Optical phonon decay in bulk aluminum nitride

We report Raman studies of the E22 and A1(LO) symmetry phonons of bulk AlN from 13to375K. Based on observed dependences of the phonon energies and linewidths, and accounting for the temperature-dependent thermal expansion, we determine that both phonon lifetimes are limited by two-phonon decay. The E22 decays symmetrically. The A1(LO) asymmetrically decays into vibrations with energies 586 and 309cm−1 which we attribute to A1(TO) and LA phonons from the M point of the Brillouin zone.