Intrinsic to extrinsic phonon lifetime transition in a GaAs-AlAs superlattice

TL;DR

This study measures and analyzes phonon lifetimes in a GaAs-AlAs superlattice, revealing a transition from intrinsic to extrinsic scattering dominance around 640 GHz and highlighting the role of interface roughness.

Contribution

It provides experimental measurements of phonon lifetimes at two frequencies and compares them with first-principles calculations, improving understanding of phonon scattering mechanisms in superlattices.

Findings

At 296 K, intrinsic and extrinsic scattering contribute equally at 320 GHz.

At 640 GHz, extrinsic effects dominate phonon lifetime.

Theoretical models predict the transition frequency but overestimate it.

Abstract

We have measured the lifetimes of two zone-center longitudinal acoustic phonon modes, at 320 GHz and 640 GHz respectively, in a 14 nm GaAs / 2 nm AlAs superlattice structure. By comparing measurements at 296 K and 79 K we separate the intrinsic contribution to phonon lifetime determined by phonon-phonon scattering from the extrinsic contribution due to defects and interface roughness. At 296 K, the 320-GHz phonon lifetime has approximately equal contributions from intrinsic and extrinsic scattering, whilst at 640 GHz it is dominated by extrinsic effects. These measurements are compared with first-principles lattice dynamics calculations of intrinsic and extrinsic scattering rates in the superlattice. The calculated room-temperature intrinsic lifetime of longitudinal phonons at 320 GHz is in agreement with the experimentally measured value of 0.9 ns. The model correctly predicts the transition from predominantly intrinsic to predominantly extrinsic scattering; however the predicted transition occurs at higher frequencies. Our analysis indicates that the 'interfacial atomic disorder' model is not entirely adequate and that the observed frequency dependence of the extrinsic scattering rate is likely to be determined by a finite correlation length of interface roughness.