Te Solid Solutions Research Articles

Optical properties of HgCdTe epitaxial films doped with arsenic

Subject of study. Epitaxial films of Hg0.7Cd0.3Te solid solutions grown by molecular beam epitaxy and doped with arsenic to obtain hole-type conductivity in order to form p-n junctions for the production of infrared photodetector structures are studied. Aim of study. The types and characteristics of defects formed during arsenic doping of epitaxial films of Hg0.7Cd0.3Te solid solutions grown by molecular beam epitaxy and the effect of doping on the level of disorder in the solid solution are determined. Method. Ellipsometry, optical transmittance, photoluminescence, and photoreflectance are used. Main results. The initial material is shown to have high quality in terms of film bulk and surface quality, and the quality was found to improve after two-stage activation thermal annealing. Annealing has been shown to activate the arsenic with the formation of shallow (7–8 meV) acceptor levels. No side defects were found to occur as a result of the introduction of arsenic into the films during growth and annealing. Practical significance. This research demonstrated the effectiveness of doping epitaxial films of Hg0.7Cd0.3Te solid solutions with arsenic as an acceptor impurity in order to produce layers with hole conductivity during the production of photodiode structures.

Growth and characterization of epitaxial films based on semimagnetic Pb1−xEuxTe solid solutions on various substrates

This paper presents the results of a study of the growth and structure properties of Pb[Formula: see text]EuxTe, ([Formula: see text]) epitaxial films with 0.5–1[Formula: see text][Formula: see text]m thickness, grown on BaF2 and SiO2 substrates oriented in the (111) direction, by the molecular beam condensation method in a vacuum of 10[Formula: see text] Pa with the use of an additional compensating source of Te vapor during the growth process. The optimal conditions for obtaining structurally perfect ([Formula: see text]–100[Formula: see text]) epitaxial films were established: [Formula: see text]–623[Formula: see text]K; [Formula: see text]K; [Formula: see text]–9 Å/s. It was determined that conductivity inversion occurs at the temperature of the compensating source 410[Formula: see text]K.

ОПТИЧНА СПЕКТРОСКОПІЯ ДЕТЕКТОРНИХ ВИСОКООМНИХ МОНОКРИСТАЛІВ CdTe (111) ТА ТВЕРДИХ РОЗЧИНІВ Cd 1-x Zn x Te (х= 0,1)

Cadmium telluride is used for the manufacture of uncooled gamma radiation detectors, and solid solutions of Cd 1-x Zn x Te (x=0.1) are used for the manufacture of X-ray and gamma radiation detectors. The study of the effect of doping on the physical properties of semiconductors is relevant both for experimenters and for the theoretical substantiation of physical processes. This paper presents the results of the study of optical reflection spectra in the spectral range (0,2-1,7) . 10 -6 m and transmittance in the region of the fundamental optical transition E 0 of high-resistivity CdTe single crystals of (111) orientation with resistivity ρ = (2÷5)·10 9 Ohm∙cm doped with chlorine, as well as solid solutions of Cd 1-x Zn x Te (x = 0.1) with resistivity ρ = (5 ÷30)∙10 9 Ohm∙cm. Since the optical reflection coefficient R = f (λ) is related to the optical transmittance T = f (λ) and absorption D = f (λ) by the ratio R+T+D=1 (with the light (electromagnetic) wave scattering in the studied samples not taken into account), the absorption spectra D=1-(R+T) versus the light (electromagnetic) wavelength λ were also constructed in this work. It is determined that the energy of the fundamental optical transition E 0 of the studied materials at T = 300 K is as follows: for CdTe - 1.44 eV; and for Cd 1-х Zn х Te (x = 0.1) - 1.5 eV. The energy relaxation time of free charge carriers τ for p-CdTe (111) single crystals and Cd 1-х Zn х Te (x = 0.1) solid solutions was estimated to be 1.343-10 -14 s and 0,878·10 -14 s, respectively. The effective "optical" mobility for single crystals of p-CdTe (111) and solid solutions of Cd 1-х Zn х Te (x = 0.1) is 274 . 10 -4 ; 179,5 . 10 -4 , respectively. It has been shown that the investigated crystals are of high (detector) quality, which is crucial for the manufacture of highly sensitive and high-resolution ionising radiation sensors. The practical value of the obtained results lies in the determination of electronic and physical parameters of technically important semiconductors CdTe and Cd 1-х Zn х Te (x=0.1).

Thermoelectric Properties of Single Crystals of a Pb-Enriched Pb0.75Sn0.25Te Solid Solution

Thermoelectric Properties of Single Crystals of a Pb-Enriched Pb0.75Sn0.25Te Solid Solution

Effect of annealing on thermoelectric properties of crystals YbxBi2−xTe3

The work is devoted to the study of the thermoelectric properties of solid crystal YbxBi[Formula: see text]Te3. This work presents the results of studies of the thermoelectric properties of YbxBi[Formula: see text]Te3 ([Formula: see text]) solid solutions before and after annealing in the temperature range 300–580[Formula: see text]K. Regularities of changes in the electrical conductivity, Seebeck coefficient, and total thermal conductivity of the samples depending on the content of ytterbium (Yb) are established. Dependences of electrical conductivity, Seebeck coefficient, and the thermal conductivity on temperature for the crystal under study are plotted. Temperature curves were recorded using a Termoscan-2 low-frequency temperature recorder at a heating rate of 283[Formula: see text]K/min. Studies of conductivity [Formula: see text], thermoelectric power (S) were carried out by the four-probe method at direct current in the temperature range of 300–600[Formula: see text]K. Ohmic contacts were applied using alloys. It has been established that the optimal combination of these thermoelectric characteristics is achieved for the compositions [Formula: see text], which are characterized by the maximum thermoelectric index ([Formula: see text]) of the figure of merit in the temperature range of 420–500[Formula: see text]K after annealing at 500[Formula: see text]K for [Formula: see text][Formula: see text]h. It was revealed that the YbxBi[Formula: see text]Te3 systems under study are n-type semiconductor thermoelectric materials in the temperature range of 300–600[Formula: see text]K.

Ab initio study of mechanical and thermal properties of GeTe-based and PbSe-based high-entropy chalcogenides

GeTe-based and PbSe-based high-entropy compounds have outstanding thermoelectric (TE) performance and crucial applications in mid and high temperatures. Recently, the optimization of TE performance of high-entropy compounds has been focused on reducing thermal conductivity by strengthening the phonon scattering process to improve TE performance. We report a first-principles investigation on nine GeTe-based high-entropy chalcogenide solid solutions constituted of eight metallic elements (Ag, Pb, Sb, Bi, Cu, Cd, Mn, and Sn) and 13 PbSe-based high-entropy chalcogenide solid solutions: Pb0.99-ySb0.012SnySe1-2xTexSx (x = 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and y = 0) and Pb0.99-ySb0.012SnySe1-2xTexSx (y = 0.05, 0.1, 0.15, 0.2, 0.25 and x = 0.25). We have investigated the mechanical properties focusing on Debye temperature (ΘD), thermal conductivity (κ), Grüneisen parameter (γα), dominant phonon wavelength (λdom), and melting temperature (Tm). We find that the lattice thermal conductivity is significantly reduced when GeTe is alloyed into the following compositions: Ge0.75Sb0.13Pb0.12Te, Ge0.61Ag0.11Sb0.13Pb0.12Bi0.01Te, and Ge0.61Ag0.11Sb0.13Pb0.12Mn0.05Bi0.01Te. This reduction is due to the mass increase and strain fluctuations. The results also show that Ge0.61Ag0.11Sb0.13Pb0.12Bi0.01Te solid solution has the lowest Young’s modulus (30.362 GPa), bulk and shear moduli (18.626 and 12.359 GPa), average sound velocity (1653.128 m/sec), Debye temperature (151.689 K), lattice thermal conductivity (0.574 W.m–1.K–1), dominant phonon wavelength (0.692 Å), and melting temperature (535.91 K). Moreover, Ge0.61Ag0.11Sb0.13Pb0.12Bi0.01Te has the highest Grüneisen parameter with a reduced and temperature-independent lattice thermal conductivity. The positive correlation between ΘD and κ is revealed. Alloying of PbSe-based high-entropy by Sb, Sn, Te, and S atoms at the Se and Pb sites resulted in much higher shear strains resulted in the reduction of phonon velocity, a reduced ΘD, and a lower lattice thermal conductivity.

Magnetic Memory and the Promising Magnetocaloric Effect of Sn0.6Cr0.1Ge0.3Te Solid Solution Synthesized by Sealed Tube Solid-State Reaction

Magnetic Memory and the Promising Magnetocaloric Effect of Sn_0.6Cr_0.1Ge_0.3Te Solid Solution Synthesized by Sealed Tube Solid-State Reaction

Between defects and inclusions: The fate of tellurium in pyrite

Tellurium (Te) is a critical commodity, essential for renewable energy technologies and other high-tech applications. Most Te is currently recovered from anode slimes, i.e., waste arising from copper refining. Rising demand and the key role for the green transition make the diversification and extension of the Te supply important. However, the nature of Te incorporation into ores is still poorly understood and hinders their economic potential. Here, we investigate the distribution of Te in pyrite from a high-grade Au-Ag-Te epithermal-type ore, where pyrite is already processed for ‘invisible’ Au, to inform metallurgical extraction methods, and secure future Te supply. Current models of Te incorporation into pyrite suggest a solid-solution limit in relation to As, similar as for ‘invisible’ Au. In this study, we identified three distinct modes of Te incorporation in pyrite, which challenge previous solubility models: (1) Te solid-solution, at concentrations (up to 285 ppma) that significantly exceed the previously suggested solubility limit. (2) Nano-telluride inclusions along cracks that formed by intra-grain remobilization. (3) Crystal defects, enriched in Te through pipe diffusion hosting up to 0.5 at. % Te. Our results therefore provide new fundamental insights into the chemical and structural coordination of Te in pyrite, which may guide future efforts for its direct recovery.

Germanium monotelluride-based solid solutions as whole-visible dielectric-metallic-transition material platforms for programmable metasurfaces

The development of next-generation programmable metasurfaces urgently requires phase change materials with dielectric-metallic transition (DMT-PCMs). Although DMT-PCMs in the infrared have been reported, DMT-PCMs in the visible spectrum are yet to be designed, limiting the nanophotonic applications of conventional programmable metasurfaces to the infrared band. Herein, we find that stoichiometric germanium monotelluride solid solutions, Ge1-xMxTe (M = Sn, Sb, Pb, and Bi), have excellent DMT performance throughout the whole visible spectrum, and they can be used as versatile material platforms for fabricating programmable metasurfaces. As a proof-of-concept, the DMT performance of stoichiometric Ge0.9Sn0.1Te solid solution is significantly superior to that of commonly studied non-stoichiometric PCMs (e.g., Ge2Sb2Te5, Sb2Te3). Through a combination of experiments and first-principle calculations, we demonstrate that the high DMT performance of Ge0.9Sn0.1Te derives from the unique bonding structure of the crystalline state with non-stoichiometric vacancy-free, high atomic number, and weak Sn-Te bonds, which is not present in conventional PCMs. Furthermore, using ultrashort-pulse lasers, we show that the crystalline Ge0.9Sn0.1Te can be arbitrarily written, erased, and modified at the subwavelength level. The resonance peaks and colors of the Ge0.9Sn0.1Te-based grating metasurface can be continuously modulated over the whole visible spectrum. These results suggest that the DMT material platforms can be used to fabricate programmable metasurfaces. Therefore, this work presents a coherent report on the physical origin, material design, and photonic devices of DMT in the visible spectrum, which may extend the applications of programmable metasurfaces from the infrared band to the visible spectrum and inspire more researches.

Characterization of wide-bandgap layers in laser structures based on CdHgTe

The results of a study of the optical and structural properties of wide-bandgap (x~0.7) layers in laser heterostructures based on Cd x Hg 1-x Te solid solutions grown by molecular beam epitaxy on (013)GaAs substrates, as well as epitaxial films similar to these layers in chemical composition, are presented. It is shown that the position of the maximum of the photoluminescence spectrum and the nature of its temperature shift are related to the disordering of the composition of the solid solution. Shallow and deep acceptor levels were found in the bandgap. The possible influence of disordering and acceptor levels in laser structures on the energy spectrum of carriers is discussed. Keywords: CdHgTe, laser structures, photoluminescence, defects, structural properties.

Data-driven discovery of high-performance multicomponent solid solution thermoelectric materials

The discovery and exploration of novel thermoelectric materials over the past decades have relied primarily on the inefficient Edisonian trial and error approach. It is urgent to develop intelligent approaches like machine learning or data-driven screening to accelerate the process of discovery and optimization of high-performance thermoelectric materials. In this study, by taking the Cu2(S, Se, Te) solid solutions as an example, we demonstrate a successful data-driven screening approach to reveal the optimal composition ranges with high thermoelectric performance. Based on the known experimental data of Cu2(S, Se, Te) and their solid solutions, we predicted the contouring diagrams of crystal structures and thermoelectric properties of Cu2(S, Se, Te) multicomponent materials. Following the prediction, we fabricated a series of Cu2(S, Se, Te) quaternary solid solutions and systematically investigated their crystal structures, phase transitions, and especially thermoelectric properties. A peak zT of 1.3 at 1000 K is achieved in Cu2S0.4Se0.3Te0.3, which is well in the predicted optimal composition range. We expect this simple yet efficient strategy to be widely applied to the quick screening of other high-performance thermoelectric materials.

Photosensitive Schottky diodes based on nanostructured thin films of graphitized carbon formed on Cd1− x Zn x Te crystalline substrates

Photosensitive Schottky diodes of graphite/n-Cd1−x Zn x Te were obtained by depositing thin films of graphitized carbon on crystalline substrates of n-Cd1−x Zn x Te solid solution by electron beam evaporation. Based on the analysis of the single-phonon Raman spectra, it was found that the obtained films can be considered as nanocrystalline carbon structures with crystallite sizes of La ≈ 4.8 nm. From the research on the temperature dependencies of the I–V-characteristics and frequency dependencies of the C–V-characteristics, the main parameters of the structure were determined as well as the role of surface energy states in the formation of the profile of energy zones in the contact area. The main mechanisms of the forward and reverse currents are established. Using the diffusion theory of rectification, the height of the potential barrier was calculated and found to coincide with the experimentally determined value. A model of the diode energy diagram is proposed, which accurately describes the experimental electrophysical phenomena. The photoelectric properties of the graphite/n-Cd1−x Zn x Te diodes were studied.

Evaluation of the double-tuned functionally graded thermoelectric material approach for the fabrication of n-type leg based on Pb0.75Sn0.25Te

Thermoelectric (TE) technologies realize the generation of electrical energy from the waste heat. The one bottleneck, which significantly restricts the wide use of these technologies, relates to the low energy conversion efficiency of the commercial devices. In this work, the double-tuned functionally graded thermoelectric material (DT-FGTM) approach was proposed to achieve the high-performance TE leg through the increase in the average TE figure of merit (ZT)ave. The essence of this idea is connected with the precise control of the bandgap Eg and chemical potential μc over the entire temperature range. Considering Pb0.75Sn0.25Te solid solution, as an example, and using the three band Kane model, we evaluated the best conditions for the highest thermoelectric performance in this material. Within the offered herein DT-FGTM approach, we fabricated the thermoelectric n-type Pb0.75Sn0.25Te1−xIx leg and measured its output energy characteristics. The efficiency of energy conversion for the prepared DT-FGTM leg reaches a very high value of ∼12.0% at temperature difference ΔT = 540 K. Furthermore, the thermal treatment of the fabricated leg should not injure the carrier concentration distribution through the leg, as the hot end of the leg is heavily doped, and the chemical diffusion between segments would be only beneficial. Our demonstration shows that the DT-FGTM approach has significant practical interest and can be utilized for the other TE materials.

Building ultra-stable K–Te battery by molecular regulation

Tellurium (Te) is an ideal electrode for potassium ion batteries (PIBs) owing to its excellent electronic conductivity and high volumetric capacity. However, the Te electrode is prone to capacity fading as the shuttle effect. To address this challenge, we propose molecular regulated Se–Te solid solutions on N-doped porous carbon as the PIBs electrode. After optimizing the Se content in Se–Te solid solutions, the resultant SeTe6.8 on N-doped porous carbon (SeTe6.8@C) delivered a capacity of over 400 mAh g−1 with a flat plateau of 1.0 V at 500 mA g−1. It also achieved a superiorly long cycle life, running for more than 1600 cycles (over 7 months with 0.015% degeneration per cycle) at 100 mA g−1 and excellent rate performance (179.9 mAh g−1 at 10000 mA g−1). This remarkable electrochemical energy storage of the Te electorde likely arises from suppression of the shuttle effect after doping the Te with strongly electronegative Se atoms (forming K5Te3 which is not easily soluble in electrolyte). This study presents a fresh approach for designing and developing ultra-stable Te-based electrodes for PIBs and beyond.

Surface chemical treatment effect on (1 1 1) PbSnTe < In > Topological crystalline insulator films

In present work, the effect of Pb1-xSnxTe < In> (111) surface chemical treatment on electrophysical and optical properties was studied. It was shown that treatment of Pb1-xSnxTe < In> (111) surface in HCl-isopropanol (HCl-iPA) solution led to removal of native oxides and surface enrichment by elemental tellurium of several nm thickness. Subsequent anneals in vacuum led to desorption of elemental tellurium and revealing (1x1) surface structure. We present angle resolved photoemission spectroscopy (ARPES) measurements of the surface states on chemically prepared (111) oriented MBE-grown films of Pb1-xSnxTe, a three-dimensional topological crystalline insulator (TCI). The surface states with Dirac-like dispersion at Γ in the surface Brillouin zone were detected. The dark current and photocurrent were found in strong dependence on the surface chemical procedure and composition. The relative simplicity of the preparation technique is encouraging, and suggests a clear path for future investigations of TCI states on alternative surface orientations in (Pb,Sn)Te solid solutions and applied aspects of TCI research.

First principles investigation of intrinsic and Na defects in XTe (X=Ca, Sr, Ba) nanostructured PbTe

Embedding isoelectronic and isostructural XTe (X = Ca, Sr, Ba) compounds in Na-doped PbTe can significantly boost thermoelectric performance through interface engineering and phonon scattering. Thus, defects in PbTe-based compounds play an essential role in improving the thermoelectric properties. In this study, we investigate the formation energies of charged intrinsic and extrinsic (Na) defects in a PbTe/PbXTe/XTe pseudo-interface. We find that different synthesis conditions of PbTe uniquely determine the lowest-energy defects. The low formation energies of NaSr1− (and NaPb1−) play an important role in increasing the Na concentration in the solid solution PbTe/SrTe interface, in good agreement with the experimental observations. A low energy Na charged defect (n-type NaTe3+) has been distinctly identified in the PbXTe solid solutions as well. Thus, the defect should be eliminated in the SrTe precipitated PbTe system for the p-type purpose. However, if experiments could synthesize the Pb0.5Sr0.5Te solid solution ingot, NaTe3+ will play an important role to achieve the n-type behavior. While low energy defects have little effect on the electronic structures in PbTe and XTe, they enhance the density of states around the Fermi level in PbXTe solid solutions. Our work therefore not only elucidates the lowest energy defects in PbTe-based materials, but it also paves the way to understanding and designing promising thermoelectrics with interface phases.

Phase equilibria in Cd0.80Mn0.20Te solid solutions

The thermal properties of Cd0.80Mn0.20Te solid solutions were investigated in this article. Two methods of heat treatment were used for thermography of alloys, which allowed investigating their thermal properties. One of the methods of thermography of samples was to heat them to the maximum temperature at which they were kept for a certain time, followed by cooling of the sample. The data obtained by this type of thermography allow obtaining graphs which characterized the crystallization parameters of the melt Cd0.80Mn0.20Te. It is shown that the crystallization of the Cd0.80Mn0.20Te melt occurs without supercooling at its overheating less than 14 °С in comparison with the beginning of melting temperature, which indicates the two-phase melt. It is also shown that the crystallization rate of the Cd0.80Mn0.20Te melt increases with decreasing crystallization temperature. Thermography of alloys by the second method of heat treatment is to conduct a series of isothermal holding during heating of the samples to the maximum temperature (1150 °C). Thus, the parameters of alloy melting were investigated. It was determined that the volume fraction of solid phase in the Cd0.80Mn0.20Te melt decreases from 100% to 0% in the temperature range 1078-1095 °С. Based on the obtained data of differential thermal analyses the Cd0.80Mn0.20Te ingot was grown under controlled conditions. After cutting this crystal we can see several monocrystalline areas of different sizes. IR microscope showed that the minimum number of inclusions &lt;7 mm in diameter distributed in different parts of the sample The value of the band gap in all samples ranges from 1.78 to 1.80 eV. The value of the resistivity of the crystal Cd0.80Mn0.20Te is 2•107 Ohm • cm at the beginning of the ingot and decreases by 2 orders of magnitude by the end of the ingot.

Thermoelectric and Mechanical Properties of Pb-Doped Sb2Te3–Bi2Te3 Solid Solutions

We have studied the properties of samples prepared by hot-pressing and extruding granules produced by solidifying molten Pb-doped Sb2Te3–Bi2Te3 solid solutions (24 and 25 mol % Bi2Te3, 0.04 to 0.14 wt % Pb) in a liquid and comminuted in a mortar, cutting mill, or planetary mill. Their microstructure and fractographs have been investigated using an optical and a scanning electron microscope. The results demonstrate that doping with Pb has no significant effect on the compressive strength of the materials, which depends on the sample preparation procedure and is lowest in the case of the samples prepared by hot-pressing granules comminuted in the cutting mill. The highest strength is offered by the samples prepared by extrusion of 25-mm-diameter rods. Doping with Pb increases carrier concentration (reduces the Seebeck coefficient) and shifts the peak in the thermoelectric figure of merit of the materials, (ZT)max, to higher temperatures. The highest thermoelectric figure of merit, (ZT)max = 1.1 ± 0.1, has been obtained at 360 K for the Bi0.5Sb1.5Te3 solid solution doped with 0.05 wt % Pb and prepared by extruding granules comminuted in the planetary mill.

Thermoelectric and mechanical properties of Bi0.4Sb1.6Te3 solid solution extruded from granules obtaining by melt crystallization

The microstructure, composition, mechanical and thermoelectric properties of samples cut from different sections of a rod with a diameter of 20 mm, a length of 300 mm, extruded from a briquette pressed from granules obtained by crystallization of Bi0.4Sb1.6Te3 solid solution in water were investigated. It was established that the composition of the samples does not change along the length of the rod, while there is a small amount of the second phase (tellurium-based eutectic) is observed both at the beginning and at the end of the rod. A compression test at room temperature showed that the ultimate strength of specimens cut from the end of a rod is ∼10% higher than that of specimens cut from the middle Thermoelectric parameters (electrical conductivity, thermal conductivity, Seebeck coefficient and thermoelectric figure of merit) at room temperature of samples cut from different areas of the rod were σ = 814 ± 55 S/cm, k = 13.2 ± 0.3 W/cm K, α = 234 ± 5 µ V/K, ZT = 0.93-1.12. Measurements of the thermoelectric properties of these samples in the temperature range of 100-600 K showed that the intrinsic conductivity occurs at temperatures above 450 K. The maximum thermoelectric figure of merit ZTmax = 1.2 ± 0.1 was obtained at a temperature of 340 K.

XAFS and SRGI-XRD studies of the local structure of tellurium corrosion of Ni–18%Cr alloy

The speciation and atomic structures of corrosion products in Ni-based alloys could provide basic information for understanding the Te corrosion mechanism. In this paper, two-dimensional synchrotron-radiation-induced grazing incidence X-ray diffraction was used to characterize the corrosion products of a Ni–18%Cr binary alloy at temperatures from 600 to 1000 °C. The results showed that a film of CrTe is preferentially formed when Te reacts with the Ni-based alloy at low temperatures (below 900 °C), while CrTe and Ni3Te2 are formed at 900 °C. Moreover, at a temperature of 1000 °C, a solid solution is formed without any changes in the Ni–Cr substrate lattice parameters. Furthermore, X-ray absorption fine structure and wavelet transform analyses were used to investigate the atomic local structure of Te. The investigation indicated that Te atoms diffuse into the Ni–Cr substrate to form a substitutional Ni–Cr–Te solid solution at 1000 °C. Notably, based on a discussion of the thermodynamics of the chemical reaction process, CrTe is considered to be the most stable and prevalent corrosion product due to its comparatively lower Gibbs free energy of formation. These results demonstrate that the Ni–18%Cr alloy is capable of resisting the diffusion of Te atoms.