Thermal stability of GaN thin films grown on (0001) Al₂O ₃, (011̄2) Al₂O₃ and (0001)_Si 6H-SiC substrates

Single crystals of GaN were grown on (0001), (011̄2) Al ₂O₃ and (0001)_Si 6H-SiC substrates using an atmospheric pressure metalorganic chemical-vapor-deposition reactor. The relationship has been studied between the thermal stability of the GaN films and the substrate's surface polarity. It appeared that the N-terminated (0001) GaN surface grown on (0001)_Si 6H-SiC has the most stable surface, followed by the nonpolar (112̄0) GaN surface grown on (011̄2) Al ₂O₃, while the Ga-terminated (0001) GaN surface grown on (0001) Al₂O₃ has the least stable surface. This is explained with the difference in the atomic configuration of each of these surfaces which induces a difference in their thermal decomposition.