Abstract

The details of the mechanisms for energizing donor-acceptor (D,A) pairs which result in recombination luminescence are still not completely understood. Recent work¹ on CdS has indicated that polaritons generated directly or as a consequence of incident photon excitation processes play the principal role in the D⁺,A⁻ to D°,A° charging process, and that the luminescence emanates from the near-surface (~1 μm) regions. Experiments we report here indicate that polaritons also generate the stored charge associated with persistent conductivity phenomena² observed in high resistivity CdS. We show that generation of stored charge in the near-surface region (~1 μm), from which edge luminescence may be emitted¹, is a precondition for polariton-energized edge emission actually to occur. This requirement, taken together with the results of more detailed studies of the correlation between persistent conductivity and edge luminescence, supports the reported restriction of edge emission to near-surface regions¹ and also establishes the spatial extent of the stored charge region at saturation of persistent conductivity as a few hundred microns into the interior. It is further shown that the stored charge associated with persistent conductivity is the source of thermoluminescence, with the glow curves associated with the free-to-bound high energy series (HES) and with the bound-to-bound low energy series (LES) peaking respectively at temperatures of 22K and 27K for a 10K/min temperature scan rate. These results, as well as those from isothermal thermoluminescence experiments, establish a low activation energy electron localized state as the source of persistent conductivity stored charge. We have associated this state with a large-lattice-relaxation³ D⁻ center, based on the luminescence as well as other experiments. Edge luminescence produced by thermal release of these charges, residing at known spatial location (depending on the accumulated fraction of saturated stored charge), complements time-resolved excitation spectroscopic photoluminescence experiments in elucidating the impurity pair charging mechanisms. Luminescence spectral response to near infrared stimulation as a function of stored charge state is also presented and discussed.

© 1984 Optical Society of America