Growth and characterization of ZnGeP2 single crystals by the modified Bridgman method

A good quality ZnGeP2 (ZGP) single crystal 15 mm in diameter and 40 mm in length was grown in a vertical three-zone tubular furnace by the modified Bridgman method, i.e. real-time temperature compensation technique (RTTCT) with descending ampoule. The starting material is high-pure and single-phase polycrystal of ZnGeP2 synthesized by the single-temperature zone and mechanical oscillation method (STZMOM). The as-grown single crystal was characterized by various methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analyzer of X-ray (EDAX), and IR and UV spectrophotometers. It is found that there is a cleavage face of (1 1 2) and second-order XRD peaks of the {1 1 2} faces are observed, the IR transmittance of a sample of 2 mm thickness is above 55% in the range from 6000 to 800 cm−1, the absorption edge is near 612.5 nm and the band gap is about 2.02 eV. The absorption coefficient (α) is within 0.015–0.022 cm−1 at the spectral region 2–8 μm. The crystal has a stoichiometry ratio Zn:Ge:P=1:1.12:1.91 which is close to the ideal stoichiometry ratio of 1:1:2. All results demonstrate that the modified growth method is a new and promising method for the ZGP single crystal and the quality of as-grown crystal is good.