Evolution process of cross-hatch patterns and reduction of surface roughness in (InAs)m(GaAs)n strained short-period superlattices and InGaAs alloy layers grown on GaAs

Abstract

We investigated the formation process of cross-hatch patterns (CHPs) and the lattice relaxation process in the growth of an (InAs)1(GaAs)4 strained short-period superlattice (SSPS) and an In0.2Ga0.8As alloy layer on GaAs(100) substrates. By using x-ray diffraction and cross-sectional transmission electron microscopy, it was found that the lattice relaxation in the (InAs)1(GaAs)4SSPS proceeded as fast as that in the In0.2Ga0.8As alloy layer. The surfaces of the grown layers showed CHPs, and the surface roughness increased by means of the evolution of the CHPs. The surface roughness of the SSPSs was larger than that of the alloy layers, whereas no apparent difference was observed in the lattice relaxation process between the SSPSs and the alloy layers. Additionally, the height of surface ridges parallel to the [01̄1] direction was higher than that parallel to the [011] direction. We observed the distribution of highly strained InAs and GaAs islands on the surfaces of strained InGaAs layers by using an atomic force microscope. As a result, it was clarified that the InAs islands were accumulated on top of the surface ridges, whereas the GaAs islands were distributed uniformly on the surface of strained InGaAs layer. It was considered that the nonuniform incorporation of In atoms during growth of layers contributes mainly to the evolution of CHPs in the InGaAs-on-GaAs heteroepitaxy. We propose a developmental model of CHPs based on the surface diffusion of the In atoms. In this model, the asymmetry of CHPs was well understood by anisotropy in surface diffusion length of In atoms. Additionally, it was clarified that the evolution of CHPs in the growth of InGaAs at a high temperature can be suppressed by growing a fully relaxed InGaAs layer at a low temperature before the high-temperature growth.