Modelling of GaN HEMTs as Terahertz Detectors Based on Self-Mixing

During recent years, Terahertz (THz) electronics has attracted much attention in the applications of medical, biological and industrial imaging, broadband communication etc. A GaN high-electron-mobility transistor (HEMT) is promising to work as a THz detector due to its high breakdown field, high carrier density and high temperature operation ability etc. Here we report a quasistatic self-mixing model to describe the main features of the THz response in a GaN HEMT. The model can explain not only the magnitude, but also the polarity of the photocurrent. Based on this model, we improve the gate design in GaN HEMTs from traditional symmetric pads to novel asymmetric pads. This novel gate design has been proved to be able to improve the THz detection responsivity by one order of magnitude.