The effect of γ-doses on the optical band gap of AgInSe 2 films

Abstract

Some optical properties of AgInSe 2 thin films are studied as a function of γ-doses. In order to determine the optical energy gap E g, the absorbance spectra of the films of different γ-doses are analyzed. The compound shows an allowed direct transition near the fundamental absorption edge E g1, in addition to transition originating from the crystal field split level E g2. The direct energy gap E g1 increases from 1.21 eV for an unirradiated film to 1.31 eV for an irradiated film (0.7 Mrad) and then decreases to 1.17 eV for higher doses (3.0 Mrad). E g2 exhibits an opposite trend of E g1, i.e. with the first dose (0.7 Mrad) it decreases from 1.76 eV for the unirradiated film to 1.66 eV and then increases to 1.75 eV as the γ-dose increases to 3.0 Mrad. The calculated band tails in the first region ( E e1) and in the second region ( E e2) revealed that the crystal field reduces the crystallinity of the composition. The influence of γ-irradiation on the optical gap was explained in terms of diminution of disorder, defects in the structural bonding and crystal field mechanism. From the absorbance spectra, the relationship between the extinction coefficient ( k) and refractive index ( n) at different γ-doses were derived.