Analysis of two-step-growth conditions for GaN on an AlN buffer layer

Gallium nitride is grown by metalorganic vapor phase epitaxy with and without a low-temperature-grown AlN buffer layer. Variations in the surface morphology and the layer properties are compared between two-step growth and direct growth to study the effects of various growth conditions. It is found that (i) conditions that stabilize the GaN(0001) surface serve as guidelines for obtaining mirrored surfaces, and (ii) raising GaN growth temperature improves crystallographic, electrical, and luminescence properties of GaN. The observed improvement in the layer properties with increase in GaN growth temperature suggests that increasing N₂ dissociation pressure does not affect GaN properties. GaN growth conditions are analyzed thermodynamically to show that NH₃ in the growth ambients has the potential to suppress thermal dissociation of GaN.