The mechanism of electroluminescence of zinc sulphide

Abstract

The impact excitation mechanism of electroluminescence is formulated and applied to the electroluminescence of ZnS. Cu crystals. A barrier similar to the Mott-Schottky exhaustion barrier exists in the crystal at each electrode. Quantum mechanical tunnelling through the barrier yields excitation in phase with the applied alternating voltage, as well as d.c. electroluminescence. Both shallow and deep donors in the exhaustion layer are prerequisite for excitation out of phase with the applied alternating voltage, and a continuous energy distribution of deep donors yields the experimental dependence on voltage of the intensity of the out of phase component of electroluminescence. Several donor distributions are theoretically analysed in detail. The conduction electrons which deviate from average behaviour by experiencing fewer collisions with lattice vibrations, thereby attaining high velocities with fields below breakdown values, probably are of importance to the mechanism. The actual excitation of the luminescence centre may be accomplished by capture of electron-hole pairs formed by impact ionization.