Thermal Stability of Low-Temperature GaN and AlN Buffer Layers During Metalorganic Vapor Phase Epitaxy Monitored by In Situ Shallow-Angle Reflectance Using Ultraviolet Light

The thermal stability of low-temperature (LT) GaN and AlN buffer layers during the annealing process in metalorganic vapor phase epitaxy (MOVPE) was monitored in situ by shallow-angle reflectance using p-polarized ultra-violet light (325 nm). A LT-GaN or LT-AlN buffer layer was grown on c-plane sapphire substrates at 600 and 700°C, respectively, by low pressure (76 Torr) MOVPE. These LT-buffer layers were annealed in H2 or N2 carrier gases and their thermal stability was examined. During annealing at 1020°C under NH3 supply with H2 carrier gas, the reflectivity dipped, indicating the desorption of the LT-GaN. In contrast, the reflectivity remained constant during annealing in N2 carrier gas, indicating the LT-GaN layer was stable in N2. The LT-AlN buffer layer was stable even in H2 carrier gas. These results indicate that N2 carrier gas stabilizes the LT-GaN buffer layer during annealing over 1000°C.