EXCITATION EFFICIENCY AND FIELD NONUNIFORMITY IN ZNS-BASED THIN-FILM ELECTROLUMINESCENT DEVICES GROWN BY ATOMIC LAYER EPITAXY

Transient measurements of the excitation efficiency were performed in ZnS-based a.c. driven electroluminescent devices grown by atomic layer epitaxy. The results evidence the build-up of a bulk space-charge in the semiconductor layer from the first pulse on, even at low levels of the transferred charge (about 0.1 mu C cm(-2)). At these levels, the semiconductor-insulator interfaces contribute to charge carrier inject ion and provide primary electrons for multiplication in the bulk. Mode ls of space-charge generation by field emission from the bulk only are not compatible with experimental data. The multiplication rates seem rather high (alpha = 5 x 10(4) cm(-1)); however, filamentary conductio n may lead to an overestimation of alpha.