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The study of the bolometer response to terahertz (THz) radiation from a double-barrier resonant tunneling diode (RTD) biased into the negative differential conductivity region of the I–V characteristic revealed that the RTD emits two pulses in a period of intrinsic self-oscillations of current. The bolometer pulse repetition rate is a multiple of the fundamental frequency of the intrinsic self-oscillations of current. The bolometer pulses are detected at two critical points with a distance between them being half or one-third of a period of the current self-oscillations. An analysis of the current self-oscillations and the bolometer response has shown that the THz photon emission is excited when the tunneling electrons are trapped in (the first pulse) and then released from (the second pulse) miniband states.

The paper presents the experimental results of studying the dynamics of electron energy relaxation in structures made of thin (d ≈ 6 nm) disordered superconducting vanadium nitride (VN) films converted to a resistive state by high-frequency radiation and transport current. Under conditions of quasi-equilibrium superconductivity and temperature range close to critical (~ Tc), a direct measurement of the energy relaxation time of electrons by the beats method arising from two monochromatic sources with close frequencies radiation in sub-THz region (ω ≈ 0.140 THz) and sources in the IR region (ω ≈ 193 THz) was conducted. The measured time of energy relaxation of electrons in the studied VN structures upon heating of THz and IR radiation completely coincided and amounted to (2.6–2.7) ns. The studied response of VN structures to IR (ω ≈ 193 THz) picosecond laser pulses also allowed us to estimate the energy relaxation time in VN structures, which was ~ 2.8 ns and is in good agreement with the result obtained by the mixing method. Also, we present the experimentally measured volt-watt responsivity (S~) within the frequency range ω ≈ (0.3–6) THz VN HEB detector. The estimated values of noise equivalent power (NEP) for VN HEB and its minimum energy level (δE) reached NEP@1MHz ≈ 6.3 × 10–14 W/√Hz and δE ≈ 8.1 × 10–18 J, respectively.

We report on the development of a heterodyne receiver at mid-infrared wavelength for high-resolution spectroscopy applications. The receiver employs a superconducting NbN hot electron bolometer as a mixer and a room temperature distributed feedback quantum cascade laser operating at 10.6 μm (28.2 THz) as a local oscillator. The stabilization of the heterodyne receiver has been achieved using a feedback loop controlling the output power of the laser. Improved Allan variance times as well as a double sideband receiver noise temperature of 5000 K and a noise bandwidth of 2.8 GHz of the receiver system are demonstrated.

UDC 520.27We develop and study a hot-electron bolometer mixer made of a two-layer NbN-Au film in situ deposited on a silicon substrate. The double-sideband noise temperature of the mixer is 750 K at a frequency of 2.5 THz. The conversion efficiency measurements show that at the superconducting transition temperature, the intermediate-frequency bandwidth amounts to about 6.5 GHz for a mixer 0.112 µm long. These record-breaking characteristics are attributed to the improved contacts between a sensitive element and a helical antenna and are reached due to using the in situ deposition of NbN and Au layers at certain stages of the process.

The bolometer response to THz radiation from a weakly coupled GaAs/AlGaAs superlattice biased in the self-oscillations regime has been observed. The bolometer signal is modulated with the frequency equal to the fundamental frequency of superlattice self-oscillations. The frequency spectrum of the bolometer signal contains higher harmonics whose frequency is a multiple of fundamental frequency of self-oscillations.

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The terahertz frequency range comprises a consid erable part of the electromagnetic spectrum between the microwave and infra red ranges. However, explo ration of this frequency region began fairly recently owing to lack of powerful terahertz sources and receiv ers capable of detecting terahertz radiation.The problem with building efficient terahertz sources which would cover a wide frequency range is that the existing technology for generating radiation of neighbouring regions does not work quite as well at terahertz frequencies. At the high frequency end of the terahertz region it is difficult to achieve stable inverse population of energy levels with a sufficiently long lifetime, as in lasers. That is the reason why, for example, quantum cascade lasers (QCL) have to be cooled down to nitrogen temperatures or below in order to generate terahertz radiation. At the low fre quency end, the maximum frequency is determined by the electron travel time in the device, as in backward wave oscillators (BWO). In consequence, high electric and magnetic fields are required to produce terahertz radiation.Solid state radiation sources, such as avalanche diodes and quantum wells, are rather attractive owing to their small size, possibility of frequency remote control in a wide range, low weight and low energy consumption. However, these sources have certain limitations posed by influence of spurious parameters that grows with frequency and results in mismatch and decreased power output. The easiest and well known way to produce terahertz radiation is to multiply the frequency of an external generator with varactor mul tiplier diodes-doublers, triplers and arrays of such diodes. Although certain progress has been made in this direction, operation in the sub millimetre range requires high power reference generators and high efficiency multipliers. In this respect, semiconducting GaAs/AlAs superlattice (SSL) nanostructures look rather promising as candidates for frequency multipli cation because of their high efficiency, and so can potentially be used as terahertz LOs. The reason for this is that SSL's current voltage (IV) curve has a region with a negative differential resistance which continues up to terahertz frequencies [1].It has been shown that SSLs can be employed in high resolution spectroscopy measurements at tera hertz frequencies [2], in phase lock loops [3], as LOs of hot electron bolometer (HEB) receivers, and as a signal source in spectroscopy systems up to 3.2 THz [4,5]. As demonstrated in [6], SSLs can operate in a wide tem perature range of 4.2-300 K, and their efficiency is increased by an order of magnitude at helium temper atures (4.2 K).In this paper we present our results of studying the output power of an SSL operated at 4.2 K, and its per formance as an LO of a terahertz NbN HEB receiver. The authors of paper [7] have shown that the optimal LO power level for quasioptical and waveguide NbN HEB receivers does not exceed 100-200 nW at tera hertz frequencies. Our HEB mixers were fabricated at MSPU from superco...