We study the broadband photovoltaic response of field effect transistors on terahertz radiation. A simple physical analytical model of the response is developed. It is based on plasma density perturbation in the transistor channel by the incoming terahertz radiation. The model shows how the non-resonant detection signal is related to static (dc) transistor characteristics. We analyze loading effects related to capacitive, inductive, and resistive coupling of the detector to the read-out circuit as a function of modulation frequencies and loading resistors. As we show, the proposed physical model completed by loading effects fully describes the experimental results on the non-resonant sub-terahertz detection by all studied III-V (GaAs, GaN) and silicon based transistors. Field effect transistors were recently proposed as the best terahertz detecting pixels for fabrication of low cost focal plane arrays for terahertz imaging. This article gives prospects for electrical simulation of these transistors and their optimal integration in the focal plane arrays.

We introduce a previously unknown spin-related transport phenomenon, consisting of a transformation (swapping) of spin currents, in which the spin direction and the direction of flow are interchanged. Swapping is due to the spin-orbit interaction in scattering. It originates from the correlation between the spin rotation and the scattering angle. This effect is more robust than the skew scattering, since it exists already in the first Born approximation. Swapping may lead to the spin accumulation with spin polarization perpendicular to the surface, unlike what happens in the spin Hall effect.