Optimal layer thickness and junction temperature of GaN HEMTs based on bias-dependent non-uniform heat source model

Accurate thermal simulation of thermal is crucial for designing reliable gallium nitride high electron mobility transistors (GaN HEMTs). Thermal analysis models that assume a uniform heat source neglect the non-uniformity and bias dependence of the heat source in the channel region, which leads to inaccurate device junction temperature and other parameter predictions. Herein, we adopt a framework of a bias-dependent non-uniform heat source model and perform detailed thermal simulations of the near-junction region of GaN HEMTs. Results show that a uniform heat source model yields an optimal GaN thickness of 2.4 μm; whereas under bias-dependent non-uniform heat sources, it remains 2.4 μm at Vg = 2 V, Vd = 3.8 V but increases to 3.1 μm at Vg = −1 V, Vd = 6.25 V. Notably, under identical power dissipation, devices on a high-thermal-conductivity diamond substrate in the saturated region exhibit a junction temperature of 377.8 K, higher than the 360.37 K observed for a low-thermal-conductivity SiC substrate in the linear region. This difference arises from heat distribution and heat flow paths related to device bias. These results provide a theoretical reference for the thermal design of high-performance GaN-based devices.