Effects Of Components Modulation On The Type Of Band Alignments For PbI₂/WS₂ Van Der Waals Heterostructure

Through interlayer assembly and stacking,van der Waals heterojunction can integrate the excellent properties of different kinds of materials and further optimize the photoelectric properties of two-dimensional materials.Van der Waals heterojunction has different band arrangement,which shows amazing performance and novel phenomenon and promotes development in the field of the photoelectric detector and photoelectric application.The band arrangement of the heterojunction determines the performance and application field of the device:Type-I heterojunction is generally used in the field of luminescence.Type-II is suitable for photocatalysis and photodetectors,while Type-III is commonly found in tunneling field-effect transistors(TFETs).Therefore,it is of great significance to explore how to control the arrangement of various band types in a single heterojunction.However,it is still a challenging task to achieve the controllable change of band arrangement between single heterojunction and further modify the performance of van der Waals heterojunction.Common regulation methods include electric field,doping,strain,defect.However,electric field and pressure regulation will destroy the material structure,and defect regulation is difficult to control in the experiment.However,ion doping is a simple and feasible method to regulate band arrangement.In this thesis,a heterojunction system composed of layered two-dimensional material PbI₂and WS₂in transition metal disulfide was built.The heterojunction system composed of layered two-dimensional material PbI₂and WS₂in transition metal disulfide was constructed.The S atom of monolayer WS₂was replaced by Se atom by controlling the proportion of chemical components.The internal physical mechanism of the improvement of electronic and optical properties after the band type change of a single heterojunction PbI₂/WS₂was explored.The main research contents of this thesis are as follows:(1)Monolayer PbI₂and WS₂were used as the original models to build PbI₂/WS₂heterojunction and select the crystal structure model,which the mismatch of less than5%and the appropriate number of atoms.Determine the doping ratio of 0%,50%,and100%Se ions,calculate the binding energy according to the configuration of PbI₂/WSSe at the same 50%doping ratio.Finally,select the most stable heterostructural type and the smallest binding energy.The band diagram,the density of states diagram,interfacial charge transfer diagram,light absorption diagram,effective mass of monomer and heterojunction obtained by theoretical calculation.The internal mechanism is thoroughly analyzed and the related mechanism of regulating energy band type is explained in detail.(2)The theoretical calculation results show that the band arrangement of heterojunction will change from Type-I to Type-II.The introduction of Se ions will gradually reduce the binding energy and bandgap of PbI₂/WS₂heterojunction.When all S atoms are replaced by Se,the PbI₂/WSe₂heterojunction is formed,effective mass(m*)of which has a minimum value.The calculated values in the direction of[100]and[010]are 0.29 and 0.49,respectively.After ion doping,the light absorption performance of heterojunction is further improved,which is still much better than that of monolayer PbI₂.Therefore,the regulation of band type arrangement by chemical composition in heterojunction has important significance in the future photoelectric application and photoelectric detection technology.