Wetting behaviour of GaN surfaces with Ga- or N-face polarity

The wetting behaviour of GaN surfaces with N-face and Ga-face polarity and the influence of different surface treatments is studied by measuring the wetting angle of highly purified water by microscopic imaging. We found that wet thermal oxidation of the surface leads to a decreased wetting angle indicating an improved wetting behaviour. The presence of Al in AlN or AlGaN leads to a further reduction of the wetting angle, which is attributed to the presence of Al₂O₃ on the surface. In addition the comparison of Ga-and N-face material revealed a lower wetting angle for all N-face samples. XPS analysis showed the enhanced formation of native oxide on the surface with N-face polarity.