Methodology for the Study of Dynamic ON-Resistance in High-Voltage GaN Field-Effect Transistors

We have developed a new methodology to investigate the dynamic ON-resistance (R_ON) of high-voltage GaN field-effect transistors. The new technique allows the study of R_ON transients after a switching event over an arbitrary length of time. Using this technique, we have investigated dynamic R_ON transients in AlGaN/GaN high-voltage, high electron-mobility transistors over a time span of ten decades under a variety of conditions. We find that right after an OFF-to-ON switching event, R_ON can be several times higher under dc conditions. The increase in R_ON is enhanced as the drain-source voltage in the OFF-state increases. The R_ON recovery process after an OFF-to-ON switching event is characterized by a fast release of trapped charge through a temperature-independent tunneling process followed by conventional thermally activated detrapping on a longer timescale. After a high-power-to-ON switching event, in contrast, detrapping only takes place through a temperature-independent process. We postulate that the fast temperature-independent detrapping originates from interface states at the AlGaN barrier/AlN spacer interface. The thermally activated detrapping can arise from traps at the surface of the device or inside the AlGaN barrier. These findings are relevant in the quest to engineer a reliable GaN power switch with minimum dynamic R_ON problems.