Modeling of frequency dispersion at low frequency for GaN HEMT

In this paper, modeling of frequency dispersion due to traps at two locations for GaN HEMT is reported. The proposed trap circuit model is simple model which has two resistance(R)-capacitance(C) circuits and two voltage-controlled current sources in addition to a common small signal equivalent circuit. In this model, we assumed there were traps at surface and buffer of GaN HEMT and their traps depend on gate voltage and drain voltage, respectively. Therefore, time constant of two R-C circuits at gate and drain was considered as the time constant of surface traps and buffer traps respectively. By the equation of Y parameters of this trap circuit model, it was found that Re[Y21] and Re[Y22] vary greatly at trap frequency which is an inverse of time constant of traps and Im[Y21] and Im[Y22] have the peak or trough at trap frequency. Moreover, this model was almost same as measurement results of both all Y parameters and all S parameters at low frequency. This model could be confirmed to describe frequency dispersion due to traps at two locations.