We used a broadband, atomic-force-microscope-based, scanning microwave microscope (AFM-SMM) to probe the axial dependence of the depletion in a GaN nanowire (NW) p-n junction structure. The NWs were c-axis oriented and grown by molecular beam epitaxy. The estimated respective doping concentrations in the n- and p-type regions were (0.20.9)×1017 cm-3 (Si) and ≈1×1018 cm-3 (Mg). The AFM-SMM operated in the range of 120 GHz. The quantity d((S_11))⁄dV, which is the derivative with respect to voltage of RF reflection coefficient S_11, varied strongly when probing axially along the NW and across the p-n junction. The axial variation in d((S_11))⁄dV essentially mapped the asymmetric depletion arising from the doping concentrations on either side of the junction. The results reveal that AFM-SMM is a useful method with which to spatially map electrical properties of a semiconductor nanostructure without the need to make separate electrical contact to the device.
Applied Physics Letters