EXTRINSIC PHOTOGALVANIC EFFECT IN CADMIUM IODIDE-CRYSTALS

The spectral dependence of the photogalvanic (PG) effect in undoped an d doped (Eu, Na, Pb) CdI2 crystals was studied at room temperature in comparison with the optical-absorption and photoconductivity spectra. The extrinsic PG effect in the doped crystals is due to the bias curre nt associated with impurity-band transitions on charged impurities as well as to lattice distortions caused by the substitution of large-siz ed Eu-Cd(2+) ions at the Cd site. The spectral dependence of the PG ef fect in Cd1-xPbxI2 solid solutions switches sign because of the change in direction of hole velocity in the region of the overlap of the ind irect band of CdI2 and the direct band of PbI2. The observed differenc e between the spectral responses of PG effect and photoconductivity st ems from the fact that the PG signal is independent of carrier lifetim e. The influence of doping on the PG effect in the intrinsic-absorptio n region is due to an increase in the contribution associated with the asymmetry of the crystalline potential.