Preparation And Photo-detective Performance Of Ti02Semiconductor Nanomaterials

Semiconductor photodetectors (PDs) are critical for applications in military and industries, such as light-wave communications, imaging sensing, environmental monitoring and photometric measurement. Si or GaAs based PDs have been widely used for ultraviolet (UV) light detection. However, the UV light selectivity is very poor owing to their low band gaps. TiO2semiconductors, have been paid more and more attentions in the photoelectric conversion, owing to the wide band gaps, materials availability, structure controllability, excellent physical and chemical properties and electron acceptance, etc. However, few studies about TiO2PDs have been reported. In addition, it is hard to obtain the high responsivity and fast response speed at the same time. Thus in this thesis, polymer with UV absorption was used to modify TiO2nanoparticles (NPs) and (nanorods) NRs to enhance the UV responsivity. And also the TiO2NPs branched TiO2NRs composite was proposed to increase the response speed further. In order to further extend the photo detection of TiO2from UV to visible light, dye and polypyrrole modified TiO2nanocomposites were synthesized.In order to enhance the UV responsivity, PSS was used to modify TiO2NPs to increase the UV light absorption and the photogenerated electron-hole pairs. In this part, TiO2NPs and PSS/TiO2NPs composite based UV PDs were fabricated. The responsivity and on/off ratio of TiO2NPs based PDs are1.2AW-1and40, respectively. The rising and decay time are22.63and15.93s, respectively. And the rejection ratio of UV to visible light is86, demonstrating an excellent UV selectivity. In order to further improve the performance of TiO2NPs based PDs, multilayered PSS functionalized TiO2NPs composite film was prepared by a layer by layer self-assembly method. The responsivity of the composite film based PDs increases with PSS layer increasing. The responsivity of10-layer PSS/TiO2NPs based PDs is10times higher than that of5-layer PSS/TiO2NPs based PDs. The responsivity and photosensitivity of10-layer PSS/TiO2NPs based PDs are602AW-1and1932, respectively. In comparison with TiO2NPs based PDs, both of them show an increase of3orders of magnitude. The responsivity in the PSS/TiO2based PDs is1-2orders of magnitude higher than that of most reported TiO2NPs based PDs. The present high responsivity is attributed to the strong UV light absorption of PSS and the good energy level match between PSS and TiO2.In order to enhace the resposivity of TiO2based UV PDs, one dimensional (1D) aligned TiO2nanorods (NRs) array and the PSS modified ones were proposed to improve the transport and the amount of photogenerated electron.1D aligned rutile TiO2NRs arrays were synthesized on the FTO glass by hydrothermal method. The TiO2NRs with length in1.56伍4.32μm were obtained by adjusting the reaction temperature, time and precursor concentration. The PEI additives could be selectively adsorbed on some crystal surface of TiO2nuclei, promoting its preferred orientation growth along the [001] direction, resulting in the TiO2NRs with a length of5.26μm. Based on TiO2NRs with different lengths, the UV PDs were organized. It is found that the UV responses are affected by light absorption and electron transfer resistance. The highest responsivity and photosensitivity of0.53AW-1and12are obtained when the TiO2NRs length is2.39μm. In the meanwhile, the rising and decay time are8.7and24.05s. After PSS coated on the TiO2NRs, the UV PDs exhibit a high responsivity and photosensitivity of2346AW-1and6558, which are higher than that of the reported1D TiO2nanostructures based UV PDs.To further improve the performance of TiO2based UV PDs, especially to decrease the response time, TiO2NPs branched1D TO2NRs composite was proposed to increase light absorption and improve the transfer rate of the charge carrier. TiO2NPs were deposited in situ on the surface and among the gaps of TiO2NRs by hydrolysis of TiCl4. The amount of TiO2NPs in the composite is controlled by the concentration and hydrolysis time of TiCl4When the two parameters are72h and0.4M, the UV PDs present the highest responsivity and on/off ratio, which are1973AW-1and1158, respectively. The rising and decay time are reduced to0.42and1.02s, indicating a decrease of one order of magnitude compared with that of the conventional metal oxide based photoconductive UV PDs. The high performance of the TiO2NPs/NRs based UV PDs is ascribed to the fast electron transfer rate of TiO2NRs, large light absorption of TiO2NPs and the homojunction formed in the interface between them.To extend the application of TiO2in the visible light, organics with visible light absorption were chosen to modify TiO2. Wavelength-tunable PDs were fabricated by dye-sensitized TiO2NPs film. The responsivity strongly depends on the absorption wavelength of the dyes. The wavelength-tunable PDs were verified by ZnO NPs based visible light PDs, indicating that full spectrum PDs with distinctive wavelength selectivity can be fabricated by other semiconductors sensitized with dyes. Polypyrrole/TiO2NRs composites were synthesized by polymerization of pyrrole with TiO2NRs as a photosensitizer. The responsivity of PPy/TiO2based visible light PDs increases first and then decreases with PPy content increasing. When the polymerization time is12h, the high responsivity and photosensitivity are obtained, which are0.45AW-1and30. The photocurrents have a good linear dependence on the light intensity, and the R2of linear fit curve is0.9996. The visible light response of PPy/TiO2based PDs is resulted from visible light absorption of PPy, synergistic ability to transfer electrons of TiO2NRs and the heterojunction formed in the interface between them.