Thermal Phonon Wave Effects in Superlattice Heat Conduction: Thermal Band Gaps and Phononic Quantum Wells

An accurate determination and precise control of thermal conduction at the nanoscale necessitate consideration of the wave and particle nature of thermal phonons simultaneously. However, current formulations are unable to combine both phonon transport phenomenon. In this talk, we incorporate the wave nature of phonons by considering that coherent interference of thermal phonons leads to two distinct wave phenomena – thermal band gaps and phononic quantum wells. We elucidate the particle formalism by employing a rigorous boundary scattering theory, extended from the Beckmann-Kirchoff formalism, to account for interface features, phonon coupling and shadowing effects, for predicting thermal phonon transport across an interface. We also investigate the conditions governing the wave effects and analyze their impact on thermal transport in Si-Ge, SiGe alloy and III-V semiconductor superlattices. A thorough spectral phonon transport analysis combining particle and wave effects paves the way for a fundamentally new approach for thermal manipulation. Analogous to photonic and electronic revolutions, thermal phonon wave effects can open new paradigms in rational thermal material and device design in the fields of optoelectronics, thermoelectrics and microelectronics.