Study On Gas Sensor Based On P-type Metal Oxide Semiconductor Hetero-composite Structure

In recent years,the rapid development of Internet of things technology lead to a strong demand for sensors.As a member of the sensor family,gas sensors play an important role in the fields of atmospheric environment detection,industrial and agricultural production,smart medical and home safety.Therefore,it is of great significance to vigorously develop high-performance gas sensors.In this paper,we focus on improving the gas sensing performance of p-type metal oxide semiconductor gas sensors,which are less studied at present.The main design idea is to build a composite heterostructure.The composite heterostructure gas sensor based on CuO and NiO were fabricated by using different preparation methods.The gas sensing performance of the sensor was systematically studied.The application of p-type metal oxide semiconductor in the field of gas sensors was expanded.The specific research contents are as follows:The research status of p-type metal oxide semiconductor CuO and NiO based gas sensors was analyzed.The gas sensing mechanism and the methods to improve the gas sensing performance are summarized.In-doped CuO nanostructures were successfully synthesized by hydrothermal method.The structure and morphology of the nanostructures were characterized by X-ray diffraction?XRD?,field emission scanning electron microscopy?FESEM?,transmission electron microscopy?TEM?and X-ray photoelectron spectroscopy?XPS?.The gas sensing properties of the pure and In-doped CuO nanostructure were investigated.Compared with pure CuO,the sensors based on 2 mol%In-doped CuO exhibited enhanced gas sensing and low working temperature obviously.The response to 300 ppm ethanol gas reached to 67.1 at 116?,which was almost 9.5 times higher than that of pure CuO.The flow and recombination of carriers at the n-p junction is the main reason for the decrease of the carrier concentration of In₂O₃-CuO gas sensors in reducing gas.Therefore,we believe that the change of carrier concentration on the surface of the material caused by In-doping could be responsible for the enhancement of the gas sensing properties.Utilizing the n-type semiconductor characteristics of ZnO,ZnO NWs-CuO NPs heterostructure gas sensor was successfully prepared by two-step water bath method.ZnO nanoflakes were prepared by electrodeposition method and E-ZnO/CuO heterostructure gas sensor was prepared by secondary growth technology.The gas sensing characteristics of the gas sensor based on the ZnO NWs-CuO NPs heterostructure and E-ZnO/CuO heterostructure were analyzed respectively.Compared with the single pure CuO gas sensor,the response of the ZnO NWs-CuO NPs heterostructure gas sensor to 200 ppm ethanol is increased by about 6 times,and the selectivity of the sensor to ethanol gas is improved.The response of the E-ZnO/CuO heterostructure gas sensor to 100 ppm ethanol is about 2.5 times that of single pure CuO gas sensor.The E-ZnO/CuO heterostructure gas sensor shows good linearity.By introducing TiO₂ quantum dots?QDs?into p-type semiconductor CuO and NiO,cubic TiO₂-CuO composite nano-heterostructure and flower-like TiO₂-NiO composite nano-heterostructure gas sensors were prepared.Scanning electron microscope?SEM?,X-ray diffraction?XRD?and energy spectrum analysis?EDS?were used to analyze the morphology and structure of the prepared samples.The gas sensing performance of the sensor was studied.The results show that the TiO₂-CuO composite nano-heterostructure grown by water bath method is nano cube with side length of 2-2.5?m,and the TiO₂-NiO composite nano-heterostructure prepared by solvothermal method is flower-like structure with diameter of 12-14?m assembled by nanosheets.At the optimum operating temperature,the response of the TiO_2-CuO sensor to 50 ppm of ethanol gas is about 1.5 times higher than that of the single CuO sensor.The response of TiO₂-CuO sensor to 50 ppm ethanol is about 1.28 times higher than that of the single NiO sensor.