In this study, the photocurrent (PC) spectroscopy of undoped p-type CIS layers has been investigated at temperatures ranging from 10 to 293 K. Three peaks, A, B, and C, corresponded to the intrinsic transition from the valence band states of Gamma(7)(A), Gamma(6)(B), and Gamma(7)(C) to the conduction band state of F6, respectively. Crystal field splitting and spin orbit splitting were found at 0.0059 and 0.2301 eV, respectively, and the temperature dependence of the optical band gap could be expressed using the empirical equation E-g(T)=E-g(0)-(8.57x10(-4))T-2/(T+129). But the behavior of the PC was different from that generally observed in other semiconductors: the PC intensities decreased with decreasing temperature. From the relation of 109 J(ph) vs 1/T, where J(ph) is the PC density, the dominant level was observed at the higher temperatures. We suggest that in undoped p-type CIS layers, the trapping center limits the PC signal due to native defects and impurities with decreasing temperature.

Keywords: copper indium diselenide; photocurrent spectroscopy; crystal field splitting; spin orbit splitting; optical band gap; trapping center