Analysis of strain and impurity distribution in II–VI epilayers with optical methods

Abstract

The detailed knowledge of strain and impurity distribution is important for the production and application of thin epilayers. In this paper, it is shown that the combination of different methods as reflection, excitation and resonant Raman scattering spectroscopy is needed to investigate these problems satisfactorily. Two II–VI epilayer systems are chosen: ZnSe and ZnTe, grown on GaAs by different growth methods (MBE, HWE, MOVPE) and at various substrate temperatures. The influence of lattice-misfit and thermally induced strain in different layer regions is analysed and described in a layer-thickness dependent strain model. In comparison with spectroscopy of the strain-split free excitons, that of the bound excitons and their excitation channels in dependence on the layer thickness and strain magnitude allows statements on the nature of the impurities and their local distribution. While in ZnSe/GaAs the main impurities (donors) lie in the lattice-misfit induced dislocation region, in ZnTe/GaAs three differently distributed acceptor-bound-exciton types are identified bound to atoms originating from source contaminations, diffused atoms stemming from the substrate material, and dislocation-related centers.