Preparation of large GaN substrates

A freestanding GaN substrate of over 2-in. size with low dislocation density was prepared by hydride vapor phase epitaxy (HVPE) using GaAs (111)A as a starting substrate. A SiO2 mask pattern with round openings was formed directly onto the GaAs (111)A substrate. Then, a thick GaN layer was grown with numerous large hexagonal inverse-pyramidal pits constructed mainly by {11–22} facets maintained on the surface. After removing the GaAs substrate and subsequent lapping and polishing, a freestanding GaN about 500 μm in thickness was obtained. Etch pit observation reveals that etch pit groups with etch pit density 2×108 cm−2 at the center exist in the matrix area with etch pit density as low as 5×105 cm−2. This distribution is due to the effect of large hexagonal pits on collecting dislocations at the bottom of the hexagonal pit. Dislocations propagate into the bottom of the pit mainly in the 〈11–20〉 or 〈1–100〉 direction parallel to (0001).