Misfit strain, relaxation, and band-gap shift in GaxIn1−xP/InP epitaxial layers

Abstract

A detailed investigation of the structural and optoelectronic properties of thick GaInP epilayers on sulfur-doped InP substrates is reported. Significant variations of the optical absorption and photoluminescence transition energies from light- and heavy-hole states are observed as a function of the epilayer composition as well as of the degree of relaxation of the misfit strain. High-resolution x-ray measurements were used to determine the Ga concentrations and the strains and indicate significant anisotropic relaxation in several films. Even small relaxations result in a significant increase in the optical linewidths and a rapid drop in the transition intensities. A model with no free parameters based on the strain Hamiltonian of Pikus and Bir provides excellent agreement with the transition energies and serves to identify unambiguously the transitions observed in the optical spectra. Within this model, isotropic in-plane relaxation produces a shift of both light- and heavy-hole energies whereas anisotropic in-plane relaxation contributes only negligibly.