Mechanism of catastrophic degradation in InGaAsP/InP double-heterostructure light emitting diodes and GaAlAs double-heterostructure light emitting diodes applied with pulsed large current

Abstract

Catastrophically degraded InGaAsP/InP double-heterostructure light emitting diodes and GaAlAs double-heterostructure light emitting diodes, by application of pulsed large current, were investigated by photoluminescence topography, electroluminescence topography, etching technique, transmission electron microscopy, and energy dispersive x-ray spectroscopy. In the case of InGaAsP/InP double-heterostructure light emitting diodes, several dark-spot defects and dark regions extending from the dark spot defects, were observed in the electroluminescence image of the light emitting region. By transmission electron microscopic observation, the dark defects were proved to be associated with mixed regions consisting of (i) micrograins of the matrix crystal, (ii) an amorphous area of the matrix crystal, and (iii) regions where the matrix crystal was alloyed with the metals of the electrode. An analysis by energy dispersive x-ray spectroscopy indicated that the dark regions consist of large amounts of Au. These defects were considered to be generated by the alloy reaction between the matrix crystal and the metals of the electrode, especially Au. While, in the case of GaAlAs double-heterostructure light emitting diodes, cross-hatched dark-line defects, lying in the two equivalent directions of the 〈110〉 and the 〈11̄0〉, were observed in the light emitting regions by photoluminescence topography. These dark-line defects were proved to correspond to bundles of dislocations similar to slip band by transmission electron microscopic observation. These dislocations were considered to be generated by dislocation glide motion alone; dislocation loops and dislocation dipoles, which were induced by climb motion, were not observed at all. The glide motion was presumably caused by the relaxation of the elastic stress concentrated on the light emitting region, which was enhanced by nonradiative recombination event of minority carriers. On the mechanism of catastrophic degradation, dislocation glide motion enhanced by nonradiative recombination is the origin in the GaAlAs double-heterostructure light emitting diodes. On the other hand, no glide motion was observed in catastrophically degraded InGaAsP/InP double-heterostructure light emitting diodes; these diodes degraded by the alloy reaction between the matrix and the metals of the electrode due to the concentration of injected carriers on the nonuniform region of the electrode.