Abstract
Thin films of CuGa0.25In0.75Se2 of different growth conditions were deposited on glass substrates by thermal evaporation. X-ray diffraction revealed the formation of amorphous films. The effect of thickness (d), heat treatment and substrate temperature (T-s) on the optical energy gap (E-opt.) and on the activation energy (Delta E) for dc conductivity and the density of localized states at the Fermi level N (E-f) were carried out. For all films deposited at room temperature, the optical transition was found to be indirect. The optical energy gap increase with increasing film thickness and with increasing temperature and time of annealing. The band tail (E-c) obeys Urabach empirical relation. Up to Ts > 500 K, it is obvious that the process of transformation to polycrystalline occurs. As a result, the two direct energy gaps which attributed to the fundamental edge E-g1 and band splitting E-g2 are found. The electrical conductivity increases with increasing thickness, with increasing the evaporation conditions (d, Ts, and annealing temperature and time) and exhibits two types of conduction mechanisms. The corresponding band is approximately half the optical energy gaps and the effect is interpreted in term of density of state by Mott and Davis.