Absolute Negative Resistance in Ballistic Variable Threshold Field Effect Transistor
Laboratoire de Physique Théorique et AstroparticulesUniversité Montpellier II, France
ECSE Department and Broadband CenterRensselaer Polytechnic Institute, Troy, NY 12180, U.S.A.
We consider a ballistic variable threshold field effect transistor (BVTFET),1-4 where the electron transport is ballistic (no collisions with impurities or lattice vibrations), see Fig. 1(a). We will use the hydrodynamic approach,5 which is justified if the electron-electron collisions are much faster than collisions with impurities andlor phonons. Qualitatively, our results hold even if this condition is not met, so long as the mean free path is greater than the characteristic length scale for the variation of the electron concentration.
Within this approach, the situation we consider is similar to a water flow through a pipe with varying cross-section, see Fig. l(b) and (c). If there is no flow, obviously the pressure is the same on both sides. In the presence of a stationary water flow, the Bernoulli law (which follows from energy conservation) tells us that the pressure will be lower in the narrow part of the pipe, where the velocity is larger. Note, that this fact does not depend on the direction of the flow. This means that when water flows from the narrow part towards the wide part, the direction of the flow is locally opposite to the pressure gradient. One can say that the interface ...