Reactive molecular-beam epitaxy of GaN layers directly on 6H–SiC(0001)

We investigate the quality of GaN layers directly grown on 6H–SiC(0001) substrates by reactive molecular-beam epitaxy. Despite a pure three-dimensional nucleation, step-flow growth is achieved by in situ adjusting conditions such that the $\text{(2×2)}$ reconstruction observed during growth is maximized in intensity. The resulting surface morphology exhibits large terraces separated by mono- and multiatomic steps, and is clearly superior to that obtained by plasma-assisted growth. Furthermore, the structural and optical properties of these layers are comparable to those of layers grown by plasma-assisted molecular-beam epitaxy.