Accurate Modeling of GaN HEMT RF Behavior Using an Effective Trapping Potential

This paper investigates the back-gating effects due to traps, and presents a new nonlinear trap modeling approach suitable for gallium nitride (GaN) high electron mobility transistors (HEMTs). It is shown that the traps have nonidentical influence on the channel compared with the gate. The potential due to trapped electrons in the buffer and the gate-source voltage need to be differentiated to model their respective influence on conductivity of the 2-D electron gas. Hence, the back-gating potential due to traps cannot be included in the transistor model by directly offsetting the gate-source voltage. A new modulation factor is therefore introduced to create an effective back-gating potential, and thereby improve the modeling of trapping effects. The proposed nonlinear trap model is shown to accurately predict the trapping behavior for a large voltage operating region. A detailed procedure is presented to derive the model parameters from basic device measurements. The model is experimentally validated and shown to accurately predict dc-, pulsed-IV, and large-signal waveform performance for a commercial GaN HEMT.