Effect of thermal annealing on the optical properties of CdGeAs2 wafers

A crack-free CdGeAs2 single crystal 15 mm in diameter and 50 mm in length was grown in a three-zone tubular furnace by the modified vertical Bridgman method. During the annealing processes, the effects of treatments with different atmosphere, different temperatures and time were investigated. The as-grown and annealed wafers were characterized using X-ray diffractometer (XRD), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and IR microscope. Conclusively, the results confirm annealing could improve the optical qualities of as-grown CdGeAs2 crystal. The best result was obtained under cover-up with CdGeAs2 polycrystalline powder at 450 °C for 150 h and the IR transmittance of the wafer measured by FTIR was up to 48.65% nearby 5.5 μm and exceeded 50% in the range of 8–12 μm. Additionally, the monolithic homogeneity of the crystal has also been greatly improved after annealing under cover-up with polycrystalline powder.

► Wafers were annealed in different conditions and characterized.
► Detailed comparisons under different annealing conditions are made.
► Optimized annealing process for bulk material of CdGeAs2 has been presented.