I. Berbezier

Surface electron-diffraction patterns of β-FeSi2 films epitaxially grown on silicon

Semiconducting β‐FeSi2 is drawing much current research interest because of hoped‐for silicon‐based optoelectronics applications. The study of heteroepitaxial film growth on silicon depends heavily upon several transmission and reflection electron‐diffraction techniques. Because of the complicated crystal structure of this material, the possibility of competing heteroepitaxial relationships, the propensity for formation of epitaxial variants by rotation twinning, and the uncertainty in the crystalline surface nets, the analysis of experimental diffraction patterns is complicated. A theoretical reference for a number of fundamental electron‐diffraction patterns is provided and they are illustrated with a broad range of experimentally obtained patterns from the surfaces of epitaxial films. In situ transmission reflection high‐energy electron diffraction (RHEED) (transmission electron diffraction with conventional RHEED instrumentation), from rough but epitaxial films, is of great utility and quite feasible ...

SiGe nanostructures: new insights into growth processes

During the last decade, Si/Si1−xGex heterostructures have emerged as a viable system for use in CMOS technology with the recent industrial production of heterojunction bipolar transistor-based integrated circuits. However, many key problems have to be solved to further expand the capabilities of this system to other more attractive devices. This paper gives a comprehensive review of the progress achieved during the last few years in the understanding of some fundamental growth mechanisms. The discrepancies between classical theories (in the framework of continuum elasticity) and experimental results are also specially addressed. In particular, the major role played by kinetics in the morphological evolution of layers is particularly emphasized. Starting from the unexpected differences in Si1−xGex morphological evolution when deposited on (001) and on (111), our review then focuses on: (1) the strain control and adjustment (from fully strained to fully relaxed 2D and 3D nanostructures)—in particular, some original examples of local CBED stress measurements are presented; (2) the nucleation, growth, and self-assembly processes, using self-patterned template layers and surfactant-mediated growth; (3) the doping processes (using B for type p and Sb for type n) and the limitations induced by dopant redistribution during and after growth due to diffusion, segregation, and desorption. The final section will briefly address some relevant optical properties of Si1−xGex strained layers using special growth processes.

Wafer Scale Formation of Monocrystalline Silicon-Based Mie Resonators via Silicon-on-Insulator Dewetting

Subwavelength-sized dielectric Mie resonators have recently emerged as a promising photonic platform, as they combine the advantages of dielectric microstructures and metallic nanoparticles supporting surface plasmon polaritons. Here, we report the capabilities of a dewetting-based process, independent of the sample size, to fabricate Si-based resonators over large scales starting from commercial silicon-on-insulator (SOI) substrates. Spontaneous dewetting is shown to allow the production of monocrystalline Mie-resonators that feature two resonant modes in the visible spectrum, as observed in confocal scattering spectroscopy. Homogeneous scattering responses and improved spatial ordering of the Si-based resonators are observed when dewetting is assisted by electron beam lithography. Finally, exploiting different thermal agglomeration regimes, we highlight the versatility of this technique, which, when assisted by focused ion beam nanopatterning, produces monocrystalline nanocrystals with ad hoc size, position, and organization in complex multimers.

Defect-free Stranski-Krastanov growth of strained Si1-xGex layers on Si

Abstract Strained Si 1- x Ge x epitaxial layers on silicon are known to exhibit a non-planar surface under certain growth conditions. In the present work, combined transmission electron microscopy and atomic force microscopy (AFM) are employed to reveal the appearance and growth of surface undulations which form in diluted Si 1- x Ge x alloys. On the basis of these experiments and theoretical considerations, the possible causes of such a surface rippling are reviewed and discussed. It appears that the partial relaxation of the elastic energy, permitted by the undulations themselves, is the driving force of this phenomenon, what is referred as defect-free Stranski-Krastanov growth mode. AFM measurements permit one also to quantify the kinetics of appearance and growth of the undulations occuring during deposition. It is found that the amplitude of the undulations follows an exponential variation with the deposition time/film thickness. Finally we propose a simple model based on partial elastic relaxation (driving force) and on surface diffusion (limitative mechanism) to describe our experimental kinetics of the surface ripples during the very first steps.

Synthesis and properties of epitaxial semiconducting silicides

Abstract The state-of-the-art in the preparation and characterization of epitaxial semiconducting silicides will be reviewed in this report. Emphasis will be put on thin FeSi 2 layers epitaxially grown on Si substrates. The mechanisms of silicide formation will be discussed through results obtained by a large variety of in-situ techniques (RHEED, Auger, photoemission, …) and ex-situ techniques (X-ray diffraction, RBS, electron microscopy). Moreover, for ultra-thin FeSi 2 films, several strained pseudomorphic and metallic phases induced by epitaxy are observed on top of Si substrates. Their transition towards the stable relaxed semiconducting β-FeSi 2 will be presented. Recent findings of the metallic α-FeSi 2 phase observed at surprisingly low temperature and its relaxation towards the β-phase will also be reported.

Ge dots self-assembling: Surfactant mediated growth of Ge on SiGe (118) stress-induced kinetic instabilities

The ordering of islands on naturally or artificially nanostructured surfaces is one of the most recent objectives among actual nanotechnology challenges. We show in this letter that, by a combination of two approaches, i.e., a two-step molecular beam epitaxy (MBE) deposition process and surfactant-mediated growth, we are able to obtain chains of nicely ordered ultrasmall islands of lateral size below 50 nm. The two-step MBE process consists of vicinal Si(001) surface self-patterning by SiGe growth instability and Ge dot ordering by subsequent Ge deposition on a SiGe template layer. The surfactant-mediated growth consists of submonolayer Sb deposition prior to Ge growth, in order to reduce the island size up to 25 nm. The best ordering of Ge islands is obtained when the island size matches the wavelength of the template layer.

Silicide epilayers: recent developments and prospects for a Si-compatible technology

Semiconducting silicides epitaxially grown on silicon may be promising materials for integrated optoelectronic devices. The structure and the physical properties of FeSi2 are reviewed in the light of results obtained with a large variety of in situ an ex situ surface techniques. Dynamical transitions from strained metallic FeSi2 toward relaxed semiconducting FeSi2 and epitaxial FeSi are clearly demonstrated. New developments for silicide heteroepitaxy on silicon using gas-source molecular beam epitaxy are also discussed.

Sb segregation in Si and SiGe: effect on the growth of self-organised Ge dots

The segregation and incorporation coefficients of antimony (Sb) in Si 1-x Ge x buried doped layers were investigated simultaneously using specific temperature sequences. We first showed an exponential kinetic evolution of Sb surface segregation in Si. In contrast such an evolution could not be observed in Si 1-x Ge x because of the Sb thermal desorption, at growth temperatures of 550°C. We also showed an increased surface segregation increasing with the partial Ge concentration in Si 1-x Ge x alloys, which was explained by a decrease of the kinetic barrier for Sb atoms mobility. It was, therefore, possible to determine the growth conditions to obtain a Si 1-x Ge x doped layer with a controlled incorporation level and a negligible surface segregation obtained by the thermal desorption of the Sb surface coverage. Finally, using Sb surfactant mediated growth, we found Ge dots with lateral sizes reduced by a factor of 2.8 and density multiplied by a factor of four as compared to dots directly deposited on Si(001).

The kinetics of dewetting ultra-thin Si layers from silicon dioxide

In this study, we investigate the kinetically driven dewetting of ultra-thin silicon films on silicon oxide substrate under ultra-high vacuum, at temperatures where oxide desorption and silicon lost could be ruled out. We show that in ultra-clean experimental conditions, the three different regimes of dewetting, namely (i) nucleation of holes, (ii) film retraction and (iii) coalescence of holes, can be quantitatively measured as a function of temperature, time and thickness. For a nominal flat clean sample these three regimes co-exist during the film retraction until complete dewetting. To discriminate their roles in the kinetics of dewetting, we have compared the dewetting evolution of flat unpatterned crystalline silicon layers (homogeneous dewetting), patterned crystalline silicon layers (heterogeneous dewetting) and amorphous silicon layers (crystallization-induced dewetting). The first regime (nucleation) is described by a breaking time which follows an exponential evolution with temperature with an activation energy EH 3.2eV. The second regime (retraction) is controlled by surface diffusion of matter from the edges of the holes. It involves a very fast redistribution of matter onto the flat Si layer, which prevents the formation of a rim on the edges of the holes during both heterogeneous and homogeneous dewetting. The time evolution of the linear dewetting front measured during heterogeneous dewetting follows a characteristic power law x t 0.45 consistent with a surface diffusion-limited

Formation of Silicene Nanosheets on Graphite

The extraordinary properties of graphene have spurred huge interest in the experimental realization of a two-dimensional honeycomb lattice of silicon, namely, silicene. However, its synthesis on supporting substrates remains a challenging issue. Recently, strong doubts against the possibility of synthesizing silicene on metallic substrates have been brought forward because of the non-negligible interaction between silicon and metal atoms. To solve the growth problems, we directly deposited silicon on a chemically inert graphite substrate at room temperature. Based on atomic force microscopy, scanning tunneling microscopy, and ab initio molecular dynamics simulations, we reveal the growth of silicon nanosheets where the substrate-silicon interaction is minimized. Scanning tunneling microscopy measurements clearly display the atomically resolved unit cell and the small buckling of the silicene honeycomb structure. Similar to the carbon atoms in graphene, each of the silicon atoms has three nearest and six second nearest neighbors, thus demonstrating its dominant sp2 configuration. Our scanning tunneling spectroscopy investigations confirm the metallic character of the deposited silicene, in excellent agreement with our band structure calculations that also exhibit the presence of a Dirac cone.