Effect of gate-length shortening on the terahertz small-signal and self-oscillations characteristics of field-effect transistors

• We simulate plasma waves in short field effect transistors.
• We use a numerical hydrodynamic model coupled to Poisson equation.
• Shortening the gate improves the conditions for plasma instability.
• High-frequency admittance exhibits regions with negative values.
• Terahertz voltage self-oscillations are obtained for particular conditions.

We investigate the shortening of the gate-length in submicrometric and nanometric field-effect transistors as a powerful tool to improve their self-oscillations performances in the terahertz frequency region due to the appearance of the Dyakonov–Shur instability. The theoretical model is based on the numerical solution of hydrodynamic equations for the electron transport in FETs/HEMTs channels. We show that a decrease of the gate length allows, on the one hand, to increase the intrinsic resonant frequencies near 1 THz and, on the other hand, to improve the conditions for the onset of the Dyakonov–Shur instability and related phenomena. The small-signal characteristics calculated under constant drain-voltage operation are compared with the drain-voltage self-oscillations calculated under constant drain-current operation.