Nucleation, relaxation and redistribution of Si layers in GaAs.

We study the structural properties of Si layers of different thickness (0.1-1.3 nm) inserted in GaAs by solidsource molecular beam epitaxy. Using high- resolution electron microscopy, we demonstrate that the Si nucleation on GaAs takes place via the formation of Si nanoclusters in a highly regular arrangement. Thicker films (several monolayers) are found to be partially intermixed with GaAs. This intermixing is caused by the segregation of a considerable fraction of the deposited Si during overgrowth, as observed by secondary ion mass spectrometry. Finally, we show that the strain relief of Si films on GaAs occurs at a thickness of about 1.2 nm via the generation of stacking faults, whereas complete dislocations are not detected.