Causes and elimination of pyramidal defects in GaSb-based epitaxial layers

Abstract

Here, the authors report on the occurrence, cause, and elimination of pyramidal defects in layers of GaSb grown by molecular beam epitaxy on GaSb substrates. These defects are typically 3–8 nm high, 1–3 μm in diameter, and shaped like pyramids. Their occurrence in the growth of GaSb buffer layers can propagate into subsequent layers such as GaSb, GaInAsSb, and GaSb/InAs superlattices. Defects are nucleated during the early stages of growth after the thermal desorption of native oxide from the GaSb substrate. These defects grow into pyramids due to a repulsive Ehrlich–Schwoebel potential on atomic step edges leading to an upward adatom current. The defects reduce in density with growth of GaSb. The insertion of a thin AlAsSb layer into the early stages of the GaSb buffer increases the rate of elimination of the defects, resulting in a smooth surface within 500 nm. The acceleration of defect reduction is due to the temporary interruption of step-flow growth induced by the AlAsSb layer. This leads to a reduced isolation of the pyramids from the GaSb epitaxial layer and allows the pyramidal defects to smooth out.