Mechanisms for low-frequency oscillations in GaAs FET's

Low-frequency oscillations in GaAs MESFET's were observed under back-gating conditions. The FET oscillations are directly related to oscillations in leakage currents in the semi-insulating GaAs substrate. The occurrence of these oscillations in the substrate is strongly dependent upon GaAs material. It is proposed that oscillating substrate leakage currents modulate the FET current in two ways; first, by modulating the active channel-substrate junction and second, by inducing periodic voltage fluctuations on the gate via gate pad contacts on the semi-insulating substrate. The latter mechanism is dominant and dependent upon gate bias and gate impedance.