Effect of initial process in formation of grain structure in GaN growth by MBE

In the growth of GaN by molecular beam epitaxy (MBE), the effects of initial process, i.e. nitridation of sapphire substrates and growth of buffer layer, on the formation of grain structure were investigated. The protrusion density on GaN buffer layers affected the density and size of grain structure in subsequent thick GaN epitaxial layers. The electrical properties of GaN epitaxial layers were improved by reduction of grain density, that is, reduction of protrusion density on buffer layers. These results suggested that a smooth buffer layer is required for improving the duality of MBE grown GaN layers.