Frequency-dependent electrical characteristics of GaAs MESFETs

Output resistance and transconductance of GaAs MESFETs have been observed to change significantly at very low frequencies. Extensive measurements of these characteristics as a function of device bias are reported. Direct measurements of the dispersive behavior between DC and 100 kHz and over a broad temperature range have been made on ion-implanted monolithic microwave IC (MMIC) devices. Conductance deep level transient spectroscopy (DLTS) and microwave S-parameter measurements have also been made to investigate this behavior. These measurements reveal that surface or channel-substrate interface traps in the material are most likely to be responsible for the observed behavior. A new equivalent-circuit model which accounts for many of the observed characteristics is developed. Unlike previously proposed equivalent circuits, the model does not rely on physically unrealistic circuit element values in order to obtain accurate performance predictions. The bias dependence of circuit element values is computed for one device. Effects not described by the model are also discussed.<
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