Electrical properties of pinholes in GaN:Mn epitaxial films characterized by conductive AFM

Mn doped GaN films have been studied by conductive Atomic Force Microscopy (AFM), Cathodoluminescence (CL) and Electron Beam Induced Current (EBIC). AFM measurements revealed the presence of pinholes with diameters between 130 and 380 nm. The distribution, density and size of the pinholes depend on the Mn doping concentration. AFM Leakage Current images (LC) show a defined contrast at the pinhole planes {101 over(1, ̄)} in the sample with Mn concentration of 6.2×10²⁰ cm^-3. For the sample with an Mn concentration of 1.1×10²⁰ cm^-3, LC contrast appears around the pinholes, while no LC contrast was observed for sample with lower Mn concentration. CL measurements indicate that the samples exhibit strain related to Mn incorporation. In correlation with LC measurements, EBIC images show that pinholes are recombination sites. The combination of these techniques enabled us to analyze the Frenkel-Poole conduction in the samples and its relationship with the residual strain and the doping concentration in the films, which would exclude the mechanism of conduction through dislocations.