Critical Role of Holes in Reliability, Robustness and Stability of GaN-on-Si HEMTs for Power and RF Applications

This study investigates the role of holes in the reliability, robustness, and stability of GaN-on-Si high-electron-mobility transistors (HEMTs) used in power switches and RF power amplifiers (PAs). Firstly, for reliability, the influence of holes on dynamic on-resistance (Ron) degradation under hard-switching stress is evaluated through over-voltage accelerated testing. The measured output capacitances (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$C$</tex> oss) before and after accelerated hard-switching stress reveal that holes and electrons trapping at the field plate regions. A p-GaN drain electrode facilitates hole injection into the device, enabling photon emission and the de-trapping of electron traps, thereby potentially mitigating hot carrier-induced damage. Secondly, for robustness, enhanced Human-Body-Model (HBM) electrostatic discharge (ESD) robustness in Schottky gate p-GaN enhancement mode (E-mode) HEMTs is achieved through gate epitaxial engineering with optimized AlGaN spacers. These devices maintain comparable DC performance while significantly improving HBM ESD forward gate-to-source capability from 300 V to 3.5 kV, meeting JEDEC JS-001-2023 Class 2 standards. At the high HBM voltage of 3.5 kV, the proposed mechanism explains the accumulation of holes at the p-GaN/AlGaN and AlGaN/GaN interfaces, which lowers barriers and improves electron conduction capabilities and uniformity under the gate, thereby alleviating current crowding. Finally, for stability, inserting an AlGaN back-barrier (BB) between the channel GaN (Ch-GaN) and carbon-doped GaN (C-GaN) in depletion-mode GaN-on-Si HEMTs for RF PAs, while maintaining the same channel-to-C-GaN distance, outperform conventional C-GaN designs. This scheme reduces current collapse from 6.49% to 4.75% and dynamic threshold voltage (Vth) from~ 0.4 V to < 0.2 V, and achieving higher/max from 76.62 GHz to 91.47 GHz. This improvement is attributed to the formation of a two-dimensional hole gas (2DHG) at the Ch-GaN/AlGaN BB interface, which compensates for trapped electrons and reduces parasitic capacitance.