Electroluminescence of Zinc Sulfide Single Crystals

Abstract

In a series of experiments designed to distinguish between ionization and recombination processes during electroluminescence, rectangular voltage pulses were applied to single crystals of zinc sulfide. During the period, the emission gradually increased to a stationary level. Removal of the voltage resulted in a burst of emission, which decayed slowly. This behavior is explained by the assumption of three field-dependent processes, namely: (a) ionization of centers in barrier regions; (b) sweeping out of the liberated electrons from the vicinity of the centers; and (c) tunnelling of electrons into the barrier regions. It was found that for a considerable voltage range the product of the light-sum (measured during the off period) by the current was proportional to the stationary emission level during the period. This proportionality strongly supports the model suggested. In many cases the current was found to be more strongly dependent on the voltage than the light sum. This result favors an ionization mechanism which is independent of the current. The model suggests furthermore an alternative explanation for the Neumark-effect, i.e., the enhancement of the thermal glow by electric fields. The explanation does not involve an impact-ionization mechanism. (auth)