Plasmon terahertz response of submicron-gate high electron mobility transistor

Terahertz response of field-effect transistors (FET) with two-dimensional electron channels is strongly affected by plasma oscillations in the channel. This phenomenon can be used for tunable resonant detection of terahertz (THz) and mid-infrared radiation. The electrostatic theory of the resonant detection of THz radiation via excitation of plasma oscillations in FET´s channel yields the responsivity of the detector to plasma oscillations with a given amplitude. However, this theory leaves aside the important question of how effectively those plasma oscillations can be excited by incoming radiation. In other words, it is the question by how much the radiation power absorbed in the channel at plasma resonance exceeds the nonresonant Drude absorption background (so called the absorption enhancement factor). In this paper we calculate the absorption enhancement factor using the full system of the Maxwell equations and show that this factor reaches 60 at the fundamental plasma resonance. The darkness factor of such resonant detector (the ratio between the absorbed power and scattered power at the plasma resonance) is surprisingly high (up to 10³).