Enhanced near-infrared optical transmission in zinc germanium phosphide crystals via precise magnesium doping

A zinc germanium phosphorus (ZnGeP₂) crystal with a chalcopyrite structure is an efficient frequency converter in the mid-infrared region. However, point defect-induced optical absorption at the pumping wavelength (near infrared region) blocked the further application of ZnGeP₂. To alleviate the absorption losses caused by point defects, in situ magnesium doping compensation was presented during the ZnGeP₂ bulk crystal growth process via the vertical Bridgman method. Combined with theoretical calculations, the structural distortion of the magnesium-doped ZnGeP₂ crystals in different orientations was illustrated. The thermodynamic and kinetic stability of the magnesium-doped ZnGeP₂ structure were demonstrated. The transmission results indicated the improvement of transmittance within a wavelength range of 1.8-2.4 μm when doped with magnesium, which revealed the powerful ability of the appropriate dopant in optimizing near-infrared optical properties. Thus, the introduction of magnesium is a practical approach to improve the transmittance performance and extend the pumping source wavelengths of ZnGeP₂ crystals.