Study On The Optical Properties Of Layered Transition Metal Dichalcogenide

Since researchers made breakthroughs in graphene in 2004,other two-dimensional materials,such as black phosphorus,hexagonal boron nitride,transition metal disulfide,have also been attracted widespread attention.Graphene remains by far the one of the most researched two-dimensional materials due to its excellent optical,electrical and thermodynamic properties.However,graphene also has some shortcomings in some aspects.Single-layer transition metal disulfides provide complementary but different properties to graphene.For example,the single-layer transition metal disulfide has a direct band gap of about 2 e V,absorbs about 20%in the visible light range,and have unique optical properties such as photoluminescence.Nevertheless,the optical properties of transition metal disulfides are still not perfect.In this paper,some simple and flexible optical structures are designed for the transition metal disulfide.The light absorption and polarization characteristics are calculated numerically,and the internal mechanism is analyzed.We systematically studied the modulation effects of the geometric parameters of the structure,the angle of incident light,and polarization,on the optical characteristics.The specific researches of this paper is as follows:（1）Absorption characteristics of multilayer MoS₂/WS₂-dielectric structures:By using the transfer matrix method,the absorption properties of multilayer dielectric structures composed of molybdenum disulfide（MoS₂）and tungsten disulfide（WS₂）in the visible light range have been investigated theoretically and numerically.The two-dimensional materials are treated as surface conductivity with infinitesimal thickness.The results show that the absorptance can be adjusted by the angle and polarization direction of the incident light,the number and thickness of the dielectric layer.Under the best choice of these factors,when the single layer of MoS₂or WS₂covers the silicon surface,the absorption rate are increased to approximately49.7%and 48.9%,respectively.（2）Silver nano-grating absorption characteristics covered with transition metal disulfides:The optical absorption characteristics of the sub-wavelength metal grating composed of MoS₂are calculated by the finite element method.The results show that the structure has a perfect absorption peak at 2.415 e V when the thickness,gap of the silver strip and the grating period are 104 nm,65 nm and 270 nm,respectively.Compared with the grating without two-dimensional materials,the absorptance is increased by 32%.In addition,these absorption peaks are also offset by the modulation of grating geometric parameters.Instead WS₂of MoS₂,the absortance is also studied and the results were similar to those of MoS₂.（3）Polarization characteristics of the transmitted light in the planar medium structure of two-dimensional materials:The transfer matrix method is used to calculate the phase difference of the transmitted lights between the TE and TM modes of the electromagnetic waves at different incident angles in the planar medium structures with MoS₂、WS₂and/or graphene inserted.In the presence of the interfacial currents from two-dimensional materials,the phase difference oscillates near the zero point.It indicates that when the linear polarized light is incident in the planar medium structure including the two-dimensional material,the transmitted light may be converted into elliptically polarized light and linearly polarized light,and is modulated by the angle of incidence.The phase characteristics of TE and TM modes in graphene-based structures also depend on the number of graphene layers,Fermi levels,and broadening width.This can be employed to obtain the number of graphene layers experimentally without contact.In this paper,the micro-nano optical structures are designed based on two-dimensional materials such as transition metal disulfides.The reflection,transmission,absorption,and polarization characteristics of these structures were simulated and calculated.These studies will broaden the application of two-dimensional materials in optoelectronic fields such as solar cells and phototransistors.