Study of the Coupling of Terahertz Radiation to Heterostructure Transistors with a Free Electron Laser Source

High electron mobility transistors can work as room-temperature direct detectors of radiation at frequency much higher than their cutoff frequency. Here, we present a tool based on a Free Electron Laser source to study the detection mechanism and the coupling of the high frequency signal into the transistor channel. We performed a mapping over a wide area of the coupling of 0.15 THz radiation to an AlGaN/GaN transistors with cut-off frequency of 30 GHz. Local, polarization-dependent irradiation allowed us to selectively couple the signal to the channel either directly or through individual transistor bias lines, in order to study the nonlinear properties of the transistor channel. Our results indicate that HEMT technology can be used to design a millimeter-wave focal plane array with integrated planar antennas and readout electronics.