| Ultraviolet (UV) detectors have been much studied in these recent years because of its important application in the very many fields. The Ge-based and Si-based UV detectors have been into the commercial application, especially Si-based UV detectors for its mature technologic level. Further UV detectors based the alloy with Ge and Si have been succeeding to be manufactured. And the UV detectors based GaAs and GaP and their alloy have been also researched much, and it makes lots of progresses in the study about them. In recent years, UV detectors have been developed quickly with the development of the preparation method on the material. The UV detectors based on the wide-band semiconductors have been important focus of attention in the last decade. The most study among them is on the GaN-based UV detector, and has most progresses. Besides it, ZnO, SiC, diamond are studied very much too. But the progresses about them are not as much as GaN due to some disadvantages. For example, the quality of the materials is not as good as the GaN's, and the preparation technology is not very mature.TiO2 is a kind of wide-band semiconductor. It not only has very good physical and chemical property, but also has good optics property. In recent years, TiO2 has been researched on the fields as gas or moistness sensor and photocatalyst and solar cell. It has already become the focus of the domestic and international relevant fields. The bandgap of TiO2 is 3.0eV～3.2eV, which makes it very attractive for the UV detector.In this paper, we present the fabrication of the metal-semiconductor-metal (MSM) structured photovoltaic detector based on the wide-band property of TiO2.First of all, we discuss the classification of the UV detectors, especially of the semiconductor UV detectors. After classification we make a deep analysis and discussion about the operation principle and main parameter of the semiconductor UV detectors, especially of the photovoltaic detector.Then we introduce the crystal struture of TiO2.There are three strutures of which include rutile anatase and brookite.We discuss their differences and applications.The methods of fabricating TiO2 are introduced, espicially the principle of gol-sel is analysed particularly.These are necessary for us to frabricate TiO2 thin film.Next, TiO2 thin films were prepared by tetrabutyl titanate (Ti (OC4H9)4), which was generally used for fabricating TiO2 thin films or TiO2 fine particles through sol-gel method. The solution was rotated on Si (110) substrates and was then annealed for 2 h at 650℃in a muffle furnace, leading to polycrystalline anatase structures. X-ray diffraction (XRD) shows that the films are composed of anatase TiO2 as indicated by the reflection peak at 25.15?. The crystallite size of TiO2 thin films can be deduced from XRD line broadening using the Scherrer equation and the average crystallite size of TiO2 was 38.02 nm. We can find out the sample has strong absorption in the ultraviolet light range and hardly absorbing in visible light range. The absorption edge of the spectrum has blue-shift phenomenon.Interdigitated Au/TiO2/Au circular structure was designed and fabricated. Au film was deposited by radio frequency magnetron sputtering. The planar interdigitated electrodes were prepared by standard photolithography and lift-off technique. The finger width and spacing both are equal to 20μm, and the total active aera is 0.38mm2. We have done some tests to the photocurrent characteristics of TiO2 detector, and made discussion.Through the I-V characteristic curve, we can find out that obvious photoresponse can be seen when the UV light irradiated on the devices, and the shorter the wavelength is, the more obvious photoresponse can be observed. The photoresponse was flat over the band gap and have a cutoff at wavelength around the absorption edge of TiO2 (~330nm). The photoresponse exhibited obvious blue shift caused by nanometer effect. The maximum responsivity of 199 A/W at 260 nm was obtained from the devices, which was much higher than any other wide bandgap photovoltaic photodectors with MSM structure. The device shows a time response with a rise time of 6 s and a decay time of 15 s by analysing the figure of time response. We deduce the time response is attributed to the defect traps which widely distributed in nanocrysal. The time response will be shorter if the crystal grows better and the finger space becomes smaller.After the discussion to the tests, we have some advices about several key problems in the current research. We think this will help us study better in the next stage. A. Inorder to weaken the impact of impurity, we should ameliorate the experimental condition through the process of fabricating TiO2 thin film. B. Use more methods to characterize the morphology of TiO2 thin film and try to find out the appropriate experimental paramters. C. The defects in the crystal should be reduced for decreasing time response of devices. D. Reduce the interval of the interdigitated electrodes as much as possible which can improve the odds of the photo-generated carriers collected by the electrodes. |
PDF Full Text Request