Single crystals of and were grown by chemical vapor transport method using as the transport. The as-grown crystals reveal transparent and light-green color. Most of them possess a well-defined (112) surface. The crystals essentially show transparent and white color in vacuum. As the was put into the atmosphere, the crystal surface gradually darkened and became brownish because of the surface reaction with humidity or hydrogen gas. After a long-term chemical reaction process, the will transform into a oxide with yellow color. From x-ray diffraction measurements, both and as-grown crystals show single-phase and isostructural to a chalcopyrite structure. The (112) face is more preferable for the formation of the chalcopyrite crystals. The energies of interband transitions of the and were determined accurately by thermoreflectance measurements in a wide energy range of 2–6 eV. The valence-band electronic structures of and have been detailed and characterized using polarized-thermoreflectance measurements in the temperature range between 30 and 300 K. The band-edge transitions belonging to the and polarizations have been, respectively, identified. The band edge of is near 3.2 eV while that of is about 3.5 eV. On the basis of the experimental analyses, optical and sensing behaviors of the chalcopyrite crystals have been realized.
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