Self-Organized ZnO Nanosize Islands with Low-Dimensional Characteristics on SiO 2 /Si Substrates by Metalorganic Chemica
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Self-Organized ZnO Nanosize Islands with Low-Dimensional Characteristics on SiO2/Si Substrates by Metalorganic Chemical Vapor Deposition Sang-Woo Kim1, Shizuo Fujita2 and Shigeo Fujita1 1 Department of Electronic Science and Engineering, Kyoto University, Yoshida-honmachi, Sakyo, Kyoto 606-8501, Japan, [email protected] 2 International Innovation Center, Kyoto University Yoshida-honmachi, Sakyo, Kyoto 606-8501, Japan ABSTRACT Self-organized ZnO nanosize islands on thermally grown SiO2 layers on Si (111) with low-dimensional quantum characteristics were realized by metalorganic chemical vapor deposition. Investigation by atomic force microscopy showed that the density and size of the ZnO nanosize islands were changed by the growth conditions. In macroscopic photoluminescence measurements at 10 K using a 325 nm He-Cd laser, we observed the broad spectra with band tails, which were located at the higher energy with respect to band edge emission of ZnO thin films with the free exciton emission located at about 3.38 eV. These results indicate that these ZnO nanosize islands have low-dimensional quantum effect characteristics.
INTRODUCTION ZnO is a semiconducting material with a wide band gap of 3.3 eV at room temperature. Due to its remarkable excitonic properties based on the large excitonic binding energy (60 meV) [1], significant exciton effects promising for achieving large oscillator strength, nonlinear optical properties, or multiexciton interaction may be expected in low-dimensional ZnO nanostructures. Therefore, the realization of ZnO nanostructure with low-dimensional quantum characteristics is strongly required. To date, ZnO nanostructures such as nanowires and nanoparticles have been reported [2,3]. However, there have been few reports to confirm quantum size effects in ZnO nanostructures grown by a conventional semiconductor growth method, such as molecular beam epitaxy or metalorganic chemical vapor deposition (MOCVD). In the present study, we report the successful growth of ZnO nanosize islands (nanoislands) with low-dimensional characteristics, which may lead to the enhancement of exciton confinement, on SiO2/Si substrates by metalorganic chemical vapor deposition by introducing either nitrous oxide (N2O) or nitrogen dioxide (NO2) gas as an oxygen source and diethylzinc (DEZn) as a zinc source on thermally grown SiO2 layers in Si (111) as a function of the growth condition.
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EXPERIMENTAL DETAILS The self-organized ZnO nanoislands in this study were prepared by MOCVD on thermally formed SiO2 layers with a thickness of 25 nm on Si substrates, where DEZn as a zinc source and both N2O and NO2 gas as an oxygen source were utilized. The flow rate of DEZn was selected at 0.5-3 µmol/min when N2O gas with the flow rates of 5000-10000 µmol/min was introduced in the MOCVD reactor maintained at 200 Torr as the total pressure. In other hands, the ZnO nanoislands grown by using NO2 gas as an oxygen source were optimized under the typical flow rates of DEZn and NO2 at 3 and 100 µmol/min, r
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