First-principles Study On Photoelectric Detection Of Monolayer 2H-MoSe₂

Since the graphene has been successfully peeled,the two-dimensional materials have gradually come to people’s eyes.The two-dimensional transition metal chalcogenides（TMDCs）has attracted the attention of many scholars because of TMDCS’s unique electrical and optical properties.As a member of TMDCs,MoSe₂ is widely used in optoelectronic devices,such as photodetectors.Research has shown that the performance of TMDCs is influenced by factors such as the number of layers and defects,and the intrinsic two-dimensional material optoelectronic properties need to be improved.Therefore,defect engineering is introduced to calculate the electronic structure and optical properties of monolayer MoSe₂,and the results can be used to prepare high-performance photodetectors.The main work of this paper is as follows:（1）The effect of doping Fe and Ag elements on the electronic structure and optical response of semiconductor phase（2H）MoSe₂,that is,to study the substitution doping in defect engineering.The results show that the electronic structures of Fe and Ag doped systems exhibit N-type semiconductor properties and metal properties,respectively.The doping system introduces more impurity bands near the Fermi level.Combining with the analysis of the density of states,it is found that the impurity bands are contributed by Fe-3d,Se-4p orbit and Se-4p,Mo-4d orbit.Within the entire visible light range,Fe and Ag effectively enhanced the optical response capacity of monolayer MoSe₂,and the Ag doped effect was better.（2）Study the effects of a single Se vacancy on the photoelectric properties of a monolayer 2H-MoSe₂,that is,the atomic vacancy in the defect engineering.The phonon spectra,energy bands,and density of states of nanosheets containing Se vacancies were calculated.In the direction of armchair,linear polarization photoelectric effect（LPGE）and circular polarization photoelectric effect（CPGE）were studied under different photon energies.The results show that the Se vacancy 2H-MoSe₂ is thermodynamically stable and has 0.38e V band gap.At the photon energy below 2.5e V,the CPGE of the intrinsic monolayer 2H-MoSe₂ is stably larger than its LPGE,and reaches the maximum at 2.7e V,which is attributed to the time reversal symmetry of elliptically polarized light.The CPGE of the Se vacancy 2H-MoSe₂ is steadily larger than the LPGE after photon energy 2.5e V.This is because the Se vacancy further destroys the spatial inversion symmetry of the material,and can be explained by electronic transitions between price bands and guides.（3）The optical response of armchair and zigzag structured devices with intrinsic monolayer 2H-MoSe₂ was studied.The photovoltaic detector based on a monolayer of MoSe₂ structure is proposed.The optical response is controlled by the sensitivity of zigzag structure to elliptically polarized light,and the sensitivity of armchair structure to bias voltage.The results show that the optical response value and extinction ratio of the armchair structure photodetector are improved under 0.1V small bias voltage,and the optical response peak appears at the photon energy of 1.6e V,corresponding to the ultraviolet wave band.The other better results correspond to the green,red and orange light in the visible light.In the zigzag structure photodetector,the optical response generated by elliptically polarized light appears at 2.7 e V,which corresponds to the blue light in the visible spectrum.In addition,the zigzag photodetector also has good light response at the corresponding energy points of orange,green and red light.