Illumination-induced changes on the optical functions and valence band splitting parameters of flash evaporated CuInTe2 films

Chalcopyrite CuInTe2 thin films have been deposited by flash evaporation technique on optically flat quartz substrates. The influence of light illumination on the structural and optical properties of CuInTe2 thin films has been reported. The structural properties of the films are investigated by energy dispersive X-ray, grazing incident in-plane X-ray diffraction and transmission electron microscope. The transmittance and reflectance spectra of the films are measured at normal incidence of light, from which, the refractive and absorption indices of the films are determined. The optical absorption process of as-deposited and illuminated CuInTe2 films is found to be characterized by three direct transitions. The triplet transitions are explained in terms of the valence band splitting under the influence of the tetragonal crystalline field and spin-orbit interaction. Below the lowest optical band gap, the absorption coefficient exhibits exponential behavior, in which Urbach's energy of as-deposited and illuminated films is determined as 0.45 and 0.41 eV, respectively. Single oscillator and Drude models are employed to determine the optical dispersion parameters for as-deposited and illuminated films.