Tuning The Electronic And Magnetic Properties Of 2H-WSe₂ And WSe₂ Monolayer Through Functional Elements Doping By First-principles Calculations

The layered transition metal chalcogenide has become a very popular material recently,owing to its unique layered structure,large band gaps as well as excellent physical and chemical properties.WSe₂,as a typical representative of the layered transition metal chalcogenide,not only has good tribological properties but also exhibits outstanding semiconductor properties.In particular,it exhibits an intriguing transition from an indirect to direct gap when the bulk material exfoliated into a single layer,which makes its great potential applications in the electrical,optical,energy storage and catalytic fields.More importantly,now the development of silicon-based devices is approaching their limits,the two-dimensional WSe₂ monolayer with its larger intrinsic direct bandgap,the surface without hanging bonds,high carrier mobility and no short channel effect has become a new generation of semiconductor materials research focus.Chemical doping is one of the most simple and effective methods to regulate the electronic structure and improve the carrier mobility,which is successfully applied in the similar material MoS2.It can not only change the carrier of the material,improve the carrier transport properties or intrude magnetic moments in the semiconductor,but also promote the material transformation from the semiconductor to metal or semi-metal.In fact,transition metal cations and nonmetallic anions doped 2H-WSe₂ and monolayer WSe₂ have been shown to be effective,but further investigation should be carried out to disclose the mechanism of tuning the electronic and magnetic properties in WSe₂.In addition,researchers have paid more attention to codoping method in recent years,so the topic of the codoping on WSe₂ also need uncover.Based on this,the mechanisms of the stability,structural,electronic and magnetic properties of transition metal and nonmetallic doped 2H-WSe₂ and WSe₂ monolayer were studied by density functional theory.Moreover,metallic and nonmetallic codoping in the most thermodynamically favourable systems was also studied to tune the electronic and magnetic properties in WSe₂ monolayer.On the one hand,we calculated the stability,structural,electronic and magneticproperties of the fifth subgroup metals?V,Nb,Ta?,3d transition metals?Sc,Ti,Cr,Mn?and nonmetals?C,N,O,F?doped 2H-WSe₂.It shows that the structures of doped systems are almost unchanged.Importantly,V,Nb,Ta,Sc,Ti,N-doped and F-intercalated WSe₂ are p-type doping,which facilitates the semiconductor to metal transition.Cr and O doping do not alter the semiconducting nature of WSe₂,but the bandgap is adjusted.C doping can introduce some impurity bands between the band gap,providing more possibilities for the electronic transition.Mn atoms doped WSe₂ shows semi-metallic characteristics with a total magenetic moment of 0.96 ?B.On the other hand,we investigated the structural,electronic and magnetic properties of the fifth subgroup of metals?V,Nb,Ta?and the halogen atom?F,Cl,Br,I?doped WSe₂ monolayer.Further,the effect of F,Nb-codoping was studied to tune electronic and magnetic properties of WSe₂ monolayer.There are different degrees of small distortion induced by the dopants,and the co-doped structure is slightly larger.Electronic and magnetic properties analysis showed that F and I doping introduce 0.90?B and 0.88 ?B magnetic moments,respectively,and the systems exhibit semi-metallic behavior.Cl,Br and V,Nb,Ta doping are n-type and p-type doping methods respectively,and they exhibit metallic behavior.Interestingly,F,Nb-codoped WSe₂ monolayers are nonmagnetic owing to the completely symmetry of energy bands and the density of states in the spin up and spin down channels,because of an extra electron provided by F and an additional hole offered from Nb cancelled each other.The systems still maintain the direct bandgap semiconductors,but the bandgap is apparently adjusted by the synergistic effect of F and Nb.