Raman Frequencies and Angular Dispersion of Polar Modes in Aluminum Nitride and Gallium Nitride

Abstract

Abstract We performed angular‐resolved Raman‐scattering experiments on AlN and GaN both grown in the wurtzite structure. Our measurements reveal that the transverse polar modes in AlN and GaN show a pronounced angular dispersion. We varied the angle between the phonon‐propagation direction and the optical axis between 41° and 90° and observed a frequency shift of the A 1 (TO) mode in the range of 28 cm −1 in AlN and of 15 cm −1 in GaN. The experimental values agree well with our theoretical calculations which were carried out using the DFT‐LDA plane‐wave pseudopotential method.