Resonant response of a FET to an AC signal: influence of magnetic field, device length, and temperature

A theoretical investigation is made of the response of a field-effect transistor (FET) to an incoming electromagnetic radiation in the presence of a perpendicular, weak magnetic field. The influence of an external friction due to electron scattering by impurities and/or phonons, and of the internal friction due to electron-electron scattering, is taken into account. The treatment is valid for a nondegenerate electron gas in which the mean-free path for electron-electron scattering λ_ee is much smaller than the device length L and than the mean-free path due to collisions with impurities and/or phonons λ_coll. These requirements, written as λ_ee≪L≪λ_coll, are fulfilled for magnetic fields sufficiently weak that Landau quantization is absent and the electron motion is described within the framework of hydrodynamics. It is demonstrated that a high-electron mobility transistor (HEMT), with a short (long) channel, yields a resonant (nonresonant) response to an ac signal induced by the incoming electromagnetic radiation at the plasma oscillation frequencies of the two-dimensional electrons in the device. Keeping the device length and temperature at control, an applied magnetic field can be tuned to achieve the desired effect on the response of the device. It is observed that the lower the temperature, i.e., the higher the mobility, the higher the responsivity of the device. Such response makes the FET a promising device for new types of sources, detectors, mixers, and multipliers. The HEMT-based devices should, in principle, operate at much higher frequencies than the conventional transit time-limited devices, since the plasma waves propagate much faster than electrons.