Optical, structural and electrical properties of co-evaporated CuIn_2Se_(3.5) thin films

摘要

Polyctystalline CuIn_2Se_(3.5) thin films have been prepared by a three-source co-evaporation technique. The optical band gap, structural and electrical properties of these co-evaporated CuIn_2Se_(3.5) thin films deposited on glass substrate held at 673 K and in situ annealed at 723 K in selenium atmosphere are reported here. Optical band gap of the films, determined from spectral transmission data, is found to be 1.22 eV. Powder X-ray diffraction (XRD) studies reveal the CuIn_2Se_(3.5) films to be polycrystalline in nature with tetragonal structure. The lattice parameters are found to be a = 0.576 nm and c = 1.151 nm. The average grain size of the films is 1 pm. The films are n-type with room temperature resistivity of 180 OMEGA cm. The activation energies, determined from the temperature dependence of electrical conductivity, are found to be 0.34 eV (320-415 K) and 0.10 eV (223-320 K) and are attributed to In_(Cu) and V_(Se) respectively.