Low-voltage electroluminescence of ZnS due to an acousto-electric instability

Abstract

We report homogeneous (without the usually observed bright dashes and points) prebreakdown electroluminescence of ZnS-I single crystals with the voltage applied with “ohmic” contacts when this voltage corresponds to a mean electric field in the crystal ⪸ 10 2 V/cm. The single crystals are obtained by the gas-transport reaction method with subsequent processing in a zinc melt. The spectral, voltage-brightness, current-voltage ( I-V) and time-dependent characteristics were investigated both at room and liquid nitrogen temperatures. The electroluminescence spectrum contains in addition to board red and blue bands an ultraviolet band extending to 330 nm. Under the excitation of electroluminescence by rectangular pulses of voltage with rise times of 0.2 μsec, a delay in the fronts of the brightness oscillogram is absent. The N-shaped form of the current-voltage characteristics and the oscillations of current and brightness indicates the appearance of mobile electron domains concentrating the electric field, which probably determines the character of this electroluminescence. The velocity of the domains calculated from the oscillations' duration, coincides with the velocity of sound in ZnS. This fact allows us to make the supposition that there exists an acousto-electric instability during the electroluminescence.