Comparative Study of Gate Work Function Effects in AlGaN/GaN HEMTs with AlGaN and InGaN Back Barriers

This study performs a TCAD-based comparative analysis of passivated AlGaN/GaN high-electron-mobility transistors (HEMTs) fabricated on a β-Ga2O3 substrate by incorporating two different back-barrier layers: Al0.08Ga0.92N and In0.01Ga0.99N. To minimize surface-state effects and enhance device reliability, a HfO2 passivation layer is integrated into the proposed structures. The impact of gate metal work-function variation (Φm ranging from 4.23 to 5.65 eV) on both DC and RF characteristics is systematically evaluated through numerical simulations. Device behavior is examined in terms of energy-band alignment, electron confinement capability, output and transfer characteristics, transconductance, capacitance response, cut-off frequency, and breakdown behavior. Simulation results indicate that the InGaN back-barrier configuration provides enhanced carrier transport and superior RF performance, yielding a maximum drain current of nearly 1.25 A/mm, a peak transconductance of approximately 0.81 S/mm, and a cut-off frequency close to 18 GHz. In contrast, the AlGaN back-barrier structure demonstrates better high-voltage capability, achieving a breakdown voltage of around 450 V. The investigation confirms that appropriate selection of back-barrier material together with optimization of gate metal work function strongly affects carrier confinement, electrostatic behavior, and overall device efficiency