Phonon Lifetimes and Phonon Decay Channels in Single Crystalline Bulk Aluminum Nitride

Abstract

ABSTRACTWe report on the Raman analysis of the phonon lifetimes and phonon decay channels of the A1(LO), E1(LO) and E2(high) phonons of single crystalline bulk AlN grown by the sublimationrecondensation method. The temperature dependence of the phonon lifetimes was investigated from 10K to 1275K. Our experimental results show that amongst the various possible decay channels, the A1(LO) phonons of AlN decay primarily into two phonons of equal energy (Klemens model), most likely longitudinal-acoustic (LA) phonons. AlN is therefore in great contrast to GaN, where a symmetric decay of the A1(LO) phonons is not possible due to a large energy gap between the acoustic and optical phonon branches. For the E2(high) phonon, we find an asymmetric phonon decay into a high-energy and a low-energy phonon. Possible decay channels of the E2(high) phonon include combinations of E2(low) and acoustic phonons. For the E1(LO) phonons, the temperature dependence of the phonon lifetime is consistent with a symmetric phonon decay. Phonon lifetimes of the A1(LO), the E1(LO) and the E2(high) phonon of 0.75ps, 1.2ps and 2.9ps, respectively, were measured at 10K.