Specific features of the surface morphology of modified AlN/sapphire substrates fabricated by thermochemical nitridation

Abstract

The influence of the reducing annealing of sapphire substrate during the thermochemical nitrida� tion of sapphire on the structure of the nitride layer in the AlN/sapphire template has been investigated. Iso� thermal annealings of (0001) and sapphire substrates have been performed at the nitridation temper� ature (1450°C) and different reducing potentials of the gas medium. It is found that the initial terracestep structure of substrates is transformed during annealing as a result of the diffusion and thermochemical etching of sapphire substrates; this process is accompanied by the fragmentation and merging of steps and by an increase in their width and height. The degree of stepstr ucture distortion increases with an increase in the reducing potential of the gas medium and the annealing time. Hexagonal etching figures are observed for (0001) sapphire substrates. It is established that the AlN/sapphire template surface relief is formed mainly in the initial stage during thermochemical etching of the stating substrate, which precedes the formation of a nitride layer. The sapphire-nitride transformation does not lead to a further increase in the surface roughness.