Observation of threading dislocations with a c plus m type Burgers vector in HVPE GaN substrates using multi-photon excitation photoluminescence and TEM

Dislocations that have a large Burgers vector are potential leakage current pathways in power devices. In this study, we analyzed the dislocations under a large pit (L-pit) produced by chemical etching in a hydride-vaporphase-epitaxy GaN substrate by using multi-photon excitation photoluminescence (MPPL) and transmission electron microscopy (TEM). Three-dimensional dislocation images reconstructed from MPPL clearly showed that two threading dislocations (TD-1 and TD-2) approached each other laterally while propagating along the growth direction [0001]. They interacted near the sample surface and merged into a single dislocation whose large Burgers vector was responsible for the L-pit formation. A TEM observation operated in large-angle convergentbeam electron diffraction mode unambiguously identified the Burgers vectors of the two dislocations as bTD- 1 = 3 [2 - 1 - 1 - 3] (c + a type) and bTD-2 = [10-1-1] (c + m type). The c + m type is extremely rare in GaN. The 1 merged dislocation appeared to constitute Burgers vectors of all three components of c, m, and a.