| 其他摘要 | In this dissertation, the synthesis, characterization, growth mechanism and optical properties of ZnTe one-dimensional nanostructures have been investigated. Zinc-blende-structured ZnTe one-dimensional nanostructures, periodically twinned nanowires and uniform nanoribbons, have been synthesized. The products have been characterized by XRD, FE-SEM, TEM, HRTEM, and EDS. It has been found that periodically twinned ZnTe nanowires grow mainly along <111> direction, while the uniform nanobelts grow along <111> and <211> directions. Based on the results, the growth model of the as-grown products with various morphologies was founded, and the growth mechanism was discussed from the point views of local temperature, contact angle, phase equilibrium diagram and energy, etc. The formation of various nanostructures was proved to be dependent on the local temperature. Periodically twinned nanowires and uniform nanoribbons dominate at low- and high-temperature zone, respectively. Moreover, the transition from the twinned nanowire to the uniform nanoribbon takes place at the middle temperature zone. Optical properties of ZnTe nanostructures have been investigated by Raman spectrum and photoluminescence (PL) spectrum. Raman spectrum confirms that the existence of Te peaks result from the existence of twin boundaries in the specimen. The emission of ZnTe nanostructures in PL spectrum has a slight red shift from the bandgap emission of bulk materials, which provides a potential application in nanodevices.
The electrical properties of ZnTe nanowires mainly involve the ohmic contact between nanowires and metal electrodes, the specific intrinsic resistivity, photoconductivity, doping to improve the conductivity, etc. Although Au, Pt, and Ni have been tried as electrodes, Ohmic contacts to individual ZnTe nanowire are formed using Ni/Au multi-layer electrodes finally. Four-terminal measurements have been used to investigate the current-voltage characteristics of contacts and nanowires. Specific contact resistivity of Ni/Au contacts is ~2.6×10-1 Ωcm2 and the intrinsic resistivity of the individual ZnTe nanowire is ~369.1 Ωcm. The photoconductivity characteristic curves of individual ZnTe nanowires have been measured under white light with different intensities, and the typical photoconductivity behavior is observed. The photoconductivity of individual ZnTe nanowires with low- and high-resistance has a 36.7% and 2 orders of magnitude improvement with a light intensity of 36.4 mW/cm2, respectively. The optical switch properties of individual ZnTe nanowires are also discovered, but the frequency response is much low.
Se and Cu doping have been used to improve the conductivity of ZnTe nanowire, and the results indicate that both Se and Cu doped ZnTe nanowires are effectively improved. Se doping is the growth process of ZnSe and ZnTe nanowires in the same tube furnace, and Se will be doped into ZnTe nanowires during the growth process, because there is an overlapping growth region between ZnSe and ZnTe. However, another way is adopted in Cu doping. Cu will be diffused into ZnTe nanowires easily during the heat treatment process. Cu content is controlled by the thickness of Cu layer sputtering on the top of ZnTe nanowires. I-V curves of Se and Cu doped ZnTe nanowires have been also tested by four-terminal measurement. The results indicate that when Se and Cu doping content in ZnTe nanowires is 3.22% and 17.5%, there is a two and five orders of magnitude improvement in the conductivity of Se and Cu doped ZnTe nanowires, respectively.
Finally, the resistivity of individual Cu doped nanowires has been investigated by conductive atomic force microscope (CAFM) with self-made Au conducting tip. The resistivity obtained with CAFM and four-terminal measurement is 5.8 × 10-3 Ωcm and 3.4 × 10-3 Ωcm, respectively, which are in the same order of magnitude.
All the work mentioned above provides much practical and theoretical basis for the application of ZnTe nanowires in nanodevices. |
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