Time Resolution and Dynamic Range of Field-Effect Transistor–Based Terahertz Detectors

We studied time resolution and response power dependence of three terahertz detectors based on significantly different types of field-effect transistors. We analyzed the photoresponse of custom-made Si junctionless FETs, Si-MOSFETs, and GaAs-based high-electron-mobility transistor detectors. Applying monochromatic radiation of a high-power, pulsed, line-tunable molecular THz laser, which operated at frequencies in the range from 0.6 to 3.3 THz, we demonstrated that all these detectors have at least nanosecond response time. We showed that detectors yield a linear response in a wide range of radiation power. At high powers, the response saturates varying with radiation power P as U = R0P/(1 + P/Ps), where R0 is the low-power responsivity and Ps is the saturation power. We demonstrated that the linear part response decreases with radiation frequency increase as R0 ∝ f− 3, whereas the power at which signal saturates increases as Ps ∝ f3. We discussed the observed dependencies in the framework of the Dyakonov-Shur mechanism and detector-antenna impedance matching. Our study showed that FET transistors can be used as ultrafast room temperature detectors of THz radiation and that their dynamic range extends over many orders of magnitude of power of incoming THz radiation. Therefore, when embedded with current driven read-out electronics, they are very well adopted for operation with high power pulsed sources.