Impedance-dependent degradation in GaN HEMTs under high-voltage RF stress: Electro-thermal and trap mechanisms

Abstract

This work investigated impedance-dependent degradation mechanisms in GaN high-electron-mobility transistors (HEMTs) under high-voltage radio frequency (RF) stress, focusing on electro-thermal coupling and trap evolution. In devices with matched impedance, slight degradation in output power (Pout), saturated drain current (Idss), and transconductance (GM) is observed after RF stress. This is attributed to an increase in trap density within the AlGaN layer and at the AlGaN/GaN interface, as evidenced by low-frequency noise results. In contrast, severe degradation in Pout, Idss, GM, and gate leakage current (IG) occurs in those devices with the 50-Ω mismatched impedance condition. Anyway, these more severe degradation effects result not only from the increased trap density after RF stress, but also primarily from the temperature rise caused by reflected power-induced Joule heating, as validated by infrared thermography. Electro-thermal simulations reveal dual lateral electric field peaks near gate edges in 50-Ω mismatched devices, redistributing peak temperature toward the source–gate region and intensifying localized Joule heating, thereby accelerating degradation. These findings highlight the critical role of impedance matching in GaN HEMT reliability, offering guidelines for designing robust power amplifiers in microwave systems.