Step bunching on the vicinal GaN(0001) surface

Abstract

Nominally $2\ifmmode^\circ\else\textdegree\fi{}$ vicinal GaN(0001) surfaces exhibit monolayer-height steps at $990\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ in the metal-organic chemical vapor deposition environment. Real-time x-ray scattering observations at $715--990\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ indicate that there is a tendency for step bunching during growth. Below $850\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ step bunches nucleated during growth remain and coarsen after growth, while above $850\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ the surface reverts to monolayer-height steps after growth. Surfaces vicinal toward the ${11\ifmmode\bar\else\textasciimacron\fi{}00}$ and the ${112\ifmmode\bar\else\textasciimacron\fi{}0}$ planes exhibit similar behavior. We suggest a simple equilibrium surface orientational phase diagram for vicinal GaN(0001) that is consistent with these observations.