Abstract: The optical absorption at 9 μm to 10 μm related to lattice vibration in ZnGeP₂ crystal limited its application in the mid- and far-infrared range. To explain the physical mechanism of the infrared cut-off edge and the absorption peak near 9 μm in ZnGeP₂, a method combining theoretical calculations and experiments was used. Thus, the ZnGeP₂ single crystal was grown by the Bridgman method, and the temperature-dominated and pressure-dominated Raman spectrum of the grown ZnGeP₂ crystal were tested. In addition, the vibration frequency of ZnGeP₂ in the center of the Brillouin zone, the crystal lattice constant and Raman shift peak under different pressures were calculated based on the first-principles method. Experimental and theoretically calculated results reveal that the frequency of the vibration red shifts with temperature increasing, simultaneously, decrease of intensity and wider half-peak width of the vibration are observed. Besides, the frequency of the vibration blue shifts with pressure increasing, simulatenously, decreases of intensity and wider half-peak width of the vibration are observed.

Key words: ZnGeP₂, Raman spectroscopy, infrared absorption, variable temperature and pressure, first-principle, multiphonic absorption, lattice vibration