Optical constants of Zn 1−xLi xO films prepared by chemical bath deposition technique

Abstract

Zn 1− x Li x O films of different Li concentrations x = 0.0 – 0.5 were successfully deposited on glass substrates using chemical bath deposition (CBD) technique. Optical properties of the films were studied extensively in the wavelength range 190–800 nm from the measurements of the optical transmittance ( T) and optical reflectance ( R). The mechanism of the optical absorption follows the rule of direct allowed transition. Both the optical energy gap E g and absorption coefficient ( α ) were found to be Li concentration-dependent. The refractive index values have been fitted to the single-oscillator models. The values obtained for the single-oscillator energy E o are consistent with the optical gap results. The dependence of the optical constants of ZnO on the photon energy ( h ν ) at selected concentrations of Li were discussed. The exponential dependence of the absorption coefficient as a function of the incident photon energy suggests that the Urbach rule is obeyed and indicated the formation of a band tail. It was found that the optical energy gap decreases with increasing Li content; on the other hand the band tail width exhibits the opposite behaviour.