Device-Level Impact of Highly Anisotropic Thermal Conductivity of AlN/GaN Digital Alloys

Abstract

AlN/GaN digital alloys (i.e., short period superlattices) have the advantage of being an ultra-wide bandgap due to the quantum confinement effect, preservation of high mobility (no strong alloy scattering), and higher thermal conductivity than AlGaN random alloys.Herein, we investigate the influence of AlN/GaN thickness combinations on digital alloy (DA) thermal conductivity. Using time-domain thermoreflectance and steady-state thermoreflectance, we measure the anisotropic thermal conductivity of AlN/GaN DA’s, with thickness combinations: (2 nm/1 nm), (4 nm/1 nm), (6 nm/1 nm), (11 nm/1 nm). DA's with thick AlN layers exhibit highly anisotropic thermal conductivity (i.e., 4x difference between cross-plane and in-plane).Using finite-element modeling, we thermally simulate AlGaN and AlN/GaN DA devices. Improved lateral heat spreading in DA devices results in lower hot-spot temperatures compared to AlGaN devices. As the first thermal measurements of AlN/GaN DA’s, this study provides guidance for future device design.