OPTICAL-ABSORPTION BEHAVIOR OF EVAPORATED ZNIN2SE4 THIN-FILMS

The optical absorption behaviour of thin films of ZnIn2Se4 formed by a vacuum deposition process was studied. The optical constants (the ref ractive index n, extinction coefficient k and dielectric constants eps ilon' and epsilon '', are estimated for ZnIn2Se4 thin films as well as the effect of heat treatments in the wavelength range 300-2500 nm. X- ray diffraction and electron microscopy were used to obtain an insight into the structural information. ZnIn2Se4 is a layer semiconductor of tetrahedral crystal structure. From the reflection and transmission d ata, the absorption coefficient was computed for amorphous and crystal line films. Analysis of the absorption coefficient data revealed the e xistence of allowed direct and indirect transitions with optical energ y gaps E(d)(opt) = 3.38 eV and E(i)(opt) = 2.22 eV at 300 K. These val ues were found to decrease with increasing annealing temperature.