Negative photoconductivity in films of alloys of II–VI compounds

Various negative photoelectric effects in films of alloys of II–VI compounds deposited from a solution are studied depending on the deposition mode and heat treatment. A combined electronic-molecular mechanism of the negative photocapacitance effect, which is for the first time found in Cd$_{1-x}$Zn$_x$S and CdS$_{1-x}$Se$_x$ films, and negative slowly relaxing photoelectric effects is established. The latter are caused by the transition of electrons arranged in a nanoscale surface layer from shallow energy levels of attachment centers to deeper levels with lower polarizability and by the presence of nanoscale clusters playing the role of a “reservoir” for minority carriers in these materials. A model, which makes it possible to interpret the main regularities of negative photoconductivity in Cd$_{1-x}$Zn$_x$S and Cd$_{1-x}$Zn$_x$Sе films deposited from a solution, is suggested. It is established that the negative residual photoconductivity is explained on the basis of a double barrier profile, while the negative differential photoconductivity is explained by the presence of nanoscalel electric domains.