High-Resolution Thermoreflectance Imaging Investigation of Self-Heating in AlGaN/GaN HEMTs on Si, SiC, and Diamond Substrates
Assaad El Helou, Pavel L. Komarov, Marko J. Tadjer, Travis J. Anderson, Daniel Francis, Tatyana I. Feygelson, Bradford B. Pate, Karl D. Hobart, Peter E. Raad
Abstract
Gallium nitride (GaN) high electron-mobility transistors (HEMTs) offer considerable high-power operation but suffer in reliability due to potentially damaging self-heating. In this study, self-heating in AlGaN/GaN HEMTs on high conductivity substrates is assessed using a high-resolution thermoreflectance (TR) imaging technique, to compare the thermal response between GaN-on-Si, GaNon-Diamond, and GaN-on-4H-SiC. The TR method accuracy at high-power density is verified using a nonlinear coefficient of TR (CTR) as a function of temperature. The acquired steady-state thermal maps give a thermal resistance of 11.5 mm · K/W for GaN-on-Si (based on peak channel temperature), compared to 2.7 and 3.3 mm · K/W for GaN-on-SiC and GaN-on-diamond substrates, respectively. The tested GaN-on-diamond HEMT exhibits similar heating rates to those seen on a SiC substrate, with a slightly higher peak temperature, which indicates a higher thermal boundary resistance that could offset the benefits of using a higher conductivity substrate and lead to faster thermally enhanced degradation. The analysis reveals the importance using high-resolution imaging to detect hotspots and areas of peak temperature that largely affect failure initiation and device reliability and which may not be otherwise observable.