Phonon density of states of bulk gallium nitride

We report the measured phonon density of states of a bulk GaN powder by time-of-Right neutron spectroscopy. The observed one-phonon excitation spectrum consists of two broad bands centered at about 23 and 39 meV corresponding to the acoustic and the first group of optical phonons; two sharp bands of upper optic modes at about 75 and 86 meV; and a gap of 45-65 meV. The phonon dispersion curves, lattice specific heat, and Debye temperature are calculated from fitting the data with a rigid-ion model. (C) 1998 American Institute of Physics.