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 degrees C, respectively, by low pressure (76 Torr) MOVPE. These LT-buffer layers were annealed in H-2 or N-2 carrier gases and their thermal stability was examined. During annealing at 1020 degrees C under NH3 supply with H-2 carrier gas, the reflectivity dipped, indicating the desorption of the LT-GaN. In contrast, the reflectivity remained constant during annealing in N-2 carrier gas, indicating the LT-GaN layer was stable in N-2. The LT-AlN buffer layer was stable even in H-2 carrier gas. These results indicate that N2 carrier gas stabilizes the LT-GaN buffer layer during annealing over 1000 degrees C.