Anion-related variations in the phonon behavior of cubic Ga 1− xAl xY semiconductors and (GaY) m/(Ga 1− xAl xY, Y = As, N) n superlattices

Abstract

We have reported a comprehensive theoretical study of anion-related variations in the phonon behavior of cubic Ga 1− x Al x Y semiconductors and (GaY) m /(Ga 1− x Al x Y,Y=As, N) n superlattices (SLs) using a microscopic rigid-ion model (RIM). The short range forces for the bulk GaAs and AIAs in the RIM are optimized by incorporating values of elastic constants, and phonons at critical points from the inelastic neutron scattering and/or Raman data. The force constants for cubic GaN, AlN are obtained from the transformed Raman scattering data of phonons for the wurtzite materials and the existing elastic constants. The long-range Coulomb forces are evaluated exactly via Ewald summation. To treat the alloying of barrier layers and disorder at the interfaces in (GaY) m /(Ga 1− x Al x Y) n SLs, we considered a generalized random-element iso-displacement model. For short period SLs, the dependence of phonons on wavevectors both parallel and perpendicular to the growth direction [0 0 1] is investigated. An interesting variation in the phonon behavior found in the two systems is explained in terms of the differences in the anion masses and effective ionic-charges.