Research On Photoelectric Properties Of Weyl Semimetal TaIrTe₄

In this paper,density functional theory（DFT）combined with non-equilibrium Green’s function（NEGF）is used to investigate the photoelectrical properties of the type-Ⅱ Weyl semimetal TaIrTe₄device and their lateral heterojunctions.Our results shed lights on the promising application of photogalvanic effects based on TaIrTe₄devices in optoelectron-ics.In Chapter 1,this chapter not only briefly introduces the concept and characteris-tics of Weyl semimetal,but also points out the research background and significance of TaIrTe₄.The second chapter expounds the theoretical knowledge of DFT and NEGF method,and further explores the numerical calculation theory of Nanodcal software in equilibrium and non-equilibrium state.In Chapter 3,the variation of TaIrTe₄band structure and the photocurrent transmis-sion of Cu-TaIrTe₄-Cu heterojunction under strain regulation are studied.In this chapter,a heterojunction model with TaIrTe₄as the central region and Cu as the two leads is es-tablished,where x,y and z are the period,transport and vacuum directions respectively.It is found that the Weyl points can be completely broken with increasing of the strain along z dirction.When strain is applied in the x direction,the Weyl points remain stable.One can obtain a large photocurrent in the Cu-TaIrTe₄-Cu heterojunction in the absence of the strain.The results also verify the good photoelectric performance of TaIrTe₄from the side.When 8%strain is applied along the x direction,the photocurrent increases signif-icantly,which is 86 times of that without strain.Accordingly,the maximum values of the photocurrent can be interpreted in terms of the band structures of the system and the transitions between peaks of density of states.Our results provide a novel route to effec-tively modulate the energy bands and the photocurrent by utilizing mechanical methods for TaIrTe₄-based devices.In Chapter 4,the photoelectrical properties of TaIrTe₄-WTe₂/MoTe₂lateral hetero-junctions are investigated.In this study,the monolayer WTe₂,the monolayer MoTe₂de-vice and the TaIrTe₄-WTe₂/MoTe₂lateral heterojunction are firstly constructed by using the crystalline body modeling software.Then,the photocurrent of the lateral heterojunc-tion and the monolayer device is calculated.Finally,the peak value of photocurrent is explained and the results are analyzed.When the infrared light illuminates the lateral het-erojunction of TaIrTe₄-WTe₂,the resulting photocurrent is significantly higher than that of the monolayer WTe₂device.At 0.9 e V,the lateral heterojunction photocurrent reach-es 8.3,which is 165 times of the monolayer WTe₂device photocurrent.The conclusion can be drawn by comparing the TaIrTe₄-MoTe₂lateral heterojunction with the monolayer MoTe₂device:The photocurrent of TaIrTe₄-MoTe₂lateral heterojunction is significantly increased,and stable photocurrent is generated in the infrared and visible regions.The results show that TaIrTe₄-WTe₂/MoTe₂lateral heterojunction has excellent photoelectric properties and is a strong candidate material for photodetectors.In Chapter 5,we not only give a brief summary and state the main research results of this thesis,but also look forward to the future work.