Atomic scale variations for example from GaAs to AlGaAs of the type indicated in the device table above lead to sharp conduction band offset. The conduction band edge in AlGaAs is higher than the one in GaAs. The layer variation GaAs-AlGaAs-GaAs produces a barrier for classical electrons traveling in the GaAs. "Classical electrons" cannot make it through such a barrier. However, the quantum mechanical wave nature allows the electrons to tunnel/leak into the barrier. A double barrier structure can therefore act like a double mirror (Fabry-Perot) for photons or electronmagnetic wave. A quantum mechanical resonance state can therefore form in the center of the double barrier structure. NEMO facilitates the resonance state analysis of 1-D structure with a Resonance Finder.

The resonance tunneling diode (RTD) shown above has attracted significant research interest in the past 20 years since it can exhibit a negative differential resistance. Proposed and explored applications have been: fast oscillators (THz), logic, and memory circuits. NEMO's major mode of operation is computation of such 1-D quantum mechanical devices.

The quantitative modeling of resonant tunneling diodes requires various degrees of sophistication. Several of the RTD modeling issues addressed in NEMO are discussed in the following web pages:
Animation of the basic operation.Animation of the temperature dependence.Basic charge distributions.Animation of the charge development.Animation of the effects of resonances in the contacts.Animation of the different contact treatments.An example of quantitative RTD modeling.A discussion on realistic electron dispersion relations.