Long-range ordering of GaN nano-grains grown on vicinal sapphire substrates

GaN nano-grains were grown on nominally 0.3°-miscut (0 0 0 1) sapphire substrates by hydride vapor phase epitaxy (HVPE). Ordering behavior of the nano-grains was investigated by utilizing scanning electron microscopy (SEM) and synchrotron X-ray scattering. SEM images and synchrotron X-ray scattering measurement revealed that the nano-grains were nucleated with long-range ordering along the sapphire [101¯0], which is the same as the miscut direction. With an increased growth time the nano-grains gradually coalesced, but the long-range ordering was still observed even after completion of the coalescence.