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2015 Fall

Nanomaterials,Nanostructures and Nano devices


Electronic & optical nature of silicon nanostructures: doping, interface effects & strain

Silicon nanostructures in all dimensionalities are investigated by researchers working in both fundamental science (nanophysics, nanotechnology) and microelectronic engineering (future CMOS technologies, sensors, photovoltaics, etc.). This symposium intends to cover theoretical, experimental and application aspects of all types of Si nanostructures with emphasize on doping, surface/interface effects, and advanced metrology methods. 




In fundamental science, Si nanostructures such as quantum wells, nanowires, or quantum dots are fabricated deliberately to study the properties of nanoscale Si with the aim of modification and utilization for a variety of applications. On the other hand, applied research on future Si-CMOS technologies is driven by the demand of miniaturization on the low nanometer scale to improve performance. With ongoing CMOS miniaturisation, there is a minute quantitative size difference between both disciplines which will vanish completely in the near future. Besides the well-known size dependent quantum confinement effects, Si nanostructures are highly susceptible to their surrounding and any kind of impurities. Many key material properties change due to the influence of an embedding matrix or surface terminating groups. For instance, it has been shown that surface functionalization and ensuing strain switches the fundamental band gap type from indirect to direct-like. Also, it was demonstrated that different types of dielectric matrices induce a charge transfer in Si nanostructures which creates energy offsets of electronic states. On the other hand, well established technological concepts such as majority carrier generation by impurity doping with e.g. phosphorous or boron are impeded in Si nanostructures due to self-purification, statistical problems, or failing dopant ionization due to quantum confinement. Likewise, problems with dopant diffusion in the channel region or dopant deactivation at the Si/SiO2 interface are hot topics in Fin-FET engineering.

In order to understand, circumvent or exploit these effects sophisticated theoretical approaches (e.g. via density functional theory simulations) and advanced metrology (e.g. atom probe tomography) are crucial for the whole range of small Si nanostructures.

The symposium will focus on the electronic, optical and structural properties of Si nanostructures in the context of doping, interface- and matrix-effects (including strain, interface charge transfer, surface functionalization etc.) as well as the novel measurement technologies to detect, image and probe these effects. Fundamental and applied researchers are encouraged to present their recent results and to exchange their knowledge and experience.


Confirmed list of invited speakers:


  • J. R. Chelikowsky, Austin, USA (tba)
  • T. Frauenheim, Bremen, Germany (tba)
  • M. Fujii, Kobe, Japan (“All-inorganiccolloidal Si nanocrystals”)
  • T. Gregorkiewicz, Amsterdam, Netherlands (“Specificprocesses of hot carrier cooling in Si NCs“)
  • A. Heinzig, Dresden, Germany (“The RFET – a reconfigurable nanowire transistor and the realization of novel CMOS circuits“)
  • U. Kortshagen, Minnesota, USA (tba)
  • U. Lemmer, Karlsruhe, Germany (“Hybrid light emitting diodes using Si nanoparticles (SiLEDs)”
  • M. T. Lusk, Golden, USA (“Carrier Collection and Transport in Thin Film Silicon with Tailored Nanocrystalline/Amorphous Structure”)
  • D. Mariotti, Ulster, UK (“Atmospheric pressure plasma for the synthesis and deviceintegration of Si-based quantum confinednanocrystals”)
  • A. Meldrum, Alberta, Canada (“Surface treated free-standing silicon quantum dots for vapor sensing”)
  • M. Perego, Agrate Brianza, Italy (“Mechanism of dopant incorporation in Si nanostructures”)
  • R. N. Pereira, Aveiro, Portugal (“Electronic doping of crystallinesiliconnanoparticles”)
  • Y. Rosenwaks, Tel Aviv, Israel (tba)
  • H. Sigg, Villigen, Switzerland (“Top down method to introduce high strain in Si and Ge for CMOS basedelectronics and photonics”)
  • S. Smith, Sydney, Australia (tba)
  • A. Stesmans, Leuven, Belgium (tba)
  • I. Sychugov, Stockholm, Sweden (“Influence of surface passivation on quantum efficiency and luminescence linewidth of Si nanocrystals”)
  • R. Tilley, Wellington, New Zealand (tba)
  • A. Vilan, Rehovot, Israel (tba) 

Confirmed list of scientific committee members:


  • C. Delerue, Lille, France
  • K. Dohnalova, Amsterdam, The Netherlands
  • S. Dyakov, Stockholm, Sweden
  • F. Gourbilleau, Caen, France
  • S. Gutsch, Freiburg, Germany
  • J. Heitmann, Freiberg, Germany
  • S. Hernandez, Barcelona, Spain
  • P. Jelínek, Prague, Czech Republic
  • J. Linnros, Stockholm, Sweden
  • T. Mikolajick, Dresden, Germany
  • S. Mirabella, Catania, Italy
  • I. Pelant, Prague, Czech Republic
  • S. Strehle, Ulm, Germany
  • J. Valenta, Prague, Czech Republic 







Proceedings of Symposium P will be published in Physica Status Solidi (c). Upon nomination by the (Guest-) Editors selected papers may be published in Physica Status Solidi (a) or (b), or in special cases in pss Rapid Research Letters (RRL). 


Student Awards & PSS Young Researcher Award:


Please send your award applications (incl. description of work, abstract, letter of support, CV) to the organizers by August 17.

Applicants have to be the main author and presenter of their contribution. Finalists will be notified and interviewed prior to the selection of the award winners. 

Start atSubject View AllNum.
09:00 Welcome & Introduction: D. Hiller    
1. Si QDs for Sensing & Biomedical Applications : K. Kusova
Authors : Ben McVey, Richard Tilley
Affiliations : University of New South Wales

Resume : Liquid phase synthesis is a powerful method for the formation of uniform sized nanoparticles and nanoparticles with a faceted morphology. General strategies for the formation of silicon and germanium nanocrystals will be outlined. Included will be the synthesis of transition metal doped silicon quantum dots and use of different capping agents to form hydrophobic and hydrophilic nanocrystals. The growth mechanism of how the particles form will also be presented along with HRTEM observations. The optical properties of the quantum dots will be discussed including the effect of surface capping molecules. The optical properties of silicon nanocrystals capped with different capping molecules and silicon nanocrystals doped with transition metal will be discussed. The biomedical applications and toxicity of the nanocrystals will also be outlined.

Authors : Keith Linehan, Darragh Carolan, Hugh Doyle
Affiliations : Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland

Resume : Semiconductor quantum dots have generated considerable interest in the last recent 20 years because of their unique optoelectronic properties making them attractive materials for applications in solar cells, optoelectronics devices and as fluorescent labelling agents suggesting enormous potential for this class of material for a number of applications. While Si NCs have found applications in bio imaging, photonics and optoelectronics, few reports exist for Si NCs as probes for chemical sensing. Luminescent water-soluble silicon nanocrystals (Si NCs) have been developed as a simple and rapid assay for the highly selective and sensitive detection of Fe3+ via quenching of their strong blue luminescence, without the need for analyte-specific labelling groups. Sensitive detection of Fe3+ was successfully demonstrated in aqueous solution, with a linear relationship between luminescence quenching and Fe3+ concentration observed from 25 – 900 μM, with a limit of detection of 20 μM. The Si NCs show excellent selectivity toward Fe3+ ions, with no quenching of the fluorescence signal induced by the presence of Fe2+ ions, allowing for solution phase discrimination between ions of the same element with different formal charges. The luminescence quenching mechanism was confirmed by static and time-resolved absorption and photoluminescence spectroscopies, showing the applicability for this platform for detection of Fe3+ in real water samples.

10:20 Coffee Break    
2. Si QDs – Influence of Surfaces & Matrix : D. König
Authors : Mark T. Lusk, Tae-Ho Park, Luigi Bagolini, Alessandro Mattoni, P. Craig Taylor, Reuben T. Collins
Affiliations : Department of Physics, Colorado School of Mines, Golden, Colorado USA; Department of Physics, Colorado School of Mines, Golden, Colorado USA; Istituto Officina dei Materiali del CNR (CNR-IOM) UOS Cagliari, Cittadella Universitaria, Monserrato (Ca), Italy; Istituto Officina dei Materiali del CNR (CNR-IOM) UOS Cagliari, Cittadella Universitaria, Monserrato (Ca), Italy; Department of Physics, Colorado School of Mines, Golden, Colorado USA; Department of Physics, Colorado School of Mines, Golden, Colorado USA;

Resume : Despite significant attention, materials composed of quantum confined silicon quantum dots are still inefficient at collecting and distributing charge carriers. This has motivated us to computationally design and experimentally synthesize quantum dots that are subsequently encapsulated within hydrogenated amorphous silicon. The matrix modifies the quantum confinement of the dots and plays a critical role in photon collection, hot carrier cooling and transport. It also offers environmental protection for the dots and a larger design space for tuning optoelectronic properties. Our investigation will be overviewed before focusing on the computational paradigm that we developed. Within the nanocrystalline setting, cooling rates and transport mobilities are governed by phonon-assisted hopping using a combination of nonadiabatic coupling (NAC) and Fermi's Golden Rule. The NAC is found to offer significant advantages over more traditional approaches to estimate electron-phonon coupling for materials in which electronic states can be spatially localized. The vibrational influence on cooling and carrier transport rates is accounted for with the aid of an analytical extension of the standard Frank-Condon formulation. The NAC is calculated using our new, parallelized time-dependent DFT routine. We apply the computational methodology to predict cooling rates and transport mobilities for amorphous silicon, crystalline silicon and layered structures in which the morphologies are alternated. Beyond the ability to quantify such processes, the explicit interplay of electronic and vibrational states allows us to create material architectures in which vibrational modes enhance carrier transport - i.e. phonon management.

Authors : P. Hapala, P. Mutombo, P. Jelinek
Affiliations : Institute of Physics of the ASCR, v.v.i. Cukrovarnicka 10, Prague 6, Czech Republic

Resume : There has been a long-standing discussion on whether or not an electronic band structure concept. i.e. energy-to-wavevector dispersion, can be assigned to zero-dimensional objects such as quantum dots or nanoscrystals (Ncs) (see e.g. [1]). To answer this question, we developed a general method [2], which allows reconstruction of electronic band structure of free standing Ncs from ordinary real-space electronic structure calculations. We combine the method with fully relaxed large-scale Density Functional Theory calculations of a realistic Si-Ncs of up to 3 nm in size with different surface passivations [2]. To demonstrate character of the band structure of Si-Ncs, we calculate band dispersion along the Γ-X direction to compare it with a bulk counterpart. Based on this comparison, we conclude that the band structure concept is applicable to free standing Si-Ncs with diameter larger than ~2 nm with certain limitations. In addition we will discuss impact of surface passivation using different polar and nonpolar molecules on atomic and electronic structure including momentum space selection rules important for light emission. Namely we will address the possibility to convert passivated Si-Ncs to direct band gap-like material [3]. [1] M. S. Hybertsen, Phys. Rev. Lett. 72, 1514 (1994) [2] P. Hapala, et al., Phys. Rev. B 87, 195420 (2013) [3] K. Kůsová et al., Adv. Mat. Interfaces 1, 1300042 (2014)

Authors : K. Kusova,* P. Hapala,* P. Jelinek,* L. Ondic,* O. Cibulka,* I. Pelant* and J. Valenta**
Affiliations : *Institute of Physics ASCR, Prague, Czech Republic **Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic

Resume : Bulk silicon is notoriously known as an inefficient light emitter due to its indirect bandgap. In order to overcome this obstacle, various sophisticated approaches, usually purely theoretical, are being proposed. Our work offers a simple but efficient solution to this problem. We show both theoretically, using DFT calculations, and experimentally that properly passivated silicon nanocrystals can be transformed into a material with fundamental direct bandgap and, as a consequence, also fast radiative transitions on par with other direct semiconductors. The transformation into a direct-bandgap material is caused by a cooperation of two processes: both quantum confinement, inherently present in nanocrystals, and tensile strain, induced in the nanocrystal's core by the attached surface groups, cooperate to give rise to a cross-over of the Delta minimum and the Gamma maximum of the silicon's bandstructure. This contribution will be focused on the experimental evidence of direct bandgap, coming from both macroscopical and microscopical photoluminescence measurements.

Authors : Keith Linehan, Hugh Doyle
Affiliations : Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland

Resume : Semiconductor nanocrystals (NCs) are attractive materials for light-emitting devices due to their size-tuneable band gap, compatibility with solution processing and high photoluminescence (PL) efficiencies. Interest in Group IV NCs has increased in recent years due to the observation of photoluminescence in quantum confined particles, allowing applications ranging from biological imaging to optoelectronic devices. Solution-phase synthesis and characterisation of size monodisperse Si NCs with core diameters between 2 to 6 nm is demonstrated. Si NCs were synthesised under inert atmospheric conditions via the reduction of Si halide salts (SiX4) by hydride reducing agents within inverse micelles. Covalent attachment of alkyl surface terminating ligands produced stable NCs which were readily dispersed in a variety of organic solvents. UV-Visible absorbance (UV-Vis) and photoluminescence spectroscopy (PL) showed strong significant quantum confinement effects, with moderate absorption in the UV spectral range, and strong emission in the blue, with a marked dependence on excitation wavelength and capping ligand. Photoluminescence quantum yields showed an inverse relationship with the NC core diameter with nanosecond luminescence lifetimes. Replacing the alkyl termination with a polarisible amine molecule reulsted in a significant chnages in the UV-Vis and PL spectrum, but no change in the luminescent lifetimes.

12:40 Lunch Break    
3. Si QDs – Surfaces, Coupling, Strain : J. Heitmann
Authors : Ilya Sychugov, Fatemeh Sangghaleh, Federico Pevere, Anna Fucikova, Zhenyu Yang*, Jonathan Veinot*, Jan Linnros
Affiliations : KTH Royal Institute of Technology, Department of Materials and Nanophysics, Stockholm, Sweden; *University of Alberta, Department of Chemistry, Edmonton, Canada

Resume : Using single-dot spectroscopy and lifetime measurements together with spectrally-resolved ensemble decay measurements the effect of surface passivation on Si nanocrystal optical properties was investigated. We found that the homogeneous linewidth strongly depends on the elastic properties of the surrounding media for these nanoparticles, where room temperature values vary by an order of magnitude (from 20 to 200 meV) for nanocrystals with oligomerized ligand passivation and with a thin passivating shell only. The measured temperature evolution of the homogeneous linewidth indicated strong exciton-phonon interaction. The phonon modes responsible for this effect were identified as low-energy “breathing” vibrations, which energy depends on the surrounding matrix. Thus values as low as 200 ueV for individual nanocrystal bandwidth could be detected for nanoparticles with a thin passivating shell at ~ 35 K. Ligand passivated nanocrystals were also found to have high quantum yields 30-70%. Their spectrally-resolved decays revealed monoexponential character corresponding to 100% internal quantum efficiency (IQE), which is quite different from oxide embedded nanocrystals typically exhibiting much lower values of the IQE. The nature of possible defects in the oxide embedded nanocrystal system, which can be responsible for non-radiative recombination of a similar strength as radiative ones affecting the IQE, is discussed based on recent temperature-dependent single dot lifetime results.

Authors : B. van Dam (a), C.I. Osorio (b), A.F. Koenderink (b), K. Dohnalova (a)
Affiliations : (a) Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands; (b) FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands

Resume : Silicon quantum dots (Si QDs) are a promising alternative to toxic and rare material QDs that are researched or used in optoelectronics, photonics and bio-imaging. For competitive emission properties, however, the radiative rate needs to be considerably improved. This is the case in Si QDs capped with organic ligands; Nevertheless, despite high radiative rates approaching those of direct bandgap QDs [1,2], the quantum yield (QY) in the visible range remains comparatively low (<20%) [1,2]. Improved understanding of the processes underlying the ensemble photoluminescence (PL) and QY of these materials can be achieved from single QD spectroscopy, allowing study of the properties of individual emitters that are otherwise obscured in ensemble measurements. As generally in all quantum emitters, the QY is critically influenced by PL blinking. In addition, poor surface passivation can further reduce the QY by introducing competing non-radiative channels. In both mechanisms surface states play a major role. By single QD spectroscopy, we examine the effect of ligand type on the blinking of colloidal Si QDs and moreover, we study the competition of the radiative and non-radiative recombination pathways by decoupling them by means of a Drexhage-type experiment. Understanding the role of surface will help us to improve the QY of Si QDs for application in lighting technologies. [1] K. Dohnalova et al., Light: Science and Applications 2 (2013) e47 [2] K. Kusova et al., ACS Nano 4 (2010)

Authors : S. Hernández,1 J. López-Vidrier,1 J. Ibáñez,2 D. Hiller,3 S. Gutsch,3 M. Busquets-Masó,1 M. Zacharias,3 A. Segura, 4 J. Valenta,5 and B. Garrido1
Affiliations : 1MIND-IN2UB, Departament d’Electrònica, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Catalonia, Spain. 2Institute of Earth Sciences Jaume Almera, ICTJA-CSIC, Lluís Soler i Sabarís s/n, 08028 Barcelona, Catalonia, Spain. 3IMTEK, Faculty of Engineering, Albert-Ludwigs-University Freiburg, Georges-Köhler-Allee 103, D-79110, Freiburg, Germany. 4Departamento de Física Aplicada-ICMUV-MALTA Consolider Team, Universitat de València, 46100 Burjassot, València, Spain.

Resume : Silicon nanocrystals (Si NCs) embedded in SiO2 have been extensively studied because of their potential to fabricate novel optoelectronic and photonic devices. Their optical properties are strongly affected by both their size and local environment. The aim of the present study is to investigate the role of the exerted pressure over the NCs on their optical emission, by means of optical characterization under high hydrostatic pressure. The samples consist of Si NC/SiO2 superlattices containing NCs with average crystalline diameters of either 4.1 or 3.2 nm. High-pressure Raman scattering and photoluminescence (PL) measurements were performed up to 5.5 GPa with a membrane-type diamond anvil cell, using the 532-nm line of a Nd:YAG laser. The Raman spectra of the two samples allowed determining the phonon pressure coefficient, yielding a value of (8.5 ± 0.3) cm-1/GPa in both samples, which is much larger than the one for bulk Si (5.1 cm-1/GPa). This result is ascribed to a strong pressure amplification effect due to the larger compressibility of the SiO2 matrix. The PL spectra exhibit a lower energy band that barely depends on pressure, which was ascribed to defects. The pressure coefficients of the higher energy band were found to be much larger than the one for bulk Si, with values very similar for both Si NC sizes: (-35 ± 8) and (-27 ± 6) meV/GPa for 4.1 and 3.2 nm, respectively. The analysis of the PL data, once the pressure amplification is included, revealed that the emission from Si NCs is consistent with that of the indirect transition of Si.

Authors : J. Laube, S. Gutsch, D. Hiller, C. Kübel, M. Zacharias
Affiliations : Laboratory for Nanotechnology, Department of Microsystems Engineering - IMTEK, University of Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg im Breisgau, Germany; Institute of Nanotechnology (INT) and Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

Resume : Silicon nanoparticles potentially enable new applications in silicon based optoelectronics and photovoltaics. Single layers of nitrogen free Si rich oxides with varying Si excess concentrations were deposited by PECVD [1,2] followed by a subsequent high temperature annealing to induce phase separation. The structural properties of the layers are investigated by plane view TEM using high resolution as well as energy filtered TEM. At low Si excess, isolated single crystalline Si particles with low density are observed indicating an incomplete phase separation. An increase of Si excess leads to larger Si particles along with an increased intrinsic crystal defect density. Furthermore, we find a transition point near SiOx=0.4, where the isolated Si particles merge into a continuous network. In addition we study the influence of annealing conditions and find negligible differences that are indicative of fast phase separation on the timescale of seconds and significantly slower pa rticle growth due diffusion processes. The importance of the results is discussed in the context of transport properties that affect a possible Si nanocrystal device performance. [1] Laube et al. JAP, 116, 223501, 2014 [2] Gutsch et al. BJnano 6, 964, 2015

15:40 Coffee Break    
4. Si QDs – Hot Carriers & Quantum Yield : P. Jelinek
Authors : Tom Gregorkiewicz
Affiliations : Van der Waals - Zeeman Institute, University of Amsterdam

Resume : Quantum confinement strongly affects properties of hot carriers in nanocrystals. In particular their cooling rates and thus effective lifetime are influenced by reduction of phonon emission and energy recycling through a combination of enhanced Auger recombination and impact excitation. This, among others, promotes enabling multiple exciton generation rates and energy transfers to the outside of the nanostructure. In my presentation, I will discuss some results of investigations of these effects in Si and Ge nanocrystals embedded in SiO2: 1. Carrier multiplication in Ge nanocrystals: I will report on the recent identification of this effect in materials prepared by co-sputtering 2. Carrier multiplication in Si nanocrystals. Here I will discuss the on-going investigations of spectral modification of emission induced by the carrier multiplication process providing a unique spectral fingerprint of this special process. 3. Energy recycling processes for hot carriers in Si nanocrystals, enabled by interplay between impact excitation and Auger recombination of multiple excitons in the same nanocrystal, leading to effective increase of free electron temperature 4. Excitation of Er emitters by hot carriers optically generated in Si nanocrystals, demonstrating that this energy transfer path can successfully compete with phonon emission. 5. Energy diffusion within an ensemble of Si nanocrystals, leading to peculiarities in exciton characteristics. [1] M.T. Trinh et al., Nature Photonics 6, 316-321 (2012). [2] S. Saeed et al., Nature Communications 5:4665 (2014) [3] F. Priolo, T. Gregorkiewicz, M. Galli, and T. Krauss, Nature Nanotechnology 9, 19 (2014) [4] S. Saeed et al., NPG Light: Science and Applications, 4, e251 (2015)

Authors : Jan Valenta, Anna Fucikova, and Mikel Greben
Affiliations : Department of Chemical Physics & Optics, Faculty of Mathematics & Physics, Charles University, Ke Karlovu 3, CZ-121 16 Prague 2, Czechia

Resume : Photo- and electro-luminescence quantum yield (QY) is a crucial parameter for materials to be used in light-emitting devices, fluorescent probes etc. We have developed a compact set-up and procedure for reliable measurements of QY over a broad excitation spectral range which uses excitation by LEDs and a carefully calibrated spectroscope [1] and applied them to various nanomaterials, mostly Si nanocrystals (SiNCs). Analysis of the QY spectral dependence can reveal important information on non-radiative recombination channels, carrier multiplication processes, collective phenomena in dense ensembles of NCs etc. [2]. In this contribution we summarize our experiments on various forms of SiNCs, namely multilayers of Si nanocrystals (NCs) separated by SiO2 barriers and doped SiNCs in the form of liquids and deposited layers. Multilayer samples enabled us to clearly demonstrate that the increase of barrier thickness from about 1 to larger than 2 nm induces doubling of the PL QY value which corresponds to the change of number of close neighbours in the hcp structure [3]. The temperature dependence of PL QY suggests that the PL QY changes are due to a thermally activated transport of excitation into non-radiative centers in dark NCs or in the matrix. Finally, we shall discuss all possible phenomena that contribute to limiting PL QY values in ensembles of SiNCs. [1] J. Valenta, Nanoscience Methods 3 (2014) 11-27 (OA). [2] D. Timmerman et al. , Nature Nanotechnology 6 (2011) 710. [3] J. Valenta et al., Appl. Phys. Lett. 105 (2014) 243107.

Authors : S. Gutsch 1, J. Valenta 2, M. Greben 2, M. Zacharias 1
Affiliations : 1 Laboratory for Nanotechnology, Albert Ludwigs University of Freiburg, Freiburg Germany 2 Laboratory of Optical Spectroscopy, Charles University, Prague, Czech Republic

Resume : The absolute photoluminescence (PL) quantum yield (QY) of multilayers of Si nanocrystals (NCs) separated by SiO2 barriers were thoroughly studied as function of the barrier thickness, excitation wavelength, and temperature. The temperature dependence of PL QY suggests that the PL QY changes are due to a thermally activated transport of excitation into non-radiative centers in dark NCs or in the matrix in agrrement with previous results obtained from time-resolved PL spectroscopy. The PL QY excitation spectra show no significant changes upon changing the barrier thickness and no clear carrier multiplication effects. Moreover, we find that there is no PL spectral shift as a function of excitation energy clearly evidencing the absence of space-separated quantum cutting effects. [1] Valenta et al., Appl. Phys. Lett. 105, 243107 (2014)

5. Poster Session : K. Kusova, D. König, D. Hiller
Authors : Issam DJABRI(a) , Nasreddine DERRADJI(a,b,*), AbdelkaderKARA(c)
Affiliations : (a) LESIMS, department of Physics, University of Badji mokhtarBP12 El Hadjar Annaba (Algeria); (b) Preparatory School of technical science ,BP 218 Safsaf City, Annaba( Algeria); (c) Department of Physics, University of Central Florida, Orlando, FL 32816, USA

Resume : Using density functional theory (DFT) to study the structural, electronic and magnetic properties of bare and Cl-terminated silicene nanoribbons (SiNRs) with either zigzag edge (ZSiNRs) or armchair edge (ASiNRs) with ribbon widths N=5,7. Based on first-principles method under the generalized gradient approximation (GGAPW91) was applied to evaluate the exchange-correlation energies of all examined structures. We have calculated the lattice constant “a” of the two types SiNRs. After geometry optimization, we found that the edge Si–Si bonds are shorter than the inner ones with identical orientation, implying a contraction relaxation of edge Si atoms and the length of the Si–Cl bond is always 2.06 Å. Our results suggest that both bare zigzag and armchair having zero gaps and large values of the density of states (DOS) (spin-up and spin-down) at the Fermi level EF, so that both bare ZSiNRs and bare ASiNRs are always metallic with a magnetic moment. In contrast, the Cl-terminated 7-ASiNR is semiconductor with small band gap and zero density (spin-up and spin-down) at the Fermi level EF where the magnetic moment became non-existent, but the Cl-terminated 5-ZSiNR having zero gap and DOS(spin-up and spin-down) peak at the Fermi level EF, demonstrating metallic character with magnetic moment has declined, degenerate flat edge-state bands appears at the Fermi level EF in broader Cl-terminated 5-ZSiNR but does not appear in Cl-terminated 7-ASiNR. Because the electronegativity is smaller and the covalent radius is larger for Si atom than electronegativity and covalent radius for Cl atom, a typical ionic bonding resulted between the edge Cl atom and the nearest Si atom. While, all sorts of the Si-Si bonds display a typical covalent bonding feature.

Authors : Keith Linehan, Daithi O’Sé, Darragh Carolan, Hugh Doyle
Affiliations : Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland

Resume : We report the synthesis and characterisation of SixGe1-x NCs dispersed in non-polar solvents with core diameters (d) between 1 -5 nm. NCs were synthesised under inert atmospheric conditions via the co-reduction of Si and Ge halide salts (SiX4, GeX4) by hydride reducing agents within inverse micelles. Composition of the silicon-germanium nanocrystals was carried out by varying the relative amounts of precursor, while the NC size is controlled by variation of the cationic quaternary ammonium salts used. Covalent attachment of alkyl- or amine-terminated monolayers to the nanocrystal surface produced NCs that stable under ambient atmospheric and lighting conditions over a period of months, which were readily dispersed in a variety of solvents. Transmission electron microscopy (TEM) imaging confirmed that the NCs are highly crystalline with a narrow size distribution; the crystal structure was confirmed by selected area electron diffraction (SAED). Energy dispersive X-ray spectroscopy (EDX) was used to quantify the relative amounts and distribution of Si and Ge within the NCs. UV-Visible absorbance (UV-Vis) and photoluminescence spectroscopy (PL) showed strong significant quantum confinement effects, with moderate absorption in the UV spectral range, and strong emission in the blue, which varied with composition. The photoluminescence quantum yield (f) of the NCs showed an inverse relationship with the NC core diameter, with a maximum over 10% measured for smaller NCs.

Authors : J. Laube, S. Gutsch, D. Hiller, M. Zacharias
Affiliations : Laboratory for Nanotechnology, Department of Microsystems Engineering - IMTEK, University of Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg im Breisgau, Germany

Resume : A monosilane (SiH4) and oxygen (O2) based plasma-enhanced chemical vapor deposition process (PECVD) for the growth of silicon-rich oxide / silicon dioxide superlattices [1] was developed. In contrast to the conventional nitrous oxide (N2O) based oxynitride-process [2], we achieved thereby PECVD-grown size-controlled silicon nanocrystals in pure, N-free silicon dioxide matrix. We present a detailed study based on optical (PL) and electrical (C-V, I-V) measurements that reveal the different properties of nominally identical Si nanocrystals in oxynitride and N-free oxide matrix. Most strikingly we find negligible differences in the optical performance (PL quantum yield), whereas substantial differences in the current transport and transient charging behaviour persist. The role of the pure oxide vs. oxinitride matrix on the properties of Si quantum dots is discussed in the context of potential applications in photovoltaics and optoelectronics. [1] M. Zacharias et al., APL 80, 2002 [2] Laube et al. JAP, 116, 223501 [3] S. Gutsch et al., JAP 113, 2013

Authors : Emanuele Marino (1), Thomas E. Kodger (1), Giovanni Mannino (2), Tom Gregorkiewicz (1), Katerina Dohnalova (1) and Peter Schall (1)
Affiliations : (1) Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (The Netherlands); (2) CNR-IMM, Strada VIII n°5, 95121 Catania, (Italy).

Resume : Silicon Nanoparticles (Si NPs) have been produced through a high throughput, low-temperature plasma synthesis which yields faceted, crystalline and monodisperse NPs ~ 100 nm in size. When deposited on a semiconductor substrate, these nanostructures have shown potential towards the trapping of light within a single NP, where the unique faceted nature of the NPs was a key factor in enhancing the photoluminescence yield of the substrate by increasing the optical path length of the impinging photons [1]. Applying this idea, we perform the assembly of the silicon NPs into large-scale superstructures, and study the resulting modifications in optical properties. This has been pursued twofold: on a substrate (2-dimensional film) and in solution (3-dimensional structure). In the latter case, the colloids have been brought together via the Critical Casimir effect [2]. The results of this investigation may be attractive for novel applications in the field of photovoltaics, possibly giving birth to a new class of thin-film silicon solar cells. While absorption qualities of bulk silicon are maintained due to large size of the Si NPs, light path is considerably enhanced and layers can be deposited by low-cost low-temperature self-assembly approaches. Furthermore, we expect that faceted Si NPs in the high quality assembly (side-to-side) will ensure high level carrier mobility. [1] Mannino et al., Sci. Rep. 5, 8354 (2015). [2] Nguyen et al., Nat. Commun. 4, 1584 (2013).

Authors : D. König* (a), S. Gutsch (b), D. Hiller (b), Hubert Gnaser (c), Michael Wahl (c), Jörg Göttlicher (d), Ralph Steininger (d), Michael Kopnarski (c), Margit Zacharias (b)
Affiliations : (a) Integrated Material Design Centre (IMDC), University of NSW, Sydney, Australia; (b) Department of Microsytems Engineering (IMTEK), Laboratory of Nanotechnology, Albert Ludwigs University Freiburg; (c) Physics Dept. and Research Center OPTIMAS, University of Kaiserslautern, Germany; (d) ANKA Synchrotron Radiation Facility, Karlsruhe Institute of Technology, Germany;

Resume : We report on phosphorous (P) doping of Si nanocrystal (SiNC)/SiO2 systems [1]. Relevant P configurations within SiNCs, at SiNC surfaces, within the sub-oxide interface shell and in the SiO2 matrix were evaluated by hybrid density functional theory (h-DFT). Atom probe tomography (APT) and its statistical evaluation provide detailed spatial P distributions. We obtain ionisation states of P atoms in SiNC/SiO2 systems at room temperature using X-ray absorption near edge structure (XANES) spectroscopy in fluorescence yield mode. This non-destructive volume characterization technique leaves the material unchanged which is paramount to probe P in its original state. P K shell energies were confirmed by h-DFT. We found that P diffuses into SiNCs and resides virtually exclusive on interstitial sites. XANES and h-DFT delivered evidence that the ionization probability of P in the SiO2/SiNC system is extremely low; free localized electrons to SiNCs are not provided. [1] D. König, S. Gutsch, H. Gnaser, et al., Sci. Rep. (Nature), Vol. 5, 09702 (2015), DOI: 10.1038/srep09702

Authors : D. König (a,b)*, Y. Yao (a,b), S. Smith (a)
Affiliations : (a) Integrated Material Design Centre (IMDC), University of NSW, Sydney, Australia; (b) School of Photovoltaic and Renewable Energy Engineering (SPREE), University of NSW, Sydney, Australia

Resume : We model fully OH- and NH2-terminated silicon nanocrystals (SiNCs) - Si35(OH)36 and Si35(NH2)36 - by hybrid-DFT [1,2]. We substitute OH [NH2] groups by double-bonded (=) O [=NH] segments and corner Si(OH)2 [Si(NH2)2] segments for bridge-bonded (>) O [>NH] groups. Correlating ground state (GS) gaps and charge transfers from SiNCs to anion groups with atomic ratios of Si to O [N] atoms, we show the specific impact of = and > anion bonds. Excited state (ES) calculations yielded the three lowest singlet transition energies (ES gap, absorption) and oscillator strengths (optical transition probabilities P_ot). ES energies closely follow the trend of GS gaps for OH-terminated SiNCs with =O, while those for SiNCs with >O show an increasing deviation from GS gaps to lower energies with rising numbers of >O. An increased modulation of charge transfer occurs due to low negative ionization of >O atoms which appears to distort the exciton field and thus increases exciton binding energies. For SiNCs with =O atoms, stronger SiNC ionization seems to improve carrier separation, decreasing exciton binding energies and lifting ES gaps. Thus, P_ot of SiNCs rise hyperlinear with the number of =O atoms, while a saturation occurs for SiNCs with >O atoms. Similar results were found for NH2-terminated SiNCs with =NH vs. >NH, with less influence on the electronic and optical SiNC behaviour due to lower SiNC ionization. [1] Phys. Rev. B 78, 035339 (2008) [2] Adv. Mater. Interf. 1, 201400359 (2014)

Authors : B. Le Borgne, M. Thomas, A. C. Salaün, R. Rogel, L. Pichon
Affiliations : Institut d’Electronique et des Télécommunications de Rennes, Département Microélectronique et Microcapteurs, UMR CNRS 6164, Université de Rennes 1, campus de Beaulieu, 263 avenue du général Leclerc, 35042 Rennes cedex, France

Resume : Thanks to their specific electronic properties, silicon nanostructures (nanowires, nanoribbons) offer great potential for high integration electronics, and for highly sensitive sensors. In our work, silicon nanostructures are synthesized following classical top-down approach using conventional UV lithography technique fully compatible with the existing silicon technology. Silicon nanowires are fabricated following the spacer method [1]. In this method, amorphous silicon layer, crystallized by thermal annealing, is deposited on a SiO2 step. An anisotropic reactive ion etching of the polycrystalline silicon layer allows sidewall spacers formation used as nanowires. Nanoribbons are made of very thin (< 50nm) polycrystalline silicon layer. However, in both cases, such silicon nanostructures show poor electrical properties due to their crystalline quality. One solution studied here to improve it is the metal induced lateral crystallization method, using a metallic catalyst to create oriented crystals. N channel silicon nanostructures based field effect transistors have been fabricated and tested with top-gate, bottom-gate and gate-all-around architectures. Silicon nanostructure/SiO2 interfaces are studied from electrical characteristics by the determination of the density of states using the incremental method of Suzuki [2]. [1] F. Demami, L. Pichon, R. Rogel, and A. C. Salaun, Mat. Sc. Eng. , 012014 (2009) [2] T. Suzuki, Y. Osaka and M. Hirose, Jap. J. Appl. Phys., vol.21 (1982)

Authors : M. Cannas, L. Vaccaro, P. Camarda, F. Messina
Affiliations : Department of Physics and Chemistry, University of Palermo (Italy)

Resume : The visible luminescence of Silicon-nanocrystals (Si-ncs) is a crucial property in determining their use in modern nanotechnologies (optoelectronics, photovoltaics, bioimaging). The research is therefore active to design convenient methods to enhance the brightness of Si-nano emitters; from a microscopic viewpoint the goal is to inhibit the non-radiative channels thus increasing the luminescence efficiency. Laser ablation in liquids responds to this requirement since it provides effective parameters (liquid reactivity) to control both the structural and the optical properties of the produced nanomaterials. This work deals with the luminescence of Si/SiO2 nanosystems produced by ns pulsed Nd:YAG laser ablation in deionized water. By using time resolved photoluminescence technique, we have carried out the study of the spectral and decay features of the Si-nc related emission centered around 1.9 eV as a function of pH. The reported results evidence that on decreasing the pH below 4 both the luminescence intensity and the lifetime increase by a factor 3. This finding demonstrates the crucial role of hydrogen in controlling the surface reactions: surface hydrogenation reduces the concentration of non-radiative centers at the Si/SiO2 interface thus favouring the radiative electron-hole recombination.

Authors : Katerina Herynkova1, Egor Podkorytov2, Miroslav Slechta1, Ondrej Cibulka1
Affiliations : 1 Department of Thin Films and Nanostructures, Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, CZ-162 53 Prague, Czech Republic; 2 Department of Solid State Engineering, Institute of Chemical Technology, Prague, Czech Republic

Resume : Silicon nanocrystals and nanoparticles are being widely studied in view of their potential use in all-silicon optoelectronics, sensors or solar energy conversion. In biological research, high surface-to-volume ratio predestinates this material for easy functionalization and biological safeness and good biodegradability might be anticipated based on experience with bulk silicon. Typical requirements for such nanoparticles used in biological research differ from that for optoelectronics, the aim is to prepare aqueous or isotonic (such as phosphate buffered saline - PBS) colloidal solutions of stable, uniform and strongly luminescing nanoparticles, with sizes suitable for the process of cell endocytosis, ideally in the range of tens to hundreds of nanometers. We have prepared colloidal solutions of luminescing porous silicon nanoparticles (size around 100 nm) obtained by electrochemical etching of silicon wafers. Adding hydrogen peroxide to the etching bath results in oxidized nanoparticle surface and hydrophilic behavior. However, the as-prepared samples agglomerate – the dynamic light scattering revealed the increase of the agglomerates size from 60 nm in fresh samples to 400 nm in one-month-old samples. The tendency to agglomerate was confirmed by zeta-potential measurements. The first attempt to steric stabilization by bovine serum albumin, glycine, glutamic acid and dextran is presented, where the increased stability was observed in the glycine- terminated samples.

Authors : Elisa Arduca (1,2), Gabriele Seguini (1), Massimo Mastromatteo (3), Davide De Salvador(3), Enrico Napolitani (3), Michele Perego (1).
Affiliations : (1) CNR-IMM Lab MDM, Via Olivetti, 2, I-20041 Agrate Brianza (MB), Italy (2) Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy (3) CNR-IMM MATIS and Dipartimento di Fisica ed Astronomia, Università degli Studi di Padova, Via Marzolo, 8, I-35131 Padova, Italy

Resume : One of the major challenges toward scaling of microelectronics devices to the nanoscale is the control of the semiconductor's electronic properties. For this aim, the incorporation of dopants with atomic accuracy alters the semiconductor's electronic structure by creating excess carriers. Unfortunately, conventional doping technologies, such as ion implantation and solid source diffusion processes, do not work at such small scales and for non-planar geometries. An alternative strategy to achieve high-quality doping profiles with areal uniformity at the nanoscale is the so-called monolayer doping. Such approach relies on a self-limiting surface reaction that leads to the formation of a monolayer of dopant-containing molecules bonded to the substrate. To date, monolayers containing different dopants have been formed on semiconductor substrate, but the process of monolayer formation has not been entirely characterized, highlighting many open questions. In this work, a systematic study of P-monolayer doping process on SiO2 substrate is presented. A proper experimental protocol is proposed to reduce the amount of contaminants introduced in the sample during the process and to obtain a P delta layer embedded in a SiO2 matrix. A multi-technique (TOF SIMS and RBS) approach allows monitoring the amount of dopants bonded to the substrate and the reproducibility of the process. The quantity of dopant is tuned by changing the processing parameters.

Authors : Katerina Dohnalova, Alexander N. Poddubny
Affiliations : Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, The Netherlands; Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 26 Politekhnicheskaya st., St. Petersburg 194021, Russia

Resume : Si-based efficient light sources, amplifiers, lasers and photodetectors are continuously sought for realization of the on-chip Si-photonics. The major showstopper, however, is the inherent indirect bandgap of the bulk Si. Two groups have recently reported occurrence of direct bandgap transitions in C-capped Si quantum dots (C-SiQDs) [1-3] – both simulated theoretically and confirmed experimentally. While our concept proposes occurrence of such transitions as a result of modified electronic density in the C-SiQD core resulting from the electronegative capping [1,2], the other group suggests that crucial role plays tensile strain induced by the C-linked ligands [3]. Despite non-unified model, experimental evidence of both groups shown dramatically enhanced radiative rate and size-tunable emission [1,3-5]. To better understand the separate role of the field, we will compare two model situations [2]: (i) covalently attached electronegative ligand (C-SiQDs) and (ii) H-capped SiQDs in locally electronegative field – a system, where only external local electrostatic field plays role and no ligand-induced strain can be present. [1] K. Dohnalova, et al., Light: Science & Applications 2 (2013) e47 [2] A. N. Poddubny, K. Dohnalova, Phys. Rev. B 90 (2014) 245439 [3] K. Kusova et al., Adv. Mater. Int. 1 (2014) 1300042 [4] K. Kusova et al., ACS Nano 4 (2010) 4495 [5] K. Dohnalova et al., Small 8 (2012) 3185

Authors : I. Karbovnyk (1), P.Savchyn (1), A. Huczko (2), M. Cestelli Guidi (3), A. I. Popov (4)
Affiliations : (1) Ivan Franko National University of Lviv, 79005, Lviv, Ukraine, (2) Department of Chemistry, Warsaw University, Poland (3) INFN-Laboratori Nazionali di Frascati, Italy (4) Institute of Solid State Physics, University of Latvia, LV-1063, Riga, Latvia

Resume : The renewed interest in SiC is connected with the synthesis of various one-dimensional nanostructures. Stable 1D silicon carbide nanostructures have been obtained via combustion synthesis route. A morphological characterization of the fabricated 3C-SiC 1D nanostructures has been performed by combining electron microscopy with cathodoluminescence measurements. FTIR spectroscopy analysis has been done Daphne Light synchrotron facility of LNF INFN, Frascati. Infrared reflectivity spectra for unpurified and purified nano-SiC were compared with the spectra of commercially available SiC nanomaterials (experiments were carried out at 20 K and at room temperature). The performed measurements have proved that FTIR technique is very sensitive for SiC nanomaterials. The manifestation of the fundamental Si and C sublattice was observed in the range of 770 to 1000 cm-1. In case of the synthesized 1D structures (nanowires) a different profile of the reflectivity peak was observed. This peak is strongly dependent on the purity of the investigated nanomaterial. For the raw synthesis product the main peak is strongly damped by background absorption. Generally, SiC nanowires show sharper reflectivity maximum than those of the nanoparticles. Small shift of the exact position of the main IR peak was also detected for 1D SiC, indicating the nanometric confinement effect.

Authors : lüHilmi Ünlü
Affiliations : İstanbul Technical University, Department of Physics Faculty of Science and Letters, Maslak 34469 İstanbul, Turkey Tel/Fax: 90 (212) 285 3201/90 (212) 285 6386,

Resume : Reliable and precise modelling of electronic and optical properties of semicondcutors heterostructures is crucial for the optimization of low dimensional electronic and optical devices. It is well known that quantum mechanical calculations electronic properties of heterostructures usually encounters computational and/or conceptual difficulties. Over the years various simplified models have been proposed in attempting to achieve the underlying physics of the interface formation and reveal new insights about the chemical trends. In this work, we propose to use an sp3 bond orbital tight binding theory [1,2] to determine the conduction and valence band energy levels and band offsets in heterostructures.. The model considers the nonorthogonality of hybrids of adjacent atoms and the interaction of bonding and antibonding states and metallic contribution to determine the condcution and valence band energies of semiconductors at high symmetry points (e.g., , L and X). The tight binding eigen-energies of given atoms (anion or cation) are obtained from the Hartree-Fock free atom values, including the Uss, Usp and Upp Coluomb corrections in the solid. The valence band offsets are then obtained from the difference between the valence band energies, screened by the optical dielectric constants of constituent semiconductors. The proposed bond orbital sp3 tight binding model considers the interactions between the sp3 hybrids at adjacent sites, with special consideration given to the overlapping of these hybrids such that it cannot be absorbed into a rescaling . This approach also allows one to determine the polarity of the bond and in turn the effective charge, bulk modulus, elastic constants, deformation potential of both valence maximum and conduction band edges at high symmetry points within the Brillouin zone of tetrahedral semiconductor energy band structure in a self-consistent manner. With such approach we provide more reliable predictions for the properties of the electronic band structure of Si1-x-yGexCy , Si1-xGex and Si1-yCy alloys, including the strain-compensated case, from the interpolation between compressive strained Si1-xGex and tensile strained Si1-yCy.

Authors : J. Ebser, D. Sommer, G. Hahn, B. Terheiden
Affiliations : University of Konstanz, Department of Physics, Box 676, 78457 Konstanz, Germany

Resume : Local rear contacts of Si solar cells can be established by contacting an Al layer point-wise by laser spots through the passivation layer to the Si bulk. In this laser fired contacts (LFC) process, Al can establish a thin p+-doped Si region below the metal/Si interface. Aim of this work is to evaluate the distribution of the electrical potential in and around the contact area. In particular the detection of nanoscopic pn-junctions within the macroscopic contact area is of interest. We apply two different methods to investigate the local hole concentration and the lateral 2D Fermi level variation. Micro Raman spectroscopy allows determination of the free hole concentration near the surface by scanning over the whole LFC area of about 50mu diameter, after etching the Al layer in HCl solution. A high local hole concentration in the range of 10^19cm^-3 is demonstrated and its lateral distribution is measured. Kelvin probe force microscopy (KPFM) evaluates the lateral 2D Fermi-level characteristics at sub-micrometer resolution. LFCs can be investigated with regard to p+-regions or pn-junctions, microcracks and inclusions of metal. KPFM is performed in AM-lift-mode applied on mechanically polished cross-sections of LFCs. The KPFM signal is not only surface sensitive, i.e. the sample preparation is of great importance, but also responsive to sample illumination and applied voltage. Combination of these two methods provides a promising approach for nanoscopic understanding of LFCs.

Authors : V.A. Georgobiani, L.A. Osminkina, K.E. Tsurikov, K.A. Gonchar, V.Yu. Timoshenko
Affiliations : Lomonosov Moscow State University, Physics Department, 119991 Moscow, Russia

Resume : Silicon nanowires (SiNWs) were prepared by metal-assisted chemical etching (MACE) of crystalline silicon (c-Si) wafers with crystallographic orientation (100), p-type conductivity and doping density about 1-10 mOhm*cm in solutions based on AgNO3/HF during 30 sec and H2O2/HF during 20–180 min. Micrographs in scanning electron microscope showed that SiNWs had porous structure and consisted of a plurality of intersecting small nanocrystals and pores. Diameters of SiNWs were 50-300 nm. SiNWs were investigated by means of the Raman scattering spectroscopy under excitation with wavelength of 632.8 nm. An asymmetrical shape of the Raman spectrum of SiNWs was observed and it was explained by evidences of the Fano resonance. A comparison of the Raman spectra for SiNWs and c-Si substrates allows us to estimate the concentration of free charge carriers in SiNWs of the order of 10^19 cm^-3. The total reflectance spectra of SiNWs at wavelength longer than 1000 nm indicate also the high concentration of free charge carriers. The reflectance values did not significantly depend on the thickness of SiNWs layer. This fact confirms the preservation of free charge carriers in the samples prepared for long etching time. The observed high concentration of free charge carriers in SiNWs can be useful for their applications in micro- and optoelectronics. The reported study was funded by RFBR according to the research project No. 16-00-00001 мол_a.

Authors : K.K.Abgaryan, I.V.Mutigullin
Affiliations : Institution of Russian Academy of Sciences Dorodnicyn Computing Centre of RAS

Resume : Manufacturing of highly effective silicon-based light-emitting diodes is a very important technological problem. It is possible to develop a silicon with photoluminescent properties by the irradiation process. Irradiation causes the formation of various defects in silicon structure, including point defects, defect clusters and extended complexes. Until this day there is no detailed experimental data on what types of defects are possible in silicon. Some experimental observations point out the possibility of self-assembly of defects (vacancies and self-interstitials) in silicon during irradiation. In this work theoretical investigation of the stability of various defect complexes including vacancies, self-interstitials and their clusters was performed by means of ab initio as well as molecular dynamic calculations. Ab initio calculations in the framework of density functional theory of silicon crystal with various defects were carried out. Meta-stable defect configurations were found. The software for the molecular dynamic calculations and for the visualization of calculation results was developed. The results of the first-principles calculations were used for the parametrical fitting of Tersoff potential of silicon. The potential was used to perform molecular dynamic calculations of the various configurations of defects in silicon. This approach allowed us to study the dynamic of the atomic system over time and temperature range.

Authors : S. Gutsch, J. Laube, M. Zacharias
Affiliations : Laboratory of Nanotechnology, Albert Ludwigs University of Freiburg, Germany

Resume : The current through dielectric embedded Silicon Nanocrystal thin films is strongly dependent on the applied electric field. Here, we demonstrate that this strong dependence can be explained by a black box model based on a space-charge limited current through insulators in the presence of traps. The result render commonly used models to fit the data superfluous.

Authors : Lukas Ondic, Katerina Kusova, Ivan Pelant
Affiliations : Institute of Physics, ASCR, Czech Republic

Resume : Silicon nanocrystals (SiNCs) are a material which may possess photoluminescence (PL) in the visible spectral range. In the case of oxide-passivated SiNCs, the PL is typically composed of a slow-decaying red–orange band (S-band) and of a fast-decaying blue–green band (F-band). Particularly the origin of the F-band is still not fully understood. In order to investigate the F-band of oxide-passivated free-standing SiNC, we have performed an experimental study which combine temperature (from 4K to 300K), temporal (with picosecond resolution) and spectrally-resolved luminescence spectroscopy. This study shows that that the F-band red-shifts only by 35 meV with increasing temperature, which is almost 6 times less than the red-shift of the S-band in a similar temperature range [Ondic et al, Nanoscale 6, 3837 (2014)]. In addition, the F-band characteristic decay time obtained from a stretched-exponential fit decreases only slightly with increasing temperature. These data suggest that the F-band arises from the core-related quasi-direct radiative recombination governed by slowly thermalizing photoholes.

Authors : K.A. Gonchar 1, L.A. Golovan 1, V.Ya. Gayvoronsky 2, V.Yu. Timoshenko 1
Affiliations : 1 Lomonosov Moscow State University, Physics Department, 119991, Moscow, Russia; 2 Institute of Physics of the National Academy of Sciences of Ukraine, 03680, Kiev, Ukraine

Resume : The dependence of the linear and nonlinear optical properties of silicon nanowires (SiNWs) on their structural properties was investigated. SiNWs with diameter between 40 and 200 nm were grown on crystalline silicon (c-Si) substrates by metal-assisted chemical etching and had a strong scattering of light in the visible and infrared spectral range. Nonmonotonic dependence of the total reflectance of light from SiNWs on their length was discovered. It was found that the indicatrix of the elastic scattering of light with a wavelength of 1064 nm in the SiNW ensembles longer than 2 μm can be approximated by the Lambert's cosine law and the intensity of the scattered light in the rear hemisphere grows logarithmically with increasing the length of SiNWs. It was found that in SiNWs the efficiency of frequency conversion of optical radiation, such as Raman scattering, coherent anti-Stokes Raman scattering and third-harmonic generation, were increased compared to c-Si substrates. Cross-correlation functions of photons scattered in SiNW arrays were measured for the first time and it was found that the interaction of light with SiNWs was multiple times increased compared to c-Si substrates. Nonmonotonic dependence of the intensity of the interband photoluminescence in the range of 1100-1200 nm from SiNWs on their length was found for the first time. The reported study was funded by RFBR according to the research project No. 14-02-31544 мол_a.

Authors : A.F. Lopeandía$,A.P. Perez-Marín$, Ll. Abad#, P. Ferrando-Villaba$, G. Garcia$, F.X. Álvarez$, F.X. Muñoz-Pascual#, J. Rodríguez-Viejo$
Affiliations : $ Physics Department, Universitat Autònoma de Barcelona, Campus UAB, 08193, Bellaterra, Spain # Institut de Microelectrònica de Barcelona (IMB-CNM-CSIC), Campus UAB, 08193, Bellaterra, Spain

Resume : During last decade, nanostructured semiconductors have raised as a promising route to fabrication of miniature chip-based Thermoelectric (TE) devices. Among them, Si has emerged as a potential TE candidate since the discovery that small diameter NWs conduct heat like a disordered solid, while maintaining reasonable values for both electrical conductivity and Seebeck coefficient if they remain crystalline, making the doping process of such structures a crucial step. Although the fabrication of miniature chips formed by Si NWs arrays may yield efficient conversion devices, the lack of reproducibility of bottom-up strategies difficult their establishment. Here, we present geometry based in Si thin films that also takes profit of the phonons scattering while easies the integration with planar technologies. As mentioned before a critical step in the fabrication process is to obtain the optimal doping level in the Si thin films. We opted to implant phosphorous ions (P+) and boron ions (B+) by plasma. To prevent effusion of dopant during post-implantation thermal treatments employed for re-crystallization, the Si thin films were capped by silicon nitride. To obtain the appropriate doping level (~10^19 at/cm^3 for TE) and with the aim to preserve the crystalline seed at the bottom of the thin films, detailed TRIM simulations, multiple implantation and annealing experiments were carried out. Withe final device, the TE properties of the p-n Si thin film couples are measured.

Authors : T. Bentrcia1, F. Djeffal2,3 and D. Arar2
Affiliations : 1) LEPCM, Department of Physics, University of Batna, Batna 05000, Algeria. 2) LEA, Department of Electronics, University of Batna, Batna 05000, Algeria. 3) LEPCM, University of Batna, Batna 05000, Algeria. E-mail:, Tel/Fax: 0021333805494

Resume : Multi-Gate Junctionless MOSFETs have emerged over the last years as promising candidates for low cost nanoelectronic applications, due to the superior electrical and fabrication process properties offered by these devices for both in digital as well as in analog applications. However, the use of uniformly doped channel, source and drain regions presents the well-known problem of the high series resistance associated to the extensions, which degrades the electrical performance of the device. Therefore, new designs and accurate models of nanoscale DGJ MOSFET including the defects at the interface Si/SiO2 are required for the comprehension of the fundamentals of such device behavior against the ageing phenomenon. Based on 2D numerical investigation of a nanoscale DGJ MOSFET, in the present work a numerical study for I-V and small signal characteristics by including both the highly doped extension regions and the interfacial defects is presented. The investigated design, which is a technologically feasible technique by introducing only one ion implantation step, provides a good solution to improve the device immunity against the interfacial defects. In this context, I-V and analog characteristics are investigated by an appropriate 2-D numerical modeling, where the obtained results are compared with those of the conventional DGJ MOSFET.

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6. Si QDs – Phosphorus & Boron Doping : D. König
Authors : Rui N. Pereira
Affiliations : Walter Schottky Institut and Physik-Department, Technische Universitaet Muenchen, 85748 Garching, Germany Department of Physics and I3N, University of Aveiro, 3810-193 Aveiro, Portugal

Resume : Crystalline silicon nanoparticles (NPs) have been attracting much research interest due to their remarkable electronic, optical, and chemical properties. Si NPs combine the processing advantages enabled by nanoparticles with the unique features of Si at the nanoscale such as wavelength tunable light emission and multiple exciton generation. The natural abundance of silicon and its dominant role in microelectronics industry may also facilitate the introduction of Si NPs in commercial products such as solar cells and light emitting devices. The important role that intentional impurity doping plays in semiconductor technology have ignited a great deal of research effort aiming at synthesizing silicon NPs doped with foreign impurities and at understanding their physical and chemical properties. In this presentation a review of the current knowledge of doping in Si NPs will be given. We will address various aspects of doped NPs such as doping efficiency, surface-related effects, confinement of dopants, and charge transport. Particular focus will be given to Si NPs synthesized from gas-phase in silane plasmas, with which many of the investigations reported so far have been carried out.

Authors : M. Perego (a), D. De Salvador (b), M. Mastromatteo (b), E. Arduca (a)(c), G. Nicotra (d), A. Carnera (b), J. Frascaroli (a)(c), G. Seguini (a), M. Scuderi (d), G. Impellizzeri (e), Cristina Lenardi (c), C. Spinella (d) and E. Napolitani (b).
Affiliations : (a) CNR-IMM Lab MDM, Via Olivetti, 2, I-20041 Agrate Brianza (MB), Italy; (b) CNR-IMM MATIS and Dipartimento di Fisica ed Astronomia, Università degli Studi di Padova, Via Marzolo, 8, I-35131 Padova, Italy; (c) Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy; (d) CNR-IMM, Z.I. VIII Strada 5, I-95121 Catania, Italy; (e) CNR-IMM MATIS, Via S. Sofia 64, I-95132 Catania, Italy.

Resume : Deterministic doping of nanostructures is a key challenge for the fabrication of future advanced nanoelectronic devices. Unfortunately, a clear understanding of doping at nanoscale is not available yet, as the physical mechanisms involved in this process are significantly different from those of bulk materials, due to additional constrains related to the presence of the interfaces and of the surrounding oxide matrix. In this regard, Si NCs embedded in a SiO2 matrix represent a paradigmatic system for the physical understanding of dopant incorporation in Si-based nanostructures. In this work the stability of P dopant impurities in Si nanocrystals at thermodynamic equilibrium was investigated. To achieve this goal samples with controlled diffusion sources that are spatially separated from the nanocrystals were fabricated and a controlled amount of dopant atoms from the dopant source was delivered to the nanocrystals by diffusing the dopants trough the SiO2 matrix. Several analytical techniques were combined to determine the amount of P atoms effectively trapped within the Si NCs. At equilibrium, high P concentrations within the Si NCs are thermodynamically favored, largely exceeding the P solid solubility in bulk Si. Finally a simple model based on diffusion Fick’s law in one dimension was used to determine the energy barriers (1 eV) for P trapping/de-trapping at the SiO2/Si NCs interface, obtaining a complete picture of the system at equilibrium.

Authors : S. Gutsch 1, J. Goettlicher 2, R. Steininger 2, M. Zacharias 1
Affiliations : 1 Laboratory of Nanotechnology, Albert Ludwigs University of Freiburg, Germany 2 ANKA Synchrotron Radiation Facility, Karlsruhe Institute of Technology, Germany

Resume : We probe the electronic structure and chemical environment of P doped silicon nanocrystal/silicon oxide multilayers by X-ray absorption spectroscopy of the P-K edge. By analyzing the energetic position of the P-K absorption edge and comparing them with reference samples, we demonstrate that the majority of P atoms are found within the nanocrystals. Comparison with DFT calculations [1] and considering optical and electrical properties of SiNC:P [2] suggests that the P atoms are rather located at interstitial lattice sites than on substitutional ones. [1] Koenig et al., Scientific Reports (Nature) 5, 9705 (2015) [2] Gutsch et al., Appl. Phys. Lett. 106, 113103 (2015)

10:40 Coffee Break    
7. Co-doping & Dopant-free Approaches : S. Gutsch
Authors : Minoru Fujii
Affiliations : Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe, 657-8501, Japan

Resume : Colloidal dispersions of semiconductor nanocrystals (NCs) can be used as “inks” for solution-based deposition of films for optoelectronic devices. A common feature of colloidal NCs is capping of the surface with organic ligands which stabilize NCs in solution by steric barriers. Recently, we developed a novel method to stabilize silicon (Si)-NCs in solution without organic ligands. The strategy is to form heavily boron (B) and phosphorus (P) doped shells on the surface of Si-NCs. The shell induces negative potential on the surface and prevents agglomeration of NCs in polar solvents (alcohol, water, etc.) by the electrostatic repulsion. Due to perfect dispersion of NCs in solution, high quality films of NCs can easily be produced from the solution by spin-coating. The solutions and films of the Si-NCs exhibit very stable size controllable luminescence in a very wide energy range (0.85-1.85 eV). In this presentation, we will discuss the structure and optical properties of Si-NCs with high B and P concentration shells with emphasis on the role of doped B and P atoms on the properties. [1] J. Phys. Chem. C 116, 17969 (2012), J. Phys. Chem. C 117, 6807 (2013), J. Phys. Chem. C 117, 11850 (2013), Nanoscale 6, 122 (2014), J. Appl. Phys., 115, 084301 (2015), J. Mater. Chem. C, 2, 5644 (2014), Nanoscale 6, 12354 (2014).

Authors : André Heinzig (1), Jens Trommer (2), Tim Baldauf (1), Thomas Mikolajick (1,2) and Walter M. Weber (1,2)
Affiliations : (1) Center for Advancing Electronics Dresden TU Dresden, 01069 Dresden, Germany; (2) Namlab gGmbH, 01187 Dresden, Germany; e-mail:

Resume : Further progress in CMOS electronics beyond the predicted end of classical scaling requires the implementation of novel devices and circuits with extended functionality. In this talk, the reconfigurable silicon nanowire field effect transistor (RFET) will be introduced, which combines the function of an n-type and p-type transistor in one single device. It consists of an undoped NiSi2–Si-NiSi2 nanowire heterostructure with independent gated Schottky junctions. Whether devices with additional functionality can be used for future CMOS applications depends on the ability to realize symmetry in the current output of n- and p-transistors. In reconfigurable devices n- to p-symmetry has to be achieved at the same device geometry, which could not be shown for any material so far. In this talk, it will be demonstrated that applying mechanical strain in transistors based on tunneling phenomena can adjust the electron (n-type) to hole (p-type) conduction. The key enabler is the selective tunability of the tunneling transmission of charge carriers. As demonstration of the circuit maturity, the integration of two identical RFETs into a single nanowire will be shown. The inverter circuit exhibits CMOS functionality and circuit reconfigurability. Finally, more complex circuit designs will be presented, illustrating that RFETs can either lead to a reduction of transistor count or can increase the system functionality as an approach for electronics beyond the limits of classical CMOS scaling.

Authors : D. König* (a), D. Hiller (b), S. Gutsch (b), M. Zacharias (b)
Affiliations : (a) Integrated Material Design Centre (IMDC), University of NSW, Sydney, Australia; (b) Department of Microsytems Engineering (IMTEK), Laboratory of Nanotechnology, Albert Ludwigs University Freiburg, Germany

Resume : Ultrasmall silicon (Si) nanoelectronic devices require an energy shift of electronic states for n- and p-conductivity. Nanocrystal (NC) self-purification and out-diffusion in field effect transistors cause doping to fail. Even if dopants manage to enter SiNCs, their ionization energy increases tremendously over values known from bulk Si; no free charge carriers can be provided [1]. We show that silicon dioxide (SiO2) and silicon nitride (Si3N4) create energy offsets of electronic states in embedded Si quantum dots (QDs) in analogy to doping [2]. Hybrid density functional theory (h-DFT), interface charge transfer (ICT), and experimental verifications arrive at the same size of QDs below which the dielectric dominates their electronic properties. Large positive energy offsets of electronic states and an energy gap increase exist for Si QDs in Si3N4 versa SiO2. Using DFT results, the SiO2/QD interface coverage is estimated with nitrogen (N) to be 0.1 to 0.5 monolayers (ML) for samples annealed in N2 versus argon (Ar). The interface impact is described as nanoscopic field effect and propose the energy offset as robust and controllable alternative to impurity doping of Si nanostructures. [1] D. König, S. Gutsch, H. Gnaser, et al., Sci. Rep. (Nature), Vol. 5, 09702 (2015), DOI: 10.1038/srep09702 [2] D. König, D. Hiller, S. Gutsch, M. Zacharias, Adv. Mater. Interfaces 1, 1400359 (2014)

12:40 Lunch Break    
8. Si QDs – Synthesis & Characterization : S. Hernandez
Authors : Davide Mariotti
Affiliations : NIBEC-Ulster University UK

Resume : In this contribution we will report on the most recent advances for the synthesis, characterization and device integration of quantum confined amorphous silicon, crystalline silicon, silicon-carbide and silicon-tin nanocrystals (NCs). In particular we will focus on the synthesis by atmospheric pressure plasmas (APPs) which offer a range of beneficial characteristics such as low-cost and versatility for direct integration/usage of NCs in devices and applications. APPs are demonstrating the capability of achieving high synthesis standards with adequate control over size, size distribution and surface terminations of the NCs. We will report on a range of materials/properties characterization results that are highly relevant for the application of Si-based NCs in photovoltaics (PVs). In addition to the analysis of the chemical composition, surface terminations and crystal structure we have also carried out measurements that have allowed the determination of the NCs full band energy structure. Finally we will describe fabrication processes of PV devices that include Si-based NCs and discuss the impact of a few device architectures and their performance. A theoretical analysis of device performance will also be included that suggest a way forward for third generation PV devices. [1] Nanoscale, 5, 138 (2013). [2] Chemical Physics Letters, 478, 224 (2009). [3] Applied Physics Letters, 97, 161502 (2010). [4] Plasma Processes and Polymers, 9, 1074 (2012).

Authors : L. Vaccaro(1), R. Popescu(2), P. Camarda(1,3) F. Messina(1), S. Agnello(1), M. Cannas(1)
Affiliations : (1) Dipartimento di Fisica e Chimica, Universit? di Palermo, Italy; (2) Laboratory for Electron Microscopy, Karlsruhe Institute of Technology, Germany; (3) Dipartimento di Fisica ed Astronomia, Universit? di Catania, Italy

Resume : Silicon nanocrystals (Si-ncs) currently attract a wide interest motivated by their use in several applications (optoelectronics, photovoltaics, bioimaging). In fact, reduction of silicon to the nanoscale introduces intriguing features related to quantum confinement and interface states; the latter, induced by surface reactions, are influenced by the production methods. Among them, laser ablation in liquids provides effective parameters (laser photon energy, fluence, pulse duration, liquid reactivity) to control the morphology and the structure of the related products. In this work we study the effect of oxidation on the nanosized material produced by laser ablation of a Si wafer in deionized water. The investigation has been carried out by combining microscopy, Infrared (IR), and time resolved luminescence techniques. Transmission electron microscopy (TEM) images and energy-dispersive X-ray spectroscopy (EDXS) analysis reveal Si-ncs and amorphous SiO2 nanoparticles produced by Si oxidation in water. The structure of these nano-materials is also evidenced by IR vibrational features. Moreover, Si-ncs are characterized by a luminescence band around 1.9 eV; SiO2 nanoparticles show emissions related to surface states and to defects such as oxygen deficient centers.

Authors : G. Seguini,1 E. Arduca,1,2 B. Han,3 Y. Shimizu,3 K. Inoue,3 Y. Nagai,3 C. Castro,4 S. Schamm-Chardon,4 G. BenAssayag,4 M. Perego1
Affiliations : (1) Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (MB), Italy. (2) Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy (3) The Oarai Center, Institute for Materials Research, Tohoku University, Ibaraki, Japan (4) CEMES-CNRS and Université de Toulouse, nMat group, BP94345, 31055 Toulouse, Cedex 4, France.

Resume : Si nanocrystals (NCs) embedded in SiO2 are intensively studied both to understand the properties of the matter at nanometric scale and for nanoelectronic, optoelectronic, and photovoltaic applications. The non-planar NCs/oxide interface evidences the competition between quantum confinement and the increased surface to volume ratio in semiconducting nanostructures. In particular, the Si NCs size, density, and composition affect the optical and electronic properties of this system. In this work, a single plane of Si NCs in SiO2 matrix was synthesized by e-beam deposition of SiO2/SiO/SiO2 structures followed by high temperature thermal treatment (1050°C, 30 min, N2). The size of the Si NCs was tuned by changing the thickness (4, 6, and 10 nm) of the SiO layer. The average size of Si NCs as well as their density, spatial distribution, and composition of the interface with the SiO2 matrix were investigated by atom probe tomography (APT) to reconstruct the 3D atom map of the samples with nearly atomic scale resolution. The APT data were validated by comparison with data extracted from Energy filtered transmission electron microscopy (EFTEM) plasmon images of plan-view and cross-section lamella. The combined APT and EFTEM analysis allows defining the interface between the NCs and the surrounding matrix in order to properly recreate the NCs structure. This study paves the way to the possibility to investigate by APT the effective impurities incorporation within the nanostructures.

Authors : Victor Timoshenko(1,2), Luibov Osminkina(1), Kirill Gonchar(1), Yerzhan Taurbaev(3), Gakhar Mussabek(3), Kairola Sekerbayev(3), Gulden Botantayeva(3), Dana Yermukhamed(3, Kadyrzhan Dikhanbayev(3), Tokhtar Taurbaev(3)
Affiliations : (1) Physics Department of Lomonosov Moscow State University, Moscow, Russia; (2) National Research Tomsk State University, Lenina Avenue 36, Tomsk 634050, Russia; (3) Physico-Technical Department of al-Farabi Kazakh National University, Almaty, Kazakhstan.

Resume : Layers of porous silicon (PSi) and silicon nanowires (SiNWs) were formed on lightly and heavily Boron-doped p-type (100) c-Si wafers by using electrochemical etching, stain etching or metal-assisted chemical one in hydrofluoric acid solutions. Theoretical analysis and experimental data showed that it was possible to select a profile of the effective refractive index of PSi layer with total thickness about 500 nm, which allowed us to achieve a very low reflection about 1-4% and transmittance up to 96% in the spectral range of 400-1100 nm. SiNWs layers with thickness above 500 nm revealed the total reflectance below 1% that could be used for antireflection coating of solar cells. Numerical simulations predict an effect of free charge carriers with concentration above 10^18 cm^-3 in the cores of SiNWs on both the reflection and absorption in the spectral range of wavelength longer than 1 µm. The obtained experimental data confirm the theory predictions and indicate that such kind of Si-based nanostructures can be useful to create modulators, optical switches and other photonic devices for the infrared spectral region.

15:40 Coffee Break    
9. Si/Organic Hybrids – Concepts & Devices : K. Kusova
Authors : Uli Lemmer
Affiliations : Light Technology Institute, Karlsruhe Institute of Technology

Resume : We discuss the photoluminescence and electroluminescence of highly efficient size-separated silicon nanocrystals (ncSi). The emission color under optical as well as electrical excitation can be tuned from the deep red down to the yellow-orange spectral region by using very monodisperse size-separated nanoparticles. High external quantum efficiencies up to 1.1% as well as low turn-on voltages are obtained for the nanocrystal emitters. We have also performed an in-depth study of the morphological and compositional changes of silicon quantum dot (SiQD) light-emitting diodes (SiLEDs) upon device operation. By means of advanced transmission electron microscopy (TEM) analysis including energy filtered TEM (EFTEM) and energy dispersive X-ray (EDX) spectroscopy, we observe drastic morphological changes and degradation for SiLEDs operated under high applied voltage ultimately leading to device failure. However, SiLEDs built from size-separated SiQDs operating under normal conditions show no morphological and compositional changes and the biexponential loss in electroluminescence seems to be correlated to chemical and physical degradation of the SiQDs. By contrast, we found that, for SiLEDs fabricated from polydisperse SiQDs, device degradation is more pronounced with three main modes of failure contributing to the reduced overall lifetime compared to those prepared from size-separated SiQDs.

Authors : Ayelet Vilan
Affiliations : Department of Materials and Interfaces, Weizmann Institute of Sciences, Israel

Resume : Chemical modifications of metal ? Si interfaces reveal that induced interface dipole is a key cause to the apparent Fermi-level pinning at hetero-junctions. While Si is traditionally known to have a very low index of interface behavior (∼0.1, i.e., severely pinned), using molecular modifications we have received an almost ideal index of interface behavior (∼0.9). Minute chemical variations can drive a given mercury / n-Si interface from accumulation to inversion or from Ohmic transport to 8 orders of magnitude rectification. My talk will introduce the operation mechanism of the interface-dipole effect and describe the fine chemical details controlling the two key elements: the dipoles magnitude and the efficiency of surface states passivation. The organic monolayers serve as a model system for understanding the interplay between interface chemistry and electrostatic characteristic, which is fundamental to any hetero interfaces.

Authors : Vedran Đerek 1, Eric Daniel Głowacki 2, Niyazi Serdar Sariciftci 2, Mile Ivanda 1
Affiliations : 1 Center of Excellence for Advanced Materials and Sensing Devices, Research Unit for New Functional Materials, Ruđer Bošković Institute, Bijenička c. 54, 10000 Zagreb, Croatia; 2 Johannes Kepler University Linz, Linz Institute for Organic Solar Cells (LIOS) / Institute of Physical Chemistry, Altenbergerstraße 69, 4040 Linz, Austria

Resume : Micro- and nanostructured silicon surfaces are often used for performance enhancement in sensing devices, with performance enhancement scaling with increased surface area of structured silicon that is exposed for sensing, or with increased light absorbance due to the light-trapping effects of rough silicon surface. We present optoelectronic devices based on hybrid silicon-organic heterojunctions formed between micro- and nano-structured p-doped silicon surfaces obtained by electrochemical anodisation, metal-assisted chemical etching, anisotropic silicon etching and their hierarchical combinations; and vacuum evaporated thin layer of ambipolar organic semiconductor, hydrogen-bonded pigment 6,6′-dibromoindigo (tyrian purple). Our heterojunctions form rectifying junctions that are photo-sensitive in visible and NIR range, up to ~2500 nm. We show how micro- and nano-structuring of silicon substrates prior to organic thin-film evaporation increases the responsivity of our devices in the telecom C-band by up to 700 times in comparison to planar silicon substrates. We also show that this improvement cannot be due only to increased surface area and/or light trapping, and we present an alternative, electric-field dependant model of performance enhancement.

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10. Si Nanostructures – Plasmonics & Interfaces : J. Valenta
Authors : N. J. Kramer, K. S. Schramke, U. R. Kortshagen
Affiliations : University of Minnesota, Mechanical Engineering, 111 Church St. SE, Minneapolis, MN 55455, USA

Resume : Degenerately doped semiconductor nanocrystals provide new opportunities for materials with localized surface plasmon resonances in the near and mid infrared. The study of their plasmonic properties also enables drawing conclusions about the behavior of dopants in nanocrystals. Here, we discuss the plasmonic behavior of boron and phosphorus doped silicon nanocrystals that are synthesized with a nonthermal plasma approach. Phosphorus doped silicon nanocrystals exhibit plasmonic resonances as-produced, however, the plasmonic response quickly disappears upon oxidation. We interpret this behavior as being due to free electrons due to substitutional dopants, which are being trapped at defect states at the silicon/silicon-oxide interface. Boron doped nanocrystals exhibit the reverse behavior in that they do not exhibit plasmon resonances immediately after synthesis but develop a plasmonic response upon oxidation. This behavior appears more consistent with surface doping. Our interpretation is supported by X-ray photoelectron spectroscopy and electron paramagnetic resonance studies. This work was supported by the Army Office of Research under MURI Grant W911NF-12-1-0407.

Authors : O.S. Ken, D.A. Yavsin, V.S. Levitskii, S.A. Gurevich, V.Yu. Davydov, O.M. Sreseli
Affiliations : Ioffe Institute, St. Petersburg, Russia

Resume : We present results on preparation and studies of novel structures based on Au/Si nanocomposites promising for implementation of plasmonic effects. Thin Au/Si films were fabricated by a laser electrodispersion technique using composite targets with different Au to Si ratio (γ). These films were deposited on p-type Si substrates forming the structures that exhibit rectifying current-voltage characteristics. The morphology, optical and photoelectric properties were studied. At γ = 0% and 100% the films consist of Si and Au amorphous nanoparticles, respectively, with the size of about 2 nm. However, at the intermediate values of γ, microscopic investigations in combination with micro-Raman spectroscopy revealed the marked changes in the film structure. In particular, the films become inhomogeneous with a wide size distribution of nano- and microparticles. With increase in γ, a significant extension of the photosensitivity spectrum of the structures towards the short-wavelength region was observed. Moreover, we have found a drastic increase in the photosensitivity at γ = 50%, namely it exceeds 5 A/W in the wide spectral range (400–1000 nm) under small reverse biases. Quantum size and plasmonic effects in Si and Au nanoparticles, respectively, formation of distributed Au-Si barriers in the nanocomposite, as well as avalanche carrier multiplication are suggested to contribute to the observed extremely high photosensitivity of the structures.

Authors : A. M. Steinbach, T. Sandner, B. Mizaikoff, S. Strehle
Affiliations : AS, TS and SS: Institute of Electron Devices and Circuits, Ulm University, Albert-Einstein-Allee 45, 89081 Ulm; TS and BM: Institute of Analytical and Bioanalytical Chemistry, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm

Resume : Silicon nanostructures such as nanowires or nanoparticles are materials widely discussed and used for various biomedical, electronic, and sensor applications. Usually, tailoring the silicon surface functionality is crucial to achieve better adhesion or enable highly specific label-free detection or drug carrier selectivity by linking biomolecular species. For this, silane modification is often the first step. Although silane chemistry is well known, the integration of a solvent-based reaction into a complex synthesis or device integration strategy still poses a challenge. Therefore, we present a gas phase silanization protocol enabling a non‐destructive and rapid silane modification, readily approachable also by non-chemists. The modification with 3-amino- and 3‐mercapto-propyltrimethoxysilane was verified on flat substrates using XPS, AFM, and IR spectroscopy. Additionally, as a model system, liquid-gate field effect transistors based on bottom-up grown boron‐doped silicon nanowires were assembled, modified and equipped with a microfluidic system. This sensor system was used for I‐V‐measurements allowing the in-situ observation of different states of the silane on the surface, e.g. oxidation state or pH-value. In conclusion, we developed a user-friendly method that is fully compatible with microfabrication technologies including commonly used resists or polymers, and combines easy handling, minimized gas consumption and versatility in terms of substrate geometry and materials.

Authors : Ayelet Vilan
Affiliations : Department of Materials and Interfaces, Weizmann Institute of Sciences, Israel

Resume : Metal-insulator-semiconductor (MIS) junctions are at the heart of modern electronics. Still, their use is generally limited to relatively thick insulators acting as capacitors, with a negligible leakage current. Reducing the insulator thickness to 1-2 nm, leads to considerable tunneling current through MIS junctions with thick insulators; such ultra-thin MIS were predicted (1960?s -70?s) to have rich transport characteristics varying from Esaki negative differential resistance to photo-multipliers. Original attempts to experimentally realize such ultra-thin MIS using oxide insulators were limited by insufficient passivation of surface states. We have recently shown that organic insulators made by chemical adsorption of 10 to 18 carbons-long alkyl chains provide a superior surface passivation, high tunneling barrier and even defect-healing mechanism. We have made Si-alkyl / metal junctions with either mercury or lead as the metal contacts. These junctions provide experimental realization for some of the long-predicted richness of ultra-thin MIS junctions.

10:40 Coffee Break    
11. Defects in Si and Si-nanostructures : D. Hiller
Authors : Liangzhi Kou, Sean Smith
Affiliations : School of Chemical Engineering, USW Australia, Sydney, NSW2052, Australia

Resume : We report the results of first-principle modelling of passivation of the boron-oxygen defect by hydrogen in p-doped Silicon. Recent experimental results indicate that defect passivation can be dramatically enhanced under illumination to generate moderate concentrations of minority (-ve) charge carriers. Our results provide useful information regarding the intrinsic structure and energetics of the defect under different charge states; the mobility of atomic hydrogen in different charge environments as well as supportive evidence for the mechanisms by which the illumination is thought to enhance the overall passivation.

Authors : Andre Stesmans
Affiliations : Department of Physics, University of Leuven

Resume : Electron spin resonance (ESR) in combination with standard electrical and optical techniques serves as an exclusive technique to atomically assess the nature of critical point defects. Here, we report on multifrequency ESR studies of Si nanoparticles (~2-5 nm across) revealing an ESR spectrum predominantly comprised of the intrinsic Pb(0) and Pb Si/SiO2 interface defects (Si dangling bond defects, generic entity Si3≡Si•) of comparable densities. Analysis of the specific ESR properties points to Si nanocrystallites with morphology of [100] truncated (111) octahedrons, affirmed by high-resolution TEM measurements. The defect densities are found to be much alike those at the standard thermal Si/SiO2 interface, thus remarkably bearing out that the microscopic Si/SiO2 interface properties can be retained down to the nanoscale. In a next part, we overview ESR results obtained on crystallographically ordered thermally oxidized Si nanowire (NW) structures, i.e., single crystalline arrays of sub-10 nm diameter Si NWs (~500 nm long) etched down into (100)Si using lithography and thermal oxidation thinning, intended for solar application. The study reveals the presence of a substantial density of Pb0s (traps) at the NW Si/SiO2 interfaces, due to enhanced interface strain, leaving NW interfaces of poor electrical quality. Based on the Pb-type defect properties, the nanopillar morphology is compatible with NWs predominantly bordered primarily by {110} facets, with cross sectional shape of {100} truncated {110} squares. The inherent interface quality is limited by the wire-narrowing thermal oxidation procedure, resulting in enhanced interface strain that in turn prevents to attain defect passivation by hydrogen to device grade level.

Authors : B. Bruhn[1], B. Brenny[2], S. Dekker[1}, A. Polman[2], K. Dohnalova[1]
Affiliations : [1]: Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands [2]: AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands

Resume : In the literature, two well known photoluminescence bands can be found for oxide-passivated silicon nanocrystals (SiNCs). On the one hand a red band is observed, being size-tunable in the NIR (starting from the bulk bandgap at 1.12 eV) due to quantum confinement and pinned at 2 eV for small NCs due to an oxygen bridging and/or double bond. On the other hand a blue band (~2.7 eV) is found in small NCs, whose origin is still debated, typically assigned either to quantum confined electron-hole pair recombination or an oxygen-related defect. Here, enhanced surface-to-volume ratio suggests the influence of large amounts of possible silica-related defects,extensively discussed in the literature, with emission bands throughout the whole visible range. . In this work we use e-beam excitation, which simultaneously excites cathodoluminescence (CL) and generates defects in the oxide shell of NCs. The variety of different SiNC samples ? porous silicon, nanolithography-defined single nanocrystals in oxide, plasma-synthesized oxide-passivated NCs, and organically capped wet-chemically synthesized NCs ? allows us to distinguish between the role of size, surface passivation and strain on the generation and emission of induced defects. We observe generation of several typical bands in the red, green and blue spectral range and demonstrate that SiNCs act as sensitizers for silica defects.

12:40 Lunch Break    
12. Si Nanowires – Doping, Properties & Applications : S. Strehle
Authors : Y. Rosenwaks, A. Henning, I. Amit, E. Koren, G. Shalev, N. Swaminathan, D. Englander, A. Shamir, D. Horvits E. Hemesath and L.J. Lauhon
Affiliations : Dept. of Physical Electronics, School of Electrical Engineering, Tel-Aviv University, Israel; Northwestern University, Illinois, U.S.A

Resume : Semiconductor nanowires (NWs) are one of the most promising building blocks for near future nano-electronics. The fabrication of nanowires is categorized into two main groups: bottom up approach, where the wires are grown by vapor-liquid-solid (VLS) chemistry, and the top down approach where the wires are patterned using standard microelectronic techniques. In this talk I will describe our recent studies of dopant profiles, electrical junctions and electronic states in both VLS grown nanowires [1], and in top down fabricated poly Si NWs [2]. In the last part of the talk I will present the electrostatically formed nanowire (EFN), which is a nanowire-like charge conducting channel that is not physically fabricated, but rather, electrostatically formed post-fabrication [3]. The comparison with the VLS grown nanowires will be discussed. [1] I. Amit et al., Nanoletters, 13, 2598 (2013). [2] I. Amit et al., Nanoletters, DOI: 10.1021/nl5024468, (2014). [3] G. Shalev, e, Asia Nature Materials, 3, (2013); A. Henning et al., Nano Research, DOI 10.1007/s 12274-01, (2015).

Authors : Sheng Ye,Muhammad Khaled Husain,Shin-ichi Saito, and Yoshishige Tsuchiya
Affiliations : Nanoelectronics and Nanotechnology group, Electronics and Computer Science, University of Southampton, Highfield Campus, Southampton, SO17 1BJ, United Kingdom

Resume : Accurate estimation of the resistivity of the heavily-doped ultra-thin silicon strip and observation of potential distribution change at the crossover between the strip and contact pads have been successfully achieved via direct surface potential imaging of the device under current flow. The test structures are fabricated on heavily-doped 30-nm-thick Silicon-on-Insulator by using top-down electron beam lithography. The samples are characterised by conventional I-V measurements as well as by Kelvin Probe Force Microscopy (KPFM), a unique tool to be able to directly measure the work function difference between the tip and surface materials. Our new set-up with in-situ biasing capability enables us to extract the local resistance from the surface potential distribution. The resistivity of 4.82 x 10-4 Ohm-cm extracted from the KPFM local potential imaging is much closer to 3.6 x 10-4 Ohm-cm that corresponds to the designed doping concentration than 8.09 x 10-4 Ohm-cm estimated from the conventional I-V characterisation. Further significant surface potential changes are observed at the crossover between the strip and the electrode pads under biasing condition. Asymmetric change of the surface potential might be due to possible inhomogeneity of the doping concentration or geometrical effects around at the crossover. The observed asymmetric nature could contribute to the increase of the contact resistance, therefore, should be more seriously taken into account for nanoscale devices.

Authors : Céline Ternon, Pauline Serre, Jean-Marie Lebrun, Maxime Legallais, Sylvain David, Thierry Luciani, Céline Pascal, Thierry Baron, Jean-Michel Missiaen
Affiliations : Dr C. Ternon, Dr P. Serre, S. David, T. Luciani, Dr T. Baron Univ. Grenoble Alpes, LTM, CNRS, LTM, Dr C. Ternon, M. Legallais, Univ. Grenoble Alpes, LMGP, CNRS, LMGP, Dr J.-M. Lebrun, Dr C. Pascal, Dr J.-M. Missiaen Univ. Grenoble Alpes, SIMAP, CNRS, SIMAP M. Legallais Univ. Grenoble Alpes, IMEP-LAHC, CNRS, IMEP-LAHC,

Resume : The development of functional devices compatible with standard microelectronic processes is central to the More-than-Moore and Beyond-CMOS electronic fields. Devices based on nanowires (NWs) are very promising, but their integration remains complex and submitted to variability limiting the potential scalability. The field of flexible electronics is another one in which the standard microelectronic industry struggles to propose a solution. Despite tremendous progress, organic materials remain highly sensitive to oxygen and humidity and deteriorate under UV irradiation, thus limiting their long-term operation. Here, we show that Si NW networks, also called Si nanonets, provide an easy-to-process single answer to develop flexible electronics and NW based devices. As a major contribution to the state of the art, we demonstrate that stable Si NW-NW junctions, insensitive to oxidation, can be formed with low variability, which opens up a new route to form reproducible and reliable devices, with long-term performances, presumably over several years, for NW-based or flexible devices using Si as active element. We anticipate that Si nanonets could play a major role in flexible electronic or in sensing application. Indeed, such a material is easy to process, bring the NW properties at the macroscopic scale, are flexible and should exhibit semiconducting electrical properties. First results concerning biosensing are also shown.

Authors : S. A. Niauzorau, K. V. Girel, H. V. Bandarenka, V. P. Bondarenko
Affiliations : Department of Micro- and Nanoelectronics, BSUIR, Minsk, Belarus

Resume : In this work we present study of structural and optical properties of Si nanowires (NWs) formed by two-step metal-assisted chemical etching (MACE) as well as possibility of their use as templates for Ag nanostructuring and further application in surface enhanced Raman spectroscopy. At the first step of MACE, Ag nanoparticles (NPs) were deposited on the surface of p- and n-type Si wafers from aqueous solution of AgNO3, HF and C2H5OH for 3 min. At the second step, Si wafers covered with Ag NPs were etched in aqueous solution of HF and H2O2 for 1 – 60 min. As a result, arrays of vertically-aligned Si NWs were fabricated. Superior anti-reflect ability of Si NWs was shown. Si band in Raman spectra was broadened and gradually shifted to the short-wavelength region at the increase of etching time. The Si NWs formed by MACE on n-type Si demonstrate high photoluminescent intensity. Ag nanorough films were deposited by immersion technique on Si NWs to fabricate SERS-active substrates. SERS spectra of rhodamine 6G (R6G) adsorbed on the Si NWs samples were registered using laser of 473 nm wavelength. Raman intensity dependence on the time of Si etching and Ag immersion deposition was estimated in 1652 cm–1 band of SERS spectra of R6G. The maximum of SERS intensity was provided by the Ag/Si NWs sample formed by etching and Ag immersion deposition for 20 and 30 min respectively. This research was financially supported by the Student Grant of Ministry of Education of Republic of Belarus.

15:40 Coffee Break    
13. Silicon & Germanium : D. König
Authors : Hans Sigg
Affiliations : Laboratory Micro- and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Resume : Strain is a widely used technique to control and modify the electrical and optical properties of semiconductors and thus has a large impact on device performance. Commonly, strain is introduced by epitaxial layer growth on (virtual) substrate with larger or smaller lattice constants, or by exploiting processing induced strains. However, epitaxial layers - as described by the Mattews-Blackslee law – can only become a few atomic layer thick for high strains of some few %, and, the efficiency of most of the processing such as the SiN capping, drops because of the restricted volumes available when scaling down CMOS transistor structures. In contrast, we developed a method1,2 to achieve ultra high strained semiconductors - above 5% is demonstrated - using a micro-mechanical approach which is not limited by this fundamental restriction and is scalable. It enables to accurately control the strain in suspended lamellas on a wafer scale by standard top-down fabrication technologies making it ultimate attractive for device applications but also for fundamental research thanks to the simplicity of the method. We will discuss the application of our method to obtain Ge with a direct bandgap for lasing application and we give design rules for homogeneous > 2.5 GPa channel stress in sub 10 nm node CMOS transistor structures3. 1 R.A. Minamisawa et al. Nat Comms 3, 1096 (2012). 2 M.J. Süess et al. Nature Photonics 7, 466 (2013). 3 M. Schmidt et al. IEEE Electron Device Lett. 35, 300 (201

Authors : M. Brehm (1), M. Grydlik (1), T. Tayagaki (2), O. Schmidt (3) F, Schäffler (1)
Affiliations : (1) Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Austria (2) Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 Japan( (3) Institute for Integrative Nanosciences, IFW Dresden, Germany

Resume : Control over the nucleation position of epitaxially grown Ge quantum dots (QDs) on Si substrates enables their addressability and, thus routes for their integration into existing Si integrated technology. Here we show that by growing Ge QDs on pit-patterned Si substrates, complete control over the self-assembly process, i.e. QD shape, densities and position can be obtained. This is only possible if the following parameters are carefully adjusted: pit-size, -depth, -period, -sidewall inclination, Si buffer layer growth, amount of deposited Ge, Ge growth temperature and rate. We demonstrate that QD shape transformations can be fully inhibited, dislocation formation delayed and arrays of one QD type can be fabricated while QD formation on unwanted nucleation sites can be fully impeded. Thus, the inter-QD-distance can be varied on one sample from a few hundred nanometers to several micrometers. Here, we have successfully measured the optical response of single epitaxial type-II QDs by PL-spectroscopy on Si-capped samples containing ordered QDs with spacing of 3.4 µm. We find that charge carrier transfer from the wetting layer to the QDs is inhibited by an activation barrier induced by the strain fields that is introduced by the QDs into the Si substrate. We describe ways to overcome this barrier, enabling optical characterization of a single QD. We find a linewidth-narrowing of the QD-related PL emission with decreasing excitation power, reaching a linewidth of 16 meV.

Authors : M. Failla, M. Myronov, C. Morrison, D. R. Leadley, J. Lloyd-Hughes
Affiliations : Department of Physics, University of Warwick, Coventry, United Kingdom.

Resume : Two dimensional hole gases (2DHGs) in strained Ge quantum wells (sGe-QWs) offer an attractive and compatible alternative for Si CMOS technology. As a consequence of the strain, the mobility is enhanced because of a reduction in the effective mass and interband scattering rate (lifted hole band degeneracy). We used THz time-domain spectroscopy (THz-TDS) to investigate, in a contactless manner, the mobility, density, effective mass and the spin-orbit coupling strength of spin-split heavy holes in high mobility sGe-QWs. An observed splitting of the cyclotron resonance (CR) is linked to the cubic Rashba interaction expected for heavy-holes. [1] This arises from the Rashba spin-orbit interaction due to structural inversion asymmetry. The cubic Rashba coefficient was estimated via two methods: (i) evaluating the different hole density for spin-up and spin-down states; (ii) modeling the split CR energies versus magnetic field. We obtain, in line with device magneto-transport measurements, [2] a Rashba splitting energy ~ 2.0 meV which is about one order of magnitude higher than previous studies of Ge-QWs. [3] We attribute this increase because of a lower strain, highlighting the promise of this material system for spintronics. [1] - R. Winkler, Spin-Orbit Coupling Effects in Two-Dimensional Electron and Hole Systems, (Springer-Verlag Berlin Heidelberg, 2003). [2] - C . Morrison et al., APL, 105, p. 182401, (2014). [3] - R. Moriya et al., PRL, 113, 086601 (2014).

17:20 Closing Remarks    
18:00 Best Student Presentation Awards Ceremony and Reception (Main Hall)    

No abstract for this day

Symposium organizers
Daniel HILLERResearch School of Engineering, Australian National University (ANU)

32 North Road, Acton ACT 2601, Australia
Dirk KÖNIGUniversity of New South Wales

School of Photovoltaic and Renewable Energy Engineering & Integrated Material Design Centre , Sydney NSW 2052, Australia
Kateřina KŮSOVÁInstitute of Physics of the Academy of Sciences of the Czech Republic

Cukrovarnická 10 162 00 Prague 6 Czech Republic

+420 220 318 414