MISFIT STRAIN, RELAXATION, AND BAND-GAP SHIFT IN GAXIN1-XP INP EPITAXIAL LAYERS/

A detailed investigation of the structural and optoelectronic properti es of thick GaInP epilayers on sulfur-doped InP substrates is reported . Significant variations of the optical absorption and photoluminescen ce 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 we re used to determine the Ga concentrations and the strains and indicat e significant anisotropic relaxation in several films. Even small rela xations result in a significant increase in the optical linewidths and a rapid drop in the transition intensities. A model with no free para meters based on the strain Hamiltonian of Pikus and Bir provides excel lent agreement with the transition energies and serves to identify una mbiguously the transitions observed in the optical spectra. Within thi s model, isotropic in-plane relaxation produces a shift of both light- and heavy-hole energies whereas anisotropic in-plane relaxation contr ibutes only negligibly.