Defect structure in selectively grown GaN films with low threading dislocation density

We have characterized by transmission electron microscopy (TEM) defect structures in GaN films grown selectively in hydride vapor-phase epitaxy (HVPE). In this experiment, growth was achieved on ${\mathrm{SiO}}_{\mathrm{2}}$ -stripe-patterned GaN layers that had been grown by metalorganic vapor-phase epitaxy (MOVPE) on sapphire substrates. Cross-sectional TEM revealed unambiguously that most of the dislocations, which originated from threading dislocations vertically aligned in the MOVPE-grown layer, propagated laterally around the ${\mathrm{SiO}}_{\mathrm{2}}$ mask in the HVPE-grown film before the film thickness amounted to about 5 μm. This change of the propagation direction prevented the dislocations from crossing the film to the surface region and thus principally led to a drastic reduction in the threading dislocation density in thicker films.