Scanning Microscopy


Research work on the general problem of the nature and thermal stability of the Si/Ge semiconductor interface is reviewed. We report on our recent studies of the interface structure in [(Si)m(Ge)n]p superlattices and (Ge)n layers buried in Si as revealed by Raman scattering, extended X-ray absorption fine structure, and X-ray techniques. Strain relaxation and interdiffusion in the superlattices caused by annealing have been investigated, and it is found that considerable strain-enhanced intermixing together with partial relaxation of Ge-Ge bonds occurs even for very short anneal times at 700°C. Further annealing leads to diffusion at a much slower rate and to the eventual formation of an alloy layer. The Ge-Ge bond lengths in as-grown samples are that expected for a fully strained Ge layer. Similar studies of the (Ge)n layers reveal that two-dimensional pseudomorphic growth proceeds up to n = 5, probably mediated by a Si-Ge interface interdiffusion over one or two monolayers of approximately 20%. A n = 12 layer gave evidence of strain relaxation by the introduction of dislocations and clustering. Interdiffusion proceeds rapidly on annealing at 750°C.

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