Preparation Of Ga₂O₃material On Si Substrate And Performance Control Of Ga₂O₃-based Oxygen Sensor

Gallium oxide（Ga₂O₃）is a new ultra-wide bandgap semiconductor materials with a bandgap value of approximately 4.9 e V,excellent electrical properties,stable physicochemical properties,and reliability in extreme environments,making it one of the research hotspots of the fourth generation semiconductor.At high temperature,the conductivity of Ga₂O₃is influenced by the ambient atmosphere and is used in high temperature Ga₂O₃based gas sensors.However,high power consumption and grain coarsening at higher operating temperatures can lead to deterioration in device sensing performance.Secondly,the Ga₂O₃material is of low thermal conductivity,so that the heat dissipation from the device is difficult,and the service life is affected.Therefore,the development of high-performance and low-temperature Ga₂O₃based gas sensors is an urgent problem to be solved today.With the development of nanomaterials,nanomaterials regarded as the ideal candidate for gas sensing due to their large surface area to volume ratio and size effect.Nanostructures exhibit higher sensitivity,faster response and enhanced detection of low gas concentrations.Furthermore,gas sensors made from nanomaterials showed lower optimal operating temperature.In recent years,the preparation and properties of nano-scale Ga₂O₃have been extensively investigated.However,few works focus on their gas sensing properties and the low-temperature serving performance.Therefore,in this thesis,Ga₂O₃materials with different micro and nano structures were prepared by modulating the growth process,and their material properties,gas-sensitive sensing characteristics and low-temperature response mechanisms were investigated as follows:（1）Ga₂O₃films were prepared by RF magnetron sputtering on Si（111）substrate.The effects of sputtering power,sputtering air pressure,annealing temperature and annealing atmosphere on the micro-crystal structure,surface morphology and vacancy defects of the films were investigated.It was found that increasing the annealing temperature was more favourable to the film recrystallisation process and that the crystalline quality of the films were effectively improved.The recrystallisation properties of the films are better and the defect density is lower in high vacuum in-situ annealing compared to annealing treatments in a muffle furnace with an air atmosphere.（2）The nanostructure,surface topography and oxygen vacancy content of Ga₂O₃are regulated by varying the substrate temperature and deposition atmosphere.It was found that the substrate temperature and the deposition atmosphere have a strong influence on the nanostructure,in which Ga₂O₃clusters appear on the surface of Ga₂O₃films at a substrate temperature of 300℃under high vacuum and high temperature anoxic environment,while Ga₂O₃nanowire structures can be obtained at 400℃.（3）The surface microscopic morphology of Ga₂O₃samples was further adjusted by regulating the deposition parameters,and nano-hybrid Ga₂O₃samples containing nanowires and nanorods with various micro-nano structures were obtained.Ga₂O₃thin films,nanowires and nano-hybrid structure samples were prepared as Ga₂O₃-based gas sensors.All as-achieved Ga₂O₃-based gas sensors exhibited the peak responses at lower operating temperatures of300-400℃.The Ga₂O₃-based sensor of the nano-hybrid structure performed the highest response of 19.95 at the ambient of 10%oxygen,and the fastest response speed of 0.7323MΩ/s and the most stable cycling performance.（4）Through oxygen vacancy analysis of Ga₂O₃materials with different surface morphologies and quantitative analysis of the material surface structure,the N₂adsorption-desorption isotherms were used to compare the surface area and pore distribution for statistical purposes.The efficient response of Ga₂O₃based gas sensors can be attributed to the gas adsorption/desorption mechanism:focusing on the relationship between the gas and the material surface,the carrier concentration changes,thus causing a resistance.The Ga₂O₃nanohybrid structure has a large specific surface area and pore volume,which increases the oxygen adsorption active sites and provides sufficient pathways for oxygen adsorption and desorption.This work revealed that reasonable controlled specific surface area was the key to realizing low-temperature oxygen sensors with high response,good stability and fast response,which was of great significance to the potential applications of nanostructured Ga₂O₃in low-temperature oxygen sensors.