Growth of low etch pit density ZnGeP2 crystals by the modified vertical Bridgman method

Based on the high-quality polycrystalline ZnGeP2 (ZGP) synthesized by the optimized two-temperature-zone method, ZnGeP2 single crystals with dimensions of 16 mm diameter and 70 mm length were successfully grown using the modified vertical Bridgman method. The etch pit density (EPD) of as-growth crystals can be reduced to a level of 510 cm−2; the full width at half maximum (FWHM) of the X-ray rocking curve of the crystals is 20″; the transmittance of the annealed and polished wafers (1.7 mm thick) can reach about 57% in the wavelength range 3-8 µm and the optical absorption coefficient is about 0.1 cm−1 at 2.1 µm; using KTP optical parametric oscillator (OPO) pumping source at 2.1 µm, the output power of ZGP OPO is 2.8 W at 3-5 µm. These results suggest that this modified vertical Bridgman method can grow high structural and optical quality ZGP single crystals for OPOs.