Defects and degradation of nitride-based laser diodes

We report on various kinds of structural defects frequently observed in nitride-based laser diodes (LDs). First, we discuss threading dislocations in the nitride-based LDs. By investigating structural analysis of epitaxial lateral overgrown (ELO) GaN layers, comparison study between short-lived LDs and long-lived LDs, and degradation analysis, we show that although threading dislocations do not multiple during the device operation, reduction of threading dislocations is primarily important for improving device reliability. Secondly, we investigate the Mg-related structural defects. The other important aspect for extending the device lifetime is optimization of Mg doping. During the course of our study of LDs, inverse pyramidal defects were often found in Mg-doped layers. We analyze the relationship between the pyramidal defects and the atomic concentration of Mg [Mg] and discuss device degradation mechanism in terms of degradation rate and Mg doping. Thirdly, we describe structural defects observed in GaInN multiple quantum wells (MQWs). Apart from previously reported structural defects such as In-rich precipitates and clusters, we found a new type of structural defects in GaInN MQWs with higher In concentrations. These defects consist of planar defects and associated dislocations. These multiple defects can be formed merely by one monolayer In-In bond.