Study On The Tunable Exciton Dynamics Based On Twisted Bilayer Molybdenum Disulfide

Tunable exciton dynamics based on band gap engineering has received extensive attention and research in the fields of photovoltaics and information storage.Two-dimensional transition metal dichalcogenides（TMDCs）represented by molybdenum disulfide have a band gap covering 1.5～2.4e V and have abundant excitonic physical properties,so they are widely used in various optoelectronic devices.The band gap of the material can be adjusted to a certain extent by means of doping,stress,etc.,so as to optimize the performance of the device.However,these methods are generally complicated to operate and difficult to quantitatively manipulate.Resulting in large fluctuations in the exciton dynamic process in the material and device performance,limits the application of these methods in engineering.This research aims to explore a stable exciton dynamics modification method and lay the foundation for the application of high-performance TMDCs optoelectronic devices.The main research contents are as follows:1.The dynamic changes of indirect excitons of double-layer MoS₂ with different interlayer twist angles are analyzed.Mainly analyze the lifetime of indirect excitons and their proportion in all excitons.The experimental results show that the lifetime of indirect excitons can be modified by the twist angle between layers.At 0°and 60°,the lifetime of indirect excitons is the shortest,respectively 5.2ns and 8.3ns,and the proportion of indirect excitons is high;When the indirect angle is close to 30°,the lifetime of the indirect excitons of the double-layer MoS₂ can be as long as 27ns,but due to the increase of the indirect band gap,indirect recombination is difficult and the content of indirect excitons is reduced.2.From the perspectives of semi-classical physics and quantum mechanics,the trend of exciton lifetime is verified.The result proves that the lifetime of indirect exciton increases with the increase of indirect exciton gyration radius（which are approximated by interlayer spacing）,which is in line with TRPL experimental results.Unanimous,due to the effect of steric effect,the interlayer spacing of the double-layer MoS₂ will increase first and then decrease with the twist angle.At 30°,the interlayer coupling effect is the smallest and the interlayer spacing is the largest.The electrons and holes of the indirect excitons are located in different layers of MoS₂.Therefore,the change of the layer spacing directly leads to the change of the electron-hole Bohr radius,that is,the larger the layer spacing,the larger the Bohr radius,and the smaller the Coulomb gravitational force.The longer the exciton’s life span.3.Preparation of TMDCs transistors and exploration of the basic applications of TMDCs are discussed.By imposing defects on the WS₂ crystal and destroying its lattice integrity,we found that the single-layer WS₂ transistor no longer exhibits a symmetrical ohmic contact characteristic curve,but a Schottky contact characteristic.The reason for this phenomenon is due to the existence of charged defects in the WS₂ lattice.Therefore,when a voltage is applied at both source and drain sides,the defects will move in the lattice after receiving Coulomb attraction,which will eventually cause the defects to gather at electrode,resulting in the different potential between the source and drain.Eventually,an asymmetric Schottky contact phenomenon happened.In this study,by simply modifying the relative orientation between the artificially stacked layers,the indirect exciton lifetime was prolonged by an order of magnitude,which could achieve precise control,laying a foundation for the study of exciton physics and the application of exciton devices.This research has also developed a single-layer TMDCs-based rectifier.Compared with the current P-N-junction rectification in the semiconductor industry,this method can replace the heterojunction with a single layer,thereby greatly reducing process costs and improving efficiency.In addition,the preparation and testing of this transistor lays the foundation for the basic application of twisted double-layer TMDCs,and it is expected that high-performance electronic devices can be achieved based on the twisted double-layer TMDCs structure.