The dynamic range of THz broadband FET detectors

Abstract

International audienceField effect transistors are promising detectors of THz radiation. They operate at room temperatures have high responsivity, low noise equivalent power, and fast response time. However, their linearity (dynamic range) and possibility of their application in the domain of high power radiation has not been yet sufficiently studied. We have investigated room temperature field effect transistors, detection at frequencies from 0.3 to 3 THz with power up to 100 kW/cm2. Several types of HEMTs and MOSFETs operating in the broadband non resonant detection regime, have been investigated. To provide a wide range of incident THz radiation intensities we used continuous-wave and pulsed sources: backward oscillators, CO2 pumped methanol laser, free electron laser, NH3, D2O, and CH3F lasers. We find that the photoresponse of HEMTs and MOSFETs is linear in radiation intensity up to a several kW/cm2 and then it saturates. The onset of the saturation depends on the radiation frequency and the transistor type. The observed saturation behavior can not be explained by the existing theoretical model which predict a square root like dependence of the photoresponse. We tentatively attribute the unusual features of the photoresponse saturation observed at high intensities considering high electric field transport phenomena, e.g., electron heating and electron velocity saturation. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

TCAD Model for TeraFET Detectors Operating in a Large Dynamic Range

“…The response saturation at high intensities of the THz radiation was also observed for Si MOSFETs [14]. Since the gate leakage could be negligible in Si MOSFETs due to the gate insulator, other mechanisms could be responsible for the response saturation.…”

“…Fig. 2 shows the dependence of the simulated detector response at 0.3 THz above threshold (V gt = 0.12 V) on the THz signal magnitude V a for the AlGaAs/InGaAs HFET TCAD model, compared with the measured data in [14] and the analytical results with the open boundary condition at the drain. To explore the device physics for the response…”

“…Fig. 4 shows the simulated detector response at 0.3 THz above threshold (V gt = 0.12 V) as a function of the THz signal magnitude V a for the AlGaN/GaN HFET TCAD model with different physical mechanisms, compared with the measured data in [14] and the analytical results with the open boundary condition at the drain. Again, from the profiles of the electron current density transverse to the channel at the positions closely (1 nm) below the Schottky gate contact in Fig.…”

“…Recent interests include operating TeraFET detectors at high incident power, which could be used to measure the duration and structure of the high-power THz pulses [13]. At large intensities of the incident THz radiation, the response has been observed to saturate in the measurements [14]. Different propositions have been made to explain this effect [15], [16], [17].…”

“…A v a , w / o V s a t s l o p e ~ V a s l o p e ~ V 2 a R e s p o n s e ( V )T H z s i g n a l m a g n i t u d e V a ( V ) Comparison of analytical and simulated drain response at 0.3 THz above threshold with the measured data in[14] as a function of the THz signal magnitude for the SOI MOSFET. The analytical and measured data are normalized to the range of the simulated results.…”