GEOMETRY AND INTERFACE STRUCTURE OF ISLAND NUCLEI FOR GASB BUFFER LAYERS GROWN ON (001) GAAS BY METALORGANIC VAPOR-PHASE EPITAXY

Atomic force microscopy and transmission electron microscopy have been used to investigate the geometry and interface structure of island nu clei formed in the initial stages of buffer layer growth for MOVPE GaS b on (001) GaAs. There is a bimodal distribution of island sizes with a high density of small, homogeneous nuclei and a lower density of lar ger, secondary nuclei. The smaller islands have pronounced crystallogr aphic facets which are consistent with those which would be expected f or minimization of surface energy and lateral growth anisotropy. The s econdary islands are present at junctions between primary nuclei and m ay have formed due to enhancement of growth rates at emergent threadin g segments of misfit dislocations. The lattice misfit is accommodated by a regular square arrangement of edge-type misfit dislocations but u nusual strain contrast arises in HREM images due to either a ''stand-o ff'' of dislocations from the interface or a corrugated interface.