| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 98 === The interface problems in nanowire-based electronics play important roles due to the reason that the reduced contact area in nanoelectronics multiplies enormously the contribution of electrical contact properties. In this study, zinc oxide (ZnO) nanowires were employed in fabricating two-probe and four-probe nanowire devices for electrical studies of nanowire-electrode contact and intrinsic nanowire properties. The ZnO nanowires with a circular cross-section and a diameter of ~50 nm were synthesized on quartz substrates by a thermal evaporation and were dispersed on silicon substrates, which were capped with a 150-nm thick SiO2 layer and were photolithographically patterned with Ti/Au (~10/60 nm in thickness) micron electrodes. Prior to the electron beam lithography process, some of the dispersed ZnO nanowires were annealed in a high vacuum (~10-6 torr) at 500 0C for 6 or 24 h to increase native oxygen defects as well as the nanowire conductivity. The electron beam lithography technique was then used to generate nanometer leads and to connect the nanowires and micron electrodes. In either two- or four-probe nanowire devices, the separation distance between two nearest-neighbor nanometer leads was kept constant to be ~ 1 μm or 500 nm. Through a study of temperature dependent electrical properties in two- and four-probe nanowire devices, the electrical contact properties and intrinsic transport of ZnO nanowires can be determined. Electron transport in the nanocontact system follows Mott variable range hopping theory of the form . The exponential parameter, p, rises from 2 to 4 with an increase of specific contact resistivity, implying a change from one to three dimensional hopping. On the other hand, the intrinsic electrical properties of ZnO nanowires exhibit thermally activated transport and three-dimensional Mott variable range hopping at high and low temperatures, respectively. In addition, it was observed that, after annealing in a high vacuum for 24 h, the resistance (resistivity) of ZnO nanowires is reduced to be hundred times smaller in comparison with those without annealing.
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