Thermal transport in high electron mobility transistors: A Boltzmann transport equation study

AlGaN/GaN based high electron mobility transistors (AG-HEMTs) are strong candidates for the future high power and high frequency applications. But the formation of hot-spots and high temperature in these localized regions can limit their applications due to performance degradation and break-down. Understanding the underlying thermal transport processes will be an important step towards solving heat dissipation challenges in these devices. The objectives of the current study is to develop a multi-scale thermal transport model based on Boltzmann Transport Equation (BTE) to predict the hot-spot temperature accurately for a given bias voltage. At present, there are no reliable models to predict the energy (temperature) distribution near the hot spot in these devices. We developed coupled electro-thermal model to extract key information about hot-spot location and dissipated power. This information is further utilized to investigate the thermal performance of the device using BTE based model which can provide detailed view of the non-equilibrium nature of the phonon transport in the hot-spot. The interface between GaN and silicon substrate is treated with diffusive mismatch model (DMM). We calculated the spatial temperature distribution in a GaN device on silicon substrate and estimated the maximum temperature of hot spots. We also compared BTE and Fourier models for estimating the temperature distribution and found that Fourier model would significantly under predict the hot spot temperature. The multi-scale model can be used to investigate thermal transport in multi-finger devices and to explore the effect of cross-talk between different fingers.