Study On Ultraviolet Photoelectric Properties Of Low-dimensional Semiconductor Nanomaterials

From the point of view of computational physics, the structure design ofmetal/semiconductor/metal (MSM) type ultraviolet (UV) detector and numerical analysisof device performance were studied. In the experiment, varieties of UV detectors based onABO3type perovskite materials were fabricated. The NaTaO3based UV detector wasreported for the first time. In addition, the influence of highly Zr doping and polymersurface modification on the properties of TiO2UV detectors was researched in detail. Themain results are as follows:In the numerical analysis of detector performance, the current transport mechanism ofMSM structured UV detector was analyzed. The material parameters of semiconductor andthe device geometry structure were analyzed through MATLAB software. The relationshipbetween these parameters and the detector performance was researched. Through the staticand transient simulation of device, the dark current, responsivity, response timeperformances were optimized. Finally, the optimal values of related parameters wereachieved, which can be used to guide the actual device fabrication. This would lay a goodfoundation for theoretical simulation study of other semiconductor UV detectors.The higher metal work function is, the lower dark current of UV detector is. Theabsorption coefficient, active layer thickness and reflectivity would affect the quantumefficiency. The active layer thickness should not be too thick or too thin, which was suitableto be around0.2μm. The optimization values of optical absorption coefficient andreflectivity were1.5×107/m and0.22, respectively. When the interdigital width or spacingwas longer than20μm, the quantum efficiency and photoresponse would no longer changewith increasing the interdigital width or spacing. The junction capacitance of the devicewould be small and the transit time would be fast with higher reverse bias and better crystalquality. The theoretical values of capacitance and transit time were4.57pF and0.4s.A variety of UV detectors based on perovskite materials were made, including SrTiO3,NaTaO3and LaAlO3. SrZr0.1Ti0.9O3nanomaterials were prepared by sol-gel method andanalyzed by many characterization methods. The MSM structured UV detectors with Auelectrodes were made on SrZr0.1Ti0.9O3thin films. The UV/visible rejection ratio was more than three orders of magnitude, which showed a high sensitivity. The dark current of thedevice was41pA, the responsivity was94mA/W, the response time was3.8and565ms,respectively.The NaTaO3thin films were synthesized by the hydrothermal method, and MSM typeNaTaO3UV detectors with capacitive efficacy were fabricated. The current-voltage,spectral response and time response characteristicis were tested. At5V bias, thephotocurrent was20.2nA, which was more than one order of magnitude larger than thedark current. The response peak of76.8mA/W appeared at260nm.Then visible-blind ultraviolet detector was fabricated based on TiO2/SrTiO3heterojunction active layer. The introduction of TiO2/SrTiO3heterojunction active layercontributed a lot to the device gain and improvement of response time. At10V bias, thedark current was0.2nA, the response peak was46.1A/W at260nm, the response timewere3.5ms and1.4s, respectively. In addition, MSM UV detectors based on LaAlO3single crystals were fabricated, which displayed excellent solar blind properties. The deviceexhibited a very low dark current and high sensitivity. The dark current of Pt electrodedevice was as low as4.1pA, the response peak was325mA/W at200nm.The influence of doping and polymer surface modification on TiO2UV detectors wasalso included in the paper. The highly Zr doped TiO2thin films were synthesized by sol-gelmethod. The ultraviolet absorption edge of Zr0.5Ti0.5O2film was in solar blind area, whichindicated that high level of Zr doping would change the bandgap width of the TiO2/ZrO2composite material. Based on this material, MSM type ultraviolet detectors were made withdifferent metal electrodes. The device showed a high response and low dark current. At5Vbias, the responsivity of Pt electrode device was620mA/W under250nm UV lightirradiation. The dark current was17pA, the response time were424.1ms and154ms,respectively. In addition, the influence of temperature and humidity on the detectorperformance was also studied. The devices showed good stability with humidity andtemperature variation.One-dimensional TiO2nanowire arrays were synthesized via solvothermal method.The material exhibited a high quality of surface morphology. The TiO2nanowires were used as electron acceptor material and the poly (9,9-2hexyl fluorene) acted as electrondonor material. Then organic/inorganic hybrid ultraviolet detector was made by spincoating PFH on TiO2nanowires. The dark current of the device was as low as1.9nA andthe photoresponse was large as568mA/W. Finally, the internal transmission mechanism ofthe carriers in the hybrid system was analyzed in detail.