Collective Behavior in Phonon Thermal Transport on Semiconductor Devices

The Kinetic-Collective model is presented to calculate the thermal conductivity of several semiconductor materials. This model is an alternative method to Callaway-like models to account for the role of normal collisions in the thermal transport. Its more rigorous treatment of the collision term in the Boltzmann Transport Equation provides a more accurate prediction of thermal conductivity. Within this model, the thermal conductivity is explained as a combination of two phonon behaviors leading to a kinetic and a collective phonon flux with significantly different expressions. The main difference between these regimes of behavior is that, in the kinetic one, relaxation-time depends on the modes independently while in the collective term relaxation-time is the same for all phonons. From this approach, very accurate thermal conductivity predictions for bulk and nanostructured samples of group IV semiconductors are obtained.