Growth and characterization of freestanding GaN substrates

A freestanding GaN substrate of over 2 inch size with low dislocation density was prepared by hydride vapor phase epitaxy (HVPE) using GaAs (1 1 1)A Lis a starting substrate. An SiO2 mask pattern with round openings was formed directly onto the GaAs (1 1 1)A Substrate. Then, a thick GaN layer was grown with numerous large hexagonal inverse-pyramidal pits constructed mainly by {1 1 (2) over bar 2} facets maintained on the surface. After removing the GaAs substrate and subsequent lapping and polishing, a freestanding GaN substrate about 500 mum in thickness was obtained. The distribution of dislocations was examined by transmission electron microscope (TEM), cathodoluminescence (CL) and etch-pit density (EPD) measurement. They show that the restricted area with high dislocation density up to I x 10(9)cm(2) exists in the area with low dislocation density as low as 2 x 10(5)cm(2). This dislocation distribution is caused by ((1122) over bar) facet growth in hexagonal pits. The dislocations are concentrated to the center of the hexagonal pit, and therefore large area with low dislocation density is formed. A new reduction mechanism of dislocation density is proposed. (C) 2002 Elsevier Science B.V. All rights reserved.