| Summary: | 碩士 === 國立虎尾科技大學 === 光電與材料科技研究所 === 96 === Zinc oxide is a II-VI semiconductor material with direct band-gap of 3.37 eV corresponding to the wavelength in the ultraviolet region. ZnO also has large exction binding energy (~60 meV). In addition, ZnO has low resistivity and high transparency in the visible region. As a result, ZnO is considered as a promising material for the application of the optoelectronics.
In this thesis, Metal-semiconductor-metal (MSM) and selective active layer ultraviolet (UV) photodetectors have been fabricated and studied over the last few years. Metal-semiconductor-metal (MSM) electrode was interdigital (IDT) structure, and ZnO mid-ultraviolet (mid-UV) potodetector was fabricated. The ZnO thin film was fabricated with radio frequency magnetron sputtering. The electrode was evaporated on the ZnO thin film by electron beam assisted evaporation. Radio frequency magnetron sputtering deposition system and electron beam assisted evaporation system were both operated at low temperature, so the flexible substrates could be used. ZnO thin film was deposited on PET, PES substrate by radio frequency magnetron sputtering method. The ZnO film was deposited on the flexible substrate by sputtering techniques. The ZnO thin film was then thermally annealed in order to achieve high transparency and decrease the concentration of oxygen vacancy. Finally, The ZnO thin films were analyzed by using XRD, FE-SEM, UV/VIS spectrophotometer, EDS, PL spectra, TEM and SAED.
Sequencely, the Ag, Pt metal was evaporated on the ZnO thin film to form the electrodes of ZnO MSM photodetector. The current-voltage behavior and responsivity of ZnO MSM photodetector were measured. Base on these results of photoelectric measurements, we concluded that the structure of ZnO / flexible substrates is suitable for short-wavelength UV photodetector.
We successfully fabricated MSM photodetector with structure of device 1: electrodes / ZnO / flexiable substrates, device 2: selective active layer photodetector with structure of electrodes / ZnO (selective) / flexiable substrates, device 3: double-Layer photodetector with structure of ZnO / electrodes / ZnO / flexiable substrates, device 4: nanorod photodetector with structure of electrodes / ZnO (nanorod) / flexiable substrates. The flexiable substrates of PET, PES were both used for MSM, selective active layer, double-Layer and nanorod photodetector, which can be used as building blocks for the future optical signal process and the optoelectronic applications.
The photo/dark contrast of Pt MSM photodetectors were 3.31 E+4, 1.06 E+5, 5.545 E+5 and 3.66 E+3 at 1 V bias, respectively ; The photo/dark contrast of Ag MSM photodetectors were 1.73 E+4, 2.85 E+4, 9.44 E+4 and 5.82 E+3 at 1 V bias, respectively. And I also use the thermionic emission theory to calculate Pt and Ag barrier height. The value was 0.859 and 0.782 eV, respectively.
The peak responsivity of those ZnO photodiodes four devices(MSM, Selective, Double-layer, Nanorod) occurs at around 370 nm and its value equals to 0.0588 A/W and 0.349 A/W (device 1), 0.0116 A/W and 0.0506 A/W (device 2), 0.0726 A/W and 0.402 A/W (device 3), 0.498 A/W and 2.07 A/W (device 4) for Pt contact electrode; 0.473 A/W and 1.33 A/W (device 1), 0.0128 A/W and 0.0504 A/W (device 2), 0.0382 A/W and 0.146 A/W (device 3), 4.13 A/W and 7.68 A/W (device 4) for Ag contact electrode when the sample was reversed biased at 1 V and 3 V, respectively . And which corresponds to quantum efficiencies of 19 %, 3.9 %, 24 % and 166 % for Pt contact electrode, respectively; quantum efficiencies of 159 %, 4.3 %, 13 % and 1384 % for Ag contact electrode, respectively. It could be found that device 3: double-Layer photodetector with structure of ZnO / Pt / ZnO / flexiable substrates was the most suitable electrode for ZnO MSM photodetectors among four device.
It is useful to develop low cost short wavelength UV photodetectors and has a great potential for the application of the short wavelength optoelectronic integrated circuit (OEIC).
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