2DHG in AlGaN Back-Barrier for Substrate Loss Suppression and RF Performance Enhancement in GaN-on-Si HEMTs

Substrate loss remains a critical challenge in GaN-on-Si high-electron-mobility transistors (HEMTs) for RF applications. In this work, we provide the experimental verification of two-dimensional hole gas (2DHG) formation at the GaN/AlGaN back-barrier (BB) interface and first demonstrate its essential role in suppressing RF substrate loss. A 2DHG shielding model is proposed and validated through TCAD simulations. In addition, a front-biasing technique is introduced, enabling direct observation of 2DHG under operating bias conditions. Small-signal modeling and S-parameter measurements reveal that the device with an AlGaN BB significantly reduces substrate parasitic capacitance, leading to improvements in ${f} _{\text {T}}$ and ${f} _{\max }$ , by 7 GHz and 15 GHz, respectively, compared to the device without an AlGaN BB. Furthermore, large-signal power and linearity measurements confirm enhanced power gain, power-added efficiency (PAE), and third-order intercept points (OIP3/IIP3), highlighting the effectiveness of the 2DHG shielding mechanism in improving radio frequency (RF) performance.