Nearly perfect GaN crystal via pit-assisted growth by HVPE
We demonstrated 5 mm-thick bulk gallium nitride (GaN) with nearly perfect crystal quality. To achieve this, intentional etch pit formation by in situ dry HCl etching and ex situ wet etching in H3PO4 solution was employed on freestanding GaN templates followed by regrowth by hydride vapor phase epitaxy (HVPE). This consecutive etching gave rise to a number of large and deep etch pits on the whole surface of the freestanding GaN. We believe that these can reveal the etch pits originating from the dislocations with the edge, and mixed components. Intentionally formed etch pits were partially covered with the fresh regrown bulk GaN layer, being transformed into voids. Dislocations cannot propagate into new GaN layers through the voids, thus resulting in the reduction of dislocation density. 5 mm-thick bulk GaN exhibits a smooth, transparent surface and extremely high crystal quality with full width at half maximum (FWHM) of 21 arcsec in (0002) X-ray rocking curve and etch pit density (EPD) of 3 × 102 per cm2. This method can provide a promising way to fabricate bulk GaN with extremely low dislocation density, suitable for the fabrication of high-performance devices.