Free-standing 2-inch bulk GaN crystal fabrication by HVPE using a carbon buffer layer

A free-standing bulk gallium nitride layer with a thickness of 365 $\mu$m and a diameter of 50 mm was obtained by hydride vapor phase epitaxy on a sapphire substrate with a carbon buffer layer. The carbon buffer layer was deposited by thermal decomposition of methane $\textit{in situ}$ in the same process with the growth of a bulk GaN layer. The bulk GaN layer grown on the carbon buffer layer self-separated from the sapphire substrate during the cooling after the growth. The dislocation density was $8\cdot10^{6}$ cm$^{-2}$. The (0002) X-Ray rocking curve full width at half maximum was 164 arcsec.