A hybrid model for thermal transport in Si nanostructures from first principles

Phonon scattering plays an i mportant role in limiting thermal conductivity. Analytical expressions used in the Callaway model to calculate normal (N) and umklapp (U) scattering serve as a valuable tool to study heat transfer. However, calculations using these empirical scattering rates lack predictive power and transferability for a range of temperature (T) relative to the more computationally expensive iterative numerical approach. We present a hybrid approach where we calculate N and U rates from the first principles and implement them in the Callaway model for the calculation of thermal conductivity in silicon (Si) over a wide T range of 10K to 425K. In addition, the model accurately captures momentum-dependent boundary roughness scattering, which is particularly important in nanostructures. Conductivities calculated using our hybrid approach are in good agreement with measured values of natural and isotopically pure Si over the entire range of T without any adjustable parameters. A central feature of this approach is that it captures the interaction between internal and boundary conditions more accurately than some iterative approaches while being much more computationally efficient. The approach we presented can be used in future thermal transport studies of nanostructures.