<title>Phonon lifetimes and decay channels in single-crystalline bulk AlN</title>

Abstract

We report on the Raman analysis of the phonon lifetimes and decay channels of the A<SUB>1</SUB>(LO) and E<SUB>2</SUB>(high) phonons of single-crystalline bulk AlN grown using the sublimation- recondensation method. The temperature dependence of the phonon lifetimes was investigated from 10 K to 1275 K. Lifetimes of the A<SUB>1</SUB>(LO) phonon and the E<SUB>2</SUB>(high) phonon of 0.75 ps and 2.9 ps, respectively, were measured at 10 K. Our experimental results show that the A<SUB>1</SUB>(LO) phonons of AlN decay primarily into two phonons of equal energy (Klemens' decay channel), most likely longitudinal- acoustic phonons. AlN is therefore in great contrast to GaN, where a symmetric decay of the A<SUB>1</SUB>(LO) phonon is not possible due to a large energy gap between the acoustic and optical phonon branches. For the E<SUB>2</SUB>(high) phonon, we find an asymmetric phonon decay. Contributions from two- and three-phonon decay channels were used for the modeling of the temperature dependence of the E<SUB>2</SUB>(high) phonon lifetime. Phonon lifetimes and decay channels of the E<SUB>1</SUB>(LO), A<SUB>1</SUB>(TO) and E<SUB>1</SUB>(TO) phonons of AlN were also investigated.