Experimental observation of ballistic to diffusive transition in AlN thin films

作     者：Hoque, Md Shafkat Bin Liao, Michael E. Zare, Saman Liu, Zeyu Koh, Yee Rui Huynh, Kenny Shi, Jingjing Graham, Samuel Luo, Tengfei Ahmad, Habib Doolittle, W. Alan Goorsky, Mark S. Hopkins, Patrick E. 

作者机构：Department of Mechanical and Aerospace Engineering University of Virginia CharlottesvilleVA22904 United States Department of Materials Science and Engineering University of California Los AngelesCA90095 United States Department of Applied Physics Hunan University Changsha410300 China George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology AtlantaGA30332 United States School of Materials Science and Engineering Georgia Institute of Technology AtlantaGA30332 United States Department of Aerospace and Mechanical Engineering University of Notre Dame Notre DameIN46556 United States School of Electrical and Computer Engineering Georgia Institute of Technology AtlantaGA30332 United States Department of Materials Science and Engineering University of Virginia CharlottesvilleVA22904 United States Department of Physics University of Virginia CharlottesvilleVA22904 United States 

出 版 物：《arXiv》 (arXiv)

年 卷 期：2024年

核心收录：

主　　题：Sapphire 

摘      要：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. Copyright © 2024, The Authors. All rights reserved.