Loading the Antenna Gap with Two-Dimensional Electron Gas Transistors: A Versatile Approach for the Rectification of Free-Space Radiation

Light conversion into dc current is of paramount interest for a wide range of upcoming energy applications. Here we integrated dipole antennas with field-effect transistors based on a two-dimensional electron gas, with the specific aim of rectifying free-space radiation exploiting both artificial and natural nonlinearities. In the present work, resonant conditions of antenna-coupled field-effect rectifiers have been identified in a terahertz experiment based on the well-established GaAs transistor technology. Rectification of free-space radiation has been observed in a broad 0.15-0.40 THz range by implementing quasi-optical coupling with a substrate lens to an AlGaAs/GaAs heterostructure transistor into the gap of a cross-dipole antenna. The short- and the open-circuit resonances have been clearly identified through a comparison between experimental photocurrent spectra, electromagnetic simulations, and antenna models. The former depends only on the dipole antenna geometry, while the latter is determined by the impedance matching between the antenna and the integrated device and, as such, can be even tuned to the desired frequency by applying a dc gate bias. In addition, the high-mobility two-dimensional electron gas supports plasma wave cavity resonances featuring natural hydrodynamic nonlinearity. The resonant peaks corresponding to the different rectification mechanisms have been identified and discussed in terms of simple lumped-element models. The demonstrated concepts are extrapolated toward infrared frequencies, where novel application demands and novel two-dimensional electron gas materials for antenna-coupled rectifiers are emerging.