The initial GaN growth mode on stepped sapphires by plasma enhanced metal organic
molecular beam epitaxy (PEMOMBE) has been analyzed using in-situ, real time synchrotron x-ray
diffraction and x-ray absorption. The sapphire substrate annealed at high temperature had flat terraces
and regular atomic steps. The crystal quality and the vicinal angle of sapphire substrate had an effect
on the width of terraces and the step arrangement. The initial growth mode of the GaN film on the
regular atomic step (AS) surface was the layer-by-layer mode and changed to the 3D growth mode
within 2 bilayer thickness. In the meanwhile, the growth mode of the GaN film grown on the sapphire
with random roughness (RR) surface made the flat surface in the early stage and changed the 3D
growth mode. As increasing the film thickness, the nucleation layer grows strain-free hexagonal GaN
on stepped sapphires
Growth mode and surface morphology of a GaN film deposited along the N-face polar direction on c-plane sapphire substrate