Strongly anisotropic behavior of A1(TO) phonon mode in bulk AlN

Abstract

Angle-dependent Raman scattering is performed on an m-plane AlN bulk crystal. The angular dependence of A1(TO) phonon mode shows strongly anisotropic behavior that the Raman intensity in xx polarization is 6.5 times larger than that in zz polarization. Both anisotropy ratio and phase difference between the independent Raman tensor elements Rxx and Rzz of the A1(TO) mode are derived from the Raman spectra. It is found that the |Rxx|/|Rzz| ratio is up to 2.54, which is noticeably higher than that of wurtzite GaN (1.30) and ZnO (1.02).