Structural properties of GaAs-on-Si with InGaAs/GaAs strained-layer superlattice

Abstract

This paper investigates structural properties of GaAs epitaxial layers formed with an in-situ thermal cycle (TC) process and/or in InGaAs/GaAs strained-layer superlattice (SLS) buffer layer. Surface etch pit density (EPD) and cross-sectional transmission electron microscopic observation show that in-situ TC followed by SLS buffer layer growth effectively reduces threading dislocations on the order of 106 cm−2 for 3.5 μm thick epilayers. The degree of reduction strongly depends on the SLS structure and the number of in-situ TC cycles. EPD profiles for in-situ TC samples with and without SLS buffer show that the SLS buffer reduces threading dislocations in the regions both above and below the SLS. This may be because SLS-induced strain, caused by lattice mismatch between the SLS layer and the underlying GaAs layer, bends and thereby reduces threading dislocations in this underlying layer. An observed PL peak shift in the underlying layer due to incorporation of the SLS buffer supports this interpretation. It is also found that the optimum InxGa1−xAs/GaAs SLS structure is one whose total thickness is 2–10 times greater than the calculated critical thickness for the average composition 〈x〉 of the SLS buffer.