Reduction of crack density in ammonothermal bulk GaN growth

Abstract

The growth of high quality GaN by the ammonothermal method is appealing due to the potential to scale and achieve very high crystal quality. Several applications could benefit from the supply of very high quality GaN such as high power light emitting diodes, laser diodes, and high power electronics. Despite steady advancement by the few groups developing ammonothermal growth technology, high quality ammonothermal GaN wafers have yet be manufactured in great quantities.This paper reviews the current progress of ammonothermal growth at SixPoint Materials. Growths were performed at T<600°C and P<300MPa on GaN seed crystals produced by hydride vapor phase epitaxy (HVPE). For thin boules, <1mm growth thickness, no cracking is observed. Historically however, SixPoint Materials’ ammonothermal growth on HVPE seeds eventually experiences a curvature flip giving extremely high radius of curvature at a critical thickness. As the growth continues the radius of curvature degrades and cracking is observed. Since IWBNSVIII, SixPoint Materials has improved the crack free area for 5mm thick boules from 5 to 80mm2 to the complete seed area. This result is repeatable in multiple reactors. Careful selection of the HVPE seeds led to the greatest reduction in cracking. Seed selection combined with an additional technique has allowed boules to be grown crack free. X-ray diffraction was carried out on an ammonothermally grown boule at 90 points along a 44mm line providing a mean (002) and (201) full width half max (FWHM) reflection of 29 and 35″ respectively using a beam spot of 0.3mmx0.3mm and an open detector. The radius of curvature is typically between 3 and 20m across the sample. Dislocation densities are routinely low 105cm−2 .