Scanning Kelvin probe microscopy and conductive atomic force microscopy were used to image surfaces of GaN grown by molecular beam epitaxy. Detailed analysis of the same area using both techniques allowed imaging and comparison of both surface potential variations arising from the presence of negatively charged threading dislocations and localized current leakage paths associated with dislocations. Correlations between the charge state of dislocations, conductivity of current leakage paths, and dislocation type were thereby established. Analysis of correlated scanning Kelvin probe microscopic and conductive atomic force microscopic images revealed a density of negatively charged features of ~3 x 108/cm2 and a localized current leakage path density of ~3 x 107/cm2, with approximately 25% of the leakage paths spatially correlated with negatively charged dislocation features. Based on correlated topography and previous studies quantifying the densities of edge, screw, and mixed dislocations, the results suggested that dislocations having an edge component behave as though negatively charged while pure screw dislocations were solely responsible for the observed leakage paths and were uncharged.

Correlated Scanning Kelvin Probe and Conductive Atomic Force Microscopy Studies of Dislocations in Gallium Nitride. B.S.Simpkins, E.T.Yu, P.Waltereit, J.S.Speck: Journal of Applied Physics, 2003, 94[3], 1448-53