Abstract
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.
Highlights
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
Become superconducting NbN HEB (Hot-Electron Bolometer) detectors that exhibit high sensitivity (NEP ≈ 2 × 10–13 W/√Hz) combined with record response time (τ ≈ 50 ps), as well as energy resolution δE ≈ 3 × 10–18 J3–5. Such unique characteristics of NbN HEB detectors made possible by the use of ultra-thin (d ≈ 3–5 nm) disordered NbN films, which are characterized by a low diffusion coefficient (D ≈ 0.5 cм2/c), high critical temperature (Tc ≈ 10 К), small width of the superconducting transition (∆Tc < 0.2 К), the strong temperature dependence of the resistance in the region of the superconducting transition
This work presents the results of studies of the energy relaxation times in the vanadium nitride (VN) thin films and the characteristics of the HEB detectors based on them for the first time
Summary
Of a spiral logarithmic antenna) and having suppressed superconductivity due to proximity effect[14]. To study the energy relaxation time of electrons in the VN structures, two series of measurements were carried out using the method of mixing of two monochromatic radiation sources in the sub-THz and in the C-band IR frequency range. To study the response of the VN structures of small size to short laser pulses of the IR range ω ≈ 193 THz, we used a DFB laser in the mode of generation of radiation of short pulses with a repetition frequency of ~ 70 MHz and a duration of < 45 ps. The amplitude modulation of THz radiation occurred at a frequency ωmod ≈ 3 (kHz) using a mechanical chopper, providing 100% modulation depth with a shape close to the meander In this experiment, only a cooled amplifier with an operating frequency band of 1 kHz–400 MHz was used. The loss of the highfrequency signal in the contact areas of the spiral logarithmic antenna will increase, and mismatched bridge and antenna impedances will be introduced[22]
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