Microscopic parameters of heterostructures with Ge nanoclusters and thin films in a Si matrix

Microstructural parameters (interatomic distances, coordination numbers, an d their anisotropy) of heterostructures with Ge nanoclusters and thin films were determined by EXAFS spectroscopy. The variation of these parameters i s correlated to the morphology of the germanium quantum points on Si(001), and adequate structural models are suggested. It is found that the pseudomo rphic four-monolayer germanium films buried in a Si matrix contain up to 50 % Si atoms. The pyramidal germanium islands (lateral size similar to 15 nm, height similar to1.5 nm) formed during further Stanski-Krastanov heteroepi taxial growth have a thinner Ge-Si intermediate boundary layer near two mon olayers and Ge-Ge interatomic distances 0.04 Angstrom shorter than those in pure germanium in agreement with the results of bond length calculations i n the framework of the valence force field (VFF) model.