Analysis of the frequency dispersion of transconductance and drain conductance in GaAs MESFETs

Experimental results on the frequency dispersions of the transconductance (G(m)) and the drain conductance (G(d)) in ion-implanted gallium arsenide (GaAs) metal-semiconductor field-effect transistors (MESFETs) are analyzed by two-dimensional device silmulations. In the experiment, G(m) exhibits negative frequency dispersion and G(d) shows positive frequency dispersion in the drain current saturation region, and the activation energy is close to 0.7 eV for both. G(m) exhibits positive dispersion with all activation energy of 0.42 eV in the linear current region, and no frequency dispersion is observed in G(d). Based on the drain voltage conditions of the experiment and the effect of a p-type buffer layer, a simulation assuming traps at 0.42 eV at the surface and 0.71 eV in the substrate has shown that features of the experimental results for G(m) and G(d) can be reproduced. These results show that the positive dispersion of G(m) in the linear region is caused by the Surface trails, and the negative dispersion of G(m) and the positive dispersion of G(d) in the saturation region by the substrate traps. Through the simulated potential and carrier distribution during the gate or drain transient, we conclude that the positive dispersion of G(d) is due to the capture delay of electrons by the traps, and the negative dispersion of G(d) in the saturation region is due to the emission delay of electrons from the substrate traps, which are accumulated by the drain current penetration into the substrate. (c) 2006 Wiley Periodicals, Inc.