Research On The Effect Of Interfacial Composition Diffusion On The Phonon Transport Across The Gan/aln Heterointerfaces

The gallium nitride(Ga N)with a wide band-gap,high electronic mobility velocity,high electronic saturation velocity,high critical breakdown electric field,high antiradiation ability,has vast potential applications in radio frequency and high power electronics.With continuous size reduction and integration promotion in Ga N electronic devices,a large amount of heat generated in these devices has seriously affected its reliability and performance.When the characteristic size of device is reduced to length scales on the order of the mean free path of heat energy carriers,the interface dominates energy transport.Ga N heterostructures widely exist in the Ga N devices.During the growth of Ga N heterostructures,the interfacial composition diffusion always occurs and has certain effect on interfacial thermal transport of heterostructures,which draw little attention.Using molecular dynamics and lattice dynamics,the effects of interfacial composition diffusion on interfacial thermal transport and phonon dynamic behaviors of Ga N/Al N heterostructure are systematically investigated in this thesis.Firstly,the nonequilibrium molecular dynamics is adopted to study the effect of three types of interfacial morphologies(ideal smooth interface,gradual composition interface and random composition interface)on interfacial thermal conductance of Ga N/Al N heterostructure.The results show that the interfacial thermal conductance of heterostructure with composition diffusion interface is significantly reduced and can be further modulated by changing the composition length.Secondly,interfacial phonon dynamic behaviors of different interfacial morphologies are studied by phonon wave packet simulation.It is found the observed phonon mode conversion and phonon localization in composition diffusion layer have significant influence on interfacial phonon transport.Simultaneously,the energy transmission coefficient of transverse and longitudinal phonons across different interfacial morphologies and composition diffusion lengths are obtained,which provides specific and exhaustive phonon mode information of interfacial phonon transport.The energy transmission coefficients of longitudinal phonons across composition interface are much lower than smooth interface due to the enhanced phonon scattering and phonon localization.However,the energy transmission coefficients of transverse phonons across composition interface are abnormally increased.It is because the enhanced phonon mode conversion in composition diffusion layer provides additional phonon channels and more energy can be transmitted.Finally,the effects of system temperature and structure size on interfacial thermal transport are further investigated.It is found the interfacial composition diffusion can relieve the temperature effect and size effect.The phonon density of states,frequency decoupled interfacial thermal conductance and frequency resolved temperature distribution are used to reveal the underlying mechanism.The thesis provides a theoretical reference for thermal management and device deign in Ga N electronics.