Effect of laser irradiation on the properties of ZnO buffer layers and its application to selective-growth of ZnO nano/microcrystals

ZnO nanocrystals, which are characterized by their configurations and fine structures, are unique oxide semiconductors. They are synthesized by nanoparticle-assisted pulsed laser deposition on ZnO buffer layers deposited on a-cut sapphire substrates. In this report, the new possibilities of UV laser-processing to the field of ZnO buffer layers and ZnO nano/microcrystals are suggested. Effects of ultraviolet laser-irradiation on morphological and electrical properties of ZnO buffer layers were investigated. After laser irradiation, surface work function increased in the region laser-irradiated at 300 mJ/cm², whereas it decreased in the region laser-irradiated at 500 mJ/cm². Then, ZnO nanowires were synthesized on the ZnO buffer layers locally laser-irradiated at 300 mJ/cm² and 500 mJ/cm² by nanoparticle-assisted pulsed laser deposition. Number densities of ZnO nan-owires were varied depend on laser fluences. It decreased in the region pre-laser-irradiated at 300 mJ/cm², whereas it increased in the region pre-laser-irradiated at 500 mJ/cm². Additionally, it was demonstrated that periodically-aligned ZnO microcrystals can be synthesized using four-beam interference laser irradiation to the ZnO buffer layers followed by nanoparticle-assisted pulsed laser deposition. Since these processes do not require any catalysts, they are expected to be the new fabrication method for ZnO nano/micro crystals.