Numerical analysis of the looping effect in GaAs MESFET's

The looping effect in the I/sub D/-V/sub D/ (drain-current-drain-voltage) characteristics of GaAs MESFETs on semi-insulating substrates has been studied using a two-dimensional numerical analysis. Both the transient and the steady-state behaviors of the looping phenomenon were simulated. Peak voltage- and frequency-dependent behaviors of the looping effect are analyzed. The I/sub D/-V/sub D/ loop is due to the difference in the distribution of ionized EL2 concentration when the drain voltage rises and falls because of the trapping process of EL2s. The output conductance is also found to be frequency-dependent and is explained by the frequency-dependent modulation of the potential barrier height at the channel/substrate interface due to the drain-voltage variation.>