OPTICAL-PROPERTIES OF ELECTROCHEMICALLY DEPOSITED CUINSE2 THIN-FILMS

Polycrystalline thin films of CuInSe2 within a wide composition range have been electrochemically deposited. Their optical properties in the near-infrared and visible range, 400-2000 nm, have been studied in relation to the deposition potential and film thickness. An absorption coefficient (alpha) as high as 10(5) cm-1 is observed at short wavelength (lambda < 700 nm), but near the band edge alpha has a value about 10(4) cm-1. The observed absorption coefficient variation is due to an allowed direct transition with an energy in the range 0.88-0.96 eV and an additional forbidden direct transition with an energy in the range 1.32-1.41 eV, where the absorption coefficient depends on the deposition potential, and the possible phase nature of the material, with band gap narrowing when the potential becomes anodic. The values of alpha and transition energies also depend on the film thickness for samples up to 0.6-mu-m thick.