Synergistic Effects of Phonon Anderson Localization and Resonance in Si/Ge Superlattice Nanowires: Toward Lower Thermal Conductivity

Abstract

Manipulating heat transfer in thermal functional materials is of great importance, with wide applications such as thermoelectrics, thermal management devices, thermal insulating materials, and thermal diodes. To influence the phonon propagation in nanostructures, Anderson localization and phonon resonance are commonly employed methods due to the wave nature of phonons. In this study, we investigate the thermal transport in Si/Ge superlattice nanowires incorporating aperiodic interfaces and resonance pillars, wherein Anderson localization and phonon resonance are simultaneously introduced. In superlattice nanowires with aperiodic interfaces, the thermal conductivity initially increases with size and then decreases, suggesting the occurrence of phonon Anderson localization when sufficient random interfaces are present. The reduction in the thermal conductivity caused by Anderson localization reaches 55.6% at a nanowire length of 109 nm. On the other hand, introducing phonon resonance via resonance pillars to the superlattice nanowires results in a reduction of 39.7% at the same nanowire length. The coexistence of Anderson localization and phonon resonance leads to a much more significant reduction of 62.6% in the thermal conductivity. Furthermore, we reveal that Anderson localization predominantly affects phonons in the medium-low frequency range (1.5–3.5 THz), while phonon resonance impacts phonons at low frequencies (0–2.2 THz). These two methods collaboratively impede phonons with different frequencies, thereby achieving exceptionally low thermal conductivity. Our findings provide new insights into regulating the thermal conductivity of materials through the wave nature of phonons.