Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications

Resonant frequencies of the two-dimensional plasma in FETs increase with the reduction of the channel dimensions and can reach the THz range for sub-micron gate lengths. Nonlinear properties of the electron plasma in the transistor channel can be used for the detection and mixing of THz frequencies. At cryogenic temperatures resonant and gate voltage tunable detection related to plasma waves resonances, is observed. At room temperature, when plasma oscillations are overdamped, the FET can operate as an efficient broadband THz detector. We present the main theoretical and experimental results on THz detection by FETs in the context of their possible application for THz imaging.Comment: 22 pages, 12 figures, review pape

Terahertz responsivity of field-effect transistors under arbitrary biasing conditions

Current biased photoresponse model of long channel field-effect transistor (FET) detectors is introduced to describe the low frequency behavior in complex circuit environment. The model is applicable in all FET working regions, including subthreshold, linear, saturated modes, includes bulk potential variations, and handles the simultaneous gate-source and drain-source detection or source-driven topologies. The model is based on the phenomenological representation that links the photoresponse to the gate transconductance over drain current ratio (gm/ID) and circuit theory. A derived method is provided to analyze the detector behavior, to characterize existing antenna coupled detectors, and to predict the photoresponse in a complex circuit. The model is validated by measurements of 180 nm gate length silicon and GaAs high electron mobility FETs

imaging the coupling of terahertz radiation to a high electron mobility transistor in the near field

We used AlGaN/GaN high electron mobility transistors as room-temperature direct detectors of radiation at 0.15 THz from a free electron laser, hence 5 times higher than their cutoff frequency of 30 GHz. By near-field active mapping we investigated the antenna-like coupling of the radiation to the transistor channel. We formulate a model for the detection based on self-mixing in the transistor channel. The noise equivalent power is found in the range of 10^{-7} W/Hz^{0.5} without any optimization of the device responsivity. Present day AlGaN/GaN fabrication technology may provide operation at higher frequency, integration of amplifiers for improved responsivity and fast switches for multiplexing, which make the detector here described the basic element of a monolithic terahertz focal plane array

APPLICATIONS OF PLASMONICS FOR TERAHERTZ DETECTION, MODULATION AND WAVEGUIDING

Ph.DDOCTOR OF PHILOSOPH

Performance limits of terahertz zero biased rectifying detectors for direct detection

Performance limits of uncooled unbiased field effect transistors (FETs) and Schottky-barrier diodes (SBDs) as direct detection rectifying terahertz (THz) detectors operating in the broadband regime have been considered in this paper. Some basic extrinsic parasitics and detector-antenna impedance matching were taken into account. It has been concluded that, in dependence on radiation frequency, detector and antenna parameters, the ultimate optical responsivity (ℜopt) and optical noise equivalent power (NEPopt) of FETs in the broadband detection regime can achieve ℜopt ~ 23 kV/W and NEPopt ~ 1⋅10⁻¹² W/Hz¹/², respectively. At low radiation frequency ν in the THz spectral region the NEPopt of SBD detectors can be better by a factor of ~1.75 as compared to that of Si MOSFETs (metal oxide semiconductor FETs) and GaAlN/GaN HFETs (heterojunction FETs) with comparable device impedances