One Dimensional Zinc Oxide Nanostructures for Optoelectronics Applications: Solar Cells and Photodiodes
Type of DegreeDissertation
DepartmentElectrical and Computer Engineering
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Several different morphologies of one-dimensional (1-D) ZnO nanostructured arrays can be controllably synthesized using novel thermal chemical vapor deposition at low temperatures. Well aligned and two dimensional periodic ZnO nanostructures like, nanorods, nanoflower, inverse nanotetrapod, nanonail, and nanotip can be controllably grown on different substrates, and have been analyzed by scanning electron microscopy, X-ray diffraction, photoluminescence, Raman spectrum and so on, in order to comprehensively study the electrical and optical properties of ZnO nanostrucutres. The purpose to growth those ZnO nanostructures are to utilize these materials for optoelectronic device applications. Raman scattering was performed to study the well-aligned ZnO nanorods. ZnO nanorods is determined to be relatively strain free by analyzing the E2(2) mode using Raman spectroscopy. The free carrier concentration as well as electron mobility was obtained by the line shape analysis of the coupled A1(LO) phonon plasmon mode for the first time of ZnO nanostructures. The position of the LO phonon peak was found to be depended on both the temperature and the LO phonon-plasmon coupling; therefore, the local temperature of the nanorod sample was estimated based on the integration ratio of Stokes to anti-Stokes Raman peak intensity. As a comparison, the LPP modes collected from single crystal bulk ZnO wafer was also investigated. Micro-Raman diagnosis of phonon lifetime of bulk ZnO, aligned ZnO nanorods, and nanopowder is performed by Raman spectrum. Experiments have observed that the Raman linewidth of most materials exhibits a finite width that indicates the presence decay channels that shorten the phonon lifetime. The Raman modes investigated in this study are the E2(2), E1(TO), A1(TO) and A1(LO). The E2(2) mode Raman linewidth becomes broaden as the dimensionality decreases from bulk to one dimensional nanorods and then to nanopowder. Dye sensitized solar cell was fabricated using a quasi-aligned 1-D ZnO nanostructure. The ZnO nanostructures were successfully grown on indium tin oxide coated glass substrate via a thermal chemical vapor deposition. Current-voltage measurements were performed to extract the working performance of the solar cell. The power conversion efficiency of our device is 0.6%, which is comparable to the DSSC fabricated based on MOCVD-grown ZnO nanostructures.