Study On The Optical And Electronic Properties Of Van Der Waals Heterostructures

Two-dimensional?2D?materials have achieved great success in preparation and application,but as the research progressed,single 2D materials often has limitations in application.Therefore,the researchers set their sights on van der Waals heterostructures,it is composed of two 2D materials stacked vertically,and rely on the combination of weak van der Waals forces between two 2D materials.Compared with traditional bulk material heterojunctions,it has less strict requirements for lattice matching between materials.In this way,it is possible to find new physical properties by constructing variety of van der Waals heterostructures.Van der Waals heterostructures can often combine the excellent properties of each monolayer,which is extremely beneficial for developing new applications,Therefore,the work of exploring heterostructures becomes more meaningful.All first-principles calculations in this work are based on density functional theory and are performed by the VASP simulation software package.This thesis focuses on the regulation of the electronic and optical properties of several 2D transition metal dichalcogenides?TMDs?and their van der Waals heterostructures.The research contents include structural parameters,stability,phonon spectrum,band structures,density of states,band arrangement,and average electrostatic potentials,charge distribution and transfer,absorption spectrum,etc.These results can provide theoretical support for finding and designing new optoelectronic devices.The research results are as follows:1.We calculate the lattice constants,band structures,density of states,and optical properties of the TMDs WS₂,WSe₂,and WTe₂monolayers,and the effects of spin orbit coupling on their band structure is considered.The effects of biaxial strains on the structure parameters,electronic properties,and optical properties of WS₂,WSe₂,and WTe₂ monolayers are studied,Finally,analyzing the mechanism of the influence of biaxial strains on the electronic structure of the monolayers.2.The six possible high-symmetry stacking methods are considered for As/MoTe₂ heterostructures,and are determined their stability by combining energy and phonon spectra.The HSE06 hybrid functional was used to analyze the projected band structure,electronic density of states,and optical properties.The results show that the As/MoTe₂ van der Waals heterostructures has a moderate direct band gap of1.504 e V and exhibits a type I band alignment,and have appreciable adsorption of visible light and ultraviolet light.Then the charge distribution and transfer of the heterostructures are analyzed.Finally,we also consider the effects of different biaxial strains and interlayer distances on the electronic and optical properties of arsenene/MoTe₂ heterostructure,and find the electronic and optical properties can be effectively modulated by biaxial strains and interlayer distances.3.We first calculate the structure and electronic properties of SnS₂ and InN monolayer.Different atomic stacking methods are considered for InN/SnS₂heterostructures.The most stable structure is found by comparing the formation energy.The projected band structure,electron density,band arrangement,and charge analysis are analyzed.The results show that the InN/SnS₂ heterostructures presents an indirect band gap with a type II band alignment,which facilitates the separation of electrons and holes.The optical properties of the InN/SnS₂ heterostructures are also calculated.Proper band gap,type II band alignment,large band shift,and excellent light absorption provide opportunities for InN/SnS₂ heterostructures to form efficient solar cells,where InN is available as an electron donor,SnS₂ is used as an electron acceptor.4.In this work,the effects of the electronic and optical properties of the InN/PtX₂?X=S,Se?van der Waals heterostructures are studied by first-principles calculations.The most stable InN/PtX₂?X=S,Se?heterostructures have an indirect band gap and a type II band alignment with lager band offsets,which is very beneficial for the separation of photo-generated electron-hole pairs and improve solar energy conversion efficiency.Moreover,the InN/PtX₂?X=S,Se?heterostructures has obvious light absorption from visible light to ultraviolet light.The electronic and optical properties of the InN/PtX₂?X=S,Se?heterostructures can be adjusted by applying a biaxial strain,the excellent ability of the InN/SnS₂ heterostructures to modulate the electronic and optical properties provides an opportunity for the application of optoelectronic devices.