Photoconductivity and recombination in amorphous Se/CdSe multilayers

Transport and recombination in single layers of a-Se, CdSe as well as amorphous multilayers of Se/CdSe have been studied by measuring temperature dependencies of the photocurrent and the exponent in the intensity dependence of the photocurrent. It has been suggested that the transport: (i) in a-Se was controlled by traps situated at 0.25 eV above the top of the valence band or the localized states of the valence band tail; (ii) in CdSe was controlled by traps at about 0.12 eV below the conduction band. The recombination was considered to be dominated by deep centers in both Se and CdSe layers. Values of around 0.6 eV and 0.7 eV above the valence band have been determined for the position of the centers dominating recombination in CdSe at temperatures lower than 110 K and higher than 200 K respectively. The position of the recombination centers in a-Se has been determined at about 0.97 eV above the valence band. This coincides with the position of the threefold coordinated Se atoms carrying a positive charge (C-3(+) defects) determined by other authors.