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

High electron mobility transistors can work as room-temperature directdetectors of radiation at frequency much higher than their cutofffrequency. Here, we present a tool based on a Free Electron Lasersource to study the detection mechanism and the coupling of the highfrequency signal into the transistor channel. We performed a mappingover a wide area of the coupling of 0.15 THz radiation to an AlGaN/GaNtransistors with cut-off frequency of 30 GHz. Local,polarization-dependent irradiation allowed us to selectively couple thesignal to the channel either directly or through individual transistorbias lines, in order to study the nonlinear properties of thetransistor channel. Our results indicate that HEMT technology can beused to design a millimeter-wave focal plane array with integratedplanar antennas and readout electronics