Terahertz plasma wave generation in ultra-short-channel Field Effect   Transistors: theory vs experiment
  Taking into account both the scattering and the velocity saturation of carriers, we examine the "shallow-water" instability of the two-dimensional electron gas in a field effect transistor. It is shown that both the scattering (which is analogous to friction in a shallow-water channel) and the carrier velocity saturation lead to damping of the plasma wave instability. Threshold diagram of instability is calculated. The actual device parameters required for observation of plasma wave generation are compared with those reported in recent sub-terahertz emission experiments. 
M. V. Cheremisin, G. G. Samsonidze