Light Emission at a Metal-Insulator Contact under High Electric Fields

Intrinsic luminescence at a metal-insulator contact has been observed in NaI, KI, and RbI single crystals with evaporated Au electrodes. The effect has been observed when a varying electric field ({} 10⁴ V/cm) is applied. The light emission is attributed to the recombination of the pairs created by impact ionization processes in a potential barrier near the contacts. Two mechanisms for the formation of the primary electrons are evidenced. A time dependence of the effect suggests the formation of space charges whose field opposes the external one. The experimental results suggest that only a few electrons among those accelerated by the internal field gain enough energy to produce the multiplication processes.