Fundamental Optical Properties of ZnIn₂S₄ Single Crystals

Abstract

The fundamental optical properties, i.e. refractive index, fundamental absorption, and infrared lattice absorption, were investigated for ZnIn 2 S 4 single crystals grown by the method of the chemical transport reactions. The refractive indexes, measured by means of interference method, are 2.20 and 2.50 at 10 µ and 480 mµ, respectively The coefficient of fundamental absorption up to 1×10 4 cm -1 in the range of 2.3∼2.9 eV varies as an exponential function of photon energy with the slope independent of temperature. This behavior may be explained to be caused by the influence of the dipolar field associated with defect. For the region of the order of 10 4 cm -1 the direct allowed band-to-band transition was assumed to be responsible, the band gap calculated being 2.86 and 2.99 eV at room temperature and 91°K, respectively. The peak of the absorption due to copper dopant is 2.54 eV at 91°K. Infrared absorption for powder samples in the range of 20∼100 µ shows two strong peaks at 33.0 and 46.6 µ, the former probably corresponding to Zn–S stretching while the latter to In (tetragonal)–S stretching.