Optical behavior and structural property of CuAlS₂ and AgAlS₂ wide-bandgap chalcopyrites

Abstract

Single crystals of CuAlS₂ and AgAlS₂ were grown by chemical vapor transport method using ICl₃ as the transport. The as-grown CuAlS₂ crystals reveal transparent and light-green color. Most of them possess a well-defined (112) surface. The AgAlS₂ crystals essentially show transparent and white color in vacuum. As the AgAlS₂ 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 AgAlS₂ will transform into a AgAlO₂ oxide with yellow color. From x-ray diffraction measurements, both CuAlS₂ and AgAlS₂ 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 CuAlS₂ and AgAlS₂ were determined accurately by thermoreflectance measurements in a wide energy range of 2-6 eV. The valence-band electronic structures of CuAlS₂ and AgAlS₂ 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 E(∥) and E(⊥) polarizations have been, respectively, identified. The band edge of AgAlS₂ is near 3.2 eV while that of AgAlS₂ is about 3.5 eV. On the basis of the experimental analyses, optical and sensing behaviors of the chalcopyrite crystals have been realized.

Wide Band Gap Chalcogenide Semiconductors

“…AgAlS 2 has a comparable band gap (∼3.2 eV) to CuAlS 2 , though CBD synthesis yields a gap of 2.3 eV. However, it has been reported as unstable in air, which limits its practical applications .…”

Recent advances in rational structure design for nonlinear optical crystals: leveraging advantageous templates

“…33) space group. It was observed that the SHG coefficients of AgGaS 2 199 and LiGaS 2 204,205 are larger than 10 pm/V, while those of AgAlS 2 206 and LiAlS 2 207 are less than 5 pm/V. Additionally, compounds containing Ag were found to have smaller energy band gaps compared to the ones containing Li.…”

“…20a). The known ternary DL metal sulfides can be classified into the following categories, including I-III-S 204,205 are larger than 10 pm/V, while those of AgAlS 2 206 and LiAlS 2 207 are less than 5 pm/V. Additionally, compounds containing Ag were found to have smaller energy band gaps compared to the ones containing Li.…”