Transverse magnetic field effects on GaAs MESFETs: analytical model and experiments

An analytical model based on the gradual channel approximation is derived, which includes the effect of a magnetic field applied in the plane of the gate on the terminal characteristics of a MESFET. The device equations are derived on the basis of a two-region model, composed of a low-field region where the drift velocity increases along the channel and a saturation region where the drift velocity remains at its saturated value. It is show that the magnetic field generates a Hall field in the active channel, which in turn modulates the drain current through the transconductance of the device. The effect of the field on the drain current is found to increase as the device operation moves from the linear region to the saturation region. The drain current is found to vary linearly with the magnetic field density over the +or-1.0-tesla range. For long-gate GaAs FETs, the model predicts a sensitivity to the applied magnetic field of about 6% per tesla, whereas for shorter-gate devices, it predicts a much larger sensitivity of about 40% per tesla. This work shows that circuits that utilize GaAs transistors with short gate lengths are susceptible to drifts and noise caused by ambient magnetic fields.<
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