Inhomogeneous Contact Potential Image of AlGaN/GaN Grown on Sapphire Substrate Measured by Kelvin Probe Force Microscopy

The contact potential of AlGaN/GaN on sapphire substrate grown by metalorganic chemical vapor deposition (MOCVD) was measured by Kelvin probe force microscopy (KFM). A clear correlation was observed between the topographic image and the contact potential image. The potential around the surface pits was about 100 mV lower than that in the surrounding region. This suggests the existence of an effect of the pits on the electrical properties of the epitaxial layer. Even though the diameters of the pits were 20–60 nm, the diameter of the affected low-potential region was as large as 0.3–0.7 µm.