ABSTRACT
Longitudinal transport in a super lattice is transport along the growth direction of the super lattice; the resonant tunnelling discussed in the preceding chapter is one of the forms of longitudinal transports. The path of the longitudinal transport is very short, only several or several tenths of nanometers. The effect of scattering on electron motion is not obvious. Electron motion is mainly controlled by the quantum effect. At the same time, electron motion velocity is generally very higher than the thermal balance velocity of carriers, therefore these kinds of devices are called quantum effect devices or hot-electron devices. The advantage of such a device is high velocity and it can be used to fabricate high-frequency devices. But due to the delay of the circuit, for example, the RC time delay the extremely high velocity in the active region cannot be represented in the whole device performance.
