Step bunching on the vicinal GaN(0001) surface

Nominally 2 degrees vicinal GaN(0001) surfaces exhibit monolayer-height steps at 990 degreesC in the metal-organic chemical vapor deposition environment. Real-time x-ray scattering observations at 715-990 degreesC indicate that there is a tendency for step bunching during growth. Below 850 degreesC, step bunches nucleated during growth remain and coarsen after growth, while above 850 degreesC, the surface reverts to monolayer-height steps after growth. Surfaces vicinal toward the {1 (1) over bar 00} and the {11 (2) over bar0} planes exhibit similar behavior. We suggest a simple equilibrium surface orientational phase diagram for vicinal GaN(0001) that is consistent with these observations.