Dielectrophoretic fabrication and characterization of a ZnO nanowire-based UVphotosensor

Abstract

Wide-gap semiconductors with nanostructures such as nanoparticles, nanorods,nanowires are promising as a new type of UV photosensor. Recently, ZnO (zinc oxide)nanowires have been extensively investigated for electronic and optoelectronic deviceapplications. ZnO nanowires are expected to have good UV response due to their largesurface area to volume ratio, and they might enhance the performance of UVphotosensors. In this paper, a new fabrication method of a UV photosensor based onZnO nanowires using dielectrophoresis is demonstrated. Dielectrophoresis (DEP)is the electrokinetic motion of dielectrically polarized materials in non-uniformelectric fields. ZnO nanowires, which were synthesized by nanoparticle-assistedpulsed-laser deposition (NAPLD) and suspended in ethanol, were trapped in themicroelectrode gap where the electric field became higher. The trapped ZnOnanowires were aligned along the electric field line and bridged the electrodegap. Under UV irradiation, the conductance of the DEP-trapped ZnO nanowiresexponentially increased with a time constant of a few minutes. The slow UV response ofZnO nanowires was similar to that observed with ZnO thin films and might beattributed to adsorption and photodesorption of ambient gas molecules such asO2 orH2O. At higher UV intensity, the conductance response became larger. TheDEP-fabricated ZnO nanowire UV photosensor could detect UV light down to10 nW cm−2 intensity, indicating a higher UV sensitivity than ZnO thin films or ZnO nanowiresassembled by other methods.