Fabrication and experimental tests of materials and optics for Terahertz range used in field effect transistor detectors arrays are described. The method using diffractive optics, fabricated in 3D printing technology, was used for tests with GaN/AIGaN based FETs sub-THz detectors working in 300 GHz atmospheric window. The lens arrays focus energy exactly on the detectors and additionally reduce mutual detector crosstalk. Finally they improve detectors signal to noise ratio by more than one order of magnitude. Moreover such lens arrays are cost-effective, easy reproducible and thin elements.

Experimental and theoretical investigations of the influence of substrate thickness on the performance of Si field effect transistor terahertz detectors are presented.. We show that in the case of planar metal antennas a significant portion of incoming radiation, instead of being coupled to the transistors, may be coupled to the substrate leading to important responsivity losses..The ways of avoiding these losses are discussed.

We report on the photoresponse of AlGaN/GaN HEMT to THz radiation of low and high intensity. We show that the response vs. gate bias dependence can be described by the theory of Dyakonov-Shur in the whole range of radiation intensity. Unusual behavior of the photoresponse vs. intensity was observed under laser irradiation: a quadratic increase of the response followed by saturation. We speculate that this phenomenon can be explained by hot electrons capture by traps in AlGaN or buffer layers.

We present results of investigations of Plasma Assisted Molecular Beam Epitaxy (PAMBE) - grown GaN/AIGaN High Electron Mobility Transistor (HEMT) structures for fabrication of detectors and emitters operating in THz spectral range. These devices are standard HEMT structures but equipped with additional antennas that ensure THz radiation coupling. THz detectors and emitters were processed using different HEMT designs. The results of emission experiments at room temperature demonstrate emission in the spectral range from 0.5 to 12 THz with a total integrated power of the single transistor of the order of 100 nW. The results of room temperature THz detection (photoresponse experiments) in the ranges 110-170 and 220-330 GHz are presented and discussed. THz experiments, transistor electrical tests and data analysis presented in this work, clearly show that PAMBE grown GaN/AIGaN transistors can used as promising elements of future THz imaging systems.

An overview of main results concerning THz detection related to plasma nonlinearities in nanometer field effect transistors is presented. In particular nonlinearity and dynamic range of these detectors are discussed. As a conclusion, we will show one of the first real world application of the FET THz detectors: a demonstrator of the imager developed for fast postal security.

We present the concept, the fabrication processes and the experimental results for materials and optics that can be used for terahertz field-effect transistor detector focal plane arrays. More specifically, we propose 3D printed arrays of a new type - diffractive multi-zone lenses of which the performance is superior to that of previously used mono-zone diffractive or refractive elements and evaluate them with GaN/AlGaN field-effect transistor terahertz detectors. Experiments performed in the 300-GHz atmospheric window show that the lens arrays offer both a good efficiency and good uniformity, and may improve the signal-to-noise ratio of the terahertz field-effect transistor detectors by more than one order of magnitude. In practice, we tested 3 × 12 lens linear arrays with printed circuit board THz detector arrays used in postal security scanners and observed significant signal-to-noise improvements. Our results clearly show that the proposed technology provides a way to produce cost-effective, reproducible, flat optics for large-size field-effect transistor THz-detector focal plane arrays.

An overview of recent results concerning THz detection related to plasma nonlinearities in nanometer field effect transistors is presented. In particular, the research on the dynamic range of these detectors is described and two different technologies GaAs and GaN are compared. As a conclusion, we will show first real world applications of the plasma field effect transistors based THz detectors: demonstrators of the imagers (cameras and linear scanners) developed for fast postal security and for nondestructive industrial quality control.