Impact Ionization Induced Breakdown and Related HTRB Behaviors in 100-V p-GaN Gate HEMTs

The impact ionization induced breakdown and related high-temperature reverse bias (HTRB) behaviors are studied in 100-V Schottky-type p-GaN gate high-electron-mobility transistors (HEMTs). It is revealed that impact ionization is initiated by the electrons injected from the source-side through the buffer layer to the high electric-field (E-field) region. The generated hot electrons, when being captured by surface states, could lead to re-distribution of E-field and delay of breakdown. Meanwhile, holes generated by impact ionization would transport to the region under the gate, and dynamically change the device threshold voltage. Under long-term HTRB stress, the impact ionization is also found to shorten the device lifetime and significantly impact the accuracy of lifetime prediction. Such a phenomenon is weakened at elevated temperatures as a result of the reduced impact ionization rate.