A complete crystallographic study of GaN epitaxial morphologies in selective area growth by hydride vapour phase epitaxy (SAG-HVPE)

GaN structures have been fabricated by selective area growth by hydride vapour phase epitaxy (SAG-HVPE) on parallel stripes-patterned equivalent 〈1 1¯ 0 0〉 sapphire and 〈1 1 2¯ 0〉 GaN/sapphire substrates, and on parallel stripes-patterned 〈1 1 2¯ 0〉 sapphire and 〈1 1¯ 0 0〉 GaN/sapphire structures. The growth morphologies of the GaN stripes were systematically investigated by scanning electron microscopy (SEM). HVPE-GaN layers exhibit (0 0 0 1), {1 1¯ 0 0} and {1 1¯ 0 1} or {2 2¯ 0 3} facets on 〈1 1 2¯ 0〉 GaN/sapphire substrates, while on the equivalent 〈1 1¯ 0 0〉 sapphire direction only (0 0 0 1) and {1 1¯ 0 0} facets coexist. On the 〈1 1¯ 0 0〉 GaN/sapphire substrate direction, (0 0 0 1), {1 1 2¯ 2} and {3 3 6¯ 2} facets compose the growth structures. Special emphasis was paid to the analysis of the crystal growth mechanisms. A crystallographic tool was developed to calculate the facets growth rates, the condensation surfaces and the surface recovered by GaN stripe in order to establish a correlation between the growth morphologies and the experimental conditions. It is shown that the growth rates of the facets, and so the morphologies, depend on the variations of the H2 ratio in the total flow rate.