First-principles Calculations On Electron-phonon Scattering Limited Transport Properties Of Some Two-dimensional Materials

Since the discovery of graphene,two-dimensional?2D?layered materials have at-tracted much attention due to their peculiar electronic properties and wide application prospects.Especially the 2D geometry is very compatible with the state-of-art tech-niques used in current semiconductor industry.Therefore,2D layered materials will perform crucial roles in future design and productions of super thin electronic devices.Other than the excellent electronic properties,such as high carrier mobility and various topological properties,2D layered materials have attracted much attention also because of the various tuning methods that can greatly improve the performance,such as strain-s,external field and structure design.Among them,great attention has been drawn on studying the transport properties of 2D layered material.There are many physical mechanisms that induce the scattering of carriers and hence limit the transport ability of material,such as electron-electron interaction,lattice vibration?phonon?,dislocation and impurity etc.Consequently,it is very important to clarify the effects of differen-t scattering processes on the design of electronic devices and the tuning of electronic transport properties.At very low temperature,the scattering process brought by var-ious impurities is the dominant physical mechanism that limit the electronic transport ability.At room temperature,carrier transport in a semiconducting or metallic material is mainly limited by electron-phonon scattering.In recent years,much experimental and theoretical works focused on the carrier mobility of material,which is a key factor for e-valuating the performance of a device,has been done.Experimentally,it has been found that the carrier mobility of many new discovered two-dimensional materials is smaller than the mobility of graphene.However,applying mechanical strain and changing the substrate are most convenient methods to adjust the carrier mobility of 2D materials.Theoretically,semi-empirical models,such as deformation potential models and piezo-electric potential models,are often adopted to get the electron-phonon interaction matrix elements and hence the mobility limited by electron-phonon interaction.However,those semi-empirical models generally rely on empirical parameters and have certain limita-tions in practical applications.In order to make exact predictions to experiments,in this paper,we use density functional theory and density functional perturbation theory to obtain real electron-phonon interaction matrix elements that do not depend on any empirical parameters.However,it is still a formidable challenge to perform an ab initio calculation on the electron-phonon scattering limited resistivity.This is because very fine Brillouin zone samplings for b oth the electronic and phonon states are essential for getting a convergent result,which often implies an unaffordable computational burden.To circumvent such a prohibitive task,we adopt a Wannier interpolation technique to treat the summation of electronic and phonon wave vectors over Brillouin zone with high precision.Then,based on the Boltzmann transport theory,the iterative method and the Ziman resistivity formula are used to solve the electron mobility and hole mobility of the MoS₂ monolayer and the resistivity of plumbene.Firstly,we theoretically study the strain effect o n t he r oom t emperature mobility?RTM?of a n-type MoS₂ monolayer limited by electron-phonon scattering.Our numer-ical results indicate that the RTM along zigzag direction of such a 2D material can be efficiently mo dulated by a un iaxial te nsile st rain.Su ch an RT M,de noted as,has a sizable reduction?enhancement?as a moderate tensile strain is applied in a parallel?perpendicular?direction.For example,when the strain strength amounts to 7%,in the two distinct cases,in which the strain applied in x and y directions,differ from each other by roughly two times.In contrast,the RTM in armchair direction is not sensitive to a tensile strain.The underlying mechanism for such a strain effect on mobility is then analyzed in depth.We find that modifications of the band structure and the interaction between the conduction band electron and the longitudinal acoustic phonon brought out by a tensile strain play the key roles.Our results are obtained completely on the level of first-principles calculations,free from any empirical s implifications.Therefore,our above findings p rovide r eliable a nd d etailed i nformation f or e xperimentally m anipulating the RTM of a n-type monolayer MoS₂ by simply stretching the sample.Then,based on first-principles calculations and iterative solution of the Boltzmann transport equation,we theoretically study the RTM of a valence band hole in a MoS₂monolayer limited by electron-phonon scattering.The hole mobility obtained by us is26.0cm²(1^-1s^-11 at 300K.This is a value much closer to the experimental result(about40.0cm²(1^-1s^-1).In contrast,the semi-empirical estimate based on the deformational potential model in previous literature gave a value of 200.5cm²(1^-1s^-1,far away from the experimental data.By a detailed analysis,we find that unlike the case of conduction band electrons,the intervalley scattering realized by longitudinal acoustic phonons plays a dominant role in influencing the hole mobility.And this is the main reason for the deformation potential model failing to give a quantitative estimate of the hole RTM in MoS₂-ML.Finally,we use iterative method and Ziman resistivity formula to study the temper-ature dependence of electron-phonon limited resistivity in high buckled plumbene.We find that the intrinsic resistivity of the plumbene is proportional to temperature at the high-temperature limit when we use the iterative method and Ziman resistivity formula in double-approximation.The results given by the Ziman resistivity formula without double-approximation deviate significantly from the linear temperature dependence.After further analysis,we find that the Ziman resistivity formula without double-ap-proximation requires a larger Fermi shell,due to the Fermi smearing effect of phonons,in which Van Hove singularity of electronic density of states exists which brings about nontrivial electron-phonon scattering.Thus,the Ziman resistivity formula cannot accu-rately describe the electron-phonon limited resistivity of some two-dimensional layered metal materials,e.g.high-buckled plumbene.