Ballistic transport in short channel field effect transistors

The feature sizes of short channel Si MOSFETs and FINFETs are now in the range, where ballistic or quasi-ballistic transport is dominant. In this regime, conventional notion of electron mobility becomes invalid, and electrons lose energy and momentum in the contacts rather than in the device channel. In these devices, electron inertia plays an important role, and oscillations of the electron density (called plasma oscillations) enable the device response at THz frequencies. At THz and sub-THz frequencies, electron inertia effects, which are the signature of the ballistic transport, are pronounced even in FETs with feature sizes as large as 1 micron. Due to these effects, the device impedance becomes an oscillatory function of frequency. Plasma wave THz detectors using oscillations of the electron density in device channels are expected to outperform more conventional THz detectors. Fig. 1 shows the calculated Si MOSFET THz detector responsivity versus frequency. Achieving their full potential of plasma wave electronics might require using grating gate structures and/or “plasmonic crystals implemented as 2D or 3D arrays of coherently operating plasmonic FETs.