Blue electroluminescence in forward-biased ZnS diodes with (SN)xelectrodes

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Abstract
Sets of Schottky (MS) and metal-insulator-semiconductor (MIS) diodes have been fabricated on semiconducting ZnS dice using either gold or polymeric sulphur nitride (SN)x as the barrier metal electrode. The semiconducting material was prepared by heating dice, cut from ZnS produced by a chemical vapour deposition process, in molten zinc containing gallium and aluminium. (SN)x is a covalent polymer, which was deposited as a thin film, approximately 1 mu m thick, with a resistivity approximately 10-2 Omega cm. It has a higher electronegativity than gold and devices with (SN)x electrodes had measured photoelectric barrier heights approximately 0.75 eV greater than those in the corresponding devices with gold electrodes. In forward bias, devices with barriers exceeding Eg/2 emitted blue (HE) electroluminescence from the vicinity of the barrier. Self-activated (SA) emission, at slightly lower photon energies, was also emitted from the reverse biased 'low resistance' counter-electrode. The resolution of the total electroluminescence emission into its two spectral components is described, and the quantum and luminous efficiency of the blue (2.815 eV) HE emission is shown to increase steeply as the electronegativity of the metal electrode is increased.