Effect of the buffer layers on lattice polarity of GaN epilayers grown on the n-face of bulk GaN single crystals by molecular-beam epitaxy

Lattice polarity of GaN epilayers grown on N-faces of bulk GaN single crystals has been investigated. The determinations of lattice polarity have been carried out by observation of surface reconstruction and surface morphology change by alkaline etching. As a result, it is found that GaN epilayers grown on N-faces using In-doped GaN buffer layers have Ga-polarity; on the other hand, GaN epilayers grown on N-faces using high-temperature (HT) AIN buffer layers have N-polarity. These results suggest that In-doping has the role of reversing the polarity of the GaN epilayers from N- to Ga-polarity, whereas HT AIN buffer layers itself do not act as the layer reversing the polarity from N- to Al-polarity.