Surface roughness and high density of cubic twins and hexagonal inclusionsin cubic GaN epilayers

Surface roughness and its correlation with the polarity of internal hexagon al inclusions and cubic twins have been investigated by atomic force micros copy (AFM), scanning electron microscopy (SEM), transmission electron micro scopy (TEM) and X-ray diffraction (XRD). The surface roughness resulted fro m large amount of strips, which prolonged in [1 (1) over bar0] direction wi th small size in [110] or [110] direction. The sidestep of each strip is ju st the top of high density of hexagonal inclusions or cubic microtwins. Mor eover, XRD shows that the amount of hexagonal inclusions and cubic microtwi ns measured in [110] direction are twice or more as much as in [110] direct ion. Therefore, it is hexagonal inclusions, cubic twins and their distribut ive polarity that is responsible to the surface characteristics of cubic Ga N epilayers.