Using Triangular Gate Voltage Pulses to Evaluate Hysteresis and Charge Trapping Effects in GaN on Si HEMTs

Abstract

Charge carrier traps due to crystal defects in GaN on Si HEMT devices are responsible for dynamic performance degradation, long-term reliability limitations, and peculiar failure modes. The behavior of traps depends on many variables including heterostructure quality, the specific device structure, and operating conditions. To study the short time dynamics of charge trapping and release on the threshold voltage shift and hysteresis of commercial normally off GaN HEMTs we use triangular 0–5 V gate voltage pulses in the μs to ms duration range. Measurements are performed for single pulses by varying pulse duration and for a train of a few pulses by varying their number. The results indicate that hysteresis and related threshold voltage shift occur after repeated pulses, suggesting an accumulation of trapped charges. However, for a triangular wave hysteresis vanishes, meaning that a dynamic balance between charge trapping and release is established in the device. This can be considered as a positive indicator of device robustness and reliability. The same method, used to measure the gate threshold voltage shift and dynamic RON after a 30 min off-state DC stress at VDS = 55 V with a floating gate, highlights an appreciable performance degradation of the device.