Charge storage and persistent photoconductivity in aCdS0.5Se0.5semiconductor alloy

Relaxation of stored charge carriers in the persistent-photoconductivity (PPC) mode in a ${\mathrm{CdS}}_{0.5}$ ${\mathrm{Se}}_{0.5}$ semiconductor alloy has been investigated. The relaxation time constant of PPC is systematically measured as a function of temperature, from which the recombination barrier height ${\mathit{E}}_{\mathrm{rec}}$ has been determined. Low-temperature exciton luminescence has also been investigated and the exciton transition linewidth, which is broadened due to the presence of compositional fluctuations, is measured. The values of ${\mathit{E}}_{\mathrm{rec}}$ deduced from the measured exciton linewidth and the localized-to-delocalized transition temperature in the PPC mode are consistent with the results obtained from the PPC-decay measurements. These experimental results are consistent with our previous interpretation that PPC in ${\mathrm{CdS}}_{0.5}$ ${\mathrm{Se}}_{0.5}$ semiconductor alloys is caused by random local potential fluctuations induced by compositional fluctuations.