Investigation on large-sized sapphire crystalline perfection by X-ray double-crystal diffraction method

The large-sized sapphire (Ø225×205 mm, 27.5 kg) was grown successfully by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at cooled center). The surface quality of the specimens was characterized by micro-Raman spectroscopy, and double crystal X-ray diffractometry (DCD) was utilized to investigate its crystalline perfection. The measurement of rocking curves was performed on various specimens from different region of large sapphire boule. The experimental results showed that CMP (chemo-mechanical polishing) with subsequent suitable chemically etching can develop the best-quality sapphire crystal surface and the values of FWHM obtained by conventional DCD were in the range from 27" to 58". The infrared spectral transmission (2.0-4.5 μm) of sapphire crystal exceeded 82%. It is confirmed of SAPMAC growth method characteristics with in-situ annealing, small temperature gradient and low residual stress level by numerical simulation analysis.