Microwave response of a high electron mobility transistor in the presence of a Dyakonov-Shur instability

The plasma-wave response of the two-dimensional electron gas that forms the active layer of a high-electron mobility transistor (HEMTs) makes a contribution to the high-frequency behavior of these devices that is distinct from their adiabatic response, i.e., unrelated to low-frequency parameters such as dc transconductance, capacitances, and channel resistance, which are usually derived from dc IV curves. Since the plasma-wave response has the potential to make the HEMT active at very high (terahertz) frequencies, it is important to frame its description within the standard language of microwave device engineering, i.e., as admittance or S-parameters of the device. In this paper a full set of microwave admittance parameters is derived for a real HEMT, based on recent work by the author [J. Appl. Phys. 87, 8056-8064 (2000)].