Degradation mechanism of Cascode GaN high electron mobility transistors device with high energy protons and heavy ions synergistic irradiations

In this study, the synergistic irradiation effects on Cascode GaN high electron mobility transistors (HEMTs) subjected to 80 MeV proton and Ge ion irradiation with a linear energy transfer (LET) of 37 MeV cm²·mg⁻¹ were investigated. The experimental results demonstrated that such synergistic irradiation leads to a 10 % reduction in the single-event burnout (SEB) threshold voltage. Geant4 and TCAD simulations revealed that high-energy proton irradiation induces a significant number of displacement defects within the GaN HEMT structure. During subsequent Ge ion irradiation, these pre-existing displacement defects near the gate region act as electron traps, forming negatively charged defect centers. This results in an enhanced electric field intensity within the channel, facilitating avalanche multiplication of carriers. Consequently, a large number of holes accumulate beneath the gate, lowering the electron barrier in the channel. This condition promotes electron injection into leakage paths via the tunneling effect, thereby forming a burnout channel between the gate-drain region of the depleted GaN HEMT and the source of the Si MOSFET. As a result, the Cascode GaN HEMT device becomes susceptible to SEB at a lower operating voltage. These findings provide important theoretical insights into SEB behavior and contribute to the reliability assessment of Cascode GaN HEMT devices in radiation environments.