Generation of hot electrons in GaN HEMTs under RF Class A and AB PAs

AlGaN/GaN HEMTs have demonstrated outstanding performance in terms of high-power and high frequency operation. However, reliability concerns constitute one of the limiting factors preventing the fully exploitation of this technology. In particular, hot electron generation has been consistently reported as one of the main mechanisms for device degradation, since high energy carriers can create electrically active traps that reduce performance [1]. Many studies of hot electron concentration have been performed on DC operation only, and those done in RF do not provide an accurate, quantitative carrier energy distribution [2]. In this work, we present a comparative study of the hot carrier generation under RF operation in Class A and Class AB power amplifier (PA) topologies. This is done in terms of the accurate simulation of the electron energy distribution function (EDF) under RF conditions, by means of our full band cellular Monte Carlo device simulator (CMC) [3], self-consistently coupled to a harmonic balance (HB) circuit solver based on the load line technique [4]. Within this framework it can be simultaneously captured the highly-non-linear, out of equilibrium carrier dynamics of the device under large signal operation, along with the full complexity of the external circuitry necessary for adequate power amplifier performance.