| Although research on nanotechnology has for long been dominated by carbon nanotubes, there has been a significant research interest on semiconducting nanostructures in recent years due to their predictable material properties and ease of growth. In addition, direct bandgap semiconductors also provide the opportunity for integration of nanoscale optical and electronic devices. Of direct bandgap semiconducting nanowires, those based on III-V Nitrides (GaN, AlN, InN, and their alloys) are especially interesting because of the large range of bandgap covered by their alloys, along with their polarization properties, high electron mobility, and chemical inertness. InN shares all the interesting properties of the III-Nitride family, and has recently generated high research interest following reports of surprisingly low bandgap (∼0.7 eV), very high electron mobility, and more uniquely, surface accumulation of electrons. In this research, we have systematically investigated growth of high quality InN nanowires (NWs) as well as their electrical and mechanical properties. Applications of these NWs in fabricating nanoscale field effect transistors and chemical sensors have also been explored.;InN NWs and their networks were synthesized in a homemade Chemical Vapor Deposition (CVD) furnace through vapor-liquid-solid growth mechanism using lithographically patterned catalyst spots. The NWs were found to grow mostly along the [110] direction at a growth rate of around 30 mum/hour, with overall diameters 10--90 nm and lengths 5 - 30 mum. It was observed that the NWs bend spontaneously or get deflected from other NWs at multiples of 30 degrees forming nanonetworks. This property can be attributed to the hexagonal symmetry of their crystal lattices, and has been exploited to obtain direction-controlled growth with lithographically patterned SiO2 barriers.;InN NW based FETs fabricated in a back-gated configuration exhibited excellent gate modulation, which has been observed for the first time for these NWs. The highest carrier mobility measured was 1108 cm 2/Vs, and the corresponding carrier concentration was 1018 cm-3, at 300 K. The maximum saturation current density was found to be 4.16 x 105 A/cm2, which is several times higher than the even the current density in state-of-the-art AlGaN/GaN high electron mobility transistors. The carrier mobility in the NWs were found to depend strongly on the NW diameter, and increased sharply from 36 to 1108 cm2/Vs as the diameter decreased from 50 to 16 nm. It has been observed that the NWs with larger diameter are usually covered with a thick layer of In2O3 shell layer, which strongly influences the mobility and carrier concentration of the carriers. The electron mobility also showed weak temperature dependence, and increased marginally as the temperature was lowered form 300 K to 4 K. The corresponding carrier concentration showed a marginal decrease. The young's modulus of the NWs was also measured, and was found to be ∼260 GPa using 3-point bending technique in an AFM set up. When used as a chem-FET type sensor, exploiting the sensing properties of the In2O3 shell layer, detection of NO2 down to 45 ppb level in ambient conditions was possible. |
