Simulation of drastic lag phenomena in GaAs-based FETs for large voltage swing

In GaAs MESFETs and HEMTs, slow current transients are often observed experimentally even if the drain voltage or the gate voltage is changed abruptly. They are called drain-lag or gate-lag and could be fatal when the high-speed and high-frequency operation is considered. As for factors of these slow transients, effects of deep traps in the semi-insulating substrate and surface states on the active layer are suggested, but the detailed mechanisms are not well clarified. In this work, we have made transient simulations of GaAs MESFETs and AlGaAs/GaAs HEMTs when the gate voltage or the drain voltage is swung significantly, and showed that the lag phenomena become very pronounced for larger changes of the voltages. This indicates that I-V characteristics should be quite different between DC and RF conditions and the lag phenomena should be considered in the modeling of GaAs-based power devices.