Effect Of Twin Interfaces On Thermal Conductivity Of Superlattice

With the rapid development of science and technology,the scale of micro-nano electronic equipment has been gradually reduced to the nanometer level,and its heat dissipation problem has seriously restricted its efficiency and lifespan.In order to solve the problems of energy reuse and device heat dissipation,nanomaterials have developed rapidly in recent years.Silicon(Si),Germanium(Ge)are among the best materials for microelectronics/optoelectronics and photovoltaic device applications,thus becoming the cornerstone of the semiconductor industry.Silicon germanium nanostructures have been increasingly used in many fields,and their thermal transport properties have attracted extensive attention.As a typical nanomaterial,Si/Ge superlattice,has a good application prospect in the field of thermoelectric conversion due to its high interface density which can effectively reduce thermal conductivity.Therefore,it is very important to reveal the different transport mechanisms of phonons in interfacial superlattices to regulate the thermal conductivity of nanomaterials.At present,the effects of smooth interface,interface roughness or interface geometry on thermal transport in superlattices have been widely studied.Therefore,in this paper,the thermal conductivity of the twinned interface silicon/germanium(Si/Ge)superlattice was investigated by non-equilibrium molecular dynamics(NEMD)method simulations and compared with the twinned interface superlattice.It is found that:(1)In the single-interface temperature distribution,the twin interface has a larger temperature gradient.At the same time,the interface thermal resistance of the twinned interface structure is larger than that of the untwinned interface structure,which are 5.6 and 4.4 GW m-2 K-1,respectively.(2)With the increase of the period length,the thermal conductivity of the two has different trends.In terms of the twin-free interface structure,the thermal conductivity first decreases and then increases with the increase of the period length.It is because phonon transport changes from coherent transport of waves to incoherent transport of particles.The thermal conductivity of the twin interface structure increases slowly with the increase of the period length.Through the analysis of the phonon participation rate,dispersion relationship and phonon group velocity,the twin interface structure destroys the coherent transport to a certain extent.The phonon localization effect is obvious and the phonon group velocity is reduced.(3)The thermal conductivity of both structures increases with the length of the system,which is due to the existence of the size effect.However,the thermal conductivity of the twinned interface structure is significantly lower than that of the untwinned interface structure,which is attributed to the stronger phonon scattering at the twinned interface through the analysis of the spectral heat flow.(4)As the temperature increases,the Umklapp scattering of phonons is enhanced,resulting in a similar decreasing trend of thermal conductivity of both,but the temperature dependence of the twin interface structure is weaker,which is due to the twinning The interface scatters the long phonon mean free path phonons that contribute to thermal conduction.The results of the phonon density of states show that the twinned interface structure significantly suppresses the number of high-frequency phonons.In order to further explore the underlying mechanism of the twin interface,we constructed Si/Ge superlattices with different twin interface distributions,namely uniform interface and random interface superlattice.The study found that:(1)Compared with the uniform interface superlattice,the thermal conductivity of the random twinned interface structure was lower by calculating the relationship between thermal conductivity and period length,which was attributed to the phonon scattering of the random interface superlattice.And the phonon localization effect is stronger.(2)With the increase of temperature,the thermal conductivity of random twinned interface superlattice relative to homogeneous twinned interface superlattice decreased by 39.97%,37.84%,32.06%,29.88% and21.64% from 200 K to 600 K,respectively,which is due to the Umklapp scattering gradually replacing the scattering at the twin interface to take the dominant role,resulting in a gradually smaller thermal conductivity difference between the two.