Degradation of AlGaN during high-temperature annealing monitored by ultraviolet Raman scattering

We have illustrated the use of ultraviolet (UV) Raman scattering to investigate the thermal stability of AlGaN layers with high-aluminum content. The degradation pathway of ${\mathrm{Al}}_{\mathrm{0.72}}{\mathrm{Ga}}_{\mathrm{0.28}}\mathrm{N}$ was monitored for high-temperature treatments up to 1200 °C. For annealing temperatures higher than 1150 °C, the ${\mathrm{Al}}_{\mathrm{0.72}}{\mathrm{Ga}}_{\mathrm{0.28}}\mathrm{N}$ film decomposes: a low- and a high-aluminum composition ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ phase emerge. At 1100 °C, prior to the ${\mathrm{Al}}_{\mathrm{0.72}}{\mathrm{Ga}}_{\mathrm{0.28}}\mathrm{N}$ decomposition, UV Raman scattering detects the buildup of a large strain in the ${\mathrm{Al}}_{\mathrm{0.72}}{\mathrm{Ga}}_{\mathrm{0.28}}\mathrm{N}$ film. The crystalline quality of ${\mathrm{Al}}_{\mathrm{0.72}}{\mathrm{Ga}}_{\mathrm{0.28}}\mathrm{N}$ is unaffected up to 1000 °C.