Fabrication And Characteristics Investigation Of Field Effect Transistor Based On Halide Perovskite Ultrathin Single Crystals

Energy,information,and materials are the three pillars of the 21st century,and the developments of novel functional materials provide a solid base for the progress of energy and information.Nowadays,halide perovskites have attracted much more attentions for their excellent optoelectrical properties.The halide perovskites have been widely investigated in many fields,such as solar cells,photodetectors,LEDs,and so on.Even so,there are still many unsolved problems in the study of halide perovskites,which limited the further applications of these new materials.For example,the stability of halide perovskites is poor,and some basic physical features of halide perovskites have not been investigated.All of these challenges are urgent to be solved.However,considering the usual methods to prepare halide perovskites are solution methods,the residual organic groups in the halide perovskites could influence the intrinsic characteristics of halide perovskites.Thus,a proper method should be investigated to prepare pure high-quality halide perovskites for the study of their intrinsic physical features.In this paper,we prepare all inorganic halide perovskite ultrathin single crystals by van der Waals epitaxy,and investigate their unique optoelectrical properties.The main contents of this thesis include following aspects:1.The preparation of all inorganic halide perovskite ultrathin single crystalsVan der Waals epitaxy is a widely used method for the preparation of2D materials.Especially,this method can be used to grow 2D materials of non-layered materials.Here,we used this method to deposite the all inorganic ultrathin platelets.The lateral dimension of the ultrathin platelets can be as large as 300μm.All of these high-quality ultrathin platelets show excellent optical properties,such as norrow full width at half-maximum,high fluorescence quantum yield.Under the femtosecond laser,the ultrathin platelets can even emit laser.By adjusting the content of halide elements,the three-primary colours can be obtained.These high-quality halide perovskite ultrathin single crystals are the solid foundation stones for further studies.2.The study of plane field effect transistors based on CsPbB3 ultrathin plateletsConsidering the poor stability of halide perovskites to polar solvents,we applied a gentle completely dry pick-up technique to minimize material defects to fabricate the field effect transistors,which can confirm the excellent quality of channel materials.At room temperature,μh and on-off ratio of these transistors were 0.3cm2/V·s and 6.7×103,respectively.We carried out temperature-dependent electrical measurement(down to 17.6K)to reduce the influence of ion migration and phonon scatterings.At 237K,μh and on-off ratio were enhanced to be 1.04 cm2/V·s and 1.3×104,respectively.The ion migration in the CsPbBr3 based transistors plays an important role in the electrical transport process at relatively high temperature(above 237K)while the interaction of holes and phonon scatterings dominates at low temperature.We believe that future work should be focused on achieving better perovskite quality with no ion vacancies in the transistor applications.3.The study of field effect transistors based on CsPbBr3 ultrathin platelets/2D materials heteroj unctionsWe prepared a series of van der Waals heterojunctions based on CsPbBr3 ultrathin platelets because they can be deposited in various substrates.We have firstly found that the optical properties of various CsPbBr3/2D heterojunctions significantly differ because of the different band alignments.Next,to further explore the advantage of the band alignment in CsPbBr3/2D heterojunction,a phototransistor based on CsPbBr3/MoS2 heterojunction was fabricated by a gentle dry transfer technique.The phototransistor exhibited excellent optical detection ability driven by an external voltage as small as 0.5V,inspite of the large channel length of 100μm.The raise and fall times were 2.5 ms and 1.8 ms,respectively.The hole mobility was 0.28 cm2/V·s and the on-off ratio was 5×103 under the 442nm laser illumination of 0.2mW/cm2.All of the measurements were performed at room temperature in ambient air.This work provides a new strategy to design and fabricate low-voltage driven air-stable optoelectronic devices based on perovskite/2D material heterojunctions.4.The study of vertical field effect transistors based on CsPbBr3 ultrathin plateletsConsidering the thickness of these CsPbBr3 ultrathin platelets can be controlled,we make use of this point to fabricate vertical transistors based on CsPbBr3 ultrathin platelets by directly vapor deposition.During these process,no damage occurred on the CsPbBr3 ultrathin platelets.Besides,the channel length was decreased remarkably.So that,the performance of these vertical transistors was improved significantly.To further take advantages of the vertical structures,we designed and fabricated an invert based on CsPbBr3 ultrathin platelets and MoS2 nanosheets,which can achieve the corresponding logical operation.The vertical structure devices can also be achieved the measurement of trap states density and mobility of the CsPbBr3 ultrathin platelets,which can help us know better about the all inorganic halide perovskites.