Structural defects in GaN crystals grown by HVPE on needle-shaped GaN seeds obtained under high N2 pressure

A bulk crystal of GaN grown by double hydride vapor phase epitaxy (HVPE) on a needle-shaped GaN single-crystalline seed, obtained by the high nitrogen pressure solution (HNPS) method, was studied by transmission electron microscopy (TEM). Structural defects at characteristic places, such as the seed–HVPE GaN interface, the first HVPE/second HVPE interface, and at morphological imperfections of the seed were characterized. The TEM studies have shown that despite high structural quality of the pressure-grown seed, structural defects are present in the HVPE-grown GaN crystal. A possible reason for strain and structural defects generation could be small lattice mismatch between highly oxygen-doped seed crystal and the HVPE GaN layer as well as between particular sectors of the HVPE GaN layer growing in different crystallographic directions. It was also observed that morphological imperfections of the seed surface may lead to the introduction of the high number of defects extending into the overgrown layer.