Raman line shape of the A1 longitudinal optical phonon in GaN

High-resolution Raman measurements of the A1 longitudinal optical (LO) phonon in GaN reveal a complex line shape that can be explained in terms of the angular dispersion of LO phonons in this material. A simple geometrical model of the line shape makes it possible to extract the true anharmonic full width at half maximum 2Γ of the A1(LO) mode. The value of this parameter, 2Γ=2.4 cm−1 at 20 K, is in much better agreement with time-domain measurements by Tsen and co-workers [Appl. Phys. Lett. 72, 2132 (1998)] than any previous frequency-domain measurement. The results indicate that angular dispersion effects must be carefully considered in any analysis of Raman spectra from noncubic crystals.