MORPHOLOGY AND DEFECT STRUCTURES OF GASB ISLANDS ON GAAS GROWN BY METALORGANIC VAPOR-PHASE EPITAXY

The initial nucleation of GaSb on (001) GaAs substrates by metalorgani c vapor phase epitaxy has been investigated using transmission electro n microscopy (TEM) and high resolution electron microscopy (HREM). TEM results showed that the GaSb islands experience a morphological trans ition as the growth temperature increases. For growth at 520 degrees C , the islands are longer along the [110] direction; at 540 degrees C, they are nearly square, and at 560 degrees C, they are longer along th e [110] direction. Possible mechanisms are proposed to describe such a transition. TEM and HREM examination showed that lattice misfit relax ation mechanisms depend on the growth temperature. For the sample grow n at 520 degrees C, the lattice mismatch strain was accommodated mainl y by 90 degrees dislocations; for the sample grown at 540 degrees C, t he misfit strain was relieved mostly by 90 degrees dislocations with s ome of 60 degrees dislocations, and for the sample grown at 560 degree s C, the strain was accommodated mainly by 60 degrees dislocations whi ch caused a local tilt of the GaSb islands with respect to the GaAs su bstrate. The density of threading dislocations was also found to be de pendent on the growth temperature. Mechanisms are proposed to explain these phenomena.