PRESSURE-DEPENDENT PHONON PROPERTIES OF III-V COMPOUND SEMICONDUCTORS

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 Grüneisen 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 Grüneisen parameter TA(X) and the transition pressure Pt. Numerical results for the lattice dynamics, one-phonon and two-phonon density of states, Debye temperature, Grüneisen constant, and linear thermal-expansion coefficient are all shown to be in reasonably good agreement with the existing experimental data. © 1990 The American Physical Society.