Propagation of threading dislocations and effects of Burgers vectors in HVPE-grown GaN bulk crystals on Na-flux-grown GaN substrates

Abstract

The propagation behavior of threading dislocations (TDs) and the effects of Burgers vectors in hydride vapor phase epitaxy (HVPE) GaN bulk crystals generated on Na-flux-grown GaN and in a commercially available HVPE-grown GaN bulk crystal were investigated. Analyses based on chemical etching and transmission electron microscopy (TEM) revealed a close correlation between the etch pit sizes and the Burgers vector of these TDs. The existence of TDs with the unique Burgers vector b\u2009=\u20091m\u2009+\u20091c was observed for the first time ever using a large-angle convergent-beam electron diffraction technique and plan-view bright-field scanning TEM. Multi-photon excitation photoluminescence microscopy observations showed that TDs with b\u2009=\u20091c had a meandering morphology in contrast to the linear morphology of TDs with b\u2009=\u20091a, 1a\u2009+\u20091c, or 1m\u2009+\u20091c in both types of HVPE-grown GaN crystals. The inclinations of TDs with b\u2009=\u20091a and 1a\u2009+\u20091c in HVPE-grown GaN on Na-flux-grown GaN were greatly affected by large symmetrical hexagonal hillocks. The TDs with b\u2009=\u20091a were inclined in the slope directions of the hillock planes, while those with b\u2009=\u20091a\u2009+\u20091c were inclined in the a directions parallel or antiparallel to the a component in their Burgers vector. These inclinations were readily explained by the isotropic elastic theory of an individual TD. The hillocks were produced around pairs of parallel mixed TDs for which the a components were opposite to one another. This phenomenon was attributed to inclusions at the interface between the Na-flux-grown GaN substrate and the HVPE-grown layer. The origins of other TDs including unusual ones having b\u2009=\u20091m\u2009+\u20091c are also discussed herein.