BLUE ELECTROLUMINESCENCE IN REVERSE-BIASED ZNS(ZN,AL) DIODES

Diodes fabricated from ZnS crystals annealed in molten zinc containing 2% aluminum have been found to yield bright blue electroluminescence under reverse-bias at room temperature. Study of the electroluminescence and cathodoluminescence spectra for these diodes together with electron microprobe analysis and measurements of their current-voltage characteristics has led to an explanation of the blue electroluminescence excitation and emission mechanisms. The surface (approximately 800 mu m) of the ZnS(Zn,Al) crystal was found to be aluminum-rich. The aluminum provided additional donors to give a low-resistivity region. This region contained ZnAl//2S//4 phases in additional to the V//Z//nAl complex defects that were thought to be responsible for the blue electroluminescence emission.