Preparation of sapphire substrates for Gas phase GaN epitaxial processes

After mechanical treatment the surface of α‐Al 2 O 3 plates with orientation (0001) for GaN epitaxy was polished in a mixture of H 3 PO 4 and H 2 SO 4 . The best mixture H 2 SO 4 /H 3 PO 4 and the best temperature for polishing were chosen. — The quality of the polished substrates was determined by structural etching in KOH. The optimum structural etching time was 3 min. at 320°C. The thickness of the layer which should be removed after mechanical treatment and the dislocation density of the starting material for GaN epitaxy was determined.