80 research outputs found
Epitaxial growth in dislocation-free strained alloy films: Morphological and compositional instabilities
The mechanisms of stability or instability in the strained alloy film growth
are of intense current interest to both theorists and experimentalists. We
consider dislocation-free, coherent, growing alloy films which could exhibit a
morphological instability without nucleation. We investigate such strained
films by developing a nonequilibrium, continuum model and by performing a
linear stability analysis. The couplings of film-substrate misfit strain,
compositional stress, deposition rate, and growth temperature determine the
stability of film morphology as well as the surface spinodal decomposition. We
consider some realistic factors of epitaxial growth, in particular the
composition dependence of elastic moduli and the coupling between top surface
and underlying bulk of the film. The interplay of these factors leads to new
stability results. In addition to the stability diagrams both above and below
the coherent spinodal temperature, we also calculate the kinetic critical
thickness for the onset of instability as well as its scaling behavior with
respect to misfit strain and deposition rate. We apply our results to some real
growth systems and discuss the implications related to some recent experimental
observations.Comment: 26 pages, 13 eps figure
Coherent Stranski-Krastanov growth in 1+1 dimensions with anharmonic interactions: An equilibrium study
The formation of coherently strained three-dimensional islands on top of the
wetting layer in Stranski-Krastanov mode of growth is considered in a model in
1+1 dimensions accounting for the anharmonicity and non-convexity of the real
interatomic forces. It is shown that coherent 3D islands can be expected to
form in compressed rather than in expanded overlayers beyond a critical lattice
misfit. In the latter case the classical Stranski-Krastanov growth is expected
to occur because the misfit dislocations can become energetically favored at
smaller island sizes. The thermodynamic reason for coherent 3D islanding is the
incomplete wetting owing to the weaker adhesion of the edge atoms. Monolayer
height islands with a critical size appear as necessary precursors of the 3D
islands. The latter explains the experimentally observed narrow size
distribution of the 3D islands. The 2D-3D transformation takes place by
consecutive rearrangements of mono- to bilayer, bi- to trilayer islands, etc.,
after exceeding the corresponding critical sizes. The rearrangements are
initiated by nucleation events each next one requiring to overcome a lower
energetic barrier. The model is in good qualitative agreement with available
experimental observations.Comment: 12 pages text, 15 figures, Accepted in Phys.Rev.B, Vol.61, No2
Defect Characterization in SiGe/SOI Epitaxial Semiconductors by Positron Annihilation
The potential of positron annihilation spectroscopy (PAS) for defect characterization at the atomic scale in semiconductors has been demonstrated in thin multilayer structures of SiGe (50 nm) grown on UTB (ultra-thin body) SOI (silicon-on-insulator). A slow positron beam was used to probe the defect profile. The SiO2/Si interface in the UTB-SOI was well characterized, and a good estimation of its depth has been obtained. The chemical analysis indicates that the interface does not contain defects, but only strongly localized charged centers. In order to promote the relaxation, the samples have been submitted to a post-growth annealing treatment in vacuum. After this treatment, it was possible to observe the modifications of the defect structure of the relaxed film. Chemical analysis of the SiGe layers suggests a prevalent trapping site surrounded by germanium atoms, presumably Si vacancies associated with misfit dislocations and threading dislocations in the SiGe films
The oxidation behaviour of mixed tungsten silicon sputtered coatings
W-Si-N coatings were deposited by sputtering and their chemical composition, structure, thermal and oxidation behaviour were characterised. Si-containing films are essentially amorphous. W69Si31 film crystallises at 750 °C as [alpha]-W and W5Si3 phases whereas no significant structural transformations were observed for W24Si21N55 film up to 1000 °C, In both cases elemental diffusion (Si and N) for the substrate was detected after thermal annealing. These coatings present much better oxidation resistance than W and W45N55 coatings.http://www.sciencedirect.com/science/article/B6TW0-3Y6PSMH-21/1/4bbc4e5d0073b4d83d325b3e19383dd
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