Geometry and interface structure of island nuclei for GaSb buffer layers grown on (001) GaAs by metalorganic vapour phase epitaxy

Abstract

Atomic force microscopy and transmission electron microscopy have been used to investigate the geometry and interface structure of island nuclei formed in the initial stages of buffer layer growth for MOVPE GaSb on (001) GaAs. There is a bimodal distribution of island sizes with a high density of small, homogeneous nuclei and a lower density of larger, secondary nuclei. The smaller islands have pronounced crystallographic facets which are consistent with those which would be expected for minimization of surface energy and lateral growth anisotropy. The secondary islands are present at junctions between primary nuclei and may have formed due to enhancement of growth rates at emergent threading segments of misfit dislocations. The lattice misfit is accommodated by a regular square arrangement of edge-type misfit dislocations but unusual strain contrast arises in HREM images due to either a “stand-off” of dislocations from the interface or a corrugated interface.