Numerical analysis of frequency dispersion of transconductance in GaAs MESFETs

A fully two-dimensional numerical model for the transconductance dispersion in GaAs MESFETs is presented. According to simulated results, the dominating surface traps belong to the hole trap type in order to obtain consistent results with reported measurements. The AC frequency-dependent modulation of negative surface charge can explain this anomalous phenomenon. The holes injecting from and emitting out of the gate metal electrode interact with the surface hole traps, and result in the change of the gate-to-source and the gate-to-drain resistances, which in turn cause the change in transconductance. The gate voltage and the gate length effects on the dispersion are also considered. Good agreement with reported results is obtained.