Han GaoFollow


Radiation tolerance of wide-bandgap Gallium Nitride (GaN) high-electron-mobility transistors (HEMT) has been studied, including X-ray-induced TID effects, heavy-ion-induced single event effects, and neutron-induced single event effects. Threshold voltage shift is observed in X-ray irradiation experiments, which recovers over time, indicating no permanent damage formed inside the device. Heavy-ion radiation effects in GaN HEMTs have been studied as a function of bias voltage, ion LET, radiation flux, and total fluence. A statistically significant amount of heavy-ion-induced gate dielectric degradation was observed, which consisted of hard breakdown and soft breakdown. Specific critical injection level experiments were designed and carried out to explore the gate dielectric degradation mechanism further. Transient device simulations determined ion-induced peak transient electric field and duration for a variety of ion LET, ion injection locations, and applied drain voltages. Results demonstrate that the peak transient electric fields exceed the breakdown strength of the gate dielectric, leading to dielectric defect generation and breakdown.

GaN power device lifetime degradation caused by neutron irradiation is reported. Hundreds of devices were stressed in the off-state with various drain voltages from 75 V to 400 V while irradiated with a high-intensity neutron beam. Observing a statistically significant number of neutron-induced destructive single-event-effects (DSEEs) enabled an accurate extrapolation of terrestrial field failure rates. Nuclear event and electronic simulations were performed to model the effect of terrestrial neutron secondary ion-induced gate dielectric breakdown. Combined with the TCAD simulation results, we believe that heavy-ion-induced

SEGR and neutron-induced SEGR share common physics mechanisms behind the failures. Overall, experimental data and simulation results provide evidence supporting the idea that both radiation-induced SBD and HBD are associated with defect-related conduction paths formed across the dielectric, in response to radiation-induced charge injection. A percolation theory-based dielectric degradation model is proposed, which explains the dielectric breakdown behaviors observed in heavy-ion irradiation experiments.

Degree Date

Summer 7-31-2023

Document Type


Degree Name



Lyle School of Engineering Electrical and Computer Engineering


Bruce Gnade

Second Advisor

Robert Baumann

Subject Area

Electrical, Electronics Engineering, Physics

Number of Pages




Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License