Relaxation of strained InGaAs/GaAs layers under thermal processing

Abstract

The relaxation of strained layers above a critical thickness is crucial for the design of stable buffer layers for future device applications. Whilst many, often disparate, models exist for predicting the critical thickness, in practice few of these models appear to be obeyed accurately. For the majority of systems the actual relaxation critical thickness measured experimentally on as-grown layers is found to be much greater than that predicted by the generally accepted “equilibrium” models and therefore such layers must be presumed metastable. Consequently it becomes essential to evaluate experimentally the degree of metastability, the relaxation behaviour and the robustness of such systems to subsequent processing steps. In these experiments double-crystal X-ray diffraction was used to follow the relaxation in single layers of In 0.1Ga 0.9As grown on GaAs as a function of anneal time and temperature. The results show a strong systematic dependence of the relaxation rate on anneal temperature, confirming that these layers are indeed metastable. However, the high temperature required to obtain appreciable relaxation suggests these layers may still be sufficiently robust for many applications.