Buffer Trap Related Knee Walkout and the Effects of Self-Heating in AlGaN/GaN HEMTs

Mixed-mode simulations of a class A amplifier is used to study the DC/RF dispersion commonly observed in AlGaN/GaN based HEMTs. We show that the observed knee walkout at frequencies greater than the emission rates of buffer traps (time constants tae > 1 week) is related to the steady state trap density and spatial location due to the DC operational bias. An increase in the drain bias point and an initial distortion of the RF signal, that is expected to disappear as the device global temperature reduces, is observed when a self-heating model is included. Finally, we propose that a reduction in the DC/RF dispersion is possible with a suitable location and concentration of an acceptor doping in the buffer