Etude physico-chimique de la nitruration superficielle de films tres minces de silice : application a la stabilisation electrique de l'interface SiO2/Si(100) de structures M.I.S.-V.L.S.I

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

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

Self-assembly and ordering mechanisms of Ge islands on prepatterned Si(001)

Ge deposition on Si 001 substrates patterned by focused ion beams is a promising route toward fabricating highly ordered quantum dots. Depending on the growth temperature T, remarkable orderings of the assembled islands are observed. At low T’s, when diffusion is limited, a metastable phase with dots nucleating in the holes prevails. At high T’s, when diffusion is not limited by kinetics, an equilibrium ordered phase is observed with dots nucleating on the terraces in between the pits. At intermediate T’s, random growth arises. Monte Carlo simulations shed light onto this phenomenon. It is shown that the average stress energy of the equilibrium ordered configuration is significantly lower than the energy of configurations with islands positioned in the pits. Random nucleation gives rise to saddle configurations between the two ordered phases

Si/Ge intermixing during Ge Stranski–Krastanov growth

The Stranski–Krastanov growth of Ge islands on Si(001) has been widely studied. The morphology changes of Ge islands during growth, from nucleation to hut/island formation and growth, followed by hut-to-dome island transformation and dislocation nucleation of domes, have been well described, even at the atomic scale, using techniques such as scanning tunneling microscopy and transmission electron microscopy. Although it is known that these islands do not consist of pure Ge (due to Si/Ge intermixing), the composition of the Ge islands is not precisely known. In the present work, atom probe tomography was used to study the composition of buried dome islands at the atomic scale, in the three-dimensional space. The core of the island was shown to contain about 55 atom % Ge, while the Ge composition surrounding this core decreases rapidly in all directions in the islands to reach a Ge concentration of about 15 atom %. The Ge distribution in the islands follows a cylindrical symmetry and Ge segregation is observed only in the {113} facets of the islands. The Ge composition of the wetting layer is not homogeneous, varying from 5 to 30 atom %

Optical properties of self-organised SSMBE and GSMBE Ge nanostructures grown on SiGe template layer on Si (118)

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Size distribution of self assembled Ge nanocrystals determined by photoluminescence

Germanium nanocrystals (NCs) were formed by in-situ thermal annealing of an amorphous Ge layer deposited by molecular beam epitaxy on a thin SiO2 layer on Si(001). The Ge NCs were then capped in situ with a thin layer of amorphous Si to prevent oxidation. For the present range of particle sizes (2.5 to 60 nm), the NC photoluminescence (PL) appeared primarily as a wide near-infrared band peaked near 800 meV. The peak energy of the PL band reflects the average NC size and its shape depends on the NC size distribution. Using both the k\ub7p and tight binding theoretical models, we have analyzed the PL spectrum in terms of the NC size distribution required to reproduce the observed asymmetric band shape, which includes, for the smaller diameter NCs, a band gap enlargement due to quantum confinement. The observed size distribution determined from transmission electron microscopy analysis allowed the determination of the nonlinear increase in the PL quantum efficiency with decreasing NC diameter. This implies that, given a good theoretical description of the system, it is possible to evaluate the size distribution of semiconductor NCs from their PL energy dependence.Peer reviewed: YesNRC publication: Ye

SiGe Nanostructures

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Configurable Compliant Substrates for SiGe Nanomembrane Fabrication

International audienceStrain-engineered SiGe epitaxial nanomembranes are shown to act as compliant substrates. Fully planar, thick and dislocation-free SiGe films are produced in (pSi substrate/Si buffer/SiGe film) systems. They are shown to be mainly ruled by the softness and tensile strain of pSi and by the elastic interactions regulated by the film and buffer thickness