Photocapacitance spectroscopy of thin film cadmium selenide electrodes

Photocapacitance spectroscopic measurements were made on thin film CdSe that was prepared by electrodeposition from a solution of selenosulfite and cadmium ions. The spectra were very similar for five spots on three films that were prepared under identical conditions. In 0.5 M KOH solution, the film appeared stable for a number of measuremens at various applied potentials. At pH 10 the film was relatively stable for applied potentials negative of 0.0 V (SCE). At more positive potentials in this solution, surface oxidation appears to occur, resulting in the formation of a surface layer that alters the spectrum. In both solutions, the photocapacitance spectrum appears independent of applied potential over the range employed. The continuous rise without any abrupt steps in the spectrum as the photon energy is increased indicated that there are probably a series of bandgap states of comparable density. The energy levels range from E_c − 1.1 eV to E_c − 1.6 eV. In contrast with thin film CdSe prepared by vacuum coevaporation, the electrodeposited material did not require low frequency (7 to 70 Hz) for the measurement.