Defect structure induced during forward-bias degradation of GaP green-light-emitting diodes

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Abstract
This paper reports evidence of a degradation‐induced defect structure in green GaP light‐emitting diodes (LED’s). The defect structure in undegraded diode material has been characterized by transmission electron microscopy (TEM). The main defects consist of pairs of dislocations and single dislocations in the n and p epitaxial layers. The origin of these dislocation pairs is traced to dislocation loops in the substrate or at the n‐layer–substrate interface. The TEM observations in slowly degraded LED’s indicate that bulk electroluminescence degradation phenomena may be accounted for by the formation of new dislocations in the vicinity of the p‐n junction. These new dislocations appear during forward biasing of the device by climb of the original dislocations in the epitaxial layers. This defect structure, which is composed of helical dipoles and dislocation loops, resembles that reported in rapidly degraded GaAlAs‐GaAs (DH) lasers suggesting that the degradation mechanisms for both the green GaP LED’s and laser devices may be similar.