“…In the future, we plan to carry out these measurements using a single mode laser. We note that for GaN, eight optical phonon modes are predicted, 1A 1 (TO), 1A 1 (LO), 2B 1 , 1E 1 (TO), 1E 1 (LO), and 2E 2 , all of which have been observed with RS, with the exception of the 2B 1 modes which are optically inactive [7][8][9]. The peak positions and intense sharp lines indicate good local crystalline quality and stress-free crystals, and the 1A 1 (LO) phonon lineshape is consistent with a low free carrier concentration.…”