Identifying a doping type of semiconductor nanowires by photoassisted kelvin probe force microscopy as exemplified for GaN nanowires

It remains a challenge to characterize the doping type in nanowires (NWs). We report in this paper a novel way to probe the doping type in GaN NWs by photoassisted kelvin probe force microscopy (KPFM), as a proper example showing that this approach is straight forward, effective and practical. Through illumination with super-bandgap light, photo-generated electrons in the n-region are swept away from the surface due to the electric field in the space-charge region, thus the holes move to the surface; while in contrast, electrons in the p-region will move to the surface. The fact that the quasi-Fermi level moves upwards in n-type while downwards in p-type identifies the doping type of GaN NWs, and is clearly revealed by the contact potential difference detected by photoassisted KPFM.