Energy Band Engineering And Performance Regulation Of Molybdenum Disulfide Photodetectors

Photodetectors are widely used in daily life,industry,medicine,and scientific research.With ever-increasing detection demands,it is urgent to develop new photodetectors with full spectral response,high sensitivity,low cost,and flexibility.MoS₂,a typical representative of two dimensional（2D）transition metal chalcogenides,has shown great potential in photoelectronic applications due to its many excellent properties,such as atomic-level thickness,adjustable band gap,high mobility,good mechanical flexibility,and strong light-matter interaction.However,up to now,the performances of MoS₂photodetectors are hardly tunable and accompanied by a large disparity among different studies,urging us to study the factors affecting the performance of photodetectors.Through the design of device structure and interface band structure,it is promising to reveal the key factors affecting the photoelectric performance,which is of great significance for regulating the performance of the photodetector to meet the specific detection requirements.Based on the above requirements and objectives,this thesis focuses on the design of energy band and device stucture of MoS₂ photodetector,conducts systematic research on the mechanism of interface interaction and accordingly develops methods for improving the photodetection performance.The major contents and results of this research are listed as follows:1.The 0D-2D In P-based quantum dot（QD）-MoS₂ hybrid structures are designed.Hybrid structures are fabricated by combining In P QDs,type I In P/Zn S,quasi-type II or type II In P/Cd S core-shell QDs with MoS₂ nanosheets.The influence of band arrangement on the interfacial interaction between QDs and MoS₂ is studied by spectroscopic characterization.The PL intensity of QDs in the hybrid structure is strongly suppressed,which indicates the existence of charge transfer or energy transfer between QDs and MoS₂.The influence of energy band arrangement on the efficiency of charge transfer and energy transfer is further distinguished through the time-resolved PL decay curves.2.The influence of In P-based QDs with different energy band structures on the photoelectric performance of MoS₂ devices are studied.The comparative photoelectric study shows that In P/3Cd S QDs increase the responsivity of the MoS₂ device up to 7 times,which is the largest enhancement factor among the four types of QDs.The results show that the band alignment between type-II In P/3Cd S QDs and MoS₂ promote the the transfer and separation of charges,prolong the lifetime of carriers,and thus increase the photoconductive gain.3.An ion-gated MoS₂ device is designed and its electrical characteristics are studied.Excellent rectification behavior with a current on-off ratio exceeding 10⁶ is achieved in a partially ionic liquid-gated MoS₂ device with two types of metal contacts.The formation of Schottky junction and p-n junction is verified by spatially resolved photocurrent mappings.The switching between the two junctions under ionic gate modulation is correlated with evolution of the energy band,further validated by the finite element simulation.4.The photoelectric properties of the ion-gated device operating in the p-n junction and Schottky junction mode are comparatively studied.When operating in the p-n junction mode,the device exhibits excellent photoelectric performance,including an open circuit voltage up to 0.84 V,a responsivity of 0.24 A·W^-1,a specific detectivity of 10¹¹ Jones,a response time of hundreds of microseconds and a linear dynamic range of up to 91 d B.The comparative study on photoelectric behavior of the device operating at p-n junction and Schottky junction modes reveals key factors affecting the photoelectric performance of MoS₂,which provides new physical insights for the development of 2D photodetectors.