Microstructure and nanoelectronics of single GaN nanowire with well-defined p-n junction

We demonstrate the first example of a well-defined p-n junction fabricated in a GaN nanowire and the systematic investigation of its transport properties down to 2.6 K. XRD, Raman spectrum, HRTEM revealed the ∼30 nm diameter wires, produced by vapor-liquid-solid synthesis in indium nanoparticle catalyst droplets, are shown to consist of a good-quality, crystalline, hexagonal GaN inner core surrounded by an amorphous GaN outer layer. Most wires grow such that the crystalline c-axis is normal to the long axis of the nanowire. The p-n junction is produced by turning on a source of Mg (a known p-dopant) halfway through the growth. The wires show excellent rectification properties with diode ideality factors as low as 5 for most nanowires. The temperature dependence of the current-voltage characteristics is consistent with electron tunneling through a voltage-dependent barrier. P-doped and n-doped GaN nanowires fabricated under similar conditions invariably produced linear current-voltage curves, indicating that the observed rectification arises as a result of the p-n junction and not from a metal-semiconductor Schottky contact junction. Surface potential imaging was employed to determine the exact position of the p-n junction along a single nanowire.