Estimation of the Influence of GaAs, GaSb and InP Substrates on the Boundaries of Stable Compositions of GaAsSb Ternary Solid Solutions in Epitaxial Layers of Various Thicknesses
Abstract:
Various III-V solid solution systems are characterized by the existence of a spinodal decomposition area, which imposes limitations on the formation of epitaxial layers, in particular on their composition and thicknesses. In this work, we have performed a comparative analysis of the change in the stability region boundaries of GaAsSb solid ternary solutions formed on GaAs, GaSb and InP substrates in the temperature range from 400 to 650 C. The cal culations have been completed using the CALPHAD method and the SGTE data. Disregarding the elastic energy generated by the lattice mismatch between forming solid solutions and substrate, the estimations show a continuous spinodal decomposition area, between near pure GaAs and GaSb compositions, that expands with decreasing tem peratures. Given the elastic energy contribution to the solid solution energy, extensive regions of stable compositions are always observed in thin epitaxial layers with thicknesses d on the order of a few monolayers. On GaAs and GaSb substrates these regions shrink rapidly, as the layer grows, to compositions corresponding to free elastic energy solid solutions. On the InP substrate, at large thicknesses, within the spinodal decomposition area, the interval of stable compositions is conserved around the isoperiodic composition with the substrate (GaAs0.51Sb0.49), and for the 500 nm epitaxial layer lies between 0.46-0.66 molar fractions of GaAs. The results obtained may be of interest for the growth of thick layers in heterostructures to obtain photodetectors for the mid-infrared wavelength range.
