Catalyst-free growth of ZnO nanorods and their nanodevice applications

We review recent research activities on catalyst-free growth of ZnO nanorods and their nanodevice applications. Since ZnO nanomaterials add excellent chemical sensing characteristics due to their large surface-to-volume ratio to intrinsic ZnO properties including semiconducting and piezoelectric properties, a wide direct band gap energy, and a large exciton binding energy, they are expected to become one of the most ideal materials for future high performance nanodevice applications. There have been extensive research activities for synthesis of high quality ZnO nanomaterials for nanodevice applications. Among the numerous growth methods, we have focused on catalyst-free metal-organic chemical vapor deposition, since this enables us to grow vertically aligned ZnO nanorods on various substrates, including Si and glass, without any special substrate treatment. This catalyst-free approach yields high purity and single crystalline nanostructures, and does not require a subsequent catalyst removal process. Furthermore, we established techniques for fabricating ZnO nanorod heterostructures with composition modulations along either radial or axial direction, which can provide more opportunities for novel optical and electronic device development. Furthermore, we briefly describe our activities on ZnO nanorod device fabrication and evaluation, including field-effect transistors, biological molecule sensors, Schottky diodes, and light emitting devices. We also address the remaining scientific issues and technical challenges, required to fully understand the device characteristics and to realise integrated nanodevices.X119sciescopu