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Hwangyou Oh and Ju-Jin Kim Department of Physics, Chonbuk National University, Chonju 561-756, Korea

Sang Sub Kima) Department of Materials Science and Engineering, Chonnam National University, Gwangju 500-757, Korea (Received 8 August 2005; accepted 12 September 2005)

Size-tuned ZnO nanorod arrays (NRAs), aligned well vertically and laterally, were synthesized by catalyst-free, metalorganic chemical vapor deposition on GaN-buffered Al2O3 (0001) substrates by adjusting the O/Zn precursor ratio in the reactor. Their electrical transport properties were investigated using field effect transistors based on individual ZnO nanorods. We find that the carrier concentrations and mobilities in the nanorods are not very sensitive to the change of the precursor ratio. This suggests that altering the precursor ratio is a way of fabricating size-tuned ZnO NRAs with quite consistent electrical properties.

I. INTRODUCTION

In recent years, nanostructures of semiconducting materials have been extensively studied due to their fundamental scientific interest as well as their potential applications in nanoscale electronic devices.1–3 As II-VI wide band gap (3.37 eV) semiconductors, ZnO nanostructures have been the subject of considerable attention. ZnO exhibits many valuable properties, including a large exciton binding energy of ∼60 meV at room temperature,4,5 which makes it a promising candidate for efficient blue or ultraviolet light-emitting devices.6 In addition, its high piezoelectric constant and chemical sensitivity enable it to be used in nanoscale mechanical devices and chemical sensors.7 According to review articles,8,9 a variety of ZnO nanostructure shapes can easily be grown by diverse methods. ZnO nanorods or nanowires have been synthesized by many different approaches such as vapor-liquid-solid processes, solution processes, and metalorganic chemical vapor deposition (MOCVD).10–12 In particular, MOCVD-grown ZnO nanorods or nanowires are relatively well-aligned in the vertical direction to the substrate, forming nanorod arrays (NRAs) without the need for any catalyst.13–16 Very recently, we accomplished size control of the vertically aligned ZnO NRAs grown by MOCVD on Al2O3 (0001) by systematically changing a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0003 132

http://journals.cambridge.org

J. Mater. Res., Vol. 21, No. 1, Jan 2006 Downloaded: 05 Feb 2015

the O/Zn precursor ratio.17 According to the study, wellaligned, fat ZnO NRAs grow at a higher O/Zn precursor ratio, whereas less well-aligned, slim ZnO NRAs grow at a lower ratio. However, the ability of this method of controlling ZnO NRA size needs to be confirmed with different substrates. In addition, the change of the O/Zn precursor ratio may produce ZnO NRAs with different stoichiometries, consequently resulting in different electrical properties. Therefore, the effect of the ratio change on the electrical properties of size-tuned ZnO NRAs also needs to be investigated. In this work, we confirmed the valid