Step bunching on the vicinal GaN(0001) surface

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