Growth and characterization of CuIn1-xAlxSe2 thin films deposited by co-evaporation

CuIn1-xAlxSe2 thin films (x = 0 - 1.0) were prepared by the four-source co-evaporation technique onto soda lime glass substrates held at 673 K. The films are found to be nearly stoichiometric as determined from Rutherford back scattering (RBS) analysis. Surface analysis of the films was carried out by x-ray photoelectron spectroscopy. X-ray diffraction and scanning electron microscopy are used to examine the structure of the films. The films are found to be single phase and chalcopyrite in structure. The lattice parameters are found to vary nonlinearly with x. Optical absorption studies reveal a three-fold optical band structure and the band gaps are found to increase nonlinearly with the increase in Al content. Crystal field and spin - orbit parameters are determined from the band gaps using a quasi-cubic model. The deformation potential and the percentage of d-orbital contribution to p-d hybridization are determined using the deduced crystal field and spin-orbit parameters. All the films are p-type conducting and the resistivity is found to increase with the increase in Al content. Room temperature Hall mobility and the carrier concentration of the films are determined.