Abstract
Spatially resolved photoluminescence measurements with a resolution of 4 mu m, have been carried out in the active p-region of n-p GaAlAs light-emitting single heterojunctions, having undergone 2000 h strong current ageing. The degraded material exhibits a characteristic pattern of dark-line defects (DLDS) well revealed in cathodoluminescence topographs and identified as dense dislocation networks in easy-glide crystallographic planes. When the scanning spot goes from undergraded to degraded zones containing DLDS, the dominant near-bandgap photoluminescence peak due to donor-to-acceptor recombination is gradually replaced by an initially weak satellite, 15 meV above, attributed to unintentionally present impurities, like carbon. This striking behaviour reveals that a redistribution of impurities or defects, connected with the gettering activity of dislocations in DLDS, occurs during current ageing. Such segregation effects induced by the stress field around dislocations have been, indeed, often observed in growth or anneal processing.
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