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The propagation of evanescent acoustic-gravity waves in the atmosphere with an arbitrary altitude temperature profile is investigated. The possibility of the existence of two types of evanescent wave modes in a vertically nonisothermal atmosphere is shown. The first type is the f-mode in which the dispersion does not depend on the altitude inhomogeneity of temperature and, therefore, is carried out at any altitude level of the nonisothermal atmosphere. The second type is a recently discovered $$\gamma $$ ‑mode in which the dispersion depends on the altitude temperature gradient and can be fulfilled only at certain altitude intervals. The possibility of realizing the f- and $$\gamma $$ - modes in the Earth’s atmosphere is considered, taking into account the model altitude temperature profile. It is shown that these modes can exist at the heights of local temperature extremes in the atmosphere. Moreover, they are realized only in a narrow range of spectral parameters for which the conditions for a decrease in the wave energy above and below the level of their propagation are satisfied. For the f-mode, this energy condition is fulfilled at the altitudes of the local temperature minima, while that for the $$\gamma $$ -mode is at the altitudes of the local maxima. Recommendations are given regarding the possibility of observing these modes in the atmosphere of the Earth and the Sun. In the Earth’s atmosphere, the f-mode can presumably be observed near the mesopause with the characteristic wavelength $${{\lambda }_{x}} \approx 75\,{\text{km}}$$ and in the solar atmosphere at the heights of the chromospheres with $${{\lambda }_{x}} \approx 1600\,{\text{km}}$$ . The period of the f‑mode propagating in the region of the temperature minimum slightly exceeds the Brent-Vaisala period at this altitude. In the Earth’s atmosphere, the $$\gamma $$ -mode can be realized in the regions of maximum temperature, for example, at the height of the stratopause with $${{\lambda }_{x}} \approx 100\,{\text{km}}$$ and a period slightly larger than the Brent-Vaisala period at the altitude of its propagation.

Electric parameters of chlorine-doped CdTe crystals with a resistivity of (3÷6)× ×10^9 Ω·cm have been studied. The heavily doped material was characterized by an almost intrinsic conductivity, which is explained on the basis of the charge-carrier statistics by an emergence of self-compensated complexes. The ionization energy and the compensation degree of the impurity responsible for the semiinsulating state of CdTe are determined. The reverse current-voltage characteristics of the Ni/CdTe/Ni structure with a Schottky diode are interpreted as those of X/y-radiation detectors with extremely low values of “dark” currents of about 5 nA at a voltage of 1500 V and a Schottky contact area of 0.1 cm2 (at 300 K). Results testifying to a detector energy resolution of 0.42% for the spectrum of 137Cs isotope at an applied voltage of 1200 V and a temperature of 300 K have been reported. The dependence of the detection efficiency on the concentration of noncompensated impurities (defects) N, which determines the width of the space charge region in the diode, is proved to be described by a function with a maximum located atN ≈ 2×1011 cm^−3 for 137Cs isotope. By comparing the spectra obtained while irradiating the detector from either the Schottky or ohmic contact side, the concentration of noncompensated impurities in the studied crystals (of about 1012 cm^−3) is determined, which is close to the optimumN value., Дослiджено електричнi характеристики кристалiв CdTe, легованих хлором, з питомим опором (3–6)·10^9 Ом·см. Практично власну електропровiднiсть сильно легованого матерiалу пояснено утворенням самокомпенсованих комплексiв, виходячи зi статистики носiїв заряду. Знайдено енергiю iонiзацiї i ступiнь компенсацiї домiшки, вiдповiдальної за напiвiзолюючий стан CdTe. Iнтерпретовано зворотнi вольт-ампернi характеристики структури Ni/CdTe/Ni з дiодом Шотткi як детекторiв X/y-променiв, що забезпечують рекордно низькi значення “темнових” струмiв ∼5 нА при напрузi 1500 В, площi контакту Шотткi 0,1 см^2 (300 К). Представлено результати, якi засвiдчують енергетичну роздiльну здатнiсть детектора у спектрi iзотопу 137Cs: 0,42% при прикладенiй напрузi 1200 В (300 К). Доведено, що залежнiсть детектуючої ефективностi вiд концентрацiї нескомпенсованих домiшок (дефектiв) N, яка визначає ширину областi просторового заряду в дiодi, описується функцiєю з максимумом, який для iзотопу 137Cs припадає наN ≈ 2 ·1011 см^−3. Iз зiставлення спектрiв, отриманих при опромiненнi детектора з боку контакту Шотткi i омiчного контакту, знайдено концентрацiю нескомпенсованих домiшок у дослiджуваних кристалах (∼10^12 см^−3), яка близька до оптимального значення N.

We developed a new concept of X- and γ-ray radiation semiconductor detectors based on a large area graphene/semi-insulating single crystal CdTe Schottky-type heterojunction. These two terminal electronic devices can be easily fabricated by forming a Van der Waals contact between large area chemical vapor deposited graphene and CdTe substrates in air and at room temperature. This approach significantly reduces the fabrication cost and improves the reproducibility and stability of electrical properties. A detailed analysis of their AC and DC electrical properties was carried out in order to determine the width of the space charge region and dominant charge transport mechanisms at reverse bias. The unoptimized graphene/CdTe heterojunction detectors exhibited a promising spectral resolution of 241Am (59 keV) and 137Cs (662 keV) isotope radiation at room temperature.

The conductivity of semi-insulating Cl-doped CdTe crystals produced by Acrorad Co. Ltd. with a resistivity ρ = (3-6)×109 Ω·cm (300 K) was investigated. It is shown that the Fermi level in the band gap is located below the Fermi level in intrinsic CdTe which indicates the hole conductivity of the material. The concentration of holes in the studied crystals is determined to be 2-3 orders of magnitude higher than the concentration of electrons. The statistics of electrons and holes in a semi-insulating semiconductor containing self-compensation complexes (centers) is considered bearing in mind that the effect of background impurities and defects in heavily Cl-doped CdTe crystal is strongly reduced. A method for determining the ionization energy and the compensation degree of deep donors contained in the complexes was applied. It is shown that virtually intrinsic conductivity of the studied CdTe crystals is provided by the donors with ionization energy 0.68-0.69 eV, whose level is located at 0.05-0.06 eV above the middle of the band gap. Due to strong compensation, the Fermi level turns out below the middle of the band gap. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Measurements of the 55Fe-isotope emission spectra and the photosensitivity of CdTe detectors with a Schottky diode, and also the temperature dependence of the resistivity of a CdTe crystal ((2–3) × 109 Ωcm at 300 K) have been used to determine the concentration of uncompensated donors (1–3) × 1012 cm−3. Similar measurements performed for Cd0.9Zn0.1Te crystals with the resistivity (3–5) × 1010 Ω cm at 300 K have shown that the concentration of uncompensated donors in this case is lower by approximately four orders of magnitude. The results of calculations show that, due to such a significant decrease in the concentration of uncompensated donors, the efficiency of X- and γ-ray radiation detection in the photon energy range 59 to 662 keV can decrease by one-three orders of magnitude (depending on the photon energy and the lifetime of charge carriers in the space-charge region). The results obtained account for the apparent poor detecting properties of the Cd0.9Zn0.1Te detectors.

Temperature dependence of electrical characteristics of p-CdTe semi4nsulating single-crystals are studied, and substantial features of their electrical conductivity not described in available publications are revealed. The activation energy of the p-type conduction material close to the intrinsic one can be both lower and higher than the half-width of the band gap of semi conductor. The results of the analysis of statistics of electrons and holes based on the electroneutrality equation showed that the observed features of electrical properties of the material can be interpreted based on the specific features of compensation processes. The procedure of determining the ionization energy and degree of compensation of acceptors responsible for electrical conductivity of the material is suggested. It is shown that, in the limits of climatic temperature variations, inversion of the conduction type can be observed, and, as a consequence, the Schottky contact can disappear in the CdTe-based detector of the X-ay and γ radiation.

Integral expressions for spectral distributions of the radiation power for systems of non-interacting point charged particles moving on arbitrary trajectory in electromagnetic fields in isotropic transparent media and in vacuum are investigated using the Lorentz self-interaction method. Special attention is given to the research of the fine structure of the synchrotron radiation spectral distribution of two electrons spiraling in vacuum in a relativistic case. The spectra of synchrotron, Cherenkov and synchrotron- Cherenkov radiations for a single electron are analyzed.

Using the exact integral relationship for the spectral distribution of radiation power of an electron moving along a spiral in vacuum, the fine structure of synchrotron radiation spectrum at the first harmonics was investigated. The variation of the power spectral distribution of synchrotron-Cherenkov radiation for an electron moving in magnetic field in a transparent medium is studied.

Indium-doped Cd 0.9 Zn 0.1 Te crystals with semi-intrinsic conductivity have been investigated. Temperature dependence of their electrical characteristics shows a number of unconventional peculiarities: the thermal activation energy of conductivity is “anomalously” low (0.60–0.62 eV); the resistivity at elevated temperatures is greater than its intrinsic value for Cd 0.9 Zn 0.1 Te; the inversion of the conduction from n- to p-type occurs at a temperature slightly above 300 K, etc. The observed features are explained in terms of statistics of electrons and holes in a semiconductor containing a compensation center, whose concentration is much higher than those of uncontrolled (background) impurities and defects. Comparison of the calculation results and experimental data leads to the conclusion that the donor level, which is far distant from the middle of the band gap (∼ 0.3 eV), dominates the conductivity of the material and its compensation is virtually complete (N d /N a = 0.99996–0.99998) as predicted by Mandel's calculations. This result is of primary importance for the Cd 1−x Zn x Te Schottky diode detectors, since the width of the space charge region (active area of detector) in these devices is determined by the concentration of uncompensated impurities rather than the resistivity of the material.

The temperature dependences of the resistivity of detector-grade semi-insulating CdTe and Cd0.9Zn0.1Te single crystals were investigated. The investigations have revealed that the thermal activation energy can be higher than Eg/2 at T → 0 K or considerably less than this value, although the Fermi level is located near the middle of the band gap. It is shown that such an “anomalous” behavior of the electrical characteristics is explained in detail by the features of the compensation of deep acceptor levels in the semiconductor band gap. A method based on the electroneutrality equation is proposed for the determination of the ionization energy and compensation degree of the impurity (defect), which is responsible for the conductivity of the material. The results extracted with the use of this method lead to the prediction that the inversion of the conductivity type of the semiconductor under certain conditions can occur as the temperature varies during operation of a Cd(Zn)Te-based device.

Analytical and numerical investigations of the radiation spectra of electrons moving in magnetic fields in transparent isotropic medium are performed. The results showed that the Doppler effect influence on the peculiarities of the radiation power spectral distribution of the electrons were essential near the Cherenkov threshold.

The spectral distribution of quantum detection efficiency of X- and γ-ray Schottky diodes based on semi-insulating CdTe or Cd0.9Zn0.1Te crystals is substantiated and obtained in analytical form. It is shown that the width of the space charge region (SCR) of 6–40 μm at zero bias in CdTe (Cd0.9Zn0.1Te) Schottky diode is optimal for detecting radiation in the photon energy range above 5–10 keV. Based on the Poisson equation, the relationship between the SCR width and the composition of impurities and the degree of their compensation are investigated. It is shown that the presence of deep levels in the bandgap leads to a considerable increase in space charge density and electric field strength near the crystal surface. However, this effect contributes a small error in the determination of the SCR width using the standard formula for the Schottky diode. It is also shown that the concentration of uncompensated impurities in CdTe and Cd0.9Zn0.1Te crystals within the 4 × 1011–1013 cm–3 range is optimal for the detection efficiency of X- and γ-rays in the photon high-energy range. The record-high values of energy resolution have been obtained in the spectra of 241Am, 57Co, 133Ba and 137Cs isotopes measured using CdTe crystals with Schottky diodes because the concentration of uncompensated donors in the CdTe crystals (1–2) × 1012 cm–3 falls on an interval of maximum detection efficiency. In the spectrum of 57Co isotope, the limiting energy resolution has been achieved.

Cd0.9Zn0.1Te:In crystals with semi-intrinsic conductivity have been investigated. Temperature dependence of their electrical characteristics shows a number of unconventional peculiarities: the thermal activation energy of conductivity is “anomalously” low (0.60–0.62 eV); the resistivity at elevated temperatures is greater than its intrinsic value for Cd0.9Zn0.1Te; the inversion of the conduction from n- to p-type occurs at a temperature slightly above 300 K, etc. The observed features are explained in terms of statistics of electrons and holes in a semiconductor containing a self-compensation complex, whose concentration is much higher than those of uncontrolled (background) impurities and defects. Comparison of the calculation results and experimental data leads to the conclusion that the donor level, which is far distant from the middle of the band gap, dominates in the conductivity of the material and its compensation is virtually complete (Na/Nd = 0.99996–0.99998) as predicted by theory.

The methods for optimization of thermoelectric powder materials are discussed. Possibilities to optimize powder thermoelectric materials by computer‐aided modelling are demonstrated.