Dislocation structure of GaN bulk crystals grown on SiC substrates by HVPE

The dislocation structure of GaN wafers was studied by transmission electron microscopy. These wafers were fabricated using hydride vapor phase epitaxy of thick GaN layers on 6H–SiC substrates and subsequent removal of the substrate by reactive ion etching. Three major types of dislocations were observed in these GaN crystals: (1) threading dislocations (TD), which are mainly parallel to the [0001] direction and extend from the former interface to the crystal surface. They were found to have edge, screw and mixed type; (2) dislocations lying on basal (0001) planes and located near TD through all the thickness of the crystal; (3) dislocations lying preferentially on prismatic planes in the top region of the crystals. Based on experimental results, the influence of initial nucleation stage of heteroepitaxial growth and post-growth cooling on the dislocation distribution in bulk GaN crystals is discussed.