Nitridation of an unreconstructed and reconstructed $(\sqrt{31}\times\sqrt{31})R\pm9^\circ$ (0001) sapphire surface in an ammonia flow

This paper is devoted to the study of the nitridation of unreconstructed and reconstructed $(\sqrt{31}\times\sqrt{31})R\pm9^\circ$ (0001) sapphire surfaces in an ammonia flow by reflection high-energy electron diffraction (RHEED). The experimental results show that sapphire nitridation occurs on the unreconstructed (1 $\times$ 1) surface, which results in AlN phase formation on the substrate surface. However, if sapphire nitridation is preceded by high-temperature annealing (1150$^\circ$C) resulting in sapphire surface reconstruction with formation of the $(\sqrt{31}\times\sqrt{31})R\pm9^\circ$ surface, the crystalline AlN phase on the sapphire surface is not formed during surface exposure to an ammonia flow.