procedure allow to assemble free-standing layers of nanowire materials with different bandgaps without any constraint related to lattice-matching or growth conditions compatibility. This concept therefore provides a large design freedom and modularity since it enables the combination of materials with very different physical and chemical properties, which cannot be achieved by monolithic growth. The properties of flexible nanowire blue, green, white and two-color LEDs will be discussed.

Authors : O. Malis
Affiliations : Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA

Resume : Intersubband transitions in the conduction band of nitride heterostructures have been intensively studied in recent years for infrared optoelectronic devices in the under-developed near- and far-infrared spectral ranges. Due to large electron effective mass, the nitride intersubband materials require the ability to fine-tune the atomic structure at an unprecedented sub-nanometer level. I will describe our work to understand, model, and control the fundamental underpinnings of light absorption and electrical transport in nitride heterostructures. Special attention will be given to the relationship between growth, structure, and optical properties in lattice-matched c-plane AlInN/GaN, and nonpolar AlGaN/GaN heterostructures. Substantial improvement of near-infrared intersubband absorption in c-plane AlInN/GaN superlattices grown by molecular beam epitaxy (MBE) was achieved through optimization of AlInN growth conditions, combined with judicious placing of the charge into delta-doping sheets. We also examined the correlation between structure and infrared optical absorption of m-plane AlGaN/GaN superlattices. We found that AlGaN layers with Al-composition above approximately 40% are kinetically unstable under metal-rich MBE growth conditions and segregate into islands atop AlN layers. Even under excess Ga flux, the effective growth rate of AlGaN is drastically reduced, likely due to suppression of Ga incorporation. The results of infrared intersubband absorption measurements will be compared with theoretical predictions of band structure calculations including many-body corrections.

Authors : T Wang
Affiliations : Department of Electronic and Electrical Engineering, The University of Sheffield

Resume : The last twenty years have seen major progresses on developing III-nitride based photonics and electronics, which are unfortunately mainly limited to III-nitrides on c-plane substrates. The polar orientation poses a number of advantages and also disadvantages for photonics and electronics. In terms of III-nitride based optoelectronics current GaN technology on c-plane substrates has approached its limits and thus the performance cannot be further improved in the very near future, while both theoretical and experimental studies suggest that semi-polar GaN is the only solution to break through the bottle-neck. Semi-polar GaN, in particular (11-22) GaN, is becoming increasingly important due to its advantages of reducing the spontaneous and piezoelectric polarization and exhibiting higher indium incorporation efficiency than either c-plane surface. This makes (11-22) semi-polar GaN be particularly important for achieving longer emission wavelength such as green and yellow emitters that have found wide applications in fabrication of phosphor-free white lighting sources, ultra-fast visible light communications (Li-Fi), polarized backlighting, and opto-genetics. However, semi-polar (11-22) GaN on industry-preferred substrates, such as sapphire, contains a high density of defects. Our group has successfully obtained (11-22) GaN with significantly improved crystal quality on 2 inch sapphire by developing a cost-effective overgrowth approach on regularly-arrayed micro-rods.1 In this presentation, I will demonstrate high performance semipolar (11-22) InGaN based LEDs overgrown on such GaN templates, emitting strong green, yellow, yellow-green and amber emission. III-nitride based semiconductors have also attracted wide attention due to an increasing demand on the fabrication of high frequency and high temperature electronics as a result of their advantages of high breakdown voltage and high saturation electron velocity. So far, AlGaN/GaN high-electron-mobility transistors (HEMTs) have been developed mainly based on the (0001) c-plane GaN system, where it is difficult to achieve normally-off operation due to the inherent high sheet carrier concentration induced as a result of spontaneous polarization. The growth of an AlGaN/GaN heterostructure along non-polar orientations is a simple and promising solution to overcome the problem by means of employing a standard modulation doping approach, where the sheet carrier density of the two dimensional electron gases formed at the interface of AlGaN and GaN can be controlled through optimizing the doping level in AlGaN. One of the major issues to achieve a non-polar AlGaN/GaN HEMT structure with good performance is due to the crystal quality of non-polar GaN. Currently, the crystal quality of non-polar GaN grown on sapphire or silicon is far from satisfactory compared to c-plane GaN. In this talk, I will demonstrate nonpolar (11-20) GaN with significantly improved crystal quality and an atomically smooth surface achieved by employing the above similar cost-effective patterning approach for the overgrowth on sapphire. It has been found that there exist significant differences between them in terms of the overgrowth mechanisms and the mechanism for defect reduction. Reference: 1. T. Wang, Semicond. Sci. Technol. 31, 093003 (2016)

Poster Session : -
Authors : Akira Kusaba(1), Guanchen Li(2)(3), Michael R. von Spakovsky(2), Yoshihiro Kangawa(1)(4)(5), Koichi Kakimoto(1)(4)
Affiliations : (1) Department of Aeronautics and Astronautics, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan; (2) Center for Energy Systems Research, Mechanical Engineering Department, Virginia Tech, Blacksburg, Virginia 24061, USA; (3) Department of Engineering Science, Oxford University, Parks Road, Oxford OX1 3PJ, UK; (4) Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan; (5) Center for Integrated Research of Future Electronics, Institute of Materials and Systems for Sustainability, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan

Resume : GaN is a promising material for the next generation of high power devices. To realize device-grade crystals, metalorganic vapor phase epitaxy (MOVPE) needs to be more precisely controlled. Thus, clearly understanding the elementary growth processes involved such as adsorption-desorption, which depends on surface reconstruction, is essential. In this study, we investigate the chemical adsorption of ammonia on GaN(0001) reconstructed surfaces under MOVPE conditions (N_ad-H+Ga-H and 3Ga-H on a 2x2 unit cell) using steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic-ensemble-based, first-principles framework that can predict the behavior of non-equilibrium processes even those far from equilibrium. The state evolution in SEAQT is a combination of reversible dynamics and irreversible relaxation where the former is based on the von Neumann equation and the latter on the principle of maximum-entropy production. SEAQT is an ideal choice to handle this problem on a first-principles basis since chemical adsorption is a highly non-equilibrium process. A result of the analysis shows that the probability of adsorption on 3Ga-H is higher than that on N_ad-H+Ga-H. This result also means that more hydrogen is produced on 3Ga-H because the adsorption reactions considered contain hydrogen as product for both surfaces. Such SEAQT modeling of elementary growth processes will lead to better control of MOVPE through the selection of preferable reconstructed surfaces.

Authors : Fabian Herrera, Jairo A. Rodriguez, Maria Moreno-Armenta
Affiliations : Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Carretera Tijuana-Ensenada No. 3918, A. Postal 360, 22860, Ensenada B.C., México; Grupo de Estudio de Materiales (GEMA), Departamento de Física, Universidad Nacional de Colombia, AA 5997 Bogotá, Colombia; Centro de Nanociencias y Nanotecnologia, Universidad Nacional Autónoma de México, Apartado Postal 356, Ensenada, Baja California, 22800, México

Resume : Interactions between graphene or its oxide with GaN ,have shown experimentally that could reduce the operational temperature at which transistors, LED’s and high potency diodes works. However theoretical papers that describe their physics are scarce. In previous works we estimated the feasibility of a graphene monolayer grew over GaN(0001) surfaces*. Here we will present Density Functional Theory (DFT) calculations, of the structure resultant from introduction of oxygen over graphene to obtain a graphene oxide monolayer. The unit cell used was 3√3•x3√3graphene/4x4(0001)GaN. We considered adsorption of a single O atom over the non-equivalent C due to their interaction with the substrate. The sites considered are: over Ga or N atoms, between two Ga, and some other sites. The total energy calculations show that the position between two Ga atoms is the preferred adsorption site. Then we introduce O up to four by unit cell. The introduction of O favors the match among the surfaces and the system changes its metallic character to a semiconductor one in relation to the O content. Finally we studied the adsorption of OH and different combinations of OHl and O. The results indicate that this could be a good method to fine tuning the gap. Acknowledgments: DGAPA project IN114817. A. Rodriguez for technical assistance. Job done at DGCTIC under project LANDCAD-UNAM-DGTIC-150.. References: *Espitia-Rico, M. et. al. Graphene monolayers on GaN (0001). Appl. Surf. Sci., 326:7–11 (2014).

Authors : Woo Tae Hong, Jin Young Park, Hyun Kyoung Yang, Jae Yong Je
Affiliations : Department of LED Convergence Engineering, Pukyong National University, Busan 485-47, Republic of Korea; Department of Radiological Technology, Dong-eui institute of technology, Busan 614-715, Republic of Korea

Resume : General white LEDs (WLEDs) are combined with blue LED chip and yellow emitting Y3Al5O12:Ce3 (YAG:Ce3 ) phosphor due to the its high efficiency and cheap cost. However, their lack of red emission occur a poor color-rendering index and a high color temperature that disturb further application. In order to improve the color rendering of the white-light, several approaches have been proposed: one is addition of the red-emitting component with the YAG:Ce3 -based WLEDs Therefore, blue-light excitable and red-emitting phosphors have been extensively studied such as nitride, sulfide and aluminate phosphor. Recently, Ca4(PO4)2O:Eu2 phosphors have been emerged due to the red emission with blue excitation. In the previous study, solid-state reaction only succeeded to synthesize Ca4(PO4)2O:Eu2 phosphors, due to the existence of oxygen in its chemical formula. The solid-state reaction requires a high sintering temperature, long heating time and subsequent grinding that results loss of emission intensity and high fabrication cost. In order to overcome these problem, using a sol-gel method is one of alternative because novel chemical compositions with excellent purity and relatively low reaction temperature can be synthesized. In this study, Ca4(PO4)2O:Eu2 phosphors were successfully synthesized by sol-gel method. The effect of synthesis temperature in crystallization, surface morphology and luminescence properties of the Ca4(PO4)2O:Eu2 phosphors were investigated.

Authors : Takahiro Yoshida,Takashi Egawa
Affiliations : Research Center for Nano-Devices and Advanced Materials, Nagoya Institute of Technology

Resume : 1. Introduction Over the years, a number of groups have studied AlGaN/GaN high-electron mobility transistors (HEMTs) owing to their attractive properties such as high breakdown voltage, high operating temperature, and high current density. A major goal of these researches is to replace Si power devices with AlGaN/GaN HEMTs. Two major problems of HEMTs are the use of Au-containing metal stacks and normally-on characteristics. Au-free metal stacks are required to fabricate AlGaN/GaN HEMTs in the conventional Si CMOS fabs because Au is contamination for the Si CMOS. The Au-containing metal stacks which require high annealing temperatures such as 850 °C cause rough surface morphology of ohmic contacts and thermal induced degradation of AlGaN/GaN HEMTs.[1] Therefore metal stacks which are Au-free and demand low annealing temperature are desirable. Normally-off characteristics are required for fail safe operation of power electronics applications. A recessed gate is an attractive method to realize normally-off characteristics.[2] As far as we know, there have been few reports about the HEMTs which have both Au-free metal stacks and normally-off characteristics.[3] In addition, the effect of low temperature annealing on characteristics of HEMTs with recessed gate have not been clarified yet. In this study, we report Au-free metal stacks which show low contact resistance at low annealing temperature, and the device characteristics of Au-free AlGaN/GaN metal-insulator-semiconductor (MIS) HEMTs with recessed gates. 2. Experimental methods The samples used in this work were the AlGaN/GaN heterostructures on a 6 in. Si substrates. A metal organic chemical vapor deposition was used to grow the AlGaN/GaN heterostructures which consist of 26.4 nm Al0.23Ga0.77N barrier layer and 400 nm GaN channel layer. The wafer was cut into small pieces for fabrication. The fabrication process started by isolation which was conducted with reactive ion etching, using BCl3. Gate recess was conducted with inductively coupled plasma dry etching, using BCl3/Cl2. Six etch durations are processed; 0, 210, 270, 330, 390, and 450 s. Etching depth and profiles were evaluated by atomic force microscope (AFM). For the gate dielectrics, 20-nm Al2O3 was grown by atomic layer deposition. Ti/Al/W metal stacks were used as Au-free ohmic contacts. They were deposited by sputtering, followed by lift-off. Ti/Al/Ni/Au metal stacks were also deposited as references using an electron beam evaporator. They were annealed at varying temperatures (350 – 850 °C) in N2. Finally, Ni/W gate contacts and Ti/Al pad electrodes were deposited by sputtering, followed by lift-off. The gate contacts were not annealed. It is notable that the process includes just one annealing to clarify the effect of low temperature annealing on AlGaN/GaN HEMTs. In this process, all metal deposits (ohmic, gate, and pad) were conducted in the last part of process. This is desirable to fabricate AlGaN/GaN HEMTs in the Si CMOS fabs in order to avoid heavy metal contamination. 3. Results and discussion The specific contact resistance ρc and sheet resistance Rsh were calculated using transmission line model (TLM). In the samples with Ti/Al/W metal stacks, ohmic characteristics were shown in samples which were annealed at 500 °C or more. The lowest ρc was shown in a sample which were annealed at 580 °C and was 2.8 × 10 -6 Ω cm2 (Contact resistance Rc = 0.43 Ω mm). The average Rsh was 563 Ω/sq. In the samples with Ti/Al/Ni/Au metal stacks, ohmic characteristics were shown in samples which were annealed at 650 °C or more. The lowest ρc was shown in a sample which were annealed at 850 °C and was 1.0 × 10 -6 Ω cm2 (Rc = 0.24 Ω mm). The average Rsh was 498 Ω/sq. Compared with Ti/Al/Ni/Au, Ti/Al/W metal stacks show slightly higher ρc. As described below, this increase have less influence on on-state resistance of AlGaN/GaN HEMTs. It is important to note that Ti/Al/W metal stacks require lower annealing temperature than Ti/Al/Ni/Au. This indicates that Ti/Al/W metal stacks can avoid thermal induced degradation of HEMTs. However, the samples with Ti/Al/W metal stacks showed unexpectedly higher Rsh. We consider that the Al2O3/AlGaN interface states, which can be reduced by high temperature annealing, decrease the electron mobility of two-dimensional electron gas. Surface morphology of annealed Ti/Al/W and Ti/Al/Ni/Au were confirmed by an optical microscope and AFM. Arithmetic average roughnesses (Ra) of Ti/Al/W and Ti/Al/Ni/Au were 4.7 and 33 nm, respectively. Ti/Al/Ni/Au metal stacks have rough surface morphology due to alloy of Al and Au induced by high temperature annealing, while Ti/Al/W metal stacks have mirror-like surface, which means that Al was not melted and maintained its shape. Transfer characteristics of AlGaN/GaN HEMTs were measured. The HEMTs have a gate-source distance Lgs = 4 μm, a gate length Lg = 2 μm, and a gate-drain distance Lgd = 4 μm. The depths of recessed gates were between 13.6 and 29.2 nm. In the HEMTs with Ti/Al/W metal stacks, positive Vth was achieved in samples which were recessed 25.7 nm or more. The maximum Vth was 1.5 V, and the maximum variation of Vth from the non-recessed sample to the recessed sample was +9.2 V. In the HEMTs with Ti/Al/Ni/Au metal stacks, positive Vth was not measured even in a sample which was recessed 29.2 nm. The maximum Vth was -0.6 V, and the maximum variation of Vth from the non-recessed sample to the recessed sample was +7.3 V. The reason of the difference in variation of Vth is not clearly understood at this point, but we consider the ohmic annealing affects interface states in Al2O3/AlGaN interface. On-state resistances calculated by I-V characteristics of AlGaN/GaN HEMTs with Ti/Al/W and Ti/Al/Ni/Au metal stacks were 11 and 10 Ω mm, respectively. This result indicates that the difference of ρc in the order of 10 -6 Ω cm2 have less influence on on-state resistance. 4. Conclusions We have studied the Au-free Ti/Al/W ohmic contacts on the AlGaN/GaN heterostructure. The minimum ρc is 4.2 × 10 -6 Ω cm2 (Rc = 0.50 Ω mm) with annealing at 580 °C, which is lower than that of the conventional Ti/Al/Ni/Au ohmic contacts. The surface morphology of annealed Ti/Al/W is smoother than that of Ti/Al/Ni/Au owing to the low annealing temperature. Applying the Ti/Al/W ohmic contacts to the AlGaN/GaN MIS-HEMTs with recessed gate, the positive variation of Vth induced by recessed gate has been as large as +9.2 V, and it is larger than that of HEMTs with Ti/Al/Ni/Au metal stacks. We also found that the samples with Ti/Al/W metal stacks have shown higher Rsh, though they were annealed at low temperature. It is inferred from these results that the ohmic annealing affects interface states in Al2O3/AlGaN interface. Further investigation is under way to clarify these results. Acknowledgment This study was partially supported by the Super Cluster program of the Japan Science and Technology Agency (JST). References [1] R. Gong, J. Wang, S. Liu, Z. Dong, M. Yu, C. P. Wen, Y. Cai, and B. Zhang, Appl. Phys. Lett. 97, 062115 (2010) [2] J. J. Feedsman, T. Egawa, Y. Yamaoka, Y. Yano, A. Ubukata, T. Tabuchi, and K. Matsumoto, Appl. Phis. Express 7, 041003 (2014) [3] H. Huang, Y. C. Liang, G. S. Samudra, C. L. L. Ngo, IEEE Electron Device Lett. 35, 569 (2014)

Authors : M. Lamprecht1, K. Thonke1, H. Teisseyre23, M. Bockowski3
Affiliations : 1Institute of Quantum Matter / Semiconductor Physics Group, University of Ulm, Albert-Einstein-Allee 45, 89069 Ulm, Germany; 1Institute of Quantum Matter / Semiconductor Physics Group, University of Ulm, Albert-Einstein-Allee 45, 89069 Ulm, Germany; 2Institute of Physics, Polish Academy of Sciences Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland, 3Institute of High Pressure, Polish Academy of Sciences, Sokolowska 29/37, PL-01142 Warsaw, Poland; 3Institute of High Pressure, Polish Academy of Sciences, Sokolowska 29/37, PL-01142 Warsaw, Poland

Resume : We investigate the broad defect-related photoluminescence band centered around 2.15 eV in gallium nitride bulk crystals co-doped by beryllium and oxygen. This yellow luminescence is similar in character to parasitic yellow luminescence observed in nominally undoped GaN, but possesses intense afterglow phosphoresce not reported before. Time-resolved photoluminescence (PL) finds an extremely slow decay of this emission with a lifetime of around 1 s, which by a thermally activated process with characteristic energy of around 260 meV becomes much shorter for temperatures above 400 K. Gated PL spectra show a redshift of the PL emission characteristic for donor-acceptor pair transitions. Excitation density dependent PL measurements show a blueshift for increasing laser power confirming this assignment. Under cw excitation, a blueshift of the band for temperatures up to around 300 K occurs, whereas for even higher temperatures it shifts red. These data hint to two different recombination processes at slightly different energies being hidden in the relatively broad PL band. Photoluminescence excitation spectra show two efficient pumping channels which seemingly are related to the two different PL recombination channels. We suggest a configuration coordinate model for these radiative transitions, and identify possibly involved impurities and their electronic states.

Authors : Takeshi Ohgaki, Isao Sakaguchi, Ohashi Naoki, Hajime Haneda
Affiliations : National Institute for Materials Science

Resume : (100)-oriented ScN films were grown on MgO(100) substrates and a-Al2O3(1-102) substrates by molecular beam epitaxy under nitrogen radical irradiation, and their crystalline orientation, crystallinity, and electric properties were examined. (100)-oriented ScN films were epitaxially grown on MgO(100) substrates with the same crystal orientations. For the ScN films grown on a-Al2O3(1-102) substrates, the epitaxial ScN films with an orientation relationship (100)ScN || (1-102)a-Al2O3 and [001]ScN || [1-120]a-Al2O3 were obtained, and their crystalline-orientation anisotropy was negligibly small. The [100] of ScN films slightly tilted in the [-1101] of a-Al2O3(1-102) substrates. The angle of [100] of ScN to the [1-102] of a-Al2O3 was 1.4–1.8 degrees, and the tilt angle increased with increasing the growth temperature. The growth-temperature dependence on the crystalline orientation, crystallinity, and electric properties differed according to the growth substrates.

Authors : Luu Thi Lan Anh, Nguyen Tuyet Mai, Nguyen Van Do, Nguyen Ngoc Trung and Nguyen Xuan Sang
Affiliations : Hanoi University of science and technology- N0 1 Dai Co Viet-Hai Ba Trung- Hanoi Vietnam, Hanoi University of science and technology - N0 1 Dai Co Viet-Hai Ba Trung- Hanoi Vietnam,Hanoi University of science and technology- N0 1 Dai Co Viet-Hai Ba Trung- Hanoi Vietnam, Hanoi University of science and technology- N0 1 Dai Co Viet-Hai Ba Trung- Hanoi Vietnam and Singapore-MIT Alliance for Research & Technology Centre.

Resume : GaN have the specific chemical stability, it is difficult to etch GaN film by general wet etching method at the room temperature. Photoenhanced chemical etching on GaN has recently identified as a method of greatly improving the chemical reactivity of GaN at the room temperature. In this study, GaN and AlGaN/GaN HEMTs was fabrication using photoenhanced chemical etching process with the etchant is KOH solution. The etching conditions can be easily controlled by the concentrations of the etchant, temperature, and lamp power. The effects of using different light sources and concentrations of KOH solution on the properties of GaN were studied for the first time. .A field emission scanning electron spectroscopy (FESEM) and an Atomic Force Microscope(AFM, Veeco) were used to characterizetheetched Surface and morphology. Observation through field emission scanning electron spectroscopy (FESEM) revealed that different types of illumination and concentrations of KOH solution resulted in different surface morphologies. The results is shown that smooth etching occurs for low solution concentration and high illumination intensity under a diffusion limited etching process. The surface roughness of 1.5nm and 50nm/min etching rate are obtained using KOH solution and Hg arc lamp

Authors : Thoan Nguyen-Hoang*, Do Nguyen-Trung, Anh Luu-Thi-Lan, Hung Pham-Phi, Trung Nguyen-Ngoc, Vinh Le-Van
Affiliations : School of Engineering Physics, Hanoi University of Science and Technology, Hanoi, Vietnam

Resume : Molecular dynamics simulations of Al1-xGaxN samples with different Al content were carried out to investigate their structures, void distributions and mechanical properties. Such effects on other microscopic characteristics, such as bond-length distance, bond-angle and coordination number distribution have been observed. Based on the common neighbor analysis, we found that GaN sample has amorphous state and AlN sample has major amorphous phase mixed with crystalline AlN. The Al1-xGaxN samples show the structures of crystalline and amorphous AlN segregated with amorphous GaN. The crystalline phase contains major fcc-AlN and minor hcp-AlN.

Authors : D.V. Nechaev (1), S.I. Troshkov (1), S.V. Ivanov (1), V.N. Jmerik (1), K. Klosek (2), G. Tchutchulashvili (2), M. Sobanska (2), Z.R. Zytkiewicz (2)
Affiliations : (1) Ioffe Institute, Russia; (2) Institute of Physics, Polish Academy of Sciences, Poland

Resume : The paper describes plasma-assisted molecular beam epitaxy (PAMBE) of planar (Al,Ga)N heterostructures on Si (111) substrates for HEMT applications. We focus on reduction of structural defects called by us “cauliflower” defects (CFD) having a diameter up to several microns, as well as on general problems typical for GaN/AlN/Si(111) buffer heterostructures, such as a large threading dislocation densities (TDD) and high tensile stress. 30-nm-thick AlN nucleation layers (NL) were grown by either standard PA MBE (3D morphology) or migration enhanced epitaxy (MEE) (2D morphology) at substrate temperatures Ts=660-800ºC. Then, AlN buffer layer was grown with thicknesses up to 300 nm at stoichiometric conditions resulting in mixed 2D-3D growth. Finally, to minimize the tensile stress as well as TD and CFD densities in the heterostructures, 1000 nm thick GaN buffer layers were grown by metal modulated epitaxy. An interaction between group-III atoms and Si (111) substrate is discussed as a potential source of CFD. We have found a strong diffusion of Ga and Si atoms along grain boundaries and other structural defects in the NL and following buffer layers to be responsible for the formation of the surface CFDs as well as microvoids at the substrate/NL interface. The best GaN surface morphology free from CFDs was achieved for 30-nm-thick AlN 2D NL grown by MEE at highest Ts~780°C and using liquid Ga as surfactant, followed by successive growth of 3D and 2D AlN buffer layers.

Authors : Hyeong-Ho Park1*, Hae Yong Jeong1, Yumin Koh1, Chu-Young Cho1, Kyung-Ho Park1, Manjeet Kumar2, Ju-Hyung Yun2*, Sunwoo Jung3, Soohwan Jang3
Affiliations : 1 Electronic device Lab., Korea Advanced Nano Fab Center, Suwon 16229, Republic of Korea; 2 Department of Electrical Engineering, Incheon National University, Incheon 406772, Republic of Korea; 3 Department of Chemical Engineering, Dankook University, Yongin, 16890, Republic of Korea

Resume : AlGaN/GaN based high electron mobility transistor (HEMT) has tremendous advantages in the application of hydrogen gas sensing. A high electron sheet carrier concentration can be easily obtained without intentional doping and the two-dimensional electron gas (2DEG) near the surface is very sensitive to the change of the atmospheric gases. In this work, platinum (Pt) was utilized as a hydrogen (H2) absorbing gate material in the HEMT device to achieve high sensitivity and fast detection. The porosity of a 10 nm-thick Pt nanostructure was controlled with various deposition rates (0.03, 0.15, and mixing of 0.03 and 0.15 nm/s) using electron beam evaporator. The electrical characteristics of HEMT device were measured before and after exposing to 5 % H2 gas at room temperature and 100 oC, respectively. Also, time dependent gas responses were measured under a series of 5 % H2 in N2 gas injections into the chamber. The Pt nanostructure, formed by a two-step deposition rate with an initial deposition rate of 0.03 nm/s and a final deposition rate of 0.15 nm/s showed the largest drain current increase and stable recovery. The sensitivity (a percentage of drain current change) was to be 3271 % under the 5 % H2 with -2.2 V of gate biasing. It is attributed to increased surface area of the Pt nanostructure, which enlarge the H2 capturing area. We will present the hydrogen sensing properties of various Pt nanostructures with controlled porosity in the conference.

Authors : Andrii Nikolenko (1), Andrian Kuchuk (1,2), Bogdan Tsykaniuk (1), Aleksandra Wierzbicka (3), Hryhorii Stanchu (1), Marta Sobanska (3), Kamil Klosek (3), Giorgi Tchutchulashvili (3), Viktor Strelchuk (1) and Zbigniew Zytkiewicz (3)
Affiliations : (1) V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Pr. Nauky 41, 03680 Kyiv, Ukraine (2) Institute for Nanoscience and Engineering, University of Arkansas, West Dickson 731, Fayetteville, Arkansas 72701, USA (3) Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland

Resume : GaN-based nanowire (NW) heterostructures are considered to be promising for application in novel optoelectronic devices, such as high-brightness light-emitting diodes and optically pumped NW lasers. The 1D geometry of the NWs allows overcoming the problems of strain relaxation through the creation of extended defects in 2D epitaxial heterostructures. However, MBE growth of complex axial NW heterostructures leads to overgrowth of their side walls, thus creating the radial core-shell structures and generating additional axial strains [1]. We report on a comprehensive experimental study of strain state of PAMBE-grown GaN NWs with single AlxGa1-xN sections of various Al contents (x = 0.2, 0.5, 1), the growth of which led to the formation of core-shell GaN/AlxGa1-xN nanowires. Confocal Raman microspectroscopy revealed the doublet behavior of the GaN E2(high) phonon mode with the dependent position of the high-frequency shoulder on the Al content in the AlxGa1-xN shell. A strong blue-shift of the near-band-edge emission from the GaN core was also observed in the photoluminescence (PL) spectra. These results can be explained by the compressive strain in the GaN core induced by the AlxGa1-xN shell. The high-resolution X-ray diffraction (HRXRD) techniques by measuring ω/2θ X-ray diffraction profiles and the reciprocal space maps were applied to elucidate the strain features and distributions in core-shell GaN/AlxGa1-xN nanowires. The correlation between Raman, PL and HRXRD results is discussed. 1. A. Reszka et. al., J. Appl. Phys. 120, 194304 (2016).

Authors : Magdalena A. Ekwińska, Jerzy Zając, Michał Zaborowski, and Dariusz Szmigiel
Affiliations : Institute of Electron Technology, al. Lotników 32/46, 02-668 Warszawa, Poland; Institute of Electron Technology, al. Lotników 32/46, 02-668 Warszawa, Poland;Institute of Electron Technology, al. Lotników 32/46, 02-668 Warszawa, Poland;Institute of Electron Technology, al. Lotników 32/46, 02-668 Warszawa, Poland

Resume : The piezoelectric materials have increasingly become adopted in various sensors and actuators based on cantilever or membrane MEMS devices. This type of MEMS structure usually consists of piezoelectric layers and other films supported onto the elastic substrate. Thus, the in-situ evaluation of the properties of the thin piezoelectric film (being a part of the layered structure) tends to be a very complex research task that involves both electrical and mechanical tests as well as simulation process. In this work Authors describe the manufacturing process of AlN films optimised with respect to deposition conditions, uniformity across the wafer and appropriate properties for piezoelectric MEMS actuation. The characterisation of MEMS test structures made at ITE (Instytut Technologii Elektronowej) was supplemented with the structural analysis of the thin films performed by XRD and Raman spectroscopy techniques.

Authors : Mustafa Gunes1*, Mustafa Akyol2, Ahmet Ekicibil2, Engin Tiras3
Affiliations : 1Department of Materials Engineering, Adana Science and Technology University, Adana, 01180, Turkey; 2Department of Physics, Çukurova University, Adana, 01330, Turkey; 3Faculty of Science, Department of Physics, Anadolu University, Yunus Emre Campus, 26470 Eskisehir, Turkey

Resume : The superconducting behavior of InN has been observed in many experiments where the origin of superconductivity is addressed to presence of i) In-In chains in ab-plane, ii) specific carrier density range limited Mott transition critical carrier density and iii) presence of In2O3 impurities1-3. Although the superconductivity can be observed when the above conditions are enough for epitaxial grown InN films, the superconductivity properties of InN, so far, have not worked comprehensively. Here, we report the magneto-resistance, upper critical field, and thermally activated flux mechanism of superconductor Mg doped InN epitaxial film grown by Molecular Beam Epitaxy (MBE). The superconducting phase transition temperature was observed at ~3.9 K at zero magnetic field. The carrier density of the film is found in the range of Mott transition and superconductivity to metal transition. The effect of magnetic field on the superconductivity of Mg-doped InN film is studied by employing the magnetoresistance and Hall resistance measurement with a typical Hall-bar shape device. The magnetoresistance analysis has been carried out by flux-flow and flux-creep models. The activation energy is found as highly sensitive with field in a range of 0.0 to 1.0 T. The upper critical field at zero temperature and coherence length estimated by Ginzburg-Landau relation were found as around 0.8 T and 216.9 Å, respectively.

Authors : O.F. Kolomys1, B.I. Tsykaniuk1, V.V. Strelchuk1, P.M. Lytvyn1, Shibin Li2,3, M.E. Ware2, Yu.I. Mazur2, M. Benamara2, A.E. Belyaev1 and G. Salamo2
Affiliations : 1.V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Pr. Nauky 41, 03680 Kiev, Ukraine. 2. Institute for Nanoscience and Engineering, University of Arkansas, West Dickson 731, Fayetteville, AR 72701, USA. 3. State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, 610054 Chengdu, China

Resume : Short-periods GaN/AlN Superlattices (SLs) have great potential as active elements in many optoelectronic devices, which cover the spectral regions from ultraviolet to infrared. The optical properties of such SL require an understanding of their strain relaxation mechanisms. The dominant strain relaxation process strongly depend on the sample structure and the growth conditions. In the present work, the depth distribution of structural quality and local strain of GaN/AlN SL with 5, 10 and 20 periods grown by MBE on GaN/Al2O3 template was examined using confocal Raman, Photoluminescence and TEM techniques. The thickness of the SL layers is determined by HRTEM analysis. Thickness fluctuations of the GaN quantum well (QW) can originate from a drift of the growth rate with time resulting in a variation in the QW thickness or spatial structural inhomogeneities. Strong PL peak in the range 3.1-3.4 eV depend on penetration depth was observed. From the frequency shift of phonons of GaN and AlN, the strains in the individual SL layers were determined. By increasing the number of SL periods the high-frequency (low-frequency) shift of the peak of the E2(high) of the GaN (AlN) phonon modes occurs related to with increase of the compressive and tensile strain in the QWs and barrier layers, respectively. The elastic strains in regions near the top surface of multilayer structures can be quite different from those in deeper regions of the samples.

Authors : M. Sznajder, R. Hrytsak
Affiliations : Faculty of Mathematics and Natural Sciences, University of Rzeszow, Pigonia 1, 35-959 Rzeszow, Poland

Resume : The AlN/diamond hybrid devices require an AlN layer with improved crystalline quality on the diamond surface. Recently, Imura et al. [1] demonstrated the single-crystal AlN/H-diamond(111) heterojunction with high-density interface hole channel, grown by MOVPE. However, the same method applied to O-diamond(111) substrate resulted in AlN layer of two-domain structure with poor crystalline quality [2]. Herein we study the early stages of wz-AlN growth process on diamond(111) surface within the DFT approach. First, we focus on the adsorption process of oxygen atoms on diamond(111) at various coverages, 0.25 ML, 0.5 ML, and 1 ML in the 2x2 lateral unit cell of a slab model. For most coverages, independently from the starting position (H3, T4, bridge, ontop), the most stable adsorption site is the ontop one. The corresponding Eads = -7.1280 eV/atom (1 ML), with the average C-O distance 1.3275 A. From the calculated atom-resolved DOS function follows that mainly oxygen p-states hybridize with p-, s-, and d-states of the four topmost C atoms, and these new states are created in the energy range of the forbidden gap of bulk diamond. Next, adsorption process of the subsequent four Al- and N-monolayers is studied on the preadsorbed O/diamond(111) surface. The corresponding energetically most stable adsorption sites are found. These are in particular T4 one for 1 ML of Al with Eads = -5.7975 eV/atom, H3 one for 1 ML of N (Eads = -7.4011 eV/atom), ontop one for 1 ML of Al (Eads = -5.4123 eV/atom), and T4 one for 1 ML of N (Eads = -7.4627 eV/atom). The obtained sequence of layers for this most energetically stable system does not correspond to that of wurtzite structure. However, the wurtzite structure of AlN can be also reproduced with slightly disturbed layer sequence: O (ontop), Al (T4), N (H3), Al (H3), N (ontop). The resulting adsorption energies for the top Al and N monolayers are then smaller by 0.2389 eV/atom and 0.3139 eV/atom, respectively. The corresponding p-DOS function confirms an interaction between oxygen and nitrogen p-states and d-states of aluminium. The computed laterally averaged profiles of the electron charge and total potential, as well as the spatial valence charge density distribution enable to trace the differences in charge transfer between the AlN layers and clean-, or O/diamond(111) surface. In particular, the adsorption of 1 ML of oxygen on the diamond clean surface is connected with electron transfer which starts form third carbon substrate monolayer (near the interface) towards O atoms. Third, second, and mostly first carbon substrate monolayers lose some electron charge in favour of C-O bonds and the area above oxygen atoms. The adsorption of first Al ML leads to further redistribution of electron charge; electrons move from the C-O bonds mainly to the oxygen monolayer, to the O-Al bonds, and slightly to the first and second carbon monolayers and bonds joining them. The adsorption of next three layers of AlN does not trigger off redistribution of electron charge originating from the oxygen monolayer. Finally, we discuss certain reconstruction patterns in analogy to those studied in [3], that lead to the enhanced adsorption energies of the Al-, N-monolayers of the diamond substrate. 1. M. Imura, R.G. Banal, M. Liao et al., J. Appl. Phys. 121 025702 (2017). 2. M. Imura, K. Nakajima, M. Liao et al., J. Cryst. Growth 312, 1325 (2010). 3. M. Sznajder, E. Wachowicz, and J.A. Majewski, J. Cryst. Growth 401, 25 (2014).

Authors : Takahiro Kawamura 1,2, Akira Kitamoto 2, Mamoru Imade 2, Masashi Yoshimura 2, Yusuke Mori 2, Yoshitada Morikawa 2, Yoshihiro Kangawa 3, Koichi Kakimoto 3
Affiliations : 1 Graduate School of Engineering, Mie University; 2 Graduate School of Engineering, Osaka University; 3 Research Institute for Applied Mechanics, Kyushu University

Resume : Oxide vapor phase epitaxy (OVPE) method, in which GaN is formed by the reaction of Ga2O with NH3, is supposed to be one of the most promising bulk GaN growth techniques [1]. We have been engaged in understanding GaN growth processes in the OVPE method, especially surface structures [2]. In this study, we investigated stable surface structures of semipolar GaN (10-11) surface under OVPE growth conditions. Because O species are included in the Ga sources, reduction of O impurity concentration is one of the important subjects. We therefore discuss the relationship between the growth conditions and O impurity incorporation. We used the first-principles molecular dynamics simulation program STATE-Senri [3] to calculate total energy of GaN (10-11) surface structure models. Stability of the simulated surface models were estimated by comparing the surface formation energy [4]. From the results, we found that two-coordinated N atoms in the ideal topmost surface are not stable. Surface structures in which those N atoms are removed and O atoms are incorporated into the N site are stable under the OVPE growth conditions (the temperature ~ 1500 K, the Ga pressure ~ 0.001 atm, and the O pressure is half the Ga pressure). Because the activation energy for desorption of O atom was estimated about 7.4 eV, we suppose that the incorporated O atom hardly desorbs from the surface. We will examine the probability that the O impurity is able to be removed from the surface by reduction with H2 gas. [1] M. Imade et al., J. Cryst. Growth 312, 676 (2010). [2] T. Kawamura et al., Phys. Status Solidi B 1600706 (2017). [3] Y. Morikawa et al., Phys. Rev. B 51, 14802 (1995). [4] C. G. Van de Wallet et al., Phys. Rev. Lett. 88, 066103 (2002).

Authors : K. Koronski1, A. Kaminska1,2, P. Strak3, A. Wierzbicka1, R. Jakiela1, E. Monroy4,5, and S. Krukowski3
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 01-142 Warsaw, Poland 2Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and Natural Sciences, Dewajtis 5, 01-815 Warsaw, Poland 3Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland 5Université Grenoble-Alpes, 38000 Grenoble, France 6CEA Grenoble, INAC-PHELIQS, 17 av. des Martyrs, 38054 Grenoble, France

Resume : The optical propreties of GaN/AlN multi-quantum-wells (MQWs) with equal well and barrier widths were analysed in comparison with ab initio calculations of the electronic and optical properties. The well/barrier widths in the series of samples changed from 1.5 to 5 nm. The investigated structures were grown by plasma-assisted molecular-beam epitaxy and characterized by x-ray diffraction and secondary ion mass spectrometry. The optical transition energies in these structures and their oscillator strengths were determined by ab intio calculations as well as investigated by photoluminescence (PL) measurements. It was shown that the optical emission energy decreased by about 1.7 eV in the structures with QWs thicknesses increasing from 1.5 nm up to 5 nm, and the respective PL decay times increased from 100 ns up to 150 µs. Comparison of experimental data with theoretical models elaborated for the same geometry structure allowed to determine directly the polarization in the AlN/GaN in nitride systems, and the dependence of built-in electric field on carrier concentration.

Authors : K. Gas,J. Domagała,R. Jakieła,R. Szukiewicz,G. Kunert,J. Stoever,A. Miszczuk, T. Baraniecki,D. Hommel,M. Sawicki
Affiliations : Institute of Experimental Physics University of Wrocław, Wrocław, Poland;Institute of Physics, Polish Academy of Sciences, Warsaw, Poland;Wrocław Research Center EIT+ Sp. z o.o., Wrocław, Poland

Resume : GaN doped with Mn, (Ga,Mn)N, is an important follower of (Ga,Mn)As in dilute ferromagnetic semiconductors family because of its superexchange driven ferromagnetism being realized in an insulating host. As it offers new avenues and different devices architectures for spin manipulations it has been timely and important to optimize the growth conditions aiming at increasing the Curie temperature, TC, while maintaining a single phase and the insulating character. To this end we fabricated a set of (Ga,Mn)N layers on GaN templated sapphire substrates in PAMBE at temperatures, Tg, ranging from 590 to 700 oC. The magnetic characterization revealed the optimum growth conditions for which the highest Mn concentration is obtained and takes place around Tg = 605 oC. This layer also shows the highest TC without any magnetic indication of any traces of other phase precipitations. We discuss the layer properties in greater detail in connection with other structural characterization including SIMS, XRD, SEM and AFM.This work has been supported by the National Science Centre (Poland) through grants FUGA (2014/12/S/ST3/00549) and OPUS (2013/09/B/ST3/04175), by the EU 7th FP “EAgLE” (REGPOT-CT-2013-316014) and the international project co-financed by Polish Ministry of Science and Higher Education, Grant Agreement 2819/7.PR/2013/2, and by WRC EIT+ within the NanoMat project (P2IG.01.01.02-02-002/08) co-financed by the ERDF (operational Programme Innovative Economy, 1.1.2).

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Session 5: Recombination in nitride devices & material characterisation : polarization, electric fields, segregation, mechanism of optical emission… I : Eva Monroy
Authors : Martin Strassburg, Peter Stauss, Martin Behringer, Hans-Jürgen Lugauer
Affiliations : OSRAM Opto Semiconductors GmbH, Leibnizstr. 4, 93055 Regensburg, GERMANY

Resume : The history of LEDs has been evolved for more than 50 years. Even though the nitride LEDs are somewhat younger, this material system enabled the lighting revolution that we are currently experiencing. The foundation has been the tremendous improvements in brightness level and efficiency that have been the in the focus of research for a long time. Material properties required design and process improvements to overcome limitations. Nowadays, it is recognized that LED offer a big variety of opportunities beyond efficient lighting. There are many applications that could only be addressed by the unique characteristics of semiconductor LED light sources. Thus, it is much more than cost cutting and efficiency triggering further research on group III nitride optoelectronics. A brief history of group III nitride based LED developments along with an introduction to OSRAM Opto Semiconductors’ numerous activities in research and development of next generation LEDs / Lasers and future trends for lighting applications will be given. Examples of technology and products for various application fields will illustrate the claimed technology leadership that is based on the close interplay of material development, thorough understanding of scientific background and of technological solutions yielding.

Authors : Motoaki Iwaya1, Takafumi Hayashi1, Noriaki Nagata1, Takashi Senga1, Lin Dong1, Sho Iwayama1, Tetsuya Takeuchi1, Satoshi Kamiyama1, Isamu Akasaki1,2, Takahiro Matsumoto3
Affiliations : 1 Faculty of Science and Technology, Meijo University, Japan 2 Akasaki Research Center, Nagoya University, Japan 3 Graduate School of Design & Architecture, Nagoya City University, Japan

Resume : UV AlGaN-based semiconductor laser diodes have wide applications such as bio-/chemical photonics, material processing, and high-density data storage. Nevertheless, the full potential of these devices has been limited by low-efficiency current injection due to the difficulty of producing low resistivity p-type high Al-content AlGaN alloys. An alternative approach to address this problem is the use of the electron beam excitation. In this presentation, we shows the electron beam excited laser in the UV region, using a nitride semiconductor device with a GaN/AlGaN MQW active layer. We also discuss that what is the point of laser oscillation by electron beam excitation. After growth of a 500-nm-thick GaN layer on GaN substrate, a 500-nm-thick Al0.15Ga0.85N cladding layer, a 100-nm-thick Al0.07Ga0.93N guide layer, GaN (3nm)/Al0.07Ga0.93N (12nm) 10QW active layer, a 100-nm-thick Al0.07Ga0.93N, and a 100-nm-thick Al0.15Ga0.85N cladding layer were stacked in that order. The cavity length of the laser was ~50 μm. Despite measuring the same sample, we found clearly difference in the threshold power density required for laser oscillation. Also, the threshold excitation power density was minimized at 20 kV. This result almost matched with the simulation result. The threshold power density and wavelength were ~ 160 kW/cm2 and 352.8 nm, respectively.

Authors : Pawel Strak, Kamil Koroński, Kamil Sobczak, Jolanta Borysiuk, Krzysztof Korona, Konrad Sakowski, Eva Monroy, Agata Kaminska, Stanislaw Krukowski
Affiliations : Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland;Institute of Physics Polish Academy of Sciences, Al. Lotników 32/46, 01-142 Warsaw, Poland;Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw;Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland;Université Grenoble-Alpes, 38000 Grenoble, France;CEA Grenoble, INAC-SP2M, 17 av. des Martyrs, 38000 Grenoble, France;Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and Natural Sciences, Dewajtis 5, 01-815 Warsaw, Poland

Resume : The new method is presented, designed for exact determination of the recombination mode of optically excited matter, measured by standard time resolved photoluminescence (TRPL) instruments. The considered processes include non-radiative Shockley-Read-Hall (SRH) monomolecular, standard bi-molecular, and Auger tri-molecular recombination. In addition the optical emission is analyzed taking into account the emission due to both monomolecular and bi-molecular process. The method allows us to determine the dominant optical emission mode and also the values of ABC parameters in fundamental time evolution equation of optically excited samples measured by TRPL [1,2]. It is shown that the method could be applied to any quantum structures and other systems investigated optically. Moreover, it is also shown that the method could be successfully applied for analysis of the processes in the nitride polar (with polarization induced electric field) and the nitride nonpolar (i.e. without polarization induced electric field) multiquatum well (MQW) systems. The analysis of temporal evolution of the emission allows to determine the recombination modes from the structure, allowing to identify basic factors affecting optical emission from nitride quantum structures. [1] R.N. Hall, Phys. Rev. 83, 228 (1951). [2] W. Shockley, W. T. Read, Phys. Rev. 87, 835 (1952).

Authors : Talgat M. Inerbaev, Takashi Matsuoka;, Yoshiyuki Kawazoe
Affiliations : L.N. Eurasian National University, Institute for Materials Research Tohoku University;, New Industry Creation Hatchry Center Tohoku University

Resume : Ga1-xInxN have attracted great interest and is intensively studied as materials for bright light emitters that cover continuously from the ultraviolet to near-infrared region by proper alloying. The band gap of the InxGa1−xN alloy system now spans the entire optical window from the near infrared to the ultraviolet. Difficulties in growing high-quality crystals are caused of the extremely high equilibrium vapor pressure of nitrogen. In present study, we report ab initio quasiparticle electronic structure calculations of InxGa1−xN, 0 ≤ x ≤1. Calculation was performed within the framework of density functional theory using the PBE functional for exchange and correlation. Beyond that, quasiparticle effects were taken into account by a subsequent GW correction of the Kohn-Sham eigenvalues within the framework of many body perturbation theory. Very good agreement between experimental and theoretical data was found. For pure GaN and InN GW calculations gives the band gap values equal to 3.2 and 0.65 eV while corresponding experimental data are 3.4 and 0.7 eV. For single wurtzite unit cell of Ga0.5In0.5N the calculated band gap is found to be equal to 1.0 eV while for model supercell with the same stoichiometry but some disorder this value is 2.0 eV that indicates strong effect of ordering on the alloy’s band gap. The almost linear dependence of the band gap value as a function of x was obtained.

10:30 Coffee break    
Session 6: Recombination in nitride devices & Material characterisation : polarization, electric fields, segregation, mechanism of optical emission… II : Chris G. Van de Walle
Authors : Juergen Christen
Affiliations : Otto-von-Guericke-University Magdeburg, Germany

Resume : The combination of luminescence spectroscopy - in particular at liquid He temperatures - with the high spatial resolution of a scanning transmission electron microscopy (STEM), as realized by the technique of low temperature scanning transmission electron microscopy cathodoluminescence microscopy (STEM-CL), provides a unique, extremely powerful tool for the optical nano-characterization. Examples will be given: We analyze the optical and structural properties of a modulation doped GaN:Ge DBR with an InGaN multiple quantum well on top. The structure was grown by metal organic vapor phase epitaxy on a sapphire substrate with a GaN buffer layer and consists of 100 pairs of GaN/GaN:Ge bilayers. Cross-sectional STEM-CL exhibits an modulation of monochromatic intensity in the DBR layers at low temperature: In the GaN:Ge DBR layer the excitonic emission (D0,X) at 356 nm is significantly reduced compared to the undoped layer. On the high energy side an electron hole band recombination (e,h) at 347 nm is apparent indicating the exceeding of the Mott transition in those GaN:Ge layers. In spectrally resolved STEM-CL-linescans the antiphase modulation is evidend. Further examples on the nano-characterization of nano-wires, core-shell heterostructures, and GaN quantum dots will be given.

Authors : Tadeusz Suski, Izabela Gorczyca
Affiliations : Institute of High Pressure Physics, UNIPRESS, 01-142 Warsaw, POLAND; Institute of High Pressure Physics, UNIPRESS, 01-142 Warsaw, POLAND

Resume : This work is concentrated on studies of the band gaps, Eg, and related photoluminescence, PL, in polar InGaN/GaN structures, which due to narrow QWs and/or barriers exhibit an electron and a hole wave function overlap (WFO) between adjacent layers. The resulting effects consist in coupling of double QWs and formation of superlattices, SLs. Depending on the strength of built-in electric field the effective Eg changes drastically and excitons formed in such systems have intra-well or inter-well indirect character. Firstly, we present examination of double InGaN QWs with different GaN barrier width d . An effective WFO for an electron and a hole from adjacent QWs leading to inter-well character of excitons occurs for d ≤1 nm. Switching of the excitons between intra-well and inter-well ones as a function of exciting laser power is demonstrated. Then we examine In(Ga)N/GaN SLs, based on the structures described above. For sufficiently thin barriers such SLs can be formed. Finally, short period SLs In(Ga)N/GaN with QW and QB thickness varying from 1 to 15 atomic layers are studied with the purpose of determining their band gaps. Contributions of the built-in electric field and the WF hybridization to evolution of Eg is analyzed. Tuning of Eg in much wider range than for InxGa1-xN alloys, including closing of the band gap, is demonstrated. Financial support by the Polish National Science Center, grant DEC 2013/11/B/ST3/04263 is acknowledged.

Authors : P. Strak[1], A. Kaminska[2,3], K. Koronski[2], A. Wierzbicka[2], E. Grzanka[1], M. Sobanska[2], K. Klosek[2], K. Sobczak[2], R. Jakiela[2], E. Monroy[4,5], Z. R. Zytkiewicz[2], and S. Krukowski[1]
Affiliations : [1] Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland [2] Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland [3] Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and Natural Sciences, Dewajtis 5, 01-815 Warsaw, Poland [4] Université Grenoble-Alpes, 38000 Grenoble, France [5] CEA Grenoble, INAC-PHELIQS, 17 av. des Martyrs, 38054 Grenoble, France

Resume : We present a study of the internal electric fields in GaN/AlxGa1-xN (3 nm/4 nm) multi-quantum-wells (MQWs) with x = 1, 0.5, and 0.25. Optical properties of the structures are investigated by ambient and high-pressure photoluminescence (PL) measurements. The structural characterisation is performed by XRD, SIMS, and TEM techniques. The optical properties are strongly affected by polarization-induced electric fields giving rise to a quantum confined Stark effect, which depends strongly on the composition of the quantum barrier. The optical emission energy redshifts by >100 meV when the Al content in the barrier increases from 25% up to 100%. Furthermore, the pressure coefficients of the PL energy are significantly reduced in comparison with bulk GaN, and they also depend on the composition of the barrier. The transition energies and their pressure dependence are modeled for tetragonally strained structures with the same geometry using a full tensorial representation of the strain in the MQWs under external pressure. The same MQWs are also simulated using density functional theory calculations. A good agreement between these two approaches verified by experimental results indicates that nonlinear effects induced by the tetragonal strain due to the lattice mismatch between the substrates and the polar MQWs are responsible for a drastic decrease of the pressure coefficients of PL energy. The research was funded by Polish National Science Center by grant: DEC-2015/19/B/ST5/02136.

Authors : E.-M. Pavelescu (1), O. Ligor (1), C. Romanitan (1), C. Obreja (1), A. Matei (1), M. Carp (1), C.M. Ticos (2), J. Mickevicius (3), A. Kadys (3), G. Tamulaitis (3).
Affiliations : (1) National Institute for Research and Development in Microtechnologies, Erou Iancu Nicolae 126A, 077190, Voluntari, Romania (2) National Institute for Laser, Plasma and Radiation Physics, 077125 Bucharest, Romania (3) Institute of Applied Research and Semiconductor Physics Department, Vilnius University, Vilnius, Lithuania

Resume : BGaN is a promising material to achieve lattice-matching with SiC or AlN if sufficient boron concentration in alloy is achieved. On the other hand, incorporation of an increasing amount of boron is accompanied by a substantial degradation of material quality, which manifests through the defect-related luminescence bands. In this study, we have studied the influence of boron incorporation on yellow luminescence (YL) band seen in photoluminescence from BGaN alloys. The BGaN thin films were grown using metalorganic chemical vapour deposition (MOCVD) on sapphire substrates. Both GaN and AlN layers have been used as buffer layers for the growth of BGaN films. The YL band has been found to red shift as the boron concentration increases at a faster rate than the BGaN bandgap. A shoulder on the lower energies side of the YL band starts developing at the expense of a gradual decrease in intensity of the YL band. As a consequence, the colour of the YL band changes from yellow to amber with increasing boron content. 6-MeV electron irradiation followed by rapid thermal annealing reduces the intensity of the YL (amber) band, especially its low energies side. The mechanisms for such transformation are discussed.

12:30 Lunch break    
Session 7: Dopants and defects: Mg, Be, Ge, DX formation, other point defects… I : Zlatko Sitar
Authors : Chris G. Van de Walle
Affiliations : Materials Department, University of California, Santa Barbara, California, USA

Resume : Point defects or unintentional impurities may act as radiative or nonradiative recombination centers. Theoretical advances now enable us to calculate the electronic and optical properties as well as radiative and nonradiative carrier capture coefficients with unprecedented accuracy. These capabilities have allowed us to evaluate Shockley-Read-Hall coefficients and identify specific defects that play a key role in limiting the efficiency of nitride devices. Bare gallium vacancies are unlikely to occur, but their complexes with hydrogen or oxygen acts as compensating and recombination centers [1]. Calcium has also been identified as a detrimental impurity [2]. Based on simple rules, one expects defect-assisted recombination to become less important in wider-gap materials; but a number of examples show a different trend. We provide an explanation by noting the crucial role of excited states in recombination processes [3]. Iron is an important example [4]. Work performed in collaboration with A. Alkauskas, C. Dreyer, G. Kresse, A. Janotti, J. Lyons, S. Marcinkevicius, J. Speck, J.-X. Shen, and D. Wickramaratne, and supported by DOE and NSF. [1] C. E. Dreyer et al., Appl. Phys. Lett. 108, 141101 (2016). [2] J.-X Shen et al., Appl. Phys. Express 10, 021001 (2017). [3] A. Alkauskas et al., Phys. Rev. B 93, 201304 (2016). [4] D. Wickramaratne et al., Appl. Phys. Lett. 109, 162107 (2016).

Authors : Klaus Thonke, Matthias Lamprecht
Affiliations : Institute of Quantum Matter / Semiconductor Physics Group, University of Ulm, Albert-Einstein-Allee 45, 89069 Ulm, Germany

Resume : In bulk AlN crystals as well as in epitaxial layers frequently broad defect-related photoluminescence (PL) bands are found in the spectral range from 1.4 – 4.5 eV. Using different spectroscopic methods like cw and time resolved PL at varying sample temperature, transmission, PL-excitation spectroscopy etc., we find clear indications of the involvement of (relatively shallow) DX states and effective-mass-like donor states related to oxygen and silicon. The capture of free electrons into these states and their thermalization properties are analysed, and their relation to Hall and optically detected EPR data is discussed. The deep acceptors acting as final states in the donor-acceptor pair-type PL transitions are most likely related to Al vacancies and their complexes with oxygen. For Be doped GaN bulk crystals unintentionally co-doped with oxygen, a broad PL band coinciding with the yellow PL at around 2.15 eV is found. This PL band has even at room temperature an exceptionally long lifetime of ~ 1 sec, which by thermal activation with an apparent energy of ~ 0.26 eV becomes much shorter for temperatures above 300 K. Gated PL spectra again indicate a donor-acceptor pair transition, with both DX-like and EMT-like donor states involved, and a Be related acceptor.

Authors : Y. Tokuda 1, T. Kogiso 1, T. Narita 2, 3, K. Tomita 2, T. Kachi 3
Affiliations : 1 Aichi Institute of Technology, Toyota 470-0392, Japan 2 Toyota Central R&D Labs., Inc., Nagakute 480-1192, Japan9 3 Nagoya University, Nagoya 464-8601 Japan

Resume : We have studied hole traps in p-type GaN grown by MOCVD using a pn junction structure by DLTS. The diode structure consists of 100-nm p(++) ([Mg]=8e19 cm-3)/700-nm p([Mg]=2e17 cm-3)/200-nm n(+)([Si]=1e19 cm-3) on n-type GaN substrate, which enables us to detect traps in p-type GaN due to the depletion region toward the p-side under negative bias condition. The Ohmic contacts were formed by Ni/Au on the top of p(++)-GaN and by Ti/Al on the back side of n(+)-GaN, respectively. No variation of the junction capacitance was observed in the frequency range up to 1 MHz, indicating negligible series resistance in the diode structure used. This enables to perform capacitance DLTS with the measurement frequency of 1 MHz. The CV measurements revealed the almost flat profile with the concentration of 2e17 /cm3 in the depth range from 170 to 280 nm which corresponded well to the ionized acceptor concentration in p-type GaN. This confirms that the depletion layer extends to the p-type region in the pn junction. DLTS measurements were performed in the temperature range from 200 to 550 K. The low measurement temperature is restricted due to the freeze-out of Mg acceptors. Four hole traps are detected with the energy levels of Ev+0.46, 0.88, 1.0 and 1.3 eV whose trap concentrations are estimated to be 1.6e15, 2.4e16, 3.7e15 and 5.3e15 /cm3, respectively. The energy level of Ev+0.88 eV is close to that of the hole trap labeled H1 observed in n-type GaN, which has been ascribed to carbon-related or Ga-vacancy-related defects [1,2]. The energy level of Ev+0.46 eV is close to the theoretically predicted energy level of nitrogen vacancy [3]. The results obtained by the admittance spectroscopy and current DLTS will be also presented. This research is supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, through its “Program for research and development of next-generation semiconductor to realize energy-saving society.” [1] Y. Tokuda, CS MANTECH, 19 (2014). [2] Y. Tokuda, ECS Transactions, 75, 39 (2016). [3] Q. M. Yan, A. Janotti, M. Scheffler, and C. G. Van de Walle, Appl. Phys. Lett. 100, 142110 (2012).

Authors : R. García-Gutiérrez1, M. Barboza-Flores1, G. A. Hirata2, O. E. Contreras2
Affiliations : 1 Department of Research in Physics, University of Sonora, 83000 Hermosillo, Son., México 2 Center of Nano-sciences and Nanotechnology, UNAM, 22800 Ensenada B. C., México

Resume : The recent discovery and understanding of inexpensive routes to grow high quality doped and un-doped gallium nitride (GaN) thick films by Hydride Chemical Vapour Deposition (HCVD) could lead to the fabrication of high efficiency low-cost optoelectronic devices, such as ultra-bright light emitting diodes and high-efficiency solar cells. HCVD technique to grow un-doped high-quality GaN thick films on different substrates, fused silica, silicon and Au/SiO2 had been described in previous works. In this research doped GaN thick films on Au/SiO2 using different dopants such as Be, Mg and Zn is presented. Ga-Be, Ga-Mg and Ga-Zn diluted alloys and ammonia as nitriding agent were used as row materials in a 3-zone horizontal quartz tube reactor to grow p-type GaN 40-μm/h films. NH4Cl is evaporated in the entrance of the reactor, argon is the carrier gas that takes the vaporized NH4Cl to middle of the reactor where it discomposes in NH3 and HCl, this reacts with the metallic alloy to yield volatile chlorides that are carried to the substrate and react with ammonia at high temperatures to grow doped GaN on the surface of the substrate. Doped and un-doped GaN synthesized by this method grow in hexagonal columns in the c-direction independently of the substrate. The best substrate to grow GaN columns is Au/Silica. Zn dopant improves luminescence of GaN better than Mg. It is possible to grow free standing un-doped, Mg- and Zn-doped GaN thick films with a columnar structure by this HCVD technique. The GaN thick films grown in this work showed the typical near band-edge emission at around 3.5 eV, and three extra-peaks around 3.3, 2.9 and 2.6 eV that are probably donor acceptor pares (DAP) with different donor levels. These GaN TFs are highly luminescent with efficiency comparable to those previously seen in thin films grown by more expensive techniques such as MOCVD and MBE, which would suggest that the material is a good candidate to be used in the fabrication of optoelectronic devices.

15:30 Coffee break    
Session 8: Dopants and defects: Mg, Be, Ge, DX formation, other point defects… II : Tadeusz Suski
Authors : Ramon Collazo [1], Pramod Reddy [1,2], Shun Washiyama [1], Felix Kaess [1], Ronny Kirste [2], Seiji Mita [2], James Tweedie [2], Michael Gerhold [3], Zlatko Sitar [1]
Affiliations : [1] Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7919, USA; [2] Adroit Materials, Inc., 2054 Kildaire Farm Rd., Cary NC 27518, USA; [3] Engineering Science Directorate, Army Research Office, P.O. BOX 12211, Research Triangle Park, NC 27703, USA.

Resume : Defect incorporation in Al/GaN is dependent on the defect formation energy and hence on associated chemical potentials and the Fermi level. For example, the formation energy of CN in Al/GaN varies as chemical potential difference (µN- µC) and -EF (Fermi level). Here, we demonstrate a systematic point defect control by employing the defect formation energy as tool by (a) chemical potential control and (b) Fermi level control. Chemical potential control (µN and µC) with a case study of C in MOCVD GaN is reported. We derive a relationship between growth parameters, metal supersaturation (i.e. input and equilibrium partial pressures) and chemical potentials of III/N and impurity atoms demonstrating successful quantitative predictions of C incorporation as a function of growth conditions in GaN. Hence growth environment necessary for minimal C incorporation within any specified constraints may be determined and C is shown to be controlled from >1019cm-3 to ~1015 cm-3. Fermi level control based point defect reduction is demonstrated by modifying the Fermi level describing the probability of the defect level being occupied/unoccupied i.e. defect quasi Fermi level (DQFL). The DQFL is modified by introducing excess minority carriers (by above bandgap illumination). A predictable (and significant) reduction in compensating point defects (CN, H, VN) in (Si, Mg) doped Al/GaN measured by electrical measurements, photoluminescence and secondary ion mass spectroscopy (SIMS) provides experimental corroboration. Further, experiments with varying steady state minority carrier densities at constant illumination prove the role of minority carriers and DQFL in defect reduction over other influences of illumination that are kept constant.

Authors : John L. Lyons
Affiliations : Center for Computational Materials Science, Naval Research Laboratory, Washington DC 20375

Resume : Acceptor impurities remain some of the most intriguing species in III-nitride semiconductors. For instance, potential carbon contamination during growth motivates investigations of C acceptors [1], which can act as a carrier trap and source of luminescence. The search for dopants more efficient than Mg has spurred interest in group-II acceptors such as Be [2]. And although isolated native acceptor species are not thought to be abundant in as-grown GaN [3], complexes between gallium vacancies and donor impurities are likely to be present. In this talk I will review recent theoretical efforts to characterize such acceptor species in III-nitride semiconductors. Density functional theory is employed to predict the formation energies, acceptor ionization energies, and optical transition levels. Hole localization is found to be a key feature of these acceptors, and hybrid density functional theory is applied so that these physics are captured. We also directly compare our calculations to recent pressure-dependent photoluminescence studies [3]. 1. J. L. Lyons, K. Krishnaswamy, L. Gordon, A. Janotti, and C. G. Van de Walle, IEEE EDL 37, 154 (2016). 2. H. Teisseyre, J. L. Lyons, A. Kaminska, D. Jankowski, D. Jarosz, M. Boćkowski, A. Suchocki and C. G. Van de Walle, J. Phys. D: Appl. Phys. 50, 22LT03 (2017). 3. J. L. Lyons and C. G. Van de Walle, NPJ Comp. Mat. 3, 1 (2017). This work was conducted in collaboration with H. Teisseyre, A. Janotti, A. Alkauskas, and C. G. Van de Walle

Authors : Hao-Tsung Chen, Yu-Feng Yao, Chia-Ying Su, Charng-Gan Tu, Chun-Han Lin, C. C. Yang
Affiliations : National Taiwan University, Taipei, Taiwan

Resume : By growing an alternating p-GaN/u-GaN layered structure with molecular beam epitaxy, we can obtain extremely low effective resistivity based on Hall measurement. With 4 and 2.5 nm in thickness for the p-GaN and u-GaN layers, respectively, a resistivity level as low as 0.038 Ohm-cm can be achieved. Such a low resistivity level is obtained by combining the high hole mobility in the u-GaN layers and the high hole concentration in the p-GaN layers. The holes can effectively diffuse into the u-GaN layers from the neighboring p-GaN layers for high-mobility migration. However, the theory behind the Hall measurement is based on the assumption of a uniform p-type layer. In such a layered structure, the Hall measurement result relies on the depth of current penetration. In other words, the relatively larger measured resistivity of a layered structure of larger layer thicknesses can be due to two possible causes: high effective resistivity and shallow current penetration in the Hall measurement. To understand the real cause, we grow samples of two thick layers with varied upper-layer thickness and low resistivity in the lower layer. By comparing the Hall measurement results of those samples, we can figure out the current penetration depth. This study can shed some light on the mechanism of Hall measurement when it is applied to an nm-scale layered doped structure. Based on the result of the current penetration depth, we can more accurately evaluate its effective resistivity.

Authors : Andrii Nikolenko (1), Viktor Strelchuk (1), Bogdan Tsykaniuk (1), Dmytro Kysylychyn (2), Giulia Capuzzo (2) and Alberta Bonanni (2)
Affiliations : (1) V. Lashkaryov Institute of Semiconductor Physics of National Academy of Sciences of Ukraine, 41 Nauky pr., 03028 Kyiv, Ukraine (2) Institut für Halbleiter-und-Festkörperphysik, Johannes Kepler University, Altenbergerstr. 69, A-4040 Linz, Austria

Resume : Functional Mn-Mgk cation complexes in GaN co-doped with Mn and Mg are expected to extend the functionality of light-emitting III-nitride systems to the near-infrared (NIR) range [1-3]. We report on the excitation-dependent resonance Raman analysis and photoluminescence measurements, performed in order to gain insight into the nature of impurity-induced Raman features in (Ga,Mn)N:Mg with IR-emitting cation complexes. We have found that in contrast to the case of (Ga,Mn)N, the resonance enhancement of Mn-induced modes in Mg co-doped samples is not observed at an excitation of 2.41 eV, but shifts down to 1.58 eV, an effect explained by a resonance process involving the excitation of holes from ionized Mn4+ donor states to the valence band of GaN. Selective excitation within the resonance Raman conditions allows to resolve the structure of the Mn-induced phonon band into two distinct components, whose relative intensity varies with the Mg/Mn ratio, and thus is related to the concentration of cation complexes. Moreover, from the relative intensity of the 2LO and 1LO Raman resonances at inter-band excitation energy, we estimate the Huang-Rhys parameter, and consequently the strength of the electron-phonon interaction, which is found to increase linearly with the Mg/Mn. This work was supported by NATO SfP Grant 984735 and by the Austrian Science Fundation - FWF P24471 and P26830. 1. G. Capuzzo et. al., Sci. Rep. 7, 42697 (2017). 2. T. Devillers et al. Sci Rep. 2, 722 (2012). 3. T. Devillers et al. Appl. Phys. Lett. 103, 211909 (2013).

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09:00 Plenary Session - Main Hall    
12:30 Lunch break    
Session 9: Nanostructures: nanowires, nanorods, quantum dots… : Martin Eickhoff
Authors : Yasuhiko Arakawa(1,2), Munetaka Arita(1), and Mark Holmes(2)
Affiliations : (1) Institute for Nano Quantum Information Electronics, The University of Tokyo; (2) Institute of Industrial Sceince, The University of Tokyo

Resume : III-Nitride quantum dots with their large band offsets and wide range of bandgaps are promising nanostructures for room temperature quantum information technologies, since excitons can be sustained at higher temperature. Growth of high-quality GaN/AlN quantum dots with Stanski-Krastnanov growth mode was developed in 2002 by Metal Organic Chemical Vapour Deposition (MOCVD) [1]. The quantum dots exhibited a large biexciton binding-energy and a strong phonon interaction, realizing a single photon emission at 200 K in 2006 [2]. However, the magnitude of the binding energy of biexciton was not large enough to realize single photon emission at room temperature. Recently, we have acheived the single photon emission at or above room temperature via a position controlled GaN/AlGaN nanowire quantum dot. The structure was grown by selective area MOCVD and consists of GaN/Al0.8Ga0.2N core-shell type nanowires with a GaN quantum dot inclusion near the tips. The quantum dots themselves typically have a lateral dimension of ∼10 nm and a vertical dimension of ∼1 nm[3]. A large binding energy of biexciton (> 60meV) realized in the quantum dot enabled single photon emissions at room temperature in 2014 and at 350 K (77℃) in 2016, respectively[4,5]. We also succeeded in the formation of interface-fluctuation GaN quantum dots in a thin GaN/AlxGa1-xN (x < 0.25) quantum well grown on a sapphire (0001) substrate. The high temperature growth process led to a striking suppression of spectral diffusion and narrow emission linewidths as low as ~90 micro-eV. A high purity single photon emission from this interface fluctuation quantum dot was achieved and resulted in a measured g(2)(0) value smaller than 0.1 at 10 K. This value is the lowest ever reported for a III-nitride quantum dots, showing the remarkable nature of these quantum dots[6]. References [1] M Miyamura, K Tachibana, and Y Arakawa, Appl. Phys. Lett. 80, 3937 (2002). [2] S. Kako, C. Santori, K. Hoshino, S. Gotzinger, Y. Yamamoto, and Y. Arakawa, Nat. Mater. 5, 887 (2006). [3] K. Choi, M. Arita, S. Kako, Y. Arakawa et al., J. Cryst. Growth 370 328 (2013). [4] M. Holmes, K Choi, S. Kako, M. Arita, and Y. Arakawa, NanoLett., 14 982 (2014). [5] M. Holmes, K Choi, S. Kako, M. Arita, and Y. Arakawa, ACS Photonics 3 543 (2016). [6] M. Arita, K. Choi, S. Kako, and Y. Arakawa, NanoLett., in press (2017).

Authors : L. Rigutti1, L. Mancini1, E. Di Russo1, J. Houard1, I. Blum1, A. Vella1, F. Vurpillot1, W. Lefebvre1, B. Deconihout1, D. Blavette1 A. Das2,3, E. Monroy2,3, C. Durand2, J. Eymery2, E. Giraud4, J.F. Carlin4, R. Butté4, N. Grandjean4
Affiliations : 1 Normandie Univ., GPM, UNIROUEN, INSA Rouen, CNRS, 76000 Rouen, France 2 CEA, CNRS, Université Grenoble Alpes, 38000 Grenoble, France 3 CEA-Grenoble, INAC-PHELIOS, 17 av. des Martyrs, 38000 Grenoble, France 4 Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland

Resume : Correlating two or more microscopy and spectroscopy techniques on the same nanoscale object may yield a relevant amount of information, which is difficult to achieve by other means. In this contribution, we present several results of correlated studies of micro-photoluminescence (μ-PL), high-resolution scanning transmission electron microscopy (HR-STEM) and laser-assisted atom probe tomography (APT) on single nano-objects containing quantum confined systems based on III-N materials. This approach can be applied to the study of heterostructure interface definition, presence of extended defects such as stacking faults or dislocations, carrier localization and optical emission in quantum confined systems [1-4]. Furthermore, the use of complementary techniques may be extremely helpful for a correct interpretation of atom probe results and for understanding the limitations of the applied techniques [3,5]. Finally, we will show the first results of PL spectroscopy in situ in an atom probe. [1] L. Rigutti et al., Nano letters (2014), 14, 107–114. [2] L. Mancini et al. Appl. Phys. Lett. (2016), 108, 042102 [3] L. Rigutti et al. J. Appl. Phys. (2016) 119, 105704. [4] L. Mancini, Ph.D. Thesis (2016) and L. Mancini et al., submitted (2017). [5] L. Mancini et al. J. Phys. Chem. C (2014) 118, 24136-24151.

Authors : N. Ben Sedrine1,*, J. Cardoso1, A. Alves1, J. Rodrigues1, A. F. Martins1, A. J. Neves1, D. Nd. Faye2, M. Belloeil3, B. Daudin3, M. Peres2, E. Alves2, K. Lorenz2, M. R. Correia1 and T. Monteiro1
Affiliations : Departamento de Física e I3N, Universidade de Aveiro, Campus Universitário de Santiago,3810-193 Aveiro, Portugal; IPFN, Instituto Superior Técnico, Campus Tecnológico e Nuclear, Estrada Nacional 10, P-2695-066 Bobadela LRS, Portugal; Univ. Grenoble Alpes, CEA/CNRS Group, “Nanophysique et Semiconducteurs”, F-38000 Grenoble, France

Resume : Group III-nitride semiconductors based on AlxGa1-xN alloys span a wide range of bandgap energies that could enable the realization of color tunable laser diodes. In particular, Favennec et al. demonstrated that materials with wider bandgaps present lower thermal quenching of rare earth (RE) luminescence, which drives our motivation to explore the case of AlGaN with high AlN molar fraction. Furthermore, in order to achieve laser diodes at the nanometer scale, or nano-emitters, AlxGa1-xN nanowires (NWs) are explored. In this work, AlxGa1-xN NWs grown by molecular beam epitaxy on Si (111) substrate, implanted with europium (Eu) ions at the same fluence of 1×1014 Eu/cm2, are studied. The as-implanted samples containing Al, were further submitted to rapid thermal annealing (RTA) treatments in nitrogen for 30 seconds, at 1000°C and 1200°C, while the GaN samples were only annealed at 1000°C. Raman spectra demonstrate that the Eu implantation did not significantly affect the AlN NWs. Furthermore, for all the AlxGa1-xN NW samples, a crystal recovery was obtained after RTA annealing. Photoluminescence (PL) measurements revealed that Eu3 luminescence was observed in all samples with the most intense emission assigned to the 5D0 - 7F2 transition in the red spectral region, indicating that such implantation and annealing conditions successfully activated the Eu ions. The same transition is found to shift by 2 nm towards longer wavelengths (from 622 to 624 nm) by increasing AlN molar fraction (from x=0 to x=1), in good agreement with results obtained for AlxGa1-xN layers. After annealing the AlxGa1-xN NWs at 1200°C, the Eu relative emission intensity at 622 nm (with respect to the yellow band intensity), was enhanced by a factor of two for each sample.

Authors : S.Matta 1,2 , J.Brault 1, T.-H. Ngo 2, B. Damilano 1, M. Korytov 1, P. Vennéguès 1, M. Nemoz 1, J. Massies 1, M. Leroux 1, B. Gil 2
Affiliations : 1 : Université Côte d’Azur, CNRS, CRHEA, 06560 Valbonne, France 2: L2C, UMR 5221, Case courrier 074-34095 Montpellier Cedex 5, France

Resume : AlxGa1-xN based ultraviolet (UV) LEDs attract a lot of attention as an alternative to mercury vapor lamps that suffer from environmental problems and technical limitations. However the low structural quality of AlxGa1-xN materials leads to a drop in the UV-LED efficiencies. Our approach to enhance the radiative efficiency in AlxGa1-xN LEDs is to confine the carriers in 3 dimensions in quantum dots (QDs) to minimize the probability of non-radiative recombinations with dislocations. In this work, we investigate the properties of AlyGa1-yN QDs (0 ≤ y ≤ 0.4) for high efficient UV emitters. The samples were grown on AlxGa1-xN (0001) with 0.5 ≤ x ≤ 0.8. The influence of the epitaxial strain and of the QD composition on the formation of high QD densities (up to 10 12 cm-2) are shown. In addition, the fabrication of ultra-small QDs (with height < 2 nm), enables to minimize the influence of the internal electric field on the QD emission energy. Time resolved photoluminescence (PL) combined with temperature (T) dependent PL measurements enabled us to determine the QD internal quantum efficiency (IQE) at low T, showing IQE values between 30% and 50% in the 270 nm – 370 nm range. In addition, the PL yield decreases only by 25% from low T to room T. A very strong reduction of the decay times (from tens of µs to a few ns) was also observed for higher Al content and smaller size QDs, due to the strong increase of the electron–hole wavefunction overlap. These properties can be related to two contributions: the QD size and/or the internal electric field reduction, which will be discussed. Finally, the design of AlyGa1-yN QD based LEDs was investigated and UV LEDs emitting in the 300-360 nm range were fabricated.

15:30 Coffee break    
Session 10: Non-polar & semi-polar structures & devices : Klaus Thonke
Authors : Robert A. Taylor, Claudius Kocher, Tong Wang, Tim J. Puchtler, John Jarman, Tongtong Zhu, Rachel A. Oliver
Affiliations : Robert A. Taylor; Claudius Kocher; Tong Wang; Tim J. Puchtler; Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK John Jarman; Tongtong Zhu; Rachel A. Oliver; Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK

Resume : Non-polar (11-20) a-plane InGaN quantum dots (QDs) are strong candidates for polarised single-photon light sources due to their large and tuneable band offsets, strong quantum confinement, and the lack of internal fields in the (11-20) direction. The resultant strong exciton oscillator strength, reduced inhomogeneous broadening and phonon scattering, and short emission lifetimes allow these polarised sources to achieve higher operation temperatures and much faster repetition rates. With these QDs embedded in nanopillars for higher extraction efficiency, or in planar LED structures for electrical pumping, we report the observation of optically-pumped ultrahigh repetition-rate, strongly polarised single photon emission with a predefined and deterministic polarization axis up to 220 K, an operation temperature easily accessible by commercial Peltier coolers. Furthermore, we report single photon electroluminescence up to 130K in our device structures. The simple planar growth method and inclusion of p and n doping also allow them to be easily made into electrically pumped devices. Hanbury Brown and Twiss (HBT), time-resolved, and polarization-resolved micro-photoluminescence (µPL) experiments were performed at various temperatures on these QDs. Sharp emission features from QDs were recorded up to 250 K in the optically pumped samples. Linearly polarised single photon emission was observed from 4.7 to 220 K. A g(2)(0) of 0.37, lifetime of 521 ps, and a degree of linear polarization (DOLP) of 0.83 were obtained at 4.7 K. All three of these characteristics remained almost insensitive to increasing temperature. At 220 K, the g(2)(0), lifetime, and DOLP became 0.47, 341 ps, and 0.80 respectively. Due to the limited emission intensity, g(2)(0) and DOLP were not obtainable at 250 K. The axis of polarization is consistently along the (1-100) m-direction. Based on the behavior of the redshift and inhomogeneous linewidth broadening, we have demonstrated temperature-insensitive quantum confinement, and a much-reduced Huang-Rhys factor and acoustic phonon coupling strength, comparing to their polar (0001) QD counterparts. These latest results demonstrate the potential of non-polar a-plane InGaN QDs as strong candidates for future on-chip Peltier-cooled polarized single photon emitters. For the electrically pumped source single photon emission was achieved under excitation with a constant current giving a second-order correlation value of 0.18.

Authors : Shigefusa F. Chichibu, Kazunobu Kojima
Affiliations : Institute of Multidisciplinary Research for Advanced Materials, Tohoku University

Resume : In the active layer of the blue light-emitting diodes (LEDs) used in the solid-state lighting, quantum wells of essentially immiscible InGaN alloys are exclusively used. For realizing compact and low power consumption light sources for high color rendering index LED lighting and for sterilization and disinfection for human lives, near- to deep-ultraviolet LEDs are indispensable and are under development using AlGaN alloys. Whereas, since the growth of high-quality crystal is herculean, equally immiscible AlInN alloys have never been used as light-emitting media, although their bandgap energies cover from UV-C to near IR wavelength regions. The authors have recently demonstrated planar vacuum fluorescent display devices using m-plane AlInN epitaxial nanostructures grown by metalorganic vapor phase epitaxy, which were composed of a dense array of approximately 50-nm-thick nanoboards. As they emitted polarized UV-C, blue, and green light despite the presence of high-concentration nonradiative recombination centers, the emission mechanisms and their microscopic origins are worth investigating. In this presentation, two distinct length-scale compositional modulations in the m-plane AlInN epilayers will be shown to discuss their origins. A few-nm-scale periodical compositional undulation along < 20-21>-axis was found in the pseudomorphic region thinner than 50 to 60 nm from the AlInN/GaN interface, and more macroscopic compositional pulling effect was seen in the nanoboard regions.

Authors : J. Suffczyński, H. Teisseyre, J. Papierska, S. Kret, B. Damilano, N. Kriouche, A. Courville, P. de Mierry
Affiliations : Institute of Exp. Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland; Institute of Physics, Polish Academy of Sciences, Warsaw, Poland; Centre de Recherche sur l’Hétéro-Epitaxie et ses Applications, CNRS, Valbonne, France; Université de Nice Sophia Antipolis, Nice, France

Resume : The research on GaN quantum structures grown on nonpolar and semipolar directions suppresses internal electric field, which increases oscillator strength of the confined exciton. However, the growth along these directions results in much-enhanced densities of extended defects, like basal (BSF) or prismatic stacking faults (PSF). Most typically they take a form of a few atomic monolayer thick, cubic-like inclusions in a wurtzite host. Our polarization and time resolved micro-photoluminescence measurements (spatial resolution <0.5 μm) conducted on GaN layers grown on semipolar (11-22) direction reveals a presence of unexpectedly sharp (FWHM down to 0.2 meV), discrete lines in the 3.20 – 3.45 eV spectral range. Planar density of these lines determined from optical measurements are of the order of 1010/cm2. The  PL dynamics in single ns temporal range excludes that donor-acceptor pairs are responsible for the observed emission. The individual lines show a high linear polarization degree, with three dominating polarization directions in the lines statistics. They clearly correspond to directions of three types of defects visible in HR-TEM images taken in plan-view near [11-22] zone axis. The defects are high density of 5-20 nm long segments of the BSF (perpendicular to c axis) and two groups of partial dislocations associated with BSF. Our results provide the first indication for the optical determination the type of the extended defects in GaN semipolar structures.

18:00 Best Student Presentation Awards Ceremony and Reception (Main Hall)    
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Session 11: Surface properties: growth mechanism, surface states & sensor applications I : Marek Godlewski
Authors : Robert Kudrawiec
Affiliations : Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology

Resume : Contactless electroreflectance (CER) spectroscopy in a very powerful tool to investigate the built-in electric field in semiconductor heterostructures as well the Fermi-level position on semiconductor surface. In this work we will present our recent progress in the application of CER spectroscopy to study these issues in GaN-based (hetero)structures. To determine the Fermi level position at the GaN surface we perform CER measurements on specially designed UD+ structures [GaN(undoped)/GaN(doped)/substrate] doped by Si and Mg. Measuring the built-in electric field in the undoped (U) layer it is possible to determine the Fermi level position at the surface. In this way we have observed that the surface Fermi level of Ga-polar GaN exhibits a bistable behavior allowing it to be located at two distinct energetic positions: ~0.6 and ~1.7 eV below the conduction band for n-type and p-type structures, respectively. Next CER results for GaN(cap)/AlGaN/GaN heterostructures will be presented. In this case a decrease of built-in electric field in GaN(cap) layer and an increase of electric field in AlGaN layer has been observed with the increase in thickness of GaN(cap) layer, while a decrease of electric field in AlGaN layer and an increase in electric field in GaN(cap) layer has been noticed with the increase in thickness of AlGaN layer. The observed results are explained solving the Schrodinger and Poisson equations in self-consistent manner for the proper surface boundary condition.

Authors : Moritz Brendel
Affiliations : Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany

Resume : In this talk, the properties of highly efficient AlGaN-based metal-semiconductor-metal photodetectors for the UVC and UVB spectral region will be reviewed in terms of experimental and simulated data. One aspect will be the illumination direction either from the top (absorber) or bottom (substrate/buffer) side. Another aspect is the role of internal polarization fields in MOVPE-grown AlGaN/AlN/c-sapphire structures and their interplay with an externally applied electric field. This explains the saturation of the external quantum efficiency above a certain bias voltage, which is determined by the AlGaN absorber layer thickness. However, this dependence is cancelled for detectors with an increased density of specific macroscopic crystal defects that form current transport paths through the absorber layer resulting in a thickness-independent saturation voltage. Furthermore, ageing experiments of UVC MSM detectors will be discussed, in order to reveal field-induced surface reactions as the root cause of degradation of un-passivated devices.

Authors : 1.Shunsuke Okada, 1.Shuichi Tanaka, 1,2. Hideto Miyake, 1. Kazumasa Hiramatsu
Affiliations : 1.Department of Electrical and Electronic Engineering, Mie University, Tsu, Japan ;2. Graduate School of Regional Innovation Studies, Mie University, Tsu, Japan

Resume : AlN has been used as the substrate for deep-ultraviolet light-emitting devices owing to its wide bandgap and high chemical stability. However, high-density of threading dislocations exists in AlN films grown on non-native substrates. Recently, we developed high-temperature face-to-face annealing (FFA) technique that can drastically improve the crystal quality of AlN films on sapphire substrates [1]. In this work, we fabricated high quality AlN films on sapphire substrates using face-to-face annealing. AlN films were grown on c-plane sapphire substrates by metalorganic vapor phase epitaxy (MOVPE). The film thickness was 20 – 1000 nm. The growth temperature and the reactor pressure were maintained at 1400 oC and 17.3kPa, respectively. Then, the AlN films were thermally annealed at 1700 oC in an ambient N2 using FFA technique. The surface roughness was increased with increasing film thickness 20 – 300 nm, whereas it decreased with increasing film thickness 300 – 1000 nm. The AlN films formed a step and terrace surface morphology with pits for 1000-nm-thick AlN film. The full width at half maximum (FWHM) of X-ray rocking curve (XRC) for AlN(0002) and AlN(10-12) reflection were 74″ and 754″, respectively. After thermal annealing for 1000-nm-thick AlN films, the smooth step and terrace surface without pits was formed. The crystallinity was drastically improved with FWHM values of XRC for 57″ for AlN(0002), 138″ for AlN(10-12). [1] H. Miyake et al., J. Cryst. Growth 456 (2016) 155.

Authors : Avakyants L.P., Aslanyan. A.E., Bokov P. Yu., Chervyakov A.V.
Affiliations : Physics Department, M.V. Lomonosov Moscow State University, Leninskie Gory 1 b. 2, 119991, Moscow, Russia

Resume : Heterostructures based on polar GaN have the strong intrinsic electric field caused by piezoelectric and spontaneous polarizations due to mismatch of the crystal cells of adjacent heterostructure layers. In present report the internal electric fields in active region of LEDs structures based on multiple InGaN/GaN QWs were investigated by electroreflectance (ER) spectroscopy. The sample under investigation is royal blue LED heterostructure with 5 QW in active area grown along [0001] direction on sapphire substrate by MOCVD technology. ER spectra were obtained at room temperature in the range of 2.2-3.5eV with different and DC bias voltages. Observed spectra were modified by Kramers–Kronig relations and approximated by sum of Lorenz functions. Obtained dependences of amplitude and peak position from the DC voltage allow to determine the inner electric field in different QWs with respect to applied bias voltages. The energies of two QWs showed independence from the external electric field and inner one is 3.0-3.5MV/cm. Other ones showed splitting in energies 75meV with changing the voltage from 0 to -4.5V which corresponds to the difference in electric field 1.8MV/cm. Such behavior of distribution of electric field is connected with the straight influence of external electric field on the two QWs and nonlinear impact on the other ones whereas internal electric field without bias voltage has the contrary dependence from the coordinate in growth direction in active area.

10:30 Coffee break    
Session 12: Surface – properties &growth mechanism, surface states & sensor applications II : Enrique Calleja
Authors : James S. Speck
Affiliations : Materials Department, University of California, Santa Barbara, CA 93106, USA

Resume : We present work from two recent areas of nitride MBE Role of calcium in the efficiency of MBE LEDs: Ca as an unintentional impurity has been investigated in III-nitride layers grown by molecular beam epitaxy (MBE). It is found that Ca originates from the substrate surface, even if careful cleaning and rinsing procedures are applied. The initial Ca surface coverage is ∼1012 cm−2. At the onset of growth, the Ca species segregates at the growth front while incorporating at low levels. The incorporation rate is strongly temperature dependent: ~0.03% at 820 °C and increases by two orders of magnitude when the temperature is reduced to 600 °C, which is the typical growth temperature for InGaN alloy. Consequently, [Ca] is as high as 1018 cm−3 in InGaN/GaN quantum well structures. Such a huge concentration might be detrimental for the efficiency of LEDs if one considers that Ca is potentially a source of Shockley-Read-Hall (SRH) defects. We thus developed a specific growth strategy to reduce [Ca] in the MBE grown LEDs, which consisted of burying Ca in a low temperature InGaN/GaN superlattice (SL) before the growth of the active region. [Young et al., APL 109, 212103 (2016)] Role of disorder in LED behavior: We review recent experimental work on unipolar analogs to LEDs to demonstrate the important role of alloy disorder in transport.

Authors : Pawel Kempisty (1,3), Yoshihiro Kangawa (2,1), Pawel Strak (3), Stanislaw Krukowski (3), Kenji Shiraishi (1)
Affiliations : (1) Center for Integrated Research of Future Electronics, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8603, Japan; (2) Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan; (3) Institute of High Pressure Physics PAS, Sokolowska 29/37, 01-142 Warsaw, Poland;

Resume : Comprehensive analysis of GaN(0001) surface under ammonia/hydrogen mixture was undertaken using results of density functional theory calculations. It was shown that the adsorption processes depend on the electronic properties of the surface. The adsorption energy of the same species may vary by several electronvolts depending on the Fermi level position at the surface. Its location is dependent, inter alia, on the surface reconstruction. There are two classes of surface: the first, wherein the Fermi level is pinned at surface states located in the bandgap (energy bands are bent), and the second, wherein Fermi level is free (energy bands are almost flat). Depending on the type, the different potential barriers at the surface exist. This could particularly affect the incorporation energy of impurities and dopants. Based on this phenomenon, we explain, for example, some unclear aspects of carbon incorporation during GaN growth by MOVPE. For practical use it is important to define the surface state in individual growth conditions, beyond the vague definition of N-rich and Ga-rich conditions. Therefore, we proposed a revised, more accurate approach, which includes also contribution derived from vibrational motion of the solid phase. This allows to calculate the thermal change of vibrational energy and entropy for differently reconstructed surfaces. The chemical potential difference contribution of the following terms: vaporization enthalpy, vaporization entropy, thermodynamic temperature related entropy change, the thermal enthalpy change and mechanical pressure was determined. Obtained results can be used to predict the true state of the hot surface.

Authors : Nicolas Kurz, Yuan Lu, Lutz Kirste, Markus Reusch, Agne Zukauskaite, Vadim Lebedev, Oliver Ambacher
Affiliations : Laboratory for Compound Semiconductor Microsystems, IMTEK-Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany; Fraunhofer Institute for Applied Solid State Physics, Tullastrasse 72, 79108 Freiburg, Germany; Fraunhofer Institute for Applied Solid State Physics, Tullastrasse 72, 79108 Freiburg, Germany;Fraunhofer Institute for Applied Solid State Physics, Tullastrasse 72, 79108 Freiburg, Germany;Fraunhofer Institute for Applied Solid State Physics, Tullastrasse 72, 79108 Freiburg, Germany;Fraunhofer Institute for Applied Solid State Physics, Tullastrasse 72, 79108 Freiburg, Germany;(3) Laboratory for Power Electronics, INATECH-Department of Sustainable Systems Engineering, Emmy-Noether-Straße 2, 79110 Freiburg, Germany

Resume : AlN thin films are widely used in electronic, optoelectronic and sensor applications due to their outstanding properties and compatibility with standard CMOS process technology. In 2009 it was shown that the piezoelectric properties can be improved tremendously by alloying AlN with ScN [1], making AlScN a promising candidate for future electronic as well as optoelectronic devices and sensors. AlScN might also have superior properties for pyroelectric sensors [2]. However, no investigation was conducted on the thermal dependence of the pyroelectric current, that would determine the suitability of AlScN for high-temperature pyroelectric sensor applications. In this work, 1 µm thick pyroelectric Al1-xScxN films (x = 0 to 0.25) were deposited on Si(100) substrates by reactive pulsed dc magnetron co-sputtering. The X-ray diffraction measurements revealed that all films have wurtzite type crystal structure and are highly c-axis oriented. To measure the pyroelectric current in the temperature range of 20 °C to 95 °C a low-frequency temperature wave dynamic method was employed. The effective pyroelectric coefficient of AlScN increased by 50% in the investigated composition range. Moreover, a decline of the effective pyroelectric coefficient with rising temperature was observed for all samples. We explain this observation qualitatively by taking into account the contribution of primary and secondary pyroelectric effect as well as the substrate clamping. [1] M. Akiyama, et al., Advanced Materials, 21(5), 2009. [2] V. Vasilyev, et al., MRS Advances, 1 (39), 2016.

Authors : Kohei Ogawa, Shun Ishijima, Yusuke Namae, Akihiro Matsuoka, Akihiko Kikuchi
Affiliations : Sophia University; Sophia Nanotechnology Research Center

Resume : Damage-free precision etching of group III nitride semiconductors is an attractive technology expected to be applied for removing the dry etching damage and precise size tuning for the next-generation nanostructure-based LEDs, solar cells, transistors, and so on. We propose a new digital wet etching technique using surface oxidation by saturated ozone water (SOW) treatment and oxide film etching with buffered hydrofluoric acid (BOE). In this etching, the side facet of InGaN/GaN nanostructure formed on the (0001) plane wafer was etched with good controllability at 0.8 nm/cycle. For the evaluation of the etching characteristics, the InGaN/GaN nanostructures with 100~240 nm in width and 140 nm in height formed by the low-damage etching technique called hydrogen environment anisotropic thermal etching (HEATE) [1] was used. The SOW was made by bubbling ozone gas into deionized water. The sample was subjected to 75 cycles of SOW treatment, deionized water rinsing (1 min), BOE (10 min), and deionized water rinsing (1 min) at room temperature. The SOW treatment time was changed into 10, 20, and 30 min. The etching rate was estimated every 25 cycles from the reduction of nanostructure width via a field emission scanning electron microscope (FE-SEM) observation. Despite of the SOW treatment (oxidation) time change, the etching rate was almost kept at 0.8 nm/cycle (~3 ML/cycle). This simple etching has a feature of highly controllable sub-nm order digital etching technique. [1] R. Kita, R. Hachiya, T. Mizutani, H. Furuhashi, and A. Kikuchi, Jpn. J. Appl. Phys. 54, 046501 (2015).

12:30 Lunch break    
Session 13: Substrates & strain relaxation : Stanisław Krukowski
Authors : Hutomo Suryo Wasisto1,2,*, Jan Gülink1,2,3, Shinta Mariana1,2, Steffen Bornemann1,2,3, Nursidik Yulianto1,2,4, Feng Yu1,2, Klaas Strempel1,2,3, Muhammad Fahlesa Fatahilah1,2, Tony Granz1,2, Nicolai Markiewicz1,2,6, Gregor Scholz1,2, Iqbal Syamsu1,2,5, Heidi Boht1,2, Daria Bezshlyakh1,2, Wenze Wu1,2, Jana Hartmann1,2,3, Hao Zhou1,2, Sönke Fündling1,2,3, Joan Daniel Prades6, Andreas Waag1,2,3
Affiliations : 1 Institute of Semiconductor Technology (IHT), Technische Universität Braunschweig, Braunschweig, Germany; 2 Laboratory of Emerging Nanometrology (LENA), Technische Universität Braunschweig, Braunschweig, Germany; 3 Epitaxy Competence Center (ec2), Technische Universität Braunschweig, Braunschweig, Germany; 4 Research Center for Physics, Indonesian Institute of Sciences (LIPI), Tangerang Selatan, Indonesia; 5 Research Center for Electronics and Telecommunication, Indonesian Institute of Sciences (LIPI), Bandung, Indonesia; 6 MIND-IN2UB, Department of Engineering - Electronics, University of Barcelona, Barcelona, Spain

Resume : 3D GaN nanostructures with well-controlled geometry, vertical architecture, and high aspect ratio are very attractive because they are expected to be an exciting new route towards extending the freedom for device design in GaN technology. Such building blocks provide large surfaces, defect free high-quality material, non-polar surface orientations, and the option to use very large area foreign substrates without implementing large area strain. All these aspects are difficult to be obtained in planar thin film approaches. To fabricate vertical 3D GaN nanoarrays, both bottom-up and top-down methods involving different nanolithography techniques can be employed offering good homogeneity. Additionally, 3D processing needs to be developed to integrate them into nanodevices for various optoelectronic sensing and electronics applications (e.g., biomedical/chemical sensors and vertical transistors). By adjusting the orientations, width and pitch of the hole/line openings, and the growth/etching parameters, different structural qualities can be evolved. In terms of the geometry, nanofins potentially offer more advantages than vertical nanowires as they can reduce edge effects, have a higher gain in effective area and be much easier accessible for material analysis. The MOCVD growth and hybrid etching results for both nanofin and nanowire structures will be compared, 3D processing will be described, and experimental results of the developed nanodevices will be presented.

Authors : Michal Bockowski
Affiliations : 1 Center for Integrated Research of Future Electronics, Institute of Materials and Systems for Sustainability, Nagoya University, C3-1 Furo-cho, Chikusa-su, Nagoya 464-8603, Japan; 2 Institute of High Pressure Physics Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland

Resume : Development of GaN-based optoelectronic and electronic devices is closely linked to ongoing work devoted to crystallizing bulk GaN. Hydride vapor phase epitaxy (HVPE) is the most popular method for obtaining commercial-grade substrates. Significant advantages of HVPE are high growth rate and high purity of new-grown GaN. Using ammonothermal GaN substrates of high crystallographic and structural quality as seeds enables growth of HVPE-GaN of the same high quality. Without intentional doping the material has a very low concentration of impurities and n-type conductivity comes from silicon with concentration close to 1×1017 cm-3. Free carrier concentration is at the level of 3-5×1016 cm-3. Controllable doping of HVPE-GaN to prepare substrates of specific parameters is still a challenge. In this work influence of different dopants on optical and electrical properties of GaN is presented. Results showing highly conductive n-type HVPE-GaN doped with silicon and germanium and semi-insulating material doped with carbon and iron with manganese will be presented. Characterization of the crystals includes their structural (X-ray diffraction, defect selective etching), optical (Raman spectroscopy, photoluminescence) and electrical (Hall measurements, Capacitance–voltage profiling) properties. Concentrations of dopants will be examined by Secondary Ion Mass Spectrometry (SIMS).

Authors : Christian Röder, Friederike Zimmermann, Mykhailo Barchuk, Tom Schneider, Gleb Lukin, Franziska C. Beyer, Olf Pätzold, Jens Kortus
Affiliations : Institute of Theoretical Physics, TU Bergakademie Freiberg, Leipziger Str. 23, D-09599 Freiberg, Germany; Institute of Applied Physics, TU Bergakademie Freiberg, Leipziger Str. 23, D-09599 Freiberg, Germany; Institute of Materials Science, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 5, D-09599 Freiberg, Germany; Institute of Nonferrous Metallurgy and Purest Materials, TU Bergakademie Freiberg, Leipziger Str. 34, D-09599 Freiberg, Germany; Institute of Nonferrous Metallurgy and Purest Materials, TU Bergakademie Freiberg, Leipziger Str. 34, D-09599 Freiberg, Germany; Institute of Applied Physics, TU Bergakademie Freiberg, Leipziger Str. 23, D-09599 Freiberg, Germany; Institute of Nonferrous Metallurgy and Purest Materials, TU Bergakademie Freiberg, Leipziger Str. 34, D-09599 Freiberg, Germany; Institute of Theoretical Physics, TU Bergakademie Freiberg, Leipziger Str. 23, D-09599 Freiberg, Germany;

Resume : High-temperature vapour phase epitaxy (HTVPE) [1] is a physical vapour transport based technique for the growth of GaN, which uses thermally evaporated, elemental gallium and ammonia as precursors. This method allows the deposition of GaN layers on (0001)-oriented sapphire substrates exhibiting a crystal and structural quality comparable to conventional growth methods. In this work, we present results on structural and optical characterization of GaN layers grown by HTVPE at various growth conditions. The resulting layers were examined by high-resolution X-ray diffraction. We find, that the FWHM of 0002 X-ray reflections are below 200 arcsec. Additionally, we assessed the threading dislocation density analysing reciprocal space maps. In order to monitor residual stress within the GaN layers with high lateral and spatial resolution we performed confocal Raman spectroscopic measurements at room temperature. We discuss the spectral position of the non-polar E2(high) Raman mode indicating compressive in-plane strain, which is reduced with increasing GaN layer thickness. Low-temperature photoluminescence spectra of HTVPE layers grown at atmospheric pressure show a suppressed near band edge emission (NBE) in comparison to the ultraviolet luminescence. The NBE intensity increases about two orders of magnitude for layers deposited at reduced pressure and with elevated growth rates indicating an improved layer quality. [1] G. Lukin et al., physica status solidi (c), 11, 491 (2014).

Authors : P. Sadovyi 1, B. Sadovyi 1 4, S. Porowski 1, I. Petrusha 2, V. Turkievich 2, A. Nikolenko 3, B. Tsykaniuk 3, V. Strelchuk 3, I. Karbovnyk 4, and I. Grzegory 1
Affiliations : 1 Institute of High Pressure Physics PAS, 29/37, Sokolowska str., 01-142 Warsaw, Poland; 2 V. N. Bakul Institute for Superhard Materials NASU, 2, Avtozavodska str., Kyiv, 04074, Ukraine; 3 V. Lashkaryov Institute of Semiconductor Physics, NASU, 45, pr. Nauky, 03028 Kyiv, Ukraine; 4 Ivan Franko National University of Lviv, 50, Dragomanova str., Lviv, 79005, Ukraine;

Resume : This report presents preliminary results of the study of crystallization of gallium nitride from Fe-Ga-N solution under N2 pressure of 1 GPa. Motivation behind choosing the Fe-Ga-N system for investigating the possibilities of GaN crystallization is based on the information about high solubility of nitrogen in iron (Geochem. Int. 49 (2011) 429-438) under the conditions identical to those, applied in classical GaN growth method from nitrogen solution in gallium (J. Phys. Chem. Solids 56 (1995) 639–644). Performed experiments allowed to determine low limit of the temperature range available for the crystallization of GaN in the abovementioned system at 1 GPa N2 pressure. This temperature is limited by iron melting temperature which is found by DTA method to be as low as 1380 °С. This value is above 200 °С below from the one reported for pure Fe iron for 1 GPa pressure (Yu. Tonkov). Temperature dependencies of nitrogen and gallium nitride solubility in Fe were studied in the range of 1380-1480 °С and at 1 GPa N2 pressure. The possibility of growing GaN single crystals at cooling of N solution in Fe80%Ga20% alloy heated up to Т = 1450 °С at 1 GPa is demonstrated. Micro-Raman and micro-photoluminescence spectra of newly grown crystals were measured and analyzed. Based on these data, experiments on crystallization of gallium nitride from Fe-Ga-N solution at 1 GPa under temperature gradient are designed. Results of these experiments will be discussed as well.


Symposium organizers
Agata KAMINSKAInstitute of Physics Polish Academy of Sciences

02-668 Warsaw, Al. Lotnikow 32/46 - Poland

+48 22 1163519; +48 501 275 572

17 rue des Martyrs, 38054 Grenoble cedex 9, France
Martin EICKHOFFUniversity of Bremen, Institute of Solid State Physics

Otto-Hahn-Allee NW1, D-28359 Bremen, Germany

+49 (0)421 218 62220
Stanisław KRUKOWSKIInstitute of High Pressure Physics

Polish Academy of Sciences, 01-142 Warsaw, Sokolowska 29/37, Poland

+48 22 8880244; +48 501 015 791