ZnSe Crystals Research Articles

Observation of the kinetic buildup of x-ray conduction current in ZnSe crystals

We have been observing the kinetic buildup of electrical conduction current upon x-ray irradiation in ZnSe single crystals. The objective is to understand the behavior of ZnSe crystals under x-ray irradiation, toward their potential use in x-ray detectors that do not require cooling and can operate above room temperature. The paper focuses on the factors that affect the behavior of traps at room temperature. A model is developed to understand the origin of the behavior of the conduction current under x-ray irradiation, taking into account the contributions from three types of traps for electrons (shallow, phosphorescent, and deep) and two luminescence centers (luminescence bands of 630 and 970 nm). Principally, the model is applied to the fitting of the experimental curves. Consequently, the work puts in evidence the role of electron accumulation on traps on the x-ray conduction current buildup on ZnSe crystals. We have obtained experimental dependencies of x-ray conduction current buildup current at 85 K, which indicates the presence of delay in comparison with x-ray luminescence buildup. This paper will demonstrate the effectiveness of our theoretical method in the framework of the multi-center model for wide-gap semiconductors.

Effect of Doping on the Electrical Characteristics of ZnSe

The effect of sulfur, iron, and chromium doping on the electrical characteristics of ZnSe single crystals was studied. The crystals, grown by the physical vapor transport method (PVT) at NASA Marshall Space Flight Center, were characterized by measuring electrical resistivity, capacitance, and dielectric constant using LCR meter. The morphology was studied by scanning electron microscopy to determine the crystallinity and micro defects. The measured resistivity and dielectric constant showed tunability as the function of frequency in the range of 100 Hz to 100,000 Hz, indicating the suitability of doped material for tuning devices. Besides, for the range from 50 mV to 1000mV, there was no difference in values for the studied frequency range, indicating no degradation or breakdown in the material. All doped ZnSe crystals with sulfur, iron, and chromium showed a similar trend as the function of frequency. Cr-ZnSe showed very high resistivity and lower dielectric constant compared to S-ZnSe and Fe-ZnSe crystals.

EXAFS study of the temperature dependence of the Debye–Waller factor in ZnSe zincblende compound

In this work, we investigate the temperature dependence of the Debye–Waller (DW) factor in a zincblende-type ZnSe crystal. For this purpose, we measured the extended x-ray absorption fine structure spectra at the Zn and Se K edges in the temperature range of 20–573 K. The DW factor can be described by two different models namely Einstein correlated model and Debye correlated model. The parallel and perpendicular DW factors, the Einstein parameters and Debye temperature are determined and discussed. The temperature dependence of the DW factor of the first, second and third bond distances corresponding to each edge are presented and discussed in terms of vibrational motion. The Einstein frequencies are compared to the vibrational densities of states. The vibrational motion of the first and second coordination shells are affected by the vibrational modes below the energy of the transverse optic modes and around the energy of the transverse acoustic modes, respectively. The DW factor extracted for each shell is influenced by different parts of the phonon spectrum.

USE OF RESINOUS SUBSTANCES BY THE EARLY NEOLITHIC POPULATION IN THE FOREST-STEPPE ISHIM AREA

In this study, the author set out to determine the chemical composition and possible use of a substance, which remnants were found on a tile fragment made of soft brown shist. This item was discovered in the occupa-tion layer of a Neolithic settlement belonging to the Boborykino culture (Mergen 3), located on the terrace of Lake Mergen in the forest-steppe of the Ishim area (south of Western Siberia). By analogy with the complexes of the Boborykino culture in the Tobol area — Yurtobor 3 (7701 ± 120 BP (UPI 559)) and Tashkovo 1 (7440 ± 60 BP (LE 1534)) — which age was determined using carbon-14 dating, the Mergen 3 settlement can be attributed to the second half of the 7th millennium Cal. BC. The fragment measuring 3.0 × 2.1 × 0.55 cm has a spherical indenta-tion in the centre measuring 2.0×2.0×0.2 cm with a volume of 0.118 cm3 (0.118 ml). The whole item probably had a square shape with rounded and slightly raised edges. A visual analysis of the spot was carried out using an MBS-10 binocular microscope at a magnification of 16×. The analysis revealed a brown substance on the edges of the indentation, which looked like a dark porous carbon-like spot in the centre. These remnants were studied using a Bruker ALPHA FT-IR spectrometer with an Eco-ATR module — a single reflection ATR sampling module equipped with a zinc selenide crystal (ZnSe) that allows you to analyse liquid, solid and powder samples without preliminary sample preparation. The measurements were performed in the wavenumber range of 300–4000 cm-1 at a resolution of 4 cm-1. Some of the most significant absorption bands (709; 975; 1,024; 1,027 cm-1) were ob-served, which characterise vibrations bending and stretching the bonds in the skeleton of an organic molecule containing single С–С and С–О bonds. The obtained spectra are most consistent with the IR absorption spectra of resin acids, in particular, dehydroabietic acid that is present in resin obtained from coniferous trees. Consider-ing the small volume of the above-mentioned substance and the limited of its burning, the author excludes the use of this tile as a lamp, the use of the substance for the preparation of glue that held together the parts of complex tools, as well as the use of the substance for healing wounds and for cosmetic purposes, which involved addi-tional ingredients. Signs of burning indicate the use of the artefact for rituals, in particular for obtaining finely dis-persed soot employed when applying tattoos. The conducted experiment showed that the soot from a burnt drop of fresh resin covered 4 cm2 of the wrist area. Soot formed at the very beginning of the combustion process (probably combustion of volatile components), then the substance was oxidised without noticeable emissions. The remnants of the porous substance on the tile confirm the importance of the moment of resin burning with the abundant production of soot. However, the possibility that there were other unknown areas of application of gali-pot obtained from coniferous trees is not excluded. In any case, it is safe to say that the early Neolithic population living in the Ishim area purposefully used natural resins in their activities.

The components of 630-nm band in ZnSe and their recombination mechanisms

A non-elemental luminescence band with a maximum at 630 nm was studied in the undoped ZnSe crystals. This broad luminescence band was expanded into components by the Alentsev-Fock method, and the two basic elemental components were identified at room temperature. For these elemental components, mechanisms of recombination were established by comparing the temperature dependences of the luminescence intensity at different wavelengths. These components were named: D+–band (hvmax= 1.875 eV, 661 nm, δ = 0.181 eV) with the hole recombination mechanism and D––band (hvmax= 2.028 eV, 611 nm, δ = 0.196 eV) with the electron recombination mechanism.

Formation of color centers at X-ray irradiation of ZnSe single crystals

In the present work we study the dose dependences of X-ray luminescence and X-ray conductivity at different temperatures and different angles of incidence of the exciting radiation and the registration of luminescence. Low-energy X-ray quanta (with energies up to 20 keV) do not create new structural defects in ZnSe crystals, but can only recharge existing ones. It was established from the dose dependences of the luminescence intensity of the 630-nm and 970-nm bands that X-rays do not create the color centers in ZnSe crystals, even those that are temperature unstable, which absorb the luminescent radiation. This fact is confirmed by the absence of conduction current change at additional optical intensive irradiation of ZnSe samples by optical quanta with wavelengths that coincide with luminescent quanta.

Correlative study of structural and optical properties of ZnSe under severe plastic deformation

The effect of plastic deformation on the optical and structural properties of ZnSe crystals has been investigated. The optical properties have been monitored by cathodoluminescence measurements as a function of the deformation degree. Remarkable differences in the defect-related emissions from the most severely deformed areas have been encountered. Deformation of the crystal lattice of ZnSe, associated with slip phenomena, has been studied by means of Electron Backscattered Diffraction and micro-Raman spectroscopy. The relation between the deformation and the optical properties of the ZnSe crystals has been described.

Free-electron Auger quenching of the Fe2+ excited state in ZnSe

The influence of free electrons in Fe2+: ZnSe crystals on the nonlinear transmission of high-power laser radiation with a wavelength of 2940 nm at room and low temperatures is experimentally found. Fe2+ : ZnSe samples additionally doped with Al are used. The transmission of an Al : Fe : ZnSe sample with electron conduction in a strong (peak intensity about 4.6 MW cm−2) field is almost the same as in a weak field both at low and room temperatures. The absence of an increase in the transmission of this sample under the action of high-power radiation is explained by increasing absorption saturation intensity of Fe2+ at this wavelength due a decrease in the lifetime of the excited state of Fe2+. The decrease in the lifetime is related to the well-known Auger quenching of impurity luminescence in semiconductors by free electrons.

Optical properties of Fe- and Nd-doped ZnSe crystals measured by pump-probe spectroscopy

We present the excited-state dynamics and optical properties of Fe- and Nd-diffusion doped zinc selenide polycrystals with different concentration measured by pump-probe spectroscopy in the visible and NIR range (400-1000 nm). The introduction of dopants allows one to control the optical properties of samples, which then can be used to create effective optoelectronic components for wide spectral ranges.

Methods of the matrix analysis and graphic ranking of the array of the experimental IR spectroscopy data in studying the inter-component processes in the mixture of pheniramine maleate and naproxen

A widespread use of complex pharmacotherapy entails the necessity of studying the processes occurred in pharmaceutical mixtures. IR spectroscopy is one of the methods used to assess the stability of substances. To increase the efficiency of interpretation of the IR spectra of mixtures, a method combining matrix methods and graphic ranking of the array of experimental data has been developed. This approach has been tested for the analysis of model mixtures of pharmaceutical substances naproxen and pheniramine maleate. Absorption spectra were obtained on an Avatar 360 FT-IR ESP Fourier transform spectrometer (Nicolet, USA) using an ATR (primary attenuation total reflection) attachment Smart Perfbmer (optical crystal ZnSe; spectral range 1.35 - 26.6 pm, 7400 - 375 cm4). The obtained IR spectra were processed using Thermo Scientific Specta embedded software. Graphs for graphical ranking were plotted in the coordinates of the mixture heating temperature —relative frequency intensity. The points on the graph represent the relative intensity of the bands for a mixture kept at a certain temperature, whereas the curves with which they are connected reflect the processes occurring in the structure of the substance. Common trends in the relative intensity for different frequencies (at the same temperature) and/or for a number of frequencies of a certain characteristic region, indicates the unidirectionality of the process. Graphic ranking is applied to the characteristic bands of pyridine and aliphatic nitrogen of pheniramine maleate and characteristic frequencies of the intermolecular hydrogen bond and carbonyl group of naproxen. We also used the method of mathematical ranking of the matrices of transmittance values. For the characteristic bands of the studied compounds, a combined use of graphical and mathematical ranking allowed us to infer a change in the structure of naproxen and pheniramine maleate under the impact of elevated temperatures: the salt of pheniramine and maleic acid in aliphatic nitrogen has one structural conformation, whereas the binding force depends on the temperature.

Intracenter excitation of the 630 nm band in ZnSe crystals

Spectral studies of a known luminescence band with a maximum wavelength of 630 nm have been carried out on undoped ZnSe crystals. The spectral position of the intracenter excitation band is determined. It is identified using the photoconductivity spectra and the luminescence excitation spectra of the 630 nm band that the transitions from the ground state to an excited state of that center. Result in an absorption band of 520 nm (2.38 eV). An intracenter luminosity spectrum is obtained from the excitation at that absorption band, with the value of the Stokes shift being ΔEC = 0.48 eV. A comparison of the luminescence spectrum at an intracenter excitation against the same at a zone-zone UV excitation and an X-ray excitation shows that they differ noticeably from each other. A half-width of the luminescence band is smallest at the intracenter excitation and the position of its spectral maximum is the same for different samples. This confirms that the 630 nm band is non-elementary for luminescence quenching of ZnSe crystals with above-bandgap energies.

Effect of annealing in zinc vapors on charge trapping properties of ZnSe, ZnSe(Te) and ZnSe(Al) scintillation crystals: Revealing the mechanisms by DFT computational studies

The mechanisms of changes of ZnSe crystals conduction due to their doping with tellurium or aluminum ions as well as due to annealing in zinc vapors are analyzed in experimental and computational studies. The electrical resistivity of undoped, Te- and Al-doped ZnSe crystals were measured before and after annealing in zinc vapors. Doping with tellurium or aluminum leads to a decrease of electrical resistivity (increase of conductivity) of ZnSe crystals, and this decrease is stronger in case of Al-doped samples. After annealing, a decrease in resistivity by 5–8 orders of magnitude in zinc vapors was observed for all samples. The electronic structures of ZnSe crystals with various point defects were calculated within the DFT approximation using the plane-wave pseudopotential method. The native vacancies VZn and VSe, substitution defects AlZn, OSe and TeSe, interstitial impurities Zni, as well as some double and triple combinations of these defects were considered in calculations. The ionization energies of the defects were calculated using the transitive level (TL) formalism. It was found that the increase of conductivity in ZnSe → ZnSe(Te) → ZnSe(Al) sequence of samples arises primarily due to formation of hole trap centers on TeSe and AlZn and also due to higher ionization energies of such centers on AlZn in comparison with TeSe. The increase of conductivity of the samples after annealing in zinc vapors arises due to formation of the deep hole traps on interstitial defects Zni, and also due to annihilation of zinc vacancies. Annihilation of VZn changes the trapping properties of the system of native and doping-related point defects (deep electron traps disappear or become shallow, hole traps are formed) and this effect provides an additional mechanism of conductivity increase due to annealing.

Evaluation of surface and subsurface damages for diamond turning of ZnSe crystal.

With single-point diamond turning (SPDT), a series of samples are processed under different cutting parameters. The brittle-ductile transition depth of ZnSe crystal is obtained, and the damages of the samples are measured from surface and subsurface damage depths as well as damage density. The effects of cutting parameters on the damages are investigated quantitatively. The results show the cutting depth has a minor while the feed has a major effects on the damages. Also, the interaction effect between feed and cutting depth is very small for surface damage depth or damage density, while it is large for subsurface damage depth. Based on the indentation mechanics and the kinetic characteristics of SPDT, a model is proposed to evaluate the surface and subsurface damage depths of ZnSe crystal by cutting parameters. The model has an average relative error less than 15.0%, which could be further used to obtain the depth and the removal characteristics of cracks in shoulder region.

Tunable terahertz reflection spectrum based on zinc-blende structure crystals excited by ultrasonic

The tunable terahertz reflection spectrum of zinc-blende structure crystals (ZnSe, CuCl and InP), formed in the first bandgap, excited by ultrasonic is investigated in the present paper. Numerical simulation results show that, under the pressure of 0 GPa–100 GPa, the volume change of the crystal indicates that the zinc-blende structure crystals are suitable acousto-optic crystal. According to the optical phonon resonance dispersion, the frequency selective bandwidth of ZnSe, CuCl and InP crystal are 22.5 meV, 21.4 meV and 32.4 meV, respectively, indicating that the frequency selection range of InP crystal is wide. The transverse optical polariton is dis-propagating in the first bandgap and reflects. With the increase of ultrasonic frequency, the reflection peaks moves towards the restrahlen band, and the amplitude of the reflection spectrum decreases until it disappears. More transverse optical phonon combinations make the width of the reflection peak wider. The tunable terahertz reflection spectrum can be achieved by adjusting the ultrasonic frequency, a satisfactory condition for tunable selection and filtering in terahertz range.

Widely tunable passively Q-switched Er3+-doped ZrF4 fiber laser in the range of 34–37 μm based on a Fe2+:ZnSe crystal

We report the first (to the best of our knowledge) tunable passively Q-switched Er3+-doped ZrF4 fiber laser around 3.5 μm. In this case, a Fe2+:ZnSe crystal is used as the saturable absorber, and a plane-ruled grating in a Littrow configuration acts as the tuning element. At the tuned wavelength of 3478.0 nm, stable Q-switching with a maximum average power of 583.7 mW was achieved with a slope efficiency of 15.2% relative to the launched 1981 nm pump power. Further power scaling is mainly limited by the available 1981 nm pump power. The corresponding pulse width, repetition rate, and pulse energy are 1.18 μs, 71.43 kHz, and 7.54 μJ, respectively. By rotating the grating, the Q-switching can be continuously tuned in the region of 3.4–3.7 μm. To the best of our knowledge, this is the first pulsed rare-earth-doped fiber laser tunable in the region beyond 3.4 μm.

Epitaxial Growth of Large‐Scale Orthorhombic CsPbBr3 Perovskite Thin Films with Anisotropic Photoresponse Property

AbstractInorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) is a promising material for developing novel electronic and optoelectronic devices. Despite the substantial progress that has been made in the development of large perovskite single crystals, the fabrication of high‐quality 2D perovskite single‐crystal films, especially perovskite with a low symmetry, still remains a challenge. Herein, large‐scale orthorhombic CsPbBr3 single‐crystal thin films on zinc‐blende ZnSe crystals are synthesized via vapor‐phase epitaxy. Structural characterizations reveal a “CsPbBr3(110)//ZnSe(100), CsPbBr3[−110]//ZnSe[001] and CsPbBr3[001]//ZnSe[010]” heteroepitaxial relationship between the covering CsPbBr3 layer and the ZnSe growth substrate. It is exciting that the epitaxial film presents an in‐plane anisotropic absorption property from 350 to 535 nm and polarization‐dependent photoluminescence. Photodetectors based on the epitaxial film exhibit a high photoresponsivity of 200 A W−1, a large on/off current ratio exceeding 104, a fast photoresponse time of about 20 ms, and good repeatability at room temperature. Importantly, a strong polarization‐dependent photoresponse is also found on the device fabricated using the epitaxial CsPbBr3 film, making the orthorhombic perovskite promising building blocks for optoelectronic devices featured with anisotropy.

Luminescent and lasing characteristics of polycrystalline Cr:Fe:ZnSe exited at 2.09 and 2.94 µm wavelengths

The luminescence of Cr2+ and Fe2+ in Cr:Fe:ZnSe polycrystals excited at room temperature by pulsed lasers at wavelengths of 2.09 and 2.94 m was studied. For comparison, we also studied the luminescence in single crystals and polycrystals of Fe:ZnSe with iron ion concentration in the range from 5.6 × 1018 to 5.7 × 1019 cm−3. Doping of the polycrystalline samples was carried out using a high-temperature diffusion process with subsequent control of the dopants concentration distribution over the crystal depth. The dependence of the luminescence lifetime τlt of Fe2+ ions on the dopants concentration in crystals excited at a wavelength of 2.94 m was obtained. It was found that chromium quenches the luminescence of Fe2+ no less actively (if no more) than iron itself. The τlt values were measured for Fe:ZnSe excited at a wavelength of 2.94 m and Cr:Fe:ZnSe samples with the same maximum Fe2+ ions concentrations (≈0.9 × 1019 cm−3) at wavelengths of 2.94 m and 2.09 m. A noticeable increase in τlt value and luminescence rise time was observed in Cr:Fe:ZnSe crystals excited at a wavelength of 2.09 m (τlt ≈ 460 ns) compared to 2.94 m (τlt ≈ 240 ns). For comparison, the value of τlt in Fe:ZnSe was about 340 ns. The obtained results confirm the fast energy transfer in Cr:Fe:ZnSe crystals from excited chromium ions to iron ions. The output characteristics of lasers on Fe:ZnSe and Cr:Fe:ZnSe polycrystalline active elements with pumping by HF laser radiation were compared. The slope efficiency with respect to the absorbed energy of Cr:Fe:ZnSe lasers was significantly lower, and the generation threshold was two times higher than for Fe:ZnSe lasers. The prospects for creating a room temperature laser, in which the excitation of iron ions will be carried out through energy transfer from chromium ions, are analyzed.

CUPID-0: A double-readout cryogenic detector for Double Beta Decay search

CUPID-0 is the first large mass neutrino-less double beta decay (0νββ) experiment based on cryogenic calorimeters with dual read-out of light and heat for background rejection. The detector assembly, consisting of 26 ZnSe crystals, 2 natural and 24 enriched at 95% in 82Se, all coupled with bolometric light detectors, has been constructed respecting very strict protocols and procedures, from the material selection during crystal growth to the new and innovative detector framework, in the attempt to achieve the best performance of the array. The successful construction of the detector lead to promising preliminary results, here presented. The array is in fact taking data underground at LNGS (Italy) since March 2017 and the particle identification, enabled by the light read-out, provides an unprecedented background level, for cryogenic calorimeters, of only 3.2 countskeV−1t−1yr−1 in the region of interest of the 0νββ search for 82Se, namely around 3 MeV.

Final Result of CUPID-0 Phase-I in the Search for the ^{82}Se Neutrinoless Double-β Decay.

CUPID-0 is the first pilot experiment of CUPID, a next-generation project for the measurement of neutrinoless double beta decay (0νDBD) with scintillating bolometers. The detector, consisting of 24 enriched and 2 natural ZnSe crystals, has been taking data at Laboratori Nazionali del Gran Sasso from June 2017 to December 2018, collecting a ^{82}Se exposure of 5.29 kg×yr. In this Letter we present the phase-I results in the search for 0νDBD. We demonstrate that the technology implemented by CUPID-0 allows us to reach the lowest background for calorimetric experiments: (3.5_{-0.9}^{+1.0})×10^{-3} counts/(keV kg yr). Monitoring 3.88×10^{25} ^{82}Se nuclei×yr we reach a 90% credible interval median sensitivity of T_{1/2}^{0ν}>5.0×10^{24} yr and set the most stringent limit on the half-life of ^{82}Se 0νDBD: T_{1/2}^{0ν}>3.5×10^{24} yr (90% credible interval), corresponding to m_{ββ}<(311-638) meV depending on the nuclear matrix element calculations.

Second-harmonic wave patterns induced by the tightly focused radially polarized beam loaded with off-axis vortices

We investigated second-harmonic wave patterns induced by the tightly focused radially polarized beam loaded with off-axis vortices. The expression of the electric field of tightly focused radially polarized beam loaded with off-axis vortices through ZnSe crystal was derived, based on which the expression of the polarization distributions of near-field second-harmonic and the intensity distributions of far-field second-harmonic at different incident crystal planes were obtained. Numerical simulations indicated the distinctive polarization distributions of near-field second-harmonic and the intensity distributions of far-field second-harmonic when the incident crystal planes were (110) and (001). The results showed that second-harmonic wave patterns could be regulated flexibly by changing the distance and number of off-axis vortices.