Annealing effects on structural, optical and electrical properties of e-beam evaporated CuIn _0.5 Ga _0.5 Te ₂ thin films

CuIn _0.5 Ga _0.5 Te ₂ (CIGT) thin films have been prepared by e-beam evaporation from a single crystal powder synthesized by direct reaction of constituent elements in a stoichiometric proportion. Post-depositional annealing has been carried out at 300 and 350 °C. The compositions of the films were determined by energy dispersive X-ray analysis (EDXA) and it was found that there was a remarkable fluctuation in atomic percentage of the constituent elements following to the post-depositional annealing. X-ray diffraction analysis (XRD) has shown that as-grown films were amorphous in nature and turned into polycrystalline structure following to the annealing at 300 °C. The main peaks of CuIn _0.5 Ga _0.5 Te ₂ and some minor peaks belonged to a binary phase Cu ₂ Te appeared after annealing at 300 °C, whereas for the films annealed at 350 °C single phase of the CuIn _0.5 Ga _0.5 Te ₂ chalcopyrite structure was observed with the preferred orientation along the (1 1 2) plane. The effect of annealing on and near surface regions has been studied using X-ray photoelectron spectroscopy (XPS). The results indicated that there was a considerable variation in surface composition following to the annealing process. The transmission and reflection measurements have been carried out in the wavelength range of 200-1100 nm. The absorption coefficients of the films were found to be in the order of 10 ⁴ cm ^-1 and optical band gaps were determined as 1.39, 1.43 and 1.47 eV for as-grown and films annealed at 300 and 350 °C, respectively. The temperature dependent conductivity and photoconductivity measurements have been performed in the temperature range of -73 to 157 °C and the room temperature resistivities were found to be around 3.4 × 10 ⁷ and 9.6 × 10 ⁶ (Ω cm) for the as-grown and annealed films at 350 °C, respectively.