Synthesis and growth of ZnGeP2 crystals: Prevention of non-stoichiometry

The causes of non-stoichiometry in both synthesis and growth process of ZnGeP2 (ZGP) have been studied. The effects of mechanical oscillation (MO) and gradient cooling (GC) techniques employed in the synthesis of ZnGeP2 polycrystals have been investigated. X-Ray Diffraction analysis (XRD) has identified that phosphorus was the main loss component. The growth of ZnGeP2 crystal was carried out in a three-section vertical Bridgman (VB) furnace. A certain amount of phosphorus was added to ZnGeP2 polycrystals before growth. The temperature gradients were controlled at 10–15 °C/cm within crystallization zone. A ZnGeP2 crystal with the size of Φ25 mm×55 mm was obtained. The proportions of P, Ge and Zn in the grown crystal were measured with Energy Dispersive Spectrometer (EDS). The results showed that the grown crystal has good stoichiometry and homogeneity. Infrared transmittance and absorption spectra show that the crystal has low absorption in 2.0–10.0 μm range. Absorption contour maps by automatic infrared microscope demonstrate that optical homogeneity of grown crystal is good.

► The causes of non-stoichiometry in both synthesis and growth of ZnGeP2 were studied.
► Mechanical Oscillation and Gradient Cooling were adopted for synthesizing ZnGeP2.
► Addition of P and proper temperature gradients were used in the growth of ZnGeP2 crystals.
► ZnGeP2 single crystals were successfully grown.
► The grown crystal has good stoichiometry and satisfactory optical performance.