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Optical images of a Cl-VPE (1243 K) GaN grown on sapphire substrate after etching in H3PO4 at 433 K (a) for 5 min and (b) for 10 min.Optical images of a Cl-VPE (1263 K) GaN grown on sapphire substrate after etching in H3PO4 at 433 K (a) for 5 min and (b) for 10 min.Refractive index of as-grown and high energy Si ion irradiated GaN.Effect of Si ion irradiation on the film thickness of the GaN layers.Extinction coefficient of as-grown and high energy Si ion irradiated GaN layers.