TRANSMISSION ELECTRON-MICROSCOPY AND TRANSMISSION ELECTRON-DIFFRACTION STRUCTURAL STUDIES OF HETEROEPITAXIAL INASYSB1-Y MOLECULAR-BEAM EPITAXIAL LAYERS

Molecular-beam epitaxy InAsySb1-y layers were grown at temperatures ra nging from 295 to 470-degrees-C across the full composition range. Tra nsmission electron microscopy and transmission electron diffraction (T ED) examinations showed that for layers grown at and below 400-degrees -C with nominal compositions 0.4 < y < 0. 8, separation into two phase s occurred resulting in a series of alternating plates approximately p arallel to the layer surface. TED showed that the cubic lattices of th e two phases were tetragonally distorted and their compositions were d educed to be typically InAs0.38Sb0.62 and InAs0.72Sb0.28. The plates w ere larger and more regular along the [110BAR] direction than the [110 ] direction. As the growth temperature increased from 295 to 400-degre es-C, for layers of nominal composition InAs0.5Sb0.5, the plate length increased from 0.1 to 2.0 mum and the plate thickness from 10 to 50 n m. Crystallographic defects were present in the layers and their occur rence was different in the phase-separated and non-phase-separated lay ers. The plates formed spontaneously at the growing surface and were s table during subsequent annealing at 350 and 370-degrees-C. It is sugg ested that they arise due to the presence of a miscibility gap at thes e growth temperatures. We have termed these spontaneously grown plate structures ''natural'' strained layer superlattices.