Theoretical Study On Photogalvanic Properties Of Two-dimensional Nanomaterial WSe₂

In recent years,new two-dimensional nanomaterials have shown increasing application potential in many fields.Graphene is favored by scientific researchers due to its high carrier mobility,excellent thermal conductivity and other properties;however,since graphene has a relatively low light absorption rate and zero bandgap,which limits Its further application in the field of optoelectronic devices.Two-dimensional transition metal chalcogenides(TMDCs)have a relatively wide bandgap and perfect physical properties in experimental and theoretical research compared with graphene.As an important member of TMDCs,ungsten diselenide(WSe₂)has a relatively large bandgap,who is the first to be verified at the same time Semiconductors with N and P-type conductivity characteristics exhibit excellent electrical properties.At the same time,WSe₂ is found to have good light absorption capacity,strong corrosion resistance and other characteristics in experiments,which has been extensively studied in many fields.In this paper,first-principles calculation method is used to carry out theoretical research on the photoelectric properties of 2H-WSe₂ with stable phase.The specific research content and results are as follows:(1)We had theoretically established the Zigzag and Armchair-type monolayer 2H-WSe₂photodetector models,and calculated the photogalvanic effect(PGE)of the two configurations under the illumination of linearly polarized light and a certain bias voltage range.Both of them can produce a larger photoresponse in almost the entire visible light range,indicating that the monolayer 2H-WSe₂has a strong broadband response capability.In addition,both of them can obtain the maximum photoresponse at a photon energy of 2.8e V under all bias voltages.We had further explained this phenomenon by analyzing the electronic band structure and density of states of the monolayer 2H-WSe₂.(2)The influence of substitutional doping on the photogalvanic effect of monolayer 2H-WSe₂was investigated.Based on the experimental results obtained by doping the monolayer 2H-WSe₂,we studied the photogalvanic effect of Nb,Ni,and Ti atoms respectively doped with W atoms from the perspective of theoretical calculations.The substitutional doping of these three elements can effectively improve the photoresponse of the monolayer 2H-WSe₂,the Ni system has the best performance,which has a tendency to transform into metal;it can obtain the largest photoresponse and the highest polarization sensitivity under zero bias voltage and the irradiation of linearly polarized light.These results indicate that the Ni-doped monolayer 2H-WSe₂ system can be considered as a high-quality material for photodetectors.In addition,we further investigated the regulation mechanism of substitutional doping on the photoelectric effect of monolayer 2H-WSe₂.(3)The effect of vacancy defects on the optical and electrical properties of monolayer 2H-WSe₂was investigated in the physical environment of zero bias voltage.We compared the change trend of the electron band structure and the density of states of the monolayer 2H-WSe₂ after the vacant Se atom.We found that the conduction band and valence band of the monolayer 2H-WSe₂have a tendency to move to the high-energy region after the vacant Se atoms,but the semiconductor characteristics are still maintained.The vacant Se atoms can effectively enhance the photoelectric effect of the monolayer 2H-WSe₂ in the entire visible light range,which can achieve maximum photoresponses at 2.8e V and 3.2e V respectively.This excellent performance is mainly attributed to the impurity level introduced by the vacancy,which becomes a bridge for electronic transition.We analyzed the total density of states of the monolayer 2H-WSe₂ containing Se vacancies,which further verifying our results.