| Ultraviolet detection technology has found a variety of applications in both military and civil fields. AlGaN-based ultraviolet photodetectors take the advantages of high breakdown-voltage, large thermal conductivity, good thermostability, anti-radiation, which enable them to operate in military, aerospace, industrial and other harsh environments. However, the performance of AlGaN-based photodetectors is still far below expectation, which is due to the problems such as high dislocation density in AlGaN, low doping efficiency of AlGaN and the device fabrication technique. Especially, the performance of AlGaN-based solar-blind ultraviolet photodetectors needs further improvement.Aiming at solving the key technical issues in AlGaN-based solar-blind ultraviolet photodetectors, we start with the optimized epitaxy of high-quality AlGaN films by metal-organic chemical vapour deposition (MOCVD). Then we investigated the fabrication of Ohmic contacts on n-AlGaN epilayers. And the performances of AlGaN-based Metal-Semiconductor-Metal (MSM) solar-blind ultraviolet photodetectors have been greatly improved by combination with localized surface plasmon of Al nanoparticles. Furthermore, we proposed the integration of Al nanostructures with other AlGaN-based photodetectors. The detail research contents in this dissertation are as follows.(1) Realization of Ohmic contacts on high-Al-content n-AlGaN epilayers. We proposed and validated that high-temperature annealing in nitrogen could recover the etching damages in the high-Al-content n-AlGaN. By optimizing the metallization scheme, as well as the temperature and time of rapid thermal annealing, we successfully prepared low-resistance Ohmic contacts on the plasma-etched and annealed n-Al0.5Ga0.5N. The recovery mechanism of etching damages by high-temperature annealing in nitrogen was clarified by X-ray photoelectron spectroscopy.(2) We utilized nanosphere lithography to fabricate metal nanostructures. We could achieve a wafer-scale self-assembled monolayer polystyrene nanosphere template of low defect density on different substrates by spin-coating or floating-transferring methods. Combining nanosphere lithography with the modifation techqiues of polystyrene nanospheres, we also have successfully produced various metal nanostructures with the nanosphere template, including metal nanoparticle arrays and nanomesh.(3) The simulation model for the triangular-prism like Al nanoparticles prepared by nanosphere lithography was established using the FDTD Solutions software. Then the effects of particle sizes and dielectric environment on the local surface plasmon resonance wavelength were studied. And we finally could flexibly regulate the localized surface plasmon resonance properties of Al nanoparticle arrays by combining theoretical simulation and experimental verification.(4) Al nanoparticle arrays prepared by nanosphere lithography were integrated with AlGaN-based MSM solar-blind ultraviolet photodetectors. We have found that the size-controlled Al nanoparticle arrays can not only reduce the detectors' dark currents but also bring about greatly enhanced responsivity. The dark currents of the devices were in the order of pA range, the peak responsivity was up to 2.34A/W at 269nm under 20V bias. The effects of Al nanoparticle sizes and the electrode structures on the performance of photodetectors were investigated. We also preliminarily explained the enhancement mechanisms of the localized surface plasmon.(5) The design scheme of AlGaN-based MSM solar-blind ultraviolet photodetectors with nanomesh interdigitated electrodes was proposed.And we have carried out preliminary simulation of the nanomesh electrodes and processing research. We tentatively integrated Al nanoparticle arrays with AlGaN-based PIN solar-blind photodetectors, but we have not got enhanced devices yet. Therefore, we need to further improve the design of metal nanostructures. |
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