The role of electron viscosity on plasma-wave instability in HEMTs

Conditions for terahertz (THz) radiation due to the plasma-wave instability in the channel of HEMTs are re-examined by considering the electron viscosity in carrier hydrodynamic transport. Not only the DC output I-V characteristics are affected, but also the window for plasma-wave instability is altered by the term with viscosity in the transport equation. The solution procedure and numerical study are presented. The analysis has been applied to recent experimental work and it is shown that the device parameters required for plasma-wave instability are more stringent than those reported in the up-to-date THz emission experiments.