Analysis of the frequency dispersion of the transconductance in recessed and unrecessed low temperature GaAs FETs

We study the behavior of low temperature (LT) GaAs FETs at 300 and 77 K. The dependence with frequency of their transconductance is measured and a decrease is observed in the MHz range at room temperature and in the kHz range at liquid nitrogen temperature. This phenomenon is related to the dielectric relaxation of the LT GaAs which is due to the residual conductivity of this material. The behavior of the transconductance is also correlated to the large signal characterization. From the results, we propose improvements of the device structure by recessing the gate into the LT GaAs. The transconductance measurements show a strong improvement in the device characteristics.