Pressure-dependent phonon properties of III-V compound semiconductors.

Abstract

Using a phenomenological lattice-dynamical theory in the quasiharmonic approximation, we present a comprehensive study to understand the effects of pressure on the vibrational properties of Ga-In pnictides that exhibit a sphalerite crystal structure. The existing pressure-induced Raman scattering data for phonon frequencies, the ultrasonic measurements of elastic and lattice constants, are used as constraints to stringently test the reliability of our rigid-ion model. The effects of high pressure on phonon dispersion curves are shown to lead to a softening in the transverse acoustic modes. At low temperatures this provides a possible driving mechanism for the decrease in the Debye temperature and the occurrence of a negative Gr\uneisen constant and thermal-expansion coefficient in semiconductors. With a few exceptions (InP, GaAs, and GaSb), our calculated values for several elemental and compound semiconductors have qualitatively satisfied the empirical linear relationship between the Gr\uneisen parameter ${\ensuremath{\gamma}}_{\mathrm{T}\mathrm{A}(\mathit{X})}$ and the transition pressure ${\mathit{P}}_{\mathit{t}}$. Numerical results for the lattice dynamics, one-phonon and two-phonon density of states, Debye temperature, Gr\uneisen constant, and linear thermal-expansion coefficient are all shown to be in reasonably good agreement with the existing experimental data.