Abstract
High temperature annealing in air has been applied as an effective ex-situ surface treatment for the α —Al2O3(0001) substrates used in molecular beam epitaxy (MBE) growth of III-nitrides. The method is based on the criterion that atomically smooth surface of terrace-and-step like structure, which is considered to be crucial in obtaining a high quality epilayer, could be produced upon high temperature annealing. The annealed surface was mostly studied by atomic force microscopy (AFM) imaging. In this work, the effects of high temperature annealing on the surface morphology, crystalline quality, optical quality and surface reconstruction behaviour of α —Al2O3(0001) substrates were fully studied using AFM, triple-axis high resolution X-ray diffraction (THRXRD), spectroscopic ellipsometry (SE) and in-situ reflection high-energy electron diffraction (RHEED). A new strategy, H2 thermal cleaning at 1100°C followed by O2 annealing at 1300°C was proposed as an efficient surface treatment for α —Al2O3(0001) substrates for MBE growth
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