Scanning Kelvin probe microscopy of surface electronic structure in GaN grown by hydride vapor phase epitaxy

Abstract

Scanning Kelvin probe microscopy is used to image surface potential variations in GaN (0001) grown by hydride vapor phase epitaxy. The influence of finite probe tip size on these measurements is analyzed, suggesting that significant differences between measured and actual surface potential variations may exist. Experimentally, localized regions in which the surface work function increases by ∼0.1–0.2 V are observed, indicating a shift in the Fermi level toward the valence band; these are attributed to the presence of negatively charged threading dislocations. The magnitudes of the observed variations in surface potential are comparable to those reported in the literature, and compare favorably with those predicted on the basis of a model in which the dislocation is represented as a filled line of acceptor states and the interaction between the sample and a probe tip of finite size is considered. In this model, the finite size of the probe tip is found to exert a substantial influence on the degree to which the full variation in surface potential is observed in scanning Kelvin probe measurements.