Evaluation of Dynamic On-Resistance and Trapping Effects in GaN on Si HEMTs Using Rectangular Gate Voltage Pulses

Abstract

Dynamic on-resistance (RON) of commercial GaN on Si normally off high-electron-mobility transistor (HEMT) devices is a very important parameter because it is responsible for conduction losses that limit the power conversion efficiency of high-power switching converters. Due to charge trapping effects, dynamic RON is always higher than in DC, a behavior known as current collapse. To study how short-time dynamics of charge trapping and release affects RON we use rectangular 0–5 V gate voltage pulses with durations in the 1 μs to 100 μs range. Measurements are first carried out for single pulses of increasing duration, and it is found that RON depends on both pulse duration and drain current ID, being higher at shorter pulse durations and lower ID. For a train of five pulses, RON decreases with pulse number, reaching a steady state after a time interval of 100 μs. The response to a five pulses train is compared to that of a square-wave signal to study the time evolution of RON toward a dynamic steady state. The DC RON is also measured, and it is a factor of ten smaller than dynamic RON at the same ID. This confirms that a reduction in trapped charges takes place in DC as compared to the square-wave switching operation. Additional off-state stress tests at VDS = 55 V reveal the presence of residual surface traps in the drain access region, leading to four times increase in RON in comparison to pristine devices. Finally, the dynamic RON is also measured by the double-pulse test (DPT) technique with inductive load, giving a good agreement with results from single-pulse measurements.