An Accurate Characterization of Capture Time Constants in GaN HEMTs

This paper provides theoretical and experimental evidence that, contrary to what is a widely reported belief, the capture time constant of GaN high-electron-mobility transistor (HEMTs) deep-level traps is not infinitesimally shorter than the modulation envelope time features of usual excitation signals. Instead, it can have a nonnegligible impact on their power amplification. A specifically conceived test bench, capable of measuring capture time constants at guaranteed invariant thermal dissipation conditions, revealed that the capture process can range from less than a microsecond up to a few tens of milliseconds. Furthermore, a theoretical justification based on the Shockley-Read-Hall statistics is provided to explain this widespread time constants' behavior of deep-level traps. As a practical application example of these findings, the detailed characterization of the capture time constants performed in this paper proved to constitute a valuable tool in understanding the behavior of GaN power amplifiers (PAs) designed for pulsed radar signals.