| Wide band-gap semiconductors have broad application prospect in the field of power electronics in the future due to the large band-gap width and high breakdown field strength.In addition to ultra-wide band-gap and high breakdown field strength,gallium oxide possesses the advantages of high thermodynamic stability,low cost and can be prepared in large quantities,which is considered as a key material to solve the core composition problems of high-power and high-frequency devices and reduce energy loss in the future.Additionally,the application of composites composed of gallium oxide and materials with excellent thermal and optoelectronic properties in power and optoelectronic devices has attracted much attention.However,the development of electronic devices to the direction of miniaturization,integration and high density brings about significant thermal effect problems,which to a large extent limit the application and development of the new generation of semiconductor gallium oxide in future power devices.Therefore,it is necessary and urgent to explore the thermal transport properties and phonon mechanism of gallium oxide and its composites,which is crucial to fully understand the thermal properties of wide band-gap semiconductor gallium oxide and accelerate its application in high voltage,high power and high frequency devices in the fields of information communication,aerospace and rail transit.In view of the problems of the thermal properties are not thoroughly investigated,the heat conduction mechanism is not clear enough and the basic calculation model of gallium oxide is missing in the existing research work,this work establishes classical interatomic potential functions and machine learning interatomic potential functions of gallium oxide by empirical fitting method and first-principles combined with machine learning method.The intrinsic thermal transport properties of gallium oxide are investigated adopting molecular dynamics(MD)methods,and the action rules of different factors on the heat transport characteristics at the interface of gallium oxide matrix composites are revealed.The microscopic mechanism of phonon transport inside gallium oxide and the phonon action mechanism between gallium oxide and the interface of composites are clarified.The specific research content and main research results of this work are as follows:(1)A empirical potential model of gallium oxide is established by using classical model,and the corresponding potential function parameters are fitted.The results show that the fitted potential function parameters can accurately describe the lattice parameters and space group structure of gallium oxide,and accurately predict the elastic constants,bulk modulus,Young’s modulus,shear modulus and Poisson’s ratio of gallium oxide.At the same time,it is found that the fitted parameters of the empirical potential function can well predict the dispersion relationship of the phonons of gallium oxide,especially the low frequency phonons.The obtained empirical potential parameters are applied to classical MD to investigate the dynamic characteristics of gallium oxide under the effect of temperature.It is found that the atomic distribution characteristics of gallium oxide at different temperatures are in good agreement with the experimental measurements and theoretical calculations.The thermal conductivity of gallium oxide has been calculated by means of equilibrium molecular dynamics method.It is found that the thermal transport properties of gallium oxide show significant anisotropy.(2)Gallium oxide/graphene heterojunction interface models are constructed,and the thermal resistance of gallium oxide/graphene heterojunction are evaluated using the transient thermal pulse method based on the MD.The influence of various factors on the thermal resistance of the interface and the potential phonon mechanism are explored.It is found that a(100)>(010)>(001)relationship exists in the thermal resistance of the gallium oxide and graphene heterojunction interfaces,and the underlying mechanism is analyzed by the density of phonon states,the(001)interface possesses the most intense phonon coupling.The effects of temperature,vacancy and graphene hydrogenation on thermal transport properties of the heterojunction interface are investigated.It is found that increasing temperature,vacancy concentration and graphene hydrogenation could enhance the phonon coupling between the interface and improve the interfacical thermal transport capacity effectively.Compared with the vacancy in gallium oxide,the vacancy in graphene can reduce the thermal resistance of heterojunction interface more effectively.Moreover,the results also show that the hydrogenation of graphene can significantly improve the energy transport efficiency between gallium oxide and graphene.The thermal resistance of the interface between gallium oxide and graphene can be reduced by 58.77%when the hydrogenation ratio is 5%.(3)The machine learning potential moment tensor potential(MTP)of gallium oxide is constructed,which can accurately describe the energy and force of atoms in gallium oxide and accurately predict the phonon dispersion relationship of gallium oxide.Combined with the Boltzmann transport equation,the lattice thermal conductivity of gallium oxide is calculated using MTP,and the mechanism of phonon heat conduction is analyzed.The results show that the optical phonons in gallium oxide play an important role in the thermal conductivity,and the contribution of optical phonons to the thermal conductivity is mainly from 0-6THz low frequency optical phonons.In addition,the obtained MTP is applied to the classical MD method to calculate the thermal conductivity of gallium oxide in a large-scale system,and the thermal transport characteristics of gallium oxide under the scattering of phonons of all orders were evaluated.It is found that due to the limitation of classical theory and the scattering of high order phonons,the thermal conductivity of gallium oxide calculated by MD method is lower than that calculated by BTE method,but it still shows significant anisotropy and the two are in good agreement with the experimental values.The comprehensive evaluation results of gallium oxide potential function show that the MTP developed in this work has realized the large-scale and efficient calculation of β-Ga2O3 heat transport characteristics,and shows the best performance in the calculation efficiency and reliability of the results. |
