Investigation on the mechanism of stability variation with gate–drain bias in AlGaN/GaN-on-Si HEMTs

This paper investigates the mechanism behind the bias-dependency of stability factor (K factor) in GaN high electron mobility transistors (HEMTs). We characterized the K factor of a GaN-on-Si HEMT to elucidate its dependence on bias conditions. The intrinsic K factor is derived from a 19-element small-signal model and validated with simulations, revealing the gate–drain capacitance (Cgd), the channel transit time (τ), and the transconductance (gm) as governing components. Furthermore, technology computer aided design (TCAD) simulations confirm that these elements are predominantly influenced by the capacitance of the gate depletion region. Through experimental parameter extraction, we demonstrate how the gate–drain bias modulates this depletion capacitance and the carrier transport process, which in turn governs the K factor. This work provides fundamental mechanistic insights for designing highly stable GaN HEMT devices.