A Compact Model for Polarization-Graded HEMTs Demonstrating Enhanced Linearity

Abstract

This article presents an approach for modeling polarization-graded gallium nitride (GaN) high-electron-mobility transistors (HEMTs). Unlike conventional GaN HEMTs, where a 2-D electron gas (2DEG) forms at the barrier–channel interface, graded structures feature a 3-D electron distribution. TCAD simulations are used to extract carrier density and energy band diagrams, which form the basis for model development. The derivation uses refined approximations for the Fermi–Dirac integral solution, ensuring differentiability while accurately correlating carrier density with the applied gate bias through the use of potential balance. A surface-potential-based approach is subsequently used to model terminal currents and charges. Validation of the model is done through comparison with on-wafer measurements and published data, including dc transfer and output characteristics and measured S-parameters over the frequency range of 10 MHz–110 GHz. Furthermore, model accuracy in representing linearity is verified by comparing to large signal and intermodulation measurements at 10 GHz.