In this paper, we demonstrate that p-type InN nanowires can be realized by direct magnesium (Mg) doping. X-ray
photoelectron spectroscopy experiments on the sidewalls of Mg-doped InN nanowires indicate no surface electron
accumulation with the background electron concentration below 1×1016 cm-3. The presence of Mg-acceptors is clearly observed by the low-temperature photoluminescence (PL) spectroscopy, which shows a band-to-band recombination PL peak and a Mg-acceptor energy level related PL peak. The peak energy separation is about 60 meV, which is consistent with the Mg activation energy in InN. Single nanowire field-effect transistors are further fabricated and investigated,
which clearly exhibits a p-type transistor behavior, representing the first direct evidence for p-type conduction in any
InN structures. The potential device applications based on InN nanowires are also discussed.
We have investigated the molecular beam epitaxial growth and characterization of InN nanowires. Detailed optical and electrical transport studies confirm that nondoped InN nanowires can exhibit extremely low (< 1015 cm-3) residual electron density. Furthermore, the near-surface Femi-level was measured to be 0.4 to 0.5 eV above the valence band maximum (VBM), suggesting the absence of Fermi-level pinning and surface electron accumulation. These features are fundamentally different from those of n-type degenerate InN nanowires or InN epilayers. The absence of surface electron accumulation was also observed in Mg-doped InN nanowires, where p-type conduction was directly measured via Mg-doped InN nanowire field-effect transistors. Furthermore, the near-surface Fermi-level can be tuned from 0.1 eV to 1 eV above the VBM, i.e., from p-type degenerate to n-type degenerate through controlled Mg and Si dopant incorporations, a first demonstration for any semiconducting nanowire structures.