A free-standing GaN substrate, over 5cm in size, with a low dislocation density was prepared by hydride vapor phase epitaxy by using GaAs (111)A as an initial substrate. A SiO2 mask pattern with round openings was formed directly onto the GaAs (111)A substrate. A thick GaN layer was then grown with numerous large hexagonal inverse-pyramidal pits constructed mainly by {11•2} facets maintained on the surface. After removing the GaAs substrate and subsequent lapping and polishing, a free-standing GaN substrate of about 500μm in thickness was obtained. The distribution of dislocations was examined by transmission electron microscopy, cathodoluminescence and etch-pit density measurements. They showed that a restricted region, with a dislocation density of up to 109cm2, existed in the area with dislocation densities as low as 2 x 105cm2. This dislocation distribution was caused by {11•2} facet growth in hexagonal pits. The dislocations were concentrated in the center of the hexagonal pit, and therefore a large area with a low dislocation density was formed.

Growth and Characterization of Free-Standing GaN Substrates. K.Motoki, T.Okahisa, S.Nakahata, N.Matsumoto, H.Kimura, H.Kasai, K.Takemoto, K.Uematsu, M.Ueno, Y.Kumagai, A.Koukitu, H.Seki: Journal of Crystal Growth, 2002, 237-239[2], 912-21