Theoretical simulation of negative differential transconductance in lateral quantum well nMOS devices

We present a theoretical study of the negative differential transconductance (NDT) recently observed in the lateral-quantum-well Si n-channel field-effect transistors [J. Appl. Phys. 118, 124505 (2015)]. In these devices, p+ doping extensions are introduced at the source-channel and drain-channel junctions, thus creating two potential barriers that define the quantum well across whose quasi-bound states resonant/sequential tunneling may occur. Our study, based on the quantum transmitting boundary method, predicts the presence of a sharp NDT in devices with a nominal gate length of 10-to-20 nm at low temperatures ( ∼10 K). At higher temperatures, the NDT weakens and disappears altogether as a result of increasing thermionic emission over the p+ potential barriers. In larger devices (with a gate length of 30 nm or longer), the NDT cannot be observed because of the low transmission probability and small energetic spacing (smaller than kBT) of the quasi-bound states in the quantum well. We speculate that the ...