“…The principle behind THz radiation detection in a FET device beyond its cut-off frequency is based on the nonlinear properties of the transistor [7,8]. Different types of FETs, such as Schottky diodes [9], Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) [10][11][12][13], Heterostructure Bipolar Transistors (HBTs) [14,15], and High Electron Mobility Transistors (HEMTs) (e.g. GaAs-based commercial HEMTs [16], nitride-based HEMTs [17,18], and gated double quantum well heterostructures [19]) were used to detect the THz radiation.…”