Nanoscale, temporal temperature mapping in AlN/GaN HEMTs via ab initio phonon Monte Carlo simulation

High-electron-mobility-transistor (HEMT) devices, which implement wide-bandgap (WBG) or ultra-wide-bandgap (UWBG) semiconductors, permit the high-voltage and high-frequency regimes necessary for 5G/6G communications and high-power electronics, but are inhibited by the associated adverse temperature rises. A critical barrier to designing effective thermal dissipation architectures is the lack of accurate temperature information provided by current thermal modeling efforts. We develop an ab initio phonon Monte Carlo (MC) framework for nanoscale, temporal temperature mapping of HEMT devices that leverages ab initio mode- and temperature-dependent phonon properties and combines ballistic phonon transport and interfacial phonon transmission to capture thermal transport across multilayered structures. We then apply it to an AlN/GaN HEMT device and demonstrate that the decreased thermal conductivity with increasing temperature and decreasing size and the phonon reflection at AlN/GaN interfaces lead to a significantly higher temperature in the hot spot area than conventional technology computer-aided design (TCAD) prediction (at 7.61 W mm^-1 and 8.43 × 10⁵ W mm^-3 heat flux, we observe a ∼80 K difference), introducing secondary heating zones and exacerbating temperature discontinuities across material interfaces. The detailed temperature map with temporal evolution not only advances our understanding of the heat dissipation process in the HEMT devices but also reiterates the necessity of accurate phonon modeling for hotspot temperature prediction. This framework can be widely applied to predict the temperature profiles of various electronic devices, including those beyond HEMTs.