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The bow-tie (BT) diodes with broken symmetry for room temperature terahertz detection were developed of AlGaN/GaN high electron mobility transistor (HEMT) structures with two dimensional electron gas (2DEG). The performance of new THz detectors was obtained at 0.3 THz frequency and compared with the most sensitive InGaAs-based BT diodes of the same design. Our experiments at sub-THz frequency revealed...
More than 60 years ago, Zener has predicted that an electron in a periodic potential subject to a static electric field will perform harmonic oscillations (socalled Bloch oscillations) in real space. We present here results which directly prove the existence of these spatial oscillations: By observing the field-induced shift of the wannier-Stark ladder, the macroscopic dipole moment associated with...
The terahertz (THz) imaging enhanced with compact diffractive lenses and sensitive room temperature THz detectors was demonstrated to be suitable for carcinoma zones screening in bio-tissues. Optical transmission of the dehydrated histological sections with a colon cancer was measured with close to wavelength-limited spatial resolution at 0.6 THz frequencies. High number of the explicit areas where...
A very simple model describing steady-state electron transport along a quantum superlattice of a finite length taking into account an arbitrary electrical characteristic of the injecting contact is considered. In the singleminiband approximation, exact formulas for the spatial distribution of the electric field in the superlattice are derived for different types of contact. Conditions under which...
The THz emission from large-area-grating coupler placed on the 2DEG AlGaN/GaN heterostructures was measured at frequency range 0.3–30 THz and temperature from 300 to 500 K with high spectral accuracy. The THz emission spectrum below 10 THz was found to be close to the thermal black-body radiation. Indistinct radiation modified with 2DEG plasma resonances was observed at frequencies below 3 THz.
Zone plates of the conventional design and the complex with integrated band-pass filter apertures were fabricated on the metal film and highly resistive silicon substrate using the direct laser writing. The focusing performance of the diffractive components was studied measuring the 0.6 THz frequency beam profiles along the optical axis. The compact lenses with the focal length of 5 and 10 mm and...
A compact THz imaging system was developed for the adenocarcinoma-affected human colon tissues measurement simultaneously in transmission and reflection geometry. The contrast between the cancer and control tissues fixed in paraffin at 0.6 THz frequency was up to 23%.
Experimental investigation of low frequency noise characteristics of the In0.53Ga0.47As/InP bow-tie terahertz detectors with a near monolayer of InAs has been carried out in (77–300) K temperature range. Spectral density of voltage fluctuations of investigated diodes at room temperature is proportional to 1/f, while below 200 K Lorentzian-type spectra dominate. Characteristic times of the observed...
Bow-tie antenna coupled field-effect transistors have been implemented in 0.25 μm AlGaN/GaN process technology and have been mounted on an aplanatic hemispherical silicon substrate lens. By asymmetric coupling of 590-GHz radiation to the channel, the transistors are used as direct power detectors, achieving system noise-equivalent power values of 166 pW/√Hz at 590 GHz (referred to the total beam power)...
A versatile and compact solid state THz radar system operating in the continuous wave mode is described. A frequency-modulated electronic THz source is used for target illumination. On the receiver side a THz sensor array is employed to increase imaging performance. The system's performance is evaluated and application examples are shown.
Properties of antenna-coupled microbolometers optimized for room temperature 300 GHz and 600 GHz resonant frequency detection is reported. Dipole antenna placed on freestanding SiN membrane is used to couple THz radiation power to the titanium-based thermo-resistor. We demonstrate that antenna-coupled micro-bolometers can be well suited for beam profile imaging of the THz pulses emitted by the photoconductive...
Strong electric field induced nonlinear effects in electrical conductivity of single wall carbon nanotube films are demonstrated. The increase of electric conductivity with increase of external electric field strength (up to 200 kV/cm) was attributed to the tunneling between the conducting paths of metallic SWCNT and hoping in one dimensional metallic constituents in carbon nanotube compound, whilst...
The dependence of the far-infrared spectra of single-wall carbon nanotube (SWCNT) thin films on nanotube length is demonstrated in the experiments. It has been shown that the main mechanism of the terahertz conductivity peak in the spectra of the SWCNT film is localized plazmon resonance in SWCNT. We have demonstrated that the compression of a short-length SWCNT film after isopropanol treatment can...
Transmission and reflection spectra of resonant metallic filters fabricated by the laser direct writing technique were investigated in terahertz frequency range. Effect of thin dielectric layer on surface waves excitation was observed as a larger redshift of the transmittance peak dependent of dielectric film thickness and metal film surface smoothness.
Zone plates with integrated band-pass filters were designed numerically via finite-difference time-domain technique and demonstrated experimentally at 0.76 THz frequency applying Fourier spectroscopy and optically pumped molecular terahertz laser.
Terahertz reflection imaging with the laser operating in TEM01 mode and large area detector was investigated. Imaging of high spatial resolution targets with up to diffraction limited resolution was demonstrated. Imaging system was also illustrated to be suitable to identify defects in silicon solar cells.
Performance of the antenna-coupled detectors was measured by the quasi-optical setup in wide frequency range from 0.1 to 1.0 THz. Studied sensors were based on the titanium microbolometers coupled with the double-dipole- or log-periodic-type antenna for room temperature THz detection. The THz radiation of the selectively filtered broadband LTG-GaAs photoconductive emitter and the system generating...
We report on an order-of-magnitude enhancement of sensitivity of CMOS-transistor-based THz detectors. At 2.54 THz, 3.13 THz and 4.25 THz, responsivity values of 336 V/W, 308 V/W, and 230 V/W and optimum noise-equivalent-power values of 63 pW/√Hz, 85 pW/√Hz, and 110 pW/√Hz are obtained.
We discuss two different implementations of field-effect-transistor based detectors (TeraFETs) optimised for imaging above 1 terahertz (THz). (i) Resonant-antenna-coupled MOSFET rectifiers have been fabricated using CMOS technology and (ii) broad-band devices by exploting GaN/AlGaN high-electron-mobilitiy transistors. Both technologies are scalable to large detector arrays and allow realisation of...
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