Contact Information

P. Douglas Yoder
Georgia Institute of Technology
School of Electrical and Computer Engineering
Atlanta, GA 30332
+1 404 385 2652
doug dot yoder at gatech dot edu

Quantum Charge Transport in Nanoelectronic Devices

On length scales approaching and smaller than an electron's de Broglie wavelength, electronic motion is influenced at a very basic level by both coherent interference effects as well as incoherent phenomena. It is in this regime, typically on the order of nanometers, that the wave-like nature of electrons may be expressed. Further, this wave-like behavior may be exploited to realize new functionality in semiconductor devices, thanks to both modern crystal growth techniques as well as electron beam lithography. An early example of such a "quantum device" is the resonant tunneling diode (RTD) which, like the Esaki diode before it, exhibits a region of negative differential resistance (NDR) with applied bias.

Intrinsic Tristability in RTDs:

Intrinsic Tristability in RTDs: Current-voltage measurements of a certain class of RTDs reflect both 1) an apparent bistability, associated with an abrupt (discontinuous) transition between high and low current states with infinitesimal change in applied voltage, and 2) a hysteresis effect, in which the threshold voltage(s) for transitions between these states depends on the direction (forward or reverse) of the voltage slewing. Such RTDs are ideal candidates for high-speed digital logic and memory applications. Recent calculations in the Yoder group based on non-equilibrium quantum statistical mechanics demonstrate unambiguously that current in such RTDs is intrinsically a continuous but multi-valued function of voltage, and that experimental measurement of bistability is in reality the fingerprint of a more complex, intrinsically tristable underlying structure. Furthermore, this analysis shows that the experimentally observed hysteresis derives from interactions between the RTD and its external circuit, which together define which stationary states of the RTD itself are exponentially stable in the context of the measurement.
Numerical simulations reveal that certain RTDs possess a continuous but multi-valued current-voltage relationship, resulting in an intrinsic tristability. A qualitatively different form of multistability may also be observed, depending on details of the external circuit. Experimentally observed bistability and hysteresis are both consequences of interactions between an intrinsically tristable RTD and its external measurement circuit, as this figure, derived from calculations, indicates.