Phonon dynamic behaviors induced by amorphous interlayer at heterointerfaces

TL;DR

This study investigates how amorphous interlayers at heterointerfaces affect phonon behavior and thermal resistance, revealing mode conversions, oscillations, and methods to optimize interface morphology for better heat conduction.

Contribution

It provides new insights into phonon mode conversions and oscillatory transmission behaviors caused by amorphous interlayers, and demonstrates interface optimization techniques to reduce thermal resistance.

Findings

Amorphous interlayer impedes phonon transport and causes mode conversions.

Phonon transmission oscillates with interlayer thickness due to multiple scattering.

Re-crystallization via annealing reduces interfacial thermal resistance by ~21%.

Abstract

Interface impedes heat flow in heterostructures and the interfacial thermal resistance (ITR) has become a critical issue for thermal dissipation in electronic devices. To explore the mechanism leading to the ITR, in this work, the dynamic behaviors of phonons passing through the GaN/AlN interface with an amorphous interlayer is investigated by using phonon wave packet simulation. It is found the amorphous interlayer significantly impedes phonon transport across the interface, and leads to remarkable phonon mode conversions, such as LA$\rightarrow$TA, TA$\rightarrow$LA, and LA$\rightarrow$TO conversion. However, due to mode conversion and inelastic scattering, we found a portion of high-frequency TA phonons, which are higher than the cut-off frequency and cannot transmit across the ideal sharp interface, can partially transmit across the amorphous interlayer, which introduces additional thermal transport channels through the interface and has positive effect on interfacial thermal conductance. According to phonon transmission coefficient, it is found the ITR increases with increasing of amorphous interlayer thickness L. The phonon transmission coefficient exhibits an obvious oscillation behavior, which is attributed to the multiple phonon scattering in the amorphous interlayer, and the oscillation period is further revealed to be consistent with the theoretical prediction by the two-beam interference equation. In addition, obvious phonon frequency shifts and phonon energy localization phenomena were observed in the amorphous interlayer. Finally, to improve phonon transmission, the interface morphology was further optimized via the annealing reconstruction technique, which results in re-crystallization of the amorphous interlayer and the decrease of ITR by ~21% as L=2 nm.