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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. 

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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 : 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

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)

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 : 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 : 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 : 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)

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 : 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)

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 : 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.

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.

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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 : 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.

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 : 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.

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


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Symposium organizers
Daniel HILLERTU Freiberg

Institute of Applied Physics (IAP), Leipziger Str. 23 - 09599 Freiberg, Germany
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