Investigation of wave interference effect in Si/Ge superlattices with interfering Monte Carlo method

The recently proposed Interference Monte Carlo (IMC) method is a mesoscale particle simulation method that is capable of modeling wave interference effect in addition to phonons' particle behavior. Using the IMC, wave interference effect, which leads to a linear increase in thermal conductivity as the number of periods of superlattices increases, has been confirmed in Si/Heavy Si superlattices. Such a trend was also experimentally observed in AlAs/GaAs superlattices and has been regarded as the evidence of the coherent phonon heat conduction. In this work, wave interference effect in 1D Si/Ge superlattices at 300 K is investigated using the IMC method. First, the IMC method is further improved and validated with Molecular Dynamics simulations. It is then used to compute thermal conductivities of both periodic and aperiodic Si/Ge superlattices with fixed period length but varied number of periods. It is found that the nearly linearly increasing trend is present in both cases. However, this increasing trend is not caused by the wave interference, but is rather caused by the ballistic transport of low-frequency phonons due to their high transmission rates. Hence for Si/Ge superlattices with an average period length of 20 nm, the wave interference effect plays an insignificant role even when the interfacial scatterings are perfectly specular.