Toward Discrete Axial p–n Junction Nanowire Light-Emitting Diodes Grown by Plasma-Assisted Molecular Beam Epitaxy

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

“…7,8 In nanophotonics, semiconducting NW heterostructures that incorporate p-n junctions have been proposed as building blocks for integrated nanophotonic devices. 4,5,[9][10][11] One cornerstone of such nanophotonic applications is the material engineering of NW heterostructures with suitable morphology and carrier densities. While electrical characterization alone is sufficient to study some aspects of the electrical properties of NWs, measurement techniques that allow for spatially resolved, quantitative imaging of bias-dependent depletion in NW p-n junctions enable the study of physical relationships between morphology and carrier density.…”

“…22 The GaN NWs used in this study were grown by molecular beam epitaxy (MBE) as described previously. 11 GaN NWs grown by the same technique have been used to demonstrate potential applications as bio-sensors 23 as well as lightemitting diodes. 11 These wires were often coalesced clusters of individual NWs resulting in slab-like cross sections (width % 400-700 nm; thickness % 200-400 nm).…”

“…11 GaN NWs grown by the same technique have been used to demonstrate potential applications as bio-sensors 23 as well as lightemitting diodes. 11 These wires were often coalesced clusters of individual NWs resulting in slab-like cross sections (width % 400-700 nm; thickness % 200-400 nm). The lengths of these NWs ranged from 4 to 6 lm with the (axial) p-n junctions located roughly in the middle of the wires.…”

“…hole concentration of n p % 10 17 cm À3 in the p-type region under the assumption that the acceptor ionization energy E A ¼ 170 meV. 24 Using methods of two-terminal conductivity 10,11 isolated to the n-type region, the free electron concentration n e was estimated to be in the range of (2-9) Â 10 16 cm À3 . From this result, and assuming a donor ionization energy E D ¼ 20 meV, 25 we inferred a Si doping density N D in the approximate range of (0.2-1.0) Â 10 17 cm À3 .…”

“…1(a) shows a SEM image of a typical NW used for the measurement. 11 Fig. 1(a) also schematically illustrates the tip in contact with a NW that is resting on an Al/Ti-coated substrate.…”