Growth of TiO2-based Thin Films and Their Application to Optoelectronic Devices
| Autor: | Wei-Shun Shih, 施位勳 |
|---|---|
| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 This dissertation includes the growth and characterization of TiO2 thin films and related electronic devices (MSM PDs and FET) by radio frequency (RF) magnetron sputtering. The optical and structural properties of TiO2 nanostructures have been characterized by field-emission scanning electron microscope (FE-SEM), photoluminescence (PL) system and atomic force microscopy (AFM), respectively. The main work can be divided into the following four parts. First, we have demonstrate that anatas TiO2 thin films were grown on Corning glass substrates by radio frequency magnetron sputtering and were then used to fabricate metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors (PDs) with different contact electrodes (Ag or Au). With a 320 nm illumination and 5 V applied bias, the responsivities for the Ag/TiO2/Ag and Au/TiO2/Au MSM PDs were 4.31 and 16.6 A/W, respectively. Additionally, the photoconductive gain and Schottky barrier height at the Ag/TiO2 and Au/TiO2 interface were also discussed in the investigation. Second, it has been demonstrated that the fabrication and characterization of MSM TiO2 PDs with various O2 plasma treatment time. After a O2 plasma treatment, it was found that the defects and oxygen vacancies could be filled. With a 5 V applied bias and 360 nm illumination, the maximum responsivities of the O2 plasma treatment time increased from 0 to 3 min were 36, 144, 135 and 53 A/W, which correspond to UV to visible rejection ratios 241, 425, 466 and 103, respectively. Third, the TiO2 films were deposited on FTO (fluorine-doped tin oxide)/glass substrate. Amorphous and anantas structure of TiO2 achieved without and with thermal process, respectively. Further, TiO2 based thin film transistors (TFT) with different structure were fabricated. After the electrical characteristics measurement, it was found that the amorphous TiO2 TFTs can be operated in the enhance mode with a threshold voltage of 3.8 V. It was also found that the field-effect mobility and on/off current of the TiO2 TFT with amorphous channel layer were 0.087 cm2/Vs and 103, respectively. On the other hand, the TiO2 TFT with anatas structure were also tested, It was found that the anatas TiO2 TFTs have the lower threshold voltage of 2.3 V than amorphous one. Besides, it was also found that the field effect mobility and on/off current ratio of the anantas TiO2 TFTs were both increased to 10.7 cm2/Vs and 104, respectively. In other words, the performance of TiO2 TFTs was related to the structure of channel layer. Finally, photodetectors with TiO2 nanorod arrays (TNAs) has been fabricated and characterized. The results show that the UV response of the PDs has been enhanced about four orders of magnitude. This giant enhancement in photoresponsivity can be attributed to TNAs, because TNAs provides a directed path for electrical transport and improves optical absorption. TNAs are useful and attractive in the application of UV detectors. With an incident wavelength of 360 nm and 5V applied bias, we found that maximum responsivity of the TNA PDs and traditional TiO2 PDs were 0.1 and 4×10-5 A/W, respectively. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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