Abstract
We report the observation of negative differential resistance (NDR) and negative transconductance at high drain and gate fields in depletion-mode AlGaAs/fnGaAs/GaAs MODFET’s with gate lengths Lg~ 0.25 μm. It is shown that under high bias voltage conditions, Vds = 2.5 V and Vgs= 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. We show that the device can be operated in two regions: 1) standard MODFET operation for Vgs< 0 V resulting in f max values = 120 GHz, and 2) NDR region which yields operation as a reflection gain amplifier for Vgs = 0 V and Vds = 2.5 V resulting in 2 dB of reflection gain at 26.5 GHz. We attribute the NDR 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 MODFET’s under high bias conditions. © 1989 IEEE