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Vertically well-aligned and epitaxial ZnO nanorod arrays (NRAs) were synthesized by catalyst-free metalorganic chemical vapor deposition on Al2O3 (0001) substrates particularly using an epitaxially grown GaN buffer layer. ZnO NRAs grown directly on Al2O3 (0001) substrates are aligned vertically, but randomly oriented in the lateral direction to the substrates. In sharp contrast, ZnO NRAs grown with a GaN buffer layer show an excellent vertical and epitaxial alignment with mosaic distributions of 0.11° and 1.28° in the out-of- and the in-plane directions, respectively. The electrical measurements using field effect transistors based on individual ZnO nanorods show a pronounced n-type gate modulation with an electron concentration of ∼7.5×1017cm−3 and an electron mobility of ∼25.1cm2∕Vs at a bias voltage of 1 V, while showing quite a high on/off ratio exceeding ∼105. In addition, their high on/off conductivity ratio of ∼103 with UV light gives a potential of their use in nanoscale UV detectors.

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