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Large-scale, defect-free, micro- and nano-circuits with controlled inter-connections represent the nexus between electronic and photonic components. However, their fabrication over large scales often requires demanding procedures that are hardly scalable. Here we synthesize arrays of parallel ultra-long (up to 0.75 mm), monocrystalline, silicon-based nano-wires and complex, connected circuits exploiting low-resolution etching and annealing of thin silicon films on insulator. Phase field simulations reveal that crystal faceting and stabilization of the wires against breaking is due to surface energy anisotropy. Wires splitting, inter-connections and direction are independently managed by engineering the dewetting fronts and exploiting the spontaneous formation of kinks. Finally, we fabricate field-effect transistors with state-ofthe- art trans-conductance and electron mobility. Beyond the first experimental evidence of controlled dewetting of patches featuring a record aspect ratio of 1/60000 and selfassembled mm long nano-wires, our method constitutes a distinct and promising approach for the deterministic implementation of atomically-smooth, mono-crystalline electronic and photonic circuits.

Large-scale, defect-free, micro- and nano-circuits with controlled inter-connections represent the nexus between electronic and photonic components. However, their fabrication over large scales often requires demanding procedures that are hardly scalable. Here we synthesize arrays of parallel ultra-long (up to 0.75 mm), monocrystalline, silicon-based nano-wires and complex, connected circuits exploiting low-resolution etching and annealing of thin silicon films on insulator. Phase field simulations reveal that crystal faceting and stabilization of the wires against breaking is due to surface energy anisotropy. Wires splitting, inter-connections and direction are independently managed by engineering the dewetting fronts and exploiting the spontaneous formation of kinks. Finally, we fabricate field-effect transistors with state-of-the-art trans-conductance and electron mobility. Beyond the first experimental evidence of controlled dewetting of patches featuring a record aspect ratio of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim$$\end{document}~1/60000 and self-assembled \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim$$\end{document}~mm long nano-wires, our method constitutes a distinct and promising approach for the deterministic implementation of atomically-smooth, mono-crystalline electronic and photonic circuits., Fabricating defect-free micro- and nano-circuits over large scales with controlled interconnections remains a challenge. Here, Bollani et al. show a dewetting strategy for engineering arrays of parallel Si-based nanowires up to 0.75 mm and complex interconnected circuits of monocrystalline Si on a chip.

We address the solid state dewetting of ultra-thin and ultra-large patches of monocrystalline silicon on insulator. We show that the underlying instability of the thin Si film under annealing can be perfectly controlled to form monocrystalline, complex nanoarchitectures extending over several microns. These complex patterns are obtained guiding the dewetting fronts by etching ad-hoc patches prior to annealing. They can be reproduced over hundreds of repetitions extending over hundreds of microns. We discuss the effect of annealing temperature and patch size on the stability of the final result of dewetting showing that for simple patches (e.g. simple squares) the final outcome is stable and well reproducible at 720 degrees C and for similar to 1 mu m square size. Finally, we demonstrate that introducing additional features within squared patches (e.g. a hole within a square) stabilises the dewetting dynamic providing perfectly reproducible complex nanoarchitectures of 5 pm size. (C) 2018 Elsevier B.V. All rights reserved.

A ternary Indium-Aliminium-Arsenic (InAlAs) is grown, by metal organic chemical vapor deposition (MOCVD), on a substrate InP (311) with polarity A and B, doped with Fer (Fe) atomic. Their optical properties have been studied by photoluminescence spectroscopy (PL) in the whole temperature range from 10 to 300 K. At low temperature region, power dependent analysis of the PL intensity reveals a conventional power law with an exponent n close to one, in agreement with the type II nature of the emission. A red shift of the type II transition has been observed from the sample with polarity A to B. The temperature-dependent PL measurements exhibit abnormal behaviors such as an S-shape in PL-peak energy, and an inverted N-shape in the full width at half maximum (FWHM). These atypical behaviors are linked to the exciton localization phenomenon, which it is more pronounced in the structure with polarity A of substrate orientation. Room temperature-PL spectra covers the both emissions of the 1.3 and the 1.55 μm for (311) A and (311) B InP oriented substrates, respectively. Our results indicate that the In0.513Al0.487As/InP (311) A/B is expected to be advantageous for their application in optical telecommunication.

International audience; We present the photoluminescence (PL) emission of Silicon and Germanium nanocrystals (NCs) of different sizes embedded in two different matrices. Formation of the NCs is achieved via solid-state dewetting during annealing in a molecular beam epitaxy ultra-high vacuum system of ultrathin amorphous Si and Ge layers deposited at room temperature on SiO2. During the dewetting process, the bi-dimensional amorphous layers transform into small pseudo-spherical islands whose mean size can be tuned directly with the deposited thickness. The nanocrystals are capped either ex situ by silicon dioxide or in situ by amorphous Silicon. The surface-state dependent emission (typically in the range 1.74 eV-1.79 eV) exhibited higher relative PL quantum yields compared to the emission originating from the band gap transition. This red-PL emission comes from the radiative transitions between a Si band and an interface level. It is mainly ascribed to the NCs and environment features deduced from morphological and structural analyses. Power dependent analysis of the photoluminescence intensity under continuous excitation reveals a conventional power law with an exponent close to 1, in agreement with the type II nature of the emission. We show that Ge-NCs exhibit much lower quantum efficiency than Si-NCs due to non-radiative interface states. Low quantum efficiency is also obtained when NCs have been exposed to air before capping, even if the exposure time is very short. Our results indicate that a reduction of the non-radiative surface states is a key strategy step in producing small NCs with increased PL emission for a variety of applications. The red-PL band is then an effective tool for the quality assessment of NCs based structures. (C) 2017 Elsevier B.V. All rights reserved.

The optical properties of In 0.21 Ga 0.79 As/GaAs MQWs, with triple unequal layer thickness NW (3 nm), MW (6 nm) and WW (9 nm) grown on (001) and (113) GaAs substrates, is studied by using continuous wave photoluminescence (cw-PL) spectroscopy. A comparative study has been performed to demonstrate the influence of electric field and QW thickness on the exciton localization. An S-shaped form in temperature-dependent PL peak energy has been observed in polar middle QW (MW (113)) but not seen in non-polar ones (MW (001)). This behavior is linked to carrier localization in triangular potential and polarity. We have observed also this atypical evolution in non-polar wide QW (WW (001)) but not in non-polar middle QW (MW (001)), which is attributed to potential fluctuation in larger ones. With the aid of modified Passler model for including the effect of localized states, we can persuasively reproduce the S-shaped temperature dependence of PL band gap energy and contribute to the estimated value of exciton localization energy. The values of σ are obtained from adjustment of experimental points, which indicate the degree of localization in QW layer.

In 0.21 Ga 0.79 As multiple quantum wells MQW, with different well thickness L, are grown on [001] and [113] A GaAs growth directions by molecular beam epitaxy MBE. An asymmetric photoluminescence PL line shape denoted LE A and LE B in the lower energies side has been observed in both structures. These emissions of deep localized states can be related to the energy potential modulation associated to Indium cluster formation. Temperature dependence of photoluminescence properties has been reported. Localized state ensemble LSE model has investigated atypical behaviors of PL peak energies and the full width at half maximum FWHM of both emissions. These abnormal behaviors are explained by carriers captured by localized recombination centers. Competition processes between localized and delocalized excitons have been occurred to interpret the PL properties. The degree of localization induced by quantum-dot-like states and critical temperatures between different temperatures regions increase as far as away [001] growth direction.

Photoluminescence study PL has been performed for the In 0.21 Ga 0.79 As multiple quantum wells MQW grown by molecular beam epitaxy MBE on (001) and (113) A GaAs substrates. The electronic structure was obtained by solving the Schrodinger equation, including piezoelectric field and strain effect on the conduction and valence bands of the unequal QWs. We critically review the explanation of S-shape in temperature dependence of PL peak energy for polar Middle In 0.21 Ga 0.79 As QW at intermediate temperatures. This abnormal behavior is merely linked to the impact of carrier localization and polarization-induced electric fields in optical properties. A significant blue shift of 18 meV for polar and a negligible shift for non-polar In 0.21 Ga 0.79 As/GaAs Middle QW has been observed. In order to follow the evolution of the PL peak energies for each QW in both samples versus temperature, three theoretical models (Varshni, Vina and Passler) have been reported. A comparison between theoretical and experimental data demonstrates that the Passler model is the most accurate fit despite none of the classical models can replicate the excitonic PL energy evolution at cryogenic temperature for Middle QW in the structure grown on (113).

Si-based nanoarchitectures are formed with unprecedented precision and reproducibility via templated dewetting of thin SOI., Dewetting is a ubiquitous phenomenon in nature; many different thin films of organic and inorganic substances (such as liquids, polymers, metals, and semiconductors) share this shape instability driven by surface tension and mass transport. Via templated solid-state dewetting, we frame complex nanoarchitectures of monocrystalline silicon on insulator with unprecedented precision and reproducibility over large scales. Phase-field simulations reveal the dominant role of surface diffusion as a driving force for dewetting and provide a predictive tool to further engineer this hybrid top-down/bottom-up self-assembly method. Our results demonstrate that patches of thin monocrystalline films of metals and semiconductors share the same dewetting dynamics. We also prove the potential of our method by fabricating nanotransfer molding of metal oxide xerogels on silicon and glass substrates. This method allows the novel possibility of transferring these Si-based patterns on different materials, which do not usually undergo dewetting, offering great potential also for microfluidic or sensing applications.

Using Ag-assisted chemical etching technique, vertical silicon nanowires (SiNWs) arrays on n-type (0 0 1) substrates has been prepared with different conditions such as etching time and illumination condition. A photoluminescence measurement at room temperature has shown a decrease of PL intensity when decreasing etching time. These results are attributed to the decrease of SiNWs density and reduction of laser capture surface. The presence of defect states lead to a non-radiative recombination. Indeed, the blue shift observed when using a low etching time is due to the confinement effect. Using a low etching time, illumination condition does not vary SiNWs density. The optimal experimental condition for photovoltaic application is observed after deposition of Poly (3-hexylthiophene-2,5-diyl) P3HT into the different silicon substrates prepared. An important charges transfer between P3HT and SiNWs is observed for high etching time (120 min under illumination). A blue shift is due to the presence of defects and electric field.

In this work, we have investigated the optical study of In0.21Ga0.79As multiple quantum wells (MQW) with different well thickness (LW = 30, 60 and 90 A), grown by molecular beam epitaxy MBE on (0 0 1) and (1 1 3) A GaAs substrates. A blue-shift of energy transition is observed for the MQW grown on (1 1 3) A. This result could be explained by the presence of significant piezoelectric field inside the structure. Yet, the exciton dynamics properties have been measured by picosecond time-resolved photoluminescence (TRPL) measurements. We have found that the piezoelectric effect in MQW grown on high index plane induces slower exciton relaxation compared with those grown on (0 0 1). The PL lifetime versus temperature was performed to study the carrier transfer between the quantum wells of both samples.

In this paper, single quantum well (SQW) structure of BxInyGa1-x-yAs/GaAs lattice-matched to GaAs has been grown by metal organic vapor phase epitaxy (MOVPE). The sample was characterized morphologically and structurally using the atomic force microscopy AFM, transmission electron microscopy TEM and high resolution X-ray diffraction HRXRD measurements. The optical study was investigated by photoluminescence (PL) spectroscopy as a function of temperature. The PL peak energy, the full width at half maximum (FWHM) and the PL intensity, versus temperature, exhibit anomalous behaviors such as S-shaped and N-shaped. They were attributed to the creation of a fluctuation potential in the band edge of the host material from the non-uniform distribution of boron atoms in the structure induced exciton localization. We investigate the localization phenomenon by excitation density variation. Then, a quasi-steady state rate-equation model for temperature dependent luminescence spectra of localized-state material system (LSE) was presented to quantitatively reinterpret the band gap emission process. The novel analytical models, compared with the classical ones, were used to fit the PL peak energy evolution. Good agreement between experimental and theoretical results has been observed using the modified Passler model. Modeling results will be discussed based on specified parameters. These results can improve the fundamental properties of quaternary based on light-emitting and optoelectronic devices.