  Real-time analysis of the growth modes during homoepitaxial (0001)GaN growth
by plasma-assisted molecular beam epitaxy was performed using reflection high
energy electron diffraction. A growth mode map was established as a function of
Ga/N flux ratio and growth temperature, exhibiting distinct transitions between
three-dimensional (3D), layer-by-layer and step-flow growth mode. The
layer-by-layer to step-flow growth transition under Ga-rich growth was
surfactant mediated and related to a Ga adlayer coverage of one monolayer.
Under N-rich conditions the transition from 3D to layer-by-layer growth was
predominantly thermally activated, facilitating two-dimensional growth at
temperatures of thermal decomposition.
