Negative Differential Transconductance Research Articles

Experimental realization of the bound state resonant tunneling transistor

Bound states resonant tunneling transistors (BSRTTs) with direct contacts to ultrathin base layers ( approximately 60 AA) have been experimentally realized. In the BSRTT structure, bound states are created in the quantum well by using a base material with a low band gap. Electrons in these bound states form a low-resistance base region for application of bias to the device. Resonant tunneling of electrons via the second energy level in the well results in negative differential transconductance (NDT) or negative differential resistance (NDR) in the output current. This NDT or NDR can be used for applications in high-speed digital circuits to reduce the complexity of conventional transistor technology. The BSRTTs studied consist of a 3000-AA In/sub 0.53/Ga/sub 0.47/As emitter layer doped at 5*10/sup 18/ cm/sup -3/, an emitter stepped barrier which includes a 500-AA n/sup +/ and a 300-AA undoped In/sub 0.52/Al/sub 0.48/ layer, a 20-AA AlAs barrier, a 60-AA In/sub 0.75/Ga/sub 0.25/As base layer doped at 5*10/sup 18/ cm/sup -3/, a 20-AA AlAs barrier, a 1000-AA undoped In/sub 0.52/Al/sub 0.48/As collector barrier, and a 5000-AA In/sub 053/GA/sub 0/./sub 47/As collector layer doped at 5*10/sup 18/ cm/sup -3/. Device testing results are reported.

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>