Phonon lifetimes in bulk AlN and their temperature dependence

We report on the Raman analysis of the phonon lifetimes of the $A_1(\mathrm{LO})$ (longitudinal optical) and $E_2(\mathrm{high})$ phonons in bulk AlN crystals and their temperature dependence from 10 to 1275 K. Our experimental results show that amongst the various possible decay channels, the $A_1(\mathrm{LO})$ phonons decay primarily into two phonons of equal energy (Klemens model), most likely longitudinal-acoustic phonons, whereas the $E_2(\mathrm{high})$ phonon decays asymmetrically into a high-energy and a low-energy phonon. Possible decay channels of the $E_2(\mathrm{high})$ phonon have been shown to include combinations of $E_2(\mathrm{low})$ and acoustic phonons. Phonon lifetimes of the $A_1(\mathrm{LO})$ phonon and the $E_2(\mathrm{high})$ phonon of 0.75 and 2.9 ps, respectively, were measured at 10 K.