Ballistic transport and electroluminescence in IIB–VI and IIA–VI compounds

The first commercially successful electroluminescence display of the thin film MISIM type (metal-insulator-semiconductor-insulator- metal) with S=ZnS:Mn rely completely on a special high field electronic transport mode called “travelling spike transport”. By this ballistic (loss-free with respect to phonons) acceleration process, optimum excitation efficiency and avalanching are achieved. Its threshold field strength is about 106V/cm in ZnS, and is low enough for the resulting electric breakdown to be made reversible via charge control, which can be achieved using a sandwich with insulating films. Very recently, ZnS like electrical behaviour of MISIM samples with S-SrS:Ce and CaS:Eu has been demonstrated. The achievement of the same transport process a fields even slightly lower in these IIA–VI compounds is highly probable. It gives rise to questions about the significance of band structure and a potentially marked difference between ZnS and the latter materials in high field transport. Some speculations about the optimum doping of SrS with rare earths are presented.