Gate-controlled negative differential resistance in drain current characteristics of AlGaAs/InGaAs/GaAs pseudomorphic MODFETs

The observation of negative differential resistance (NDR) and negative transconductance at high drain and gate fields in depletion-mode AlGaAs/InGaAs/GaAs MODFETs with gate lengths L/sub g/ approximately 0.25 mu m is discussed. It is shown that under high bias voltage conditions, V/sub ds/>2.5 V and V/sub gs/>0 V, the device drain current characteristic switches from a high current state to a low current state, resulting in reflection gain in the drain circuit of the MODFET. The decrease in the drain current of the device corresponds to a sudden increase in the gate current. It is shown that the device can be operated in two regions: (1) standard MODFET operation for V/sub gs/<0 V resulting in f/sub max/ values of >120 GHz, and (2) a NDR region which yields operation as a reflection gain amplifier for V/sub gs/ >0 V and V/sub ds/>2.5 V, resulting in 2 dB of reflection gain at 26.5 GHz. The NDR is attributed to the redistribution of charge and voltage in the channel caused by electrons crossing the heterobarrier under high-field conditions. The NDR gain regime, which is controllable by gate and drain voltages, is a new operating mode for MODFETs under high bias conditions.<
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