First-principles Study Of Na Doped MoS₂ And MoS₂/ZnO Heterojunction

At present,integrated circuits have played an important role in various industries.The continuous development of integrated circuits cannot be separated from the contributions of two-dimensional ultra-thin materials.In 2004,the first graphene monolayer was exfoliated.Due to its excellent optical,electrical and mechanical properties,it has important application prospects in materials,micro-nano processing,energy,etc.,and also promoted the rapid development of two-dimensional materials.However,the intrinsic graphene is a zero band gap,and the switching power supply current is small.It is necessary to adjust the band width by changing the stress and increasing the voltage,so as to broaden its application in photoelectric devices.In recent years,graphene-like materials have entered people's field of vision.As a typical representative of graphene-like materials,2-d transition metal sulfur compound MoS₂ is a direct band-gap semiconductor with a band gap of about 1.9eV.The absorption window is in the visible region with high absorption efficiency.ZnO has a wide band gap?about 3.4eV?,and the absorption window is in the ultraviolet region,but the absorption efficiency is low.By stripping MoS₂ and ZnO into a single layer and forming a heterojunction,their respective advantages can be effectively brought into play and complementary performance can be achieved.In addition,MoS₂ can be modified by doping to obtain properties more conducive to its wide application.In this article,we adopted the first principles calculation based on density functional theory and analysis of the single-layer MoS₂ doped with different concentrations of Na element,the influence of different Na doping concentration for the system are discussed,and then constructs the mixed with different concentrations of Na MoS₂ and ZnO heterojunction,analyzed the different heterojunction stacking structure,layer spacing,Na concentration of doped heterojunction structure,the influence of the electronic properties and optical properties,the conclusion is as follows:Firstly,Na elements were doped into the monolayer MoS₂ by displacement doping.A3×3×1 supercell structure was selected,and one,two and three Na atoms were added,with doping concentrations of 11%,22%and 33%,respectively.Meanwhile,the influences of bond lengths and bond angles of the system at different concentrations were discussed.The results show that with the increase of doping concentration,the band width of the structure shows a trend of gradually decreasing,which makes the transition of electrons easier and the conductivity further improved.It can be seen from the state density and partial wave state density that with the increase of doping concentration,the energy level density in the system is larger,and it is mainly contributed by the 4d orbital of Mo atom and the 3p orbital of S atom.With the increase of doping concentration of Na atom,the contribution of 3s orbital gradually increases.In the optical properties section,it can be clearly seen that with the increase of Na atomic concentration,the static dielectric constant of the system increases,and the lower the energy required for the absorption rate to reach the peak,the lower the energy required for the electron transition.At the same time,we conclude that the conductivity of the doped system is higher than that of the eigensystem by comparing the integral of the real part and the imaginary part of the complex conductivity.Then,the Na doped monolayer MoS₂ and ZnO formed heterojunction to further explore their properties.Firstly,the effects of different stacking forms and heterojunction spacing on the system stability are discussed.After structural optimization,we obtained that when the layer spacing was 3.3a and the stacking mode was 2H,the system was relatively stable.Based on the stable heterojunction structure,the energy band arrangement,density of states and optical properties of MoS₂/ZnO system were analyzed.We found that the gap gap between the energy band arrangement of the two layers of single-layer materials doped with Na elements is getting larger and larger,which is conducive to the application of photovoltaic devices.In terms of the state density,the orbital contribution of the atom can also be seen,which is mainly contributed by 4d orbital of Mo atom,3p orbital of S atom,3d and 4s orbital of Zn atom,and 2s and 2p orbital of O atom.In terms of optical properties,as the doping concentration continues to increase,the energy of the optical absorption rate reaching the absorption peak at the time of high doping Na atoms decreases.In both the real and imaginary parts of the conductivity,it can be seen that the doping of Na atoms makes the electron transition of the system easier,and the system properties after doping are obviously better than the eigenvalue.