THE OPTICAL-PROPERTIES OF CUINSE2 THIN-FILMS

The optical constants of vacuum deposited CuInSe2 thin films of different thicknesses (60-135 nm) were determined in the photon energy from 1.03 to 3.1 eV. It was found that both the refractive index n and the absorption index k are independent of the film thickness. The analysis of the experimental points of the refractive index revealed the existence of normal dispersion and fits Sellmeier dispersion formula for single oscillator model. Using the previous model the optical dielectric constant as well as the oscillator energy and dispersion parameter have been calculated. CuInSe2 is found to be a direct gap semiconductor with a gap energy of 1.03 eV. At energies well above the absorption edge, the absorption behaviour can be explained by the existence of a forbidden direct transition with the same direct energy gap and an indirect one with energy gap of 0.85 eV.