Preparation Of Quasi-two-dimensional Bi_xSn_1-xO₂ Films And UV Detection Performance Study

Two-dimensional materials have been at the forefront of international research in recent years and have shown excellent performance in various aspects,such as optical and electronic properties and specific physicochemical properties,and have shown great potential for applications in the field of photodetectors.The preparation of high quality large-size SnO₂films has been challenging,and liquid metal transfer is a new method for preparing 2D metal oxide films in recent years,which can conveniently prepare large-size SnO₂films.In this thesis,quasi-dimensional SnO₂and Bi_xSn_1-xO₂（BTO）thin films were prepared on SiO₂/Si substrates by liquid metal transfer method,respectively.The film size is about 0.48mm²,thickness 2.1～11 nm,and Bi content x is about 0.2%.The prototype photodetection devices were constructed by pressing indium grains onto the quasi-dimensional SnO₂and BTO films as electrodes.The photodetector devices based on the quasi-dimensional SnO₂films showed a significant response to UV light in the wavelength range of 280 nm～400 nm,and the response increased with thickness.The device has a low dark current of 2.7×10^-7A and a photocurrent of 5.36×10^-6μA at 280nm.The responsivity of the quasi-2D SnO₂film with a thickness of 10.5 nm reached 7.56×10^-2A/W,and the responsivity of the annealed 2D-BTO film increased to 9.5×10^-1A/W.The UV photodetector based on the Bi_xSn_1-xO₂（BTO）quasi-2D film was constructed with a response wavelength range of 280 nm to 460 nm,and the device exhibited a narrow-band UV response The device exhibits a narrowband UV response with a half-height width of 49 nm and a peak responsivity of 589 A/W under 300 nm UV irradiation.For both the quasi-two-dimensional SnO₂and Bi_xSn_1-xO₂（BTO）films,they exhibited significant persistent photoconductivity（PPC）phenomenon after turning off the UV light for a duration of up to 1.65×10³s,which was not conducive to the rapid recovery of the devices.After turning off the UV light source,we reduced the duration of the persistent photoconductivity（PPC）effect from 1.65×10³s to 2.53×10^-2s by dropping ethanol on the device surface.in addition,the significant recovery time could also be reduced by methanol,propylene glycol,NaNO₂and Na₂SO₃.We investigate the physical mechanism by which ethanol can significantly attenuate the PPC effect of quasi-two-dimensional Bi_xSn_1-xO₂（BTO）films,and suggest that the photogenerated holes in BTO films are rapidly consumed by solutions such as ethanol through oxidation reactions.The results of this thesis show that quasi-two-dimensional BTO films have promising applications for high-performance UV photodetection and propose an innovative route to attenuate the PPC effect by introducing reducibility on the semiconductor surface.The main content of this thesis is arranged as follows:Chapter 1 introduces the preparation method of SnO₂crystal structure and its application in various fields,and expounds the research status and main problems of SnO₂in the field of photodetector and photocatalysis.The second chapter introduces the instruments used in the preparation of the device and the characterization of the device morphology and performance in this paper,and briefly introduces the working principle of the relevant instruments.In addition,the preparation process and testing process of quasi-two-dimensional SnO₂and BTO thin films are introduced.The third chapter analyzes the photoelectric properties of the quasi-two-dimensional SnO₂film before and after annealing.The prepared quasi-two-dimensional SnO₂film photodetector has obvious photoelectric response in the range of 280 nm～400 nm ultraviolet light,and shows obvious PPC effect.After annealing,the responsivity is improved but the response speed is slowed down.The fourth chapter analyzes the quasi-two-dimensional BTO thin film elements,morphology,thickness and photoelectric performance characterization results,and explores the effect of reducing solution on the PPC of the device.The quasi-two-dimensional BTO film has photoelectric response in the range of 280 nm to 460 nm.And shows PPC.The device PPC showed a significant improvement under the action of the reducing solution.The fifth chapter summarizes the whole research and expounds the innovation points of this paper.