Green Electroluminescence from Gallium Phosphide Diodes near Room Temperature

Abstract

Detailed spectral properties of green near-bandgap electroluminescence have been studied between ∼50° and ∼380°K in several GaP diodes containing different concentrations of nitrogen impurities. The observed evolution of the room-temperature green bands from the readily identifiable low-temperature bands and a comparison of the room-temperature spectrum with the intrinsic luminescence band calculated from the absorption-edge spectrum show that intrinsic transitions are of minor importance for these diodes near 300°K. The observed room-temperature green luminescence in lightly doped diodes is identified with the recombination of bound and free excitons induced by isoelectronic nitrogen impurities, whereas radiative recombination of free holes at neutral shallow donor centers predominates in heavily doped diodes. The intensity of the green luminescence generally increased more rapidly than the red Zn, O acceptor-donor pair luminescence near 300°K, both with increase in temperature and in diode current. We have observed green electroluminescence external efficiencies approaching 10−4 for exciton recombination at room temperature in exceptional diodes containing relatively low concentrations of deep centers (notably those with low oxygen content). The calculated rate constant for intrinsic transitions and the largest observed mean minority-carrier lifetimes together suggest that intrinsic green luminescence of efficiency approaching 10−4 might be observable at room temperature from diodes containing currently attainable minimal concentrations of nitrogen and oxygen impurities, if the luminescence is not confined to the junction depletion layer.