Effects Of Doping And Vacancy Defects On The Electronic Structure And Photoelectric Effect Ofmonolayer 2H-Mo Te₂

Transition metal chalcogenides（TMDCs）are favored by researchers as an al Ternative to two-dimensional ma Terials due to their suitable layered structure,open band gaps,and excellent optical and electrical properties.As a member of the transition metal chalcogenide,Mo Te₂has a honeycomb structure like graphene,and is formed by the less van der Waals force between layers.In engineering,various methods can be used to prepare single-layer Mo Te₂.And its band gap width is far less than that of other members of the transition metal chalcogenide.It not only makes it widely used in two-dimensional ma Terials,but also has great application prospects in photoelectric de Tection.Therefore,based on the first principle,this paper improves the electrical and optical properties of 2H-Mo Te₂by using substitution doping and vacancy defects.The specific research is as follows:（1）The phonon spectrum,electronic structure and photoelectric effect of one Te atom,two Te atoms and one Mo atom vacancy defect in single-layer 2H-Mo Te₂have been studied.The intrinsic and three vacancy defect monolayer 2H-Mo Te₂have no imaginary frequency,indicating that the four structures have thermodynamic stability.Compared with the intrinsic 2H-Mo Te₂electronic band structure,the energy band structure of the three vacancy defects can reduce the band gap width,and the two Te atom vacancy defects can make the energy band of 2H-Mo Te₂directly pass through the Fermi energy level and change into metal properties.The photoelectric effect shows that when the irradia Ted photon energy is grea Ter than the band gap width（1.16 e V）of the intrinsic monolayer 2H-Mo Te₂,the three kinds of vacancy defects significantly increase the photocurrent of the monolayer 2H-Mo Te₂device.2Te vacancy is the most excellent.It not only obtains the maximum photocurrent,but also has multiple peaks in the whole calcula Ted photon energy range,and these peaks are generally grea Ter than the maximum photocurrent values of the other two vacancy defects.（2）The substitutional doping of Nb,Ti and W with Mo atoms was studied,and the energy band structures of intrinsic and substitutional doping were calcula Ted.The results show that the substitution doping makes the valence band and conduction band of 2H-Mo Te₂shift to the Fermi level,reducing the band gap of 2H-Mo Te₂,and the substitution of Nb atoms makes the energy band of 2H-Mo Te₂pass through the Fermi level,showing metal charac Teristics.The influence of the photoelectric effect of the four structural sys Tems is calcula Ted,which shows that the three substitutional doping can effectively improve the photocurrent of the single-layer 2H-Mo Te₂device.And Nb substitution doping has the best performance,obtaining the maximum photocurrent and extinction ratio.We further analyzed the microscopic mechanism of doping on the photoelectric effect of single-layer2H-Mo Te₂through electronic transmission spectrum.