Field Effect Transistor with Electrodeposited Nanowire Channels

Zinc oxide is one of the most intense studied materials these days and the applications sought range from energy production and photocathalysis to light emitting devices, sensors or logic circuits. A wide band gap (3.3 eV) semiconductor, with an excitonic binding energy of 60 meV zinc oxide is attractive besides other properties to its high occurrence/low cost and non-toxicity. The material is also remarkable from the point of view of polymorphism of its nanostructures, from belts and rods to platelets and flowers, tunable as a function of preparation method and specific conditions. Different electronic devices were fabricated using zinc oxide, among them of utmost importance being field effect transistors. ZnO nanowires were prepared by electrochemical deposition in polycarbonate ion track templates. After the deposition process the polymer templates were dissolved in dichloromethane and the nanowires were harvested by ultrasonication in isopropyl. A droplet of nanowire suspension was placed on a Si/SiO₂substrate patterned with interdigitated electrodes. By means of electron beam lithography single nanowires were selected and provided with electrical contacts. We found that in order to obtain reliable electrical contacts and typical field effect characteristics the electrode deposition process needs to be adapted to the 3 D shape of the wires and that annealing and passivation treatments are necessary. Our results show an excellent behaviour of the nanowire based devices, including here typical field effect transistor behaviour, with saturated source – drain characteristics and I_on to I_off ratios of about 10⁴. The transport properties show carrier mobility in excess of 100 cm²/Vs.