Infrared blocking materials

AlN thin films on the flexible polymeric Teflon and Mylar substrates show characteristics of efficient infrared (IR) blocking filters (IR “stealth”). They can suppress heat flows from the warm parts of objects (T ~ 300÷500 K) and block IR radiation from them, but are transparent in visible, microwave, and THz spectral regions in contrast to special paints that demonstrate a relatively high emissivity in the IR spectral rangeТонкі плівки AlN на гнучких полімерних підкладках тефлону та майла у характеризуються властивостями ефективних інфрачервоних (ІЧ) блокуючих фільтрів. Вони можуть придушувати теплові потоки від гарячих частин об'єктів (T ~ 300ч500 K) і блокувати ІЧ випромінювання від них, але є прозорими у видимому, мікрохвильовому та ТГц спектральних діапазонах на відміну від спеціальних фарб, що демонструють відносно високу випромінювальну здатність в ІЧ області спектра.Тонкие пленки AlN на гибких полимерных подложках тефлона и майлара характеризуются свойствами эффективных инфракрасных (ИК) блокирующих фильтров. Они могут подавлять тепловые потоки от нагретых частей объектов (T ~ 300ч500 K) и блокировать ИК излучение от них, но являются прозрачными в видимом, микроволновом и ТГц спектральных диапазонах в отличии от специальных красок, которые демонстрируют относительно высокую излучательную способность в ИК области спектра

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

Dislocations as internal sources of infrared radiation in crystals subjected to ultrasonic influence

We have carried out a systematic study of mercury cadmium telluride crystals subjected to the high-frequency and high-intensity ultrasonic influence. The charge carrier transport parameters were determined from the Hall coefficient and conductivity measurements. Temperature dependences of the electron concentration without and during the ultrasonic load were calculated. A good agreement between the experimental and theoretical data was obtained. A model of internal source of the infrared radiation associated with a dislocation is proposed for the explanation of sonically stimulated effects in the semiconductor system. We have considered a possibility of the thermooptical excitation in Hg₁₋xCdxTe alloys during sonication, which can result in the nonequilibrium charge carrier generation and changes in electrical parameters of the material

Noise spectra and dark current investigations in n⁺-p-type Hg₁₋xCdxTe (x ≈ 0.22) photodiodes

The dark current and noise spectra were investigated in Hg₁₋xCdxTe (x≅0.22) photodiodes at zero and low reverse bias voltages. The photodiodes were prepared by boron implantation into LPE films. The 1/f noise is proved to be correlated with tunneling current via the deep defect states in the gap at low reverse biases U≤0.1 V. In the photodiodes, where the tunneling current is found to be dominating, the 1/f noise is observed up to frequencies 10⁴ Hz. The decrease of tunneling current results in the decrease of 1/f noise

Ellipsometric control of quality of polished MgF₂ optical ceramics

In this work, ellipsometric measurements were used to optimise the technology of machine working the polished parts made of MgF₂ optical ceramics. The ellipsometry is a high-performance contactless method to control quality of optical surfaces, which is used here due to a sharp response of light polarisation conditions to the properties and parameters of surface and subsurface layers in investigated reflective systems. It is shown that the highly productive technology of diamond polishing provides achievement of ellipsometric parameters at a level of conventional methods of polishing

Influence of elastic deformation on the residual ellipticity of polished optical materials

The elastic deformation of thin mirrors is widely used in systems of adaptive optics, however, there are no data upon investigations of influence of elastic deformations on parameters of reflected polarised light in the literature. Using the method of ellipsometry, the influence of elastic deformation on the residual ellipticity of polished samples made of optical materials was studied. The results obtained during the researches have shown that the application of elastic deformations leads to essential changes of the minimum ellipticity tgp of polished samples, which testifies to the necessity to take into account this circumstance for devices of adaptive optics, input windows, cryostats and other optical parts working with the changing temperature

Composition and concentration dependences of electron mobility in semi-metal Hg₁₋xCdxTe quantum wells

Modeled in this work is the electron mobility in the n-type Hg⁰.³²Cd⁰.⁶⁸Te/Hg₁₋xCdxTe/Hg⁰.³²Cd⁰.⁶⁸Te quantum well being in the semi-metal state at T = 77 K. Calculations take into account longitudinal polar optical phonon scattering, charged impurities scattering and electron-hole scattering. The Boltzmann transport equation has been solved directly to account the inelasticity of optical phonon scattering. Numerical modeling showed that the intrinsic electron mobility at liquid nitrogen temperature is sufficiently low. This mobility can be increased up to the values close to 10⁵…10⁶ cm² /(V·s) by increasing the electron concentration in the well. A higher electron concentration could be reached by doping the barriers or by applying the top gate voltage. The effect of mobility growth could be explained by the enhancement of 2DEG screening and the decrease of holes concentration

Simulated properties of printed antennas on silicon substrates for THz/sub-THz arrays

Some properties of printed antennas and arrays for uncooled silicon plasmon detector arrays based on field effect transistors are shortly discussed. Antenna geometry has been optimised for maximising gain at 300 GHz. It is shown that for bow-tie antennas in the arrays in diffraction limit approximation, there are almost no cross-talks between the neighbour antennas. It is shown that the gain for one antenna is higher than that for antenna, in the array

Layer structure formation in Hg₁₋xCdxTe films after high-frequency sonication

Electrophysical parameters of Hg₁₋xCdxTe thin films grown by liquid-phase epitaxy and molecular-beam epitaxy were investigated before and after the high-frequency sonication ( fUS = 7.5 MHz, WUS ~ 10⁴ W/m²). It was determined that parameters of MBE-grown Hg₁₋xCdxTe thin films are stable to ultrasound effect, while for thin films grown by LPE the sonically stimulated change of the conductivity type was observed. The best agreement between experiment and calculation was obtained in the frame of the assumption about forming of the thin layer with another conductivity type. The possible nature of the observed effect was analyzed

Determination of parameters of cadmium telluride films on silicon by the methods of main angle and multiangular ellipsometry

The multiangular ellipsometric measurements were conducted at two wavelengths 435 and 579 nm on the system that contains cadmium telluride film deposited onto the monocrystalline silicon substrate. The refraction index and the film thickness as well as their distribution over the sample area were determined. It has been shown that the refraction index of the film (2.15…2.35) is less than that of the monocrystalline cadmium telluride (~3) that can testify the porous structure of the film or about roughness of the film surface. Obtained dependences of values of the film optical parameters from the angle of incidence testify weak heterogeneity of film properties along its depth. It was detected that there are the false solutions of the ellipsometric equation for each angle of incidence