STUDY OF THE OPTICAL-TRANSITIONS IN ELECTRODEPOSITED CUINSE2 THIN-FILMS

Optical absorption coefficients of electrodeposited CuInSe2 thin films were determined from the measured transmittance and reflectance at normal incidence of light in the wavelength range 400 to 2000 nm. As-deposited CuInSe2 is found to be a direct-gap semiconductor with an allowed direct transition whose gap energy is E(ga) = 0.96 eV and a forbidden direct transition whose gap energy is E(gf) = 1.38 eV. After heat treatment of the films at 400-degrees-C, a decrease in the optical absorption was observed at energies below 1.1 eV. Heat-treated films showed an allowed direct transition with E'ga = 1.00 eV, close to the value for as-deposited samples, but in the last case the forbidden direct transition was not observed.