The gallium nitride (GaN) is used as the wide band gap material for next generation power semiconductors and high frequency devices. We have prepared the samples of the GaN epi-layer on the sapphire substrate with a different atom (Ga-face or N-face) that composed the outermost surface. The nanoscale investigations of the samples of topography and surface potential in the same region by an instrument that the frequency modulation atomic force microscope (FM-AFM) combined with the Kelvin probe force microscope (KFM) were performed. It is estimated that band bending of the samples from the surface potential image, and drawn to the energy band diagram. In comparison with the topographic images, it was confirmed that the N-face layer had occurred many crystal defects more than Ga-face one. Since the different potential state for a crystal defect were observed, and it was considered to correspond to the dislocation types.
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