Luminescence Properties And Regulation Of Excitons In Van Der Waals Heterojunctions

Atomically thin layers of semiconducting transition metal dichalcogenides（TMDs）possess tightly-bound excitons and strong light-mater interactions.The weak vd W interactions between layers allow it to be easily dissociated into a single layer and constructed into heterojunction devices with different structures,which significantly affects the properties of electrons and excitons in the systems.Manipulation of the excitons in TMDs vd W heterostructures and realizing the transform of light and excitons hold great promise for the development of excitonic integrated circuits.In addition,the abundant exciton properties in TMDs vd W heterostructures provide an unprecedented platform for people to study the internal physical mechanisms of the kind of materials.Especially,the discovery of twisted heterojunction provides a new opportunity for the construction of integrated optoelectronic devices.Therefore,we firstly constructed the twisted-angle double-layer optical devices under different substrates for the advantages of stable exciton emission and strong spin-orbit coupling effect of single-layer TMDs.Combined with the moirésuperlattice patterns,the properties of exciton under moiréperiodic potential field tuning are analyzed.Then,a single layer TMDs optical device with floating gate structure is constructed,and the tuning effect of floating gate effect on excitons is studied.Specific research contents are as follows:1.The dissociation technique of large-area TMDs was explored and the preparation process of bilayer twisted-angle TMDs was optimized,which lay a foundation for the acquisition of high-quality interface.The moirésuperlattice patterns of the double-layer WS₂/WS₂devices were obtained by the Kelvin probe force microscope（KPFM）technology,and the distribution of triangular domains in the moirésuperlattices prove the reorganization of atoms and the nearly 0°stacking of the bilayer materials.Moiréexciton with very narrow spectral lines（about 1 me V）were observed at low temperature by fluorescence measurement.The existence of biexciton was confirmed by using the super-linear enhancement behavior of biexciton at different power,and neutral and charged exciton were distinguished under gate voltage regulation.2.A floating gate optical device based on single-layer TMDs is constructed.The exciton tuning principle of the device is studied systematically,comparing the spectrum of positive and negative voltage writing with the state after withdrawal,reflecting the difference of the spectrum under the opposite doping effect.The state is basically unchanged at low temperature,and the information can be stored stably,which confirm floating storage function.At room temperature,when the positive voltage is written,the state is basically unchanged,and the information can also be stored stably.Then,we study the synaptic properties of the device at different temperatures and prove the larger barrier for carrier tunneling in low temperature as well as the existence of asymmetric barriers.Meanwhile,the device shows good stability at different temperature,which provides a new idea for the application of steady-state excitonic devices.