Contact boundary conditions and the Dyakonov–Shur instability in high electron mobility transistors

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Abstract
Dyakonov and Shur have proposed a novel device structure based on dc biasing an ordinary high electron mobility transistor (HEMT) while subjecting it to unusual ac boundary conditions at its source and drain [M. Dyakonov and M. Shur, Phys. Rev. Lett. 71, 2465 (1993)]. Under these conditions, the drifting two-dimensional electron gas within the HEMT channel acts as a trapped one-component plasma which exhibits damped normal-mode oscillations similar to those of an organ pipe under zero dc bias, and an unexpected instability and gain at large dc biases. In this article, the work of Dyakonov and Shur is generalized by allowing the plasma more hydrodynamic degrees of freedom. In particular, it is found that the description used by Dyakonov and Shur must be generalized to incorporate a more complicated picture of the plasma modes.