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Dynamic characteristics of GaN HEMT grown on a native substrate were systematically investigated at 300K and 150K. Transfer and output characteristics of the GaN HEMT were measured after various off-state stressing conditions and recovery durations. In addition, a high-speed scheme was employed to finish the measurement within 75 μs, and to ensure maximum preservation of stressing/recovery consequences. The threshold voltage instability and current collapse commonly observed at room temperature were mostly diminished at 150K, which was attributed to reduced number of electrons through the metal-semiconductor contact and insufficient number of carriers overcoming the capture potential barrier. Two pulsed I-V measurements, including evaluations with various off-state quiescent bias points and "on-the-fly" on-resistance sampling, confirmed an inefficient electron capture process at 150K, with a time constant larger than dozens of seconds. The output characteristic comparison between hard switch and soft switch at 150K provided direct experimental evidence for electron capture promotion by hot carriers.

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