Investigation of CuInSe2 thin films deposited by laser ablation method

Chalcopyrite copper indium diselenide (CuInSe2) thin films have been deposited on Corning 7059 glass substrates by pulsed laser ablation method. Structural and optical properties of thin films deposited under pressure conditions, varying from 10(-3) to 10(-6) Torr, have been investigated. The X-ray diffraction spectra revealed the chalcopyrite tetragonal structure of copper indium diselenide with (112), (220) and (312) orientations. The films were found to be highly polycrystalline in nature, which was further improved along the (112) orientation with a decrease in pressure. Lattice strain and dislocation densities in the films were also estimated using the broadening of diffraction peaks. The Raman spectra show a strong peak at 170 cm(-1), corresponding to the dominant A1 vibrational mode of copper indium diselenide, and shift towards 174 cm(-1) with decreasing pressure. The optical transmittance of the films was measured in the wavelength range of 300-2200 nm. The optical bandgap of the films was found to be in the range of 1.05-1.3 eV using Tauc's plot. The Urbach energy calculations suggest a decrease in the degree of disorder in the films deposited at low pressure.