Condensed Matter Physics and Materials Science Department

III-Nitride based semiconductors have been under intense research focus in recent years largely due to their electronic and optoelectronic applications. In comparison to large are devices, III-Nitide nanowire based devices provide unique opportunity to dramatically improve device efficiency and scope of integration, as well as, reduce device cost. In this talk, we will present the growth, device fabrication, and electrical and structural characterization of GaN nanowires (~20 nm typical diameter) grown by direct reaction between metallic Ga and ammonia. GaN nanowires were grown on SiO2 covered doped Si substrates using Ni catalyst in, and transistors were fabricated with both bottom gate and top gate geometries. The special device geometry was adopted to avoid the necessity of directional growth for device fabrication. The transistor I-V curves showed saturation in many cases, and single nanowire FETs have shown saturation currents as much as 3 – 4 microamperes, with mobility estimates as much as a few hundred cm2/V/s. Interesting behavior of the nanowire devices were observed when I-V characteristics were measured in two-terminal configuration with only the source and drain bias. The devices studied showed interesting behavior, and could be categorized into ones showing purely schottky characteristics, purely ohmic characteristics, premature saturation, and those showing drain current dependency on the direction of the bias sweep. Since the ohmic contact metal stack was not annealed (to avoid damage to the SiO2 insulator and shorting) schottky contact was formed, and schottky barrier heights of ~0.7 eV have preliminarily been estimated from the I-V characteristics. The devices showing variable drain current exhibited two different states of drain current for the same bias, depending on the direction of the sweep.
Structural characterization using scanning probe microscopy was performed to explain the difference in electrical characteristics observed for different