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Imaging the p-n junction in a gallium nitride nanowire with a scanning microwave microscope



Atif A. Imtiaz, Thomas M. Wallis, Joel C. Weber, Kevin J. Coakley, Matthew D. Brubaker, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford


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 (0.2—0.9)×1017 cm-3 (Si) and ≈1×1018 cm-3 (Mg). The AFM-SMM operated in the range of 1—20 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
Created July 2, 2014, Updated January 27, 2020