Electrodeposition and impedance spectroscopy characterization of ZnO nanowire arrays

Abstract

An overview of the electrodeposition of ZnO nanowire arrays from the reduction of dissolved molecular oxygen in zinc chloride solutions was reported. In spite of the internal structure of ZnO which favours the anisotropic growth along the [0001] direction, the change in the local composition of the electrolyte around the nanowire during the electrodeposition was proposed as a major parameter to affect the nanowire growth mechanism. The influence of the ratio between the O2 reduction rate and the diffusion of Zn2+ to the cathode was emphasized. Due to the particular morphology of the nanowire arrays, no lateral growth was observed when the reduction of O2 was relatively fast, while the corresponding deposition efficiency was very low. The decrease of the O2 reduction rate resulted in an enhancement of the deposition efficiency. The highest efficiencies (40–55%) were attained by using high chloride concentrations ([KCl] = 3.4 M) resulting not only in an enhancement of the longitudinal growth, but also in a considerable lateral growth. The influence of the electrodeposition conditions on the donor density of ZnO nanowires was investigated by using electrochemical impedance spectroscopy. Donor densities from 5 × 1019 cm–3 to 3 × 1020 cm–3 were obtained for as deposited samples. They decreased to values in the range of 1017–1018 cm–3 after annealing in air (1 hour at 450 °C). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)