Structural and optical properties of Cd2GeSe4 and Cd2GeSe4:Co2+ films prepared on indium-tin-oxide substrates

Cd2GeSe4 and Cd2GeSe4:Co2+ films were prepared on indium-tin-oxide (ITO)- coated glass substrates. X-ray diffraction spectra showed that the Cd2GeSe4 and the Cd2GeSe4:Co2+ films were preferentially grown with the (113) orientation. The crystal structure was rhombohedral (hexagonal) with lattice constants a = 7.405 A and c = 36.24 A for Cd2GeSe4 films and a = 7.43 A and c = 36.81 A for Cd2GeSe4:Co2+ films. From X-ray photoelectron spectroscopy, the binding energies of the Cd-3d, the Ge-3d, and the Se-3d core levels due to the formations of Cd2GeSe4 and Cd2GeSe4:Co2+ were found to be 404.5 eV and 411.3 eV, 30.4 eV and 31.3 eV, and 54.7 eV and 58.9 eV, respectively. The optical energy band gaps, measured at room temperature, of the as-deposited Cd2GeSe4 and Cd2GeSe4:Co2+ films were 1.97 eV and 1.72 eV and those of the 400 .deg. C-annealed films were 1.85 eV and 1.7 eV, respectively. The dynamical behaviors of the charge carriers in the Cd2GeSe4 and Cd2GeSe4:Co2+ films were investigated by using the photoinduced discharge characteristics (PIDC) technique.