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High temperature annealing of (α-Al2O3)(0001) substrates in air/oxygen ambient has been applied as an effective surface treatment method to (α-Al2O3)(0001) substrates in molecular beam epitaxy (MBE) growth of III-nitrides. The method is based on the criterion that the terrace-and-step like atomic flat surface considered to be crucial in obtaining a high quality epilayer, could be induced upon high temperature annealing, and was mostly assessed by atomic force microscopy (AFM) analysis. In this work, the surface morphology, surface quality, crystalline quality and surface reconstruction behaviour of (α-Al2O3)(0001) substrates after high temperature annealing are fully studied using AFM analysis, 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 followed by O2 annealing at high temperature is developed to obtain better surface quality of (α-Al2O3)(0001) substrates for MBE growth. |