EXPERIMENTAL AND THEORETICAL STUDIES OF LOW-VOLTAGE ELECTROLUMINESCENCE OF ZNS SINGLE CRYSTALS

Blue electroluminescence of undoped ZnS single crystals has been detected at 1.6 V d.c. with a quantum efficiency of 10-11 photons/electron. The crystals were heat-treated in molten zinc. Previous models considered for electroluminescence with applied voltages less than the band gap, including injection and recombination via p-n junctions, are shown to be inadequate to explain our observations. An impact ionization-tunneling mechanism is proposed involving an n*-n junction. Energetic electrons are injected through a blocking contact into the higher conductivity n* region and at the n*-n junction impact ionize an acceptor level in the n region creating a conduction electron in the n* region. Radiative recombination then occurs in the n region between an ionized luminescent center and a second injected electron. © 1969.