| Although there are a lot of studies on multiple two-dimensional materials in recent years,black phosphorus is still one of the most promising one with its excellent overall properties.Black phosphorus has a direct band gap of 0.3?2 eV,which just makes up for the gap between graphene with zero band gap and transition metal chalcogenides with wide band gaps.Meanwhile,black phosphorus has a hole mobility of up to 1000 em2V-1s-1 at room temperature,and can even reach 6000 cm2V-1s-1 at low temperatures,a value far exceeding that of most other two-dimensional semiconductor materials.However,the preparation of black phosphorus films still mainly relies on mechanical exfoliation,and suffers from low yield,small size and large thickness,which limits its application.Meanwhile,the environmental stability of black phosphorus is poor,so effective passivation is necessary.In addition,black phosphorus is a p-type semiconductor material,and effective methods need to be found to control its carrier transport properties.The above shortcomings undoubtedly limit the research and application of black phosphorus,so this dissertation has carried out in-depth research around solving the above several problems:(1)Improvement of mechanical exfoliation of black phosphorus.Metals and PDMS were used to assist in mechanically exfoliating black phosphorus.The basic characterization of the obtained black phosphorus thin film was performed.The performance of the field effect transistor based on it was measured.The results show that the metal-assisted exfoliated black phosphorus film has high yield,large size(>100 ?m),small thickness(?4 nm)and complete lattice,so it is a very high-quality black phosphorus film;PDMS-assisted exfoliated black phosphorus films' yield,size(10-100 ?m)and thickness(?10 nm)are all between metal-assist and traditional mechanical exfoliation.In particular,we found that the thickness of the black phosphorus films prepared by the PDMS method is more suitable for the preparation of black phosphorus field effect transistors.Statistics show that these field effect transistors have considerable hole mobility and on/off ratio.(2)Passivation of black phosphorus.Black phosphorus was passivated by alumina and hafnium oxide,respectively.Alumina-passivated black phosphorus has more than one week of environmental stability and is classified as physical encapsulation passivation;Hafnium oxide-passivated black phosphorus has environmental stability of at least three weeks.The black phosphorus film is thinned after passivation,and the on/off ratio of the field effect transistor increases by an average of 34 times.The device turns ambipolar.Comprehensive analysis shows that these effects are mainly due to the formation of phosphorus-hafnium bonds.Therefore,hafnium oxide passivation is classified as chemical protection passivation(3)Surface charge transfer doping of black phosphorus.Hafnium oxide,magnesium oxide and metal oxide/hexagonal boron nitride/black phosphorus field effect transistor structures were used to realize the surface charge transfer doping of black phosphorus,respectively.Among them,the highest electron mobility of black phosphorus field effect transistors directly modified by hafnium oxide and magnesium oxide reached 21 cm-V-1s-1 and 123 cm-V-1s-1,respectively,while the electron mobility of hafnium oxide/hexagonal boron nitride/black phosphorus and magnesium oxide/hexagonal boron nitride/black phosphorus reached 65 cm2V-1s-1 and 305 cm2V-1s-1,respectively.In particular,magnesium oxide/hexagonal boron nitride/black phosphorus field effect transistor also has a high hole mobility of 1150 cm2V-1s-1.which is also a high value for black phosphorus grown by chemical vapor transport methodIn summary,we have carried out systematic research on three aspects of black phosphorus including film preparation,passivation,and surface charge transfer doping,respectively,and have obtained some valuable results for further research and practical application of black phosphorus. |
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