Experimental observation of ballistic to diffusive transition in AlN thin films
Abstract
Bulk AlN possesses high thermal conductivity due to long phonon mean-free-paths, high group velocity, and long lifetimes. However, the thermal transport scenario becomes very different in a thin AlN film due to phonon-defect and phonon-boundary scattering. Herein, we report experimental observation of ballistic to diffusive transition in a series of AlN thin films (1.6 - 2440 nm) grown on sapphire substrates. The ballistic transport is characterized by constant thermal resistance as a function of film thickness due to phonon scattering by defects and boundaries. In this transport regime, phonons possess very small group velocities and lifetimes. The lifetime of the optical phonons increases by more than an order of magnitude in the diffusive regime, however, remains nearly constant afterwards. Our study is important for understanding the details of nano and microscale thermal transport in a highly conductive material.
Keywords
Cite
@article{arxiv.2409.14328,
title = {Experimental observation of ballistic to diffusive transition in AlN thin films},
author = {Md Shafkat Bin Hoque and Michael E. Liao and Saman Zare and Zeyu Liu and Yee Rui Koh and Kenny Huynh and Jingjing Shi and Samuel Graham and Tengfei Luo and Habib Ahmad and W. Alan Doolittle and Mark S. Goorsky and Patrick E. Hopkins},
journal= {arXiv preprint arXiv:2409.14328},
year = {2024}
}