A mechanism was discovered which could significantly reduce the dislocation density during the growth of GaN single crystals in the Na flux method. The significant reduction of the dislocation density occurred in the later stage of LPE growth, rather than solely at the seed-LPE interface for which evidence had already been reported indicating the presence of bundling dislocations. The two-step dislocation reduction was the key in achieving extremely low dislocation density using this method. A two-inch GaN crystal with a thickness of 2mm was grown in order to confirm that the dislocation density decreased as the growth thickness increases. As a result, 75% of the surface area exhibited dislocation density of the order 102/cm2, and the FWHM of the X-ray rocking curve measurement in (00•2) face was 28arcsec. A two-step dislocation reduction mechanism based upon LPE growth in the Na flux method was reported.

Growth of GaN Single Crystals with Extremely Low Dislocation Density by Two-Step Dislocation Reduction. F.Kawamura, M.Tanpo, N.Miyoshi, M.Imade, M.Yoshimura, Y.Mori, Y.Kitaoka, T.Sasaki: Journal of Crystal Growth, 2009, 311[10], 3019-24