Thermal stability of GaN investigated by Raman scattering

We have investigated the thermal stability of GaN using Raman scattering. Noninvasive optical monitoring of structural damage to GaN by high-temperature anneals in nitrogen ambient has been demonstrated. Characteristic features in the Raman spectrum identify three thermal stability regimes. Thermal damage between 900 and 1000 °C results in the appearance of a broad Raman peak between the E2 and A1(LO) phonon. For anneals at temperatures higher than 1000 °C emerging macroscopic disorder gives rise to distinct Raman modes at 630, 656, and 770 cm−1. Below 900 °C no thermal damage has been observed. The evolution of the Raman spectrum of GaN with increasing annealing temperature is discussed in terms of disorder-induced Raman scattering. We find clear indications for a reaction at the GaN/sapphire interface for anneals higher than 1000 °C.