Role of the wetting layer for the SiGe Stranski-Krastanow island growth on planar and pit-patterned substrates

We investigate the homogeneity and thickness of a Ge wetting layer (WL) both on planar and pit-patterned Si(0 0 1) substrates by utilizing a combination of atomic force microscopy and selective chemical etching. On planar substrates, the WL is thinner or Si richer around the islands, while on the patterned ones it is thinner on the pit sidewall regions. On planar substrates, a substantial amount of Ge is transferred from the WL to the islands at the initial stage of island formation, while on patterned substrates this scenario is not observed due to the fact that islands form within the pits before the WL reaches the critical thickness on the planar surface in the regions between the pits. The WL thickness increases with increasing Ge deposition after island formation both on planar and patterned substrates, caused by Si-Ge intermixing in the WL at a relatively high growth temperature. By using the WL as etch-stop, we use the same etching solution to investigate the shape of buried SiGe islands.