Direct Formation of Transparent ITO Top Electrodes on High-Density ZnO Nanowires by Magnetron Sputtering

Abstract

Transparent indium tin oxide (ITO) was directly deposited by magnetron sputtering to form two-dimensional top electrodes on vertically arrayed one-dimensional ZnO nanowires. Deposition at 5 mTorr resulted in almost complete coverage and interconnection of the nanowires, which maintained high transmittance. The use of lower pressure reduced ITO coverage over large areas of the nanowiresduetotheretardationoflateralcoalescence.ThesputteredITOlayersdidnotcovertheentirelengthsoftheZnOnanowires, although thin ITO coating was observed along the sidewalls of the nanowires for some distance from the surface. The ITO layers on the nanowire arrays had high conductivity, comparable to conventional In metal, because of the use of a plasma atmosphere and high temperature during deposition. This resulted in improved Ohmic contact and photodiode properties, which allowed direct electrical connection of the active nanowires without filling the spaces between them with insulating materials.