Physics-Based Modeling and Charge Density Saturation in GaN/AlGaN MOS-HEMTs

AlGaN/GaN high-electron-mobility transistors (HEMTs) are key devices for high-frequency and high-power applications due to their large bandgap, strong polarization fields, and excellent electron transport properties. However, conventional Schottky-gate HEMTs often suffer from significant gate leakage, particularly under high electric fields. Introducing a MOS gate stack into the HEMT architecture is an effective strategy that has already been realized in practical device technologies. We developed a comprehensive physics-based modelling framework for GaN/AlGaN MOS-HEMTs, emphasizing explicit analytical formulations that capture the electrostatics and polarization effects. A key outcome of our model is the prediction of charge density saturation in the two-dimensional electron gas (2DEG), a phenomenon that does not occur in conventional MOSFETs and typically unobservable in standard HEMTs due to the onset of gate leakage at similar bias conditions. Our formulation demonstrates that this saturation is an intrinsic physical effect arising from the interplay between polarization charges, quantum confinement and MOS structure. We show that the onset of charge density saturation is strongly dependent on system parameters, including the AlGaN barrier thickness, aluminum content and the properties of the gate dielectric. These explicit modelling results can further be used to support accurate circuit-level implementation, including integration within FOSS toolchains, enabling reliable design and optimization of next-generation GaN/AlGaN MOS-HEMT technologies.