Investigation of the electrical activity of V-defects in GaN using scanning force microscopy

We report on the characterization of V-defects in GaN-based heterostructures via scanning force microscopy techniques. The diameter and density of the V-defects are found to strongly depend on growth thickness and temperature of the top layer, respectively, while no correlation between the V-defect formation and the type of doping could be identified. Kelvin probe force microscopy measurements revealed for both, n- and p-doped GaN top layers, a decrease of the Kelvin voltage within the V-defects, which indicates an enhanced work function of the facets of the V-defects with respect to the planar surface. Surprisingly, an increase of the current flow within the V-defects is found by conductive atomic force microscopy in case of the n-doped top layer, while current flow into the V-defect is suppressed for the p-doped top layer. For a consistent explanation of these results we suggest a model, which is based on an enhanced electron affinity of the {10-11}-surfaces within the V-defects as compared to the planar (0001)-surface.