Exploring optimum growth for high quality InAs/GaSb type-II superlattices

Abstract

Fundamental material issues in the growth of InAs/GaSb type-II superlattice (SL) structures using molecular beam epitaxy (MBE) have been addressed. The effect of starting substrate surface morphology on buffer and SL layers was studied using a 51 Å InAs/40 Å GaSb SL structure. Epi-ready wafers from various manufacturers had significantly different influence on the quality of buffer and SL layers. Intrinsic defects in the substrate from different manufacturing processes formed unique defects in the buffer layer that propagated into and through the SL structure. The growth temperature of a buffer layer was an important factor especially in reducing the defect level in the SL structure as studied by transmission electron microscopy. Correlations of SL layer quality with photoresponse signal strength were made. During a strain balancing process, a dramatic structural degradation was observed with InSb interfaces (IFs) thickness beyond 1.0 monolayer. SL layers with poor structural quality caused by excessive InSb IFs showed zero photoresponse. High quality micron thick, InAs/GaSb SLs with a reduced lattice mismatch were routinely obtained by optimizing growth conditions.