Improvement of terahertz field effect transistor detectors by substrate thinning and radiation losses reduction.

International audiencePhenomena of the radiation coupling to the field effect transistors based terahertz (THz) detectors are studied. We show that in the case of planar metal antennas a significant portion of incoming radiation, instead of being coupled to the transistors, is coupled to an antenna substrate leading to responsivity losses and/or cross-talk effects in the field effect based THz detector arrays. Experimental and theoretical investigations of the responsivity versus substrate thickness are performed. They clearly show how to minimize the losses by the detector/ array substrate thinning. In conclusion simple quantitative rules of losses minimization by choosing a proper substrate thickness of field effect transistor THz detectors are presented for common materials (Si, GaAs, InP, GaN) used in semiconductor technologies

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/P-s), where R-0 is the low-power responsivity and P-s is the saturation power. We demonstrated that the linear part response decreases with radiation frequency increase as R-0 proportional to f(-3), whereas the power at which signal saturates increases as P-s proportional to f(3). 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