LOW-FIELD LOW-FREQUENCY DISPERSION OF TRANSCONDUCTANCE IN GAAS-MESFETS WITH IMPLICATIONS FOR OTHER RATE-DEPENDENT ANOMALIES

A theory that emphasizes the role of surface states in the operation of GaAs MESFETs and that is intended to tie together hitherto unconnected anomalies in device behavior is presented. Such undesirable effects are consistent with the DC and microwave characteristics of the FET being modified by charge exchange with surface states. Generally speaking, these states are relatively slow, having characteristic frequencies of typically 1 kHz, but they nevertheless affect the microwave scattering parameters of the FET through the distortion they introduce to the shape of the depletion region in the transistor under given bias conditions. It is argued that the FET structure behaves as a natural 'probe' of surface states and so constitutes a useful analytic tool for studying states on a variety of unpassivated and passivated surfaces.