Compounds CdTe Research Articles

Investigating the physical properties of the binary compound CdTe under different pressures using FP-LMTO method

The structural, electronic and optical properties of Cadmium Telluride (CdTe) are investigated at different pressures using the full potential linear muffin-tin orbital FP-LMTO method based on density functional theory (DFT), within the local density approximation LDA and the generalized gradient approximation GGA approximations were used to calculate the exchange-correlation potential. The ground state properties of CdTe compound were determined for diverse phases, and the band structure and optical parameters were calculated at pressures ranging from 0 GPa to 50 GPa. Optical parameters, including real part, imaginary part of the dielectric function, reflectivity, refractive index, extinction coefficient and energy loss function, were calculated for over an energy range from 0 eV to 13.6058 eV. The results were compared with available experimental and theoretical data, showing good agreement with earlier reported result. These particularities reveal that CdTe as favorable material for optoelectronic applications, as it exhibits together important electronic and optical responses under different pressure.

Temperature-Dependent Structural and Elastic Properties of CdS, CdSe, and CdTe Compounds Studied by Statistical Moment Method

The statistical moment method has been applied to investigate the temperature effects on the lattice parameters and elastic properties of the zinc-blende CdX (X = S, Se, Te) compounds. The analytical expressions of thermal-induced atomic displacement, lattice constant, elastic moduli (Young’s modulus, bulk modulus and shear modulus) and elastic constants (including C11,C12 and C44) of the zinc-blende compounds have been derived. We have pointed out that the temperature effects on the elastic properties of CdS and CdSe are almost the same. And the elastic quantities of CdS and CdSe are more strongly dependent on temperature than those of CdTe semiconductor. This phenomenon is caused by the weaker coupling force of Cd-Te bonds compared to those of Cd-S and Cd-Se bonds. Furthermore, from the calculated Debye temperatures of CdX (X = S, Se, Te) compounds we conclude that CdS has higher phonon thermal conductivity and is therefore more thermally conductive among the three semiconductor compounds. The calculations of present work can be used as an appropriate reference for the experiments in future.

Design and optimization of a high efficiency CdTe–FeSi2 based double-junction two-terminal tandem solar cell

This article theoretically demonstrates an enormously efficient CdTe–FeSi2 based dual-junction tandem solar cell accompanied by slender semiconductor layers. The peak efficiency of the device has been ensured through the optimization of its various attributes of window, CdTe (bandgap 1.5 eV) top absorber, FeSi2 (bandgap 0.87 eV) bottom absorber and back surface layers. Additionally, the impacts of thickness, doping and the level of defects in different window, base and rear surface layers have been examined to observe how different layers affect the solar cell's performance. The optimized n-CdS/p-CdTe/p+-MoS2--n-CdS/p-FeSi2/p+-Cu2SnS3 dual-junction tandem solar device displays an efficiency of 43.9% with a voltage at no load, VOC of 1.928 V, current density under a closed circuit, JSC of 25.34 mA/cm2, and fill factor of 89.88%, respectively. These results disclose the high potential of the suggested solar cell based on CdTe and FeSi2 compounds.

CdSe and CdTe Mechanical Properties Revealed by COMSOL Multiphasics

Two Metal chalcogenide compounds CdTe and CdSe have been studied in depth because they are used in many optoelectronic and electronic devices. High pressure causes structural phase transitions in semiconductor materials, which have been the subject of much research. CdTe is a direct band-gap IIeVI semiconductor. Cadmium-tellurium crystalline compound has been used in more and more industries. High dislocation density is one of the problems with bulk-grown CdTe. Comsol Multiphysics was used to evaluate mechanical stress on a material. COMSOL Multiphysics 5.5 allows you to access a database of physics simulations. (CdSe and CdTe) were simulated to show the effects of mechanical stress. We use a physical model called Solid Mechanics to model the effect of mechanical stress. The results show that when pressure was applied at different levels (50pa, 100pa, 200pa, 300pa, 400pa), the strain values of (CdSe or CdTe) were similar, but (CdSe) was more resistant to deformation than (CdTe).

Photoluminescence of CdTe and CdZnTe compounds doped with 2% selenium

The addition of 2 % of selenium in CdTe and CdZnTe (CZT) exhibited an additional acceptor-bound exciton in photoluminescence (PL). From the PL and inductively coupled plasma mass spectrometer (ICP/MS) analyses, the additional acceptor-bound exciton emission is associated with a Cu impurity in the relatively low-purity (5N) precursor CdSe starting material. In addition, thermal quenching of the acceptor/donor bound exciton emissions do not require a shift to any higher excited states or to the free exciton state. ICP/MS analysis also showed a higher concentration of Sn in CdZnTeSe (CZTS) compared to CdTe and CZT which is known to form a deep level trap at around EC – 0.83 eV. The trapping and de-trapping times indicate that the Sn-related deep trap acts as an electron trapping center. The relatively low electron mobility-lifetime product of CZTS might be correlated with the concentration of Sn in the impure CdSe material. Pulse height spectra using an Eu-152 gamma-ray source was taken for a 2-mm-thick planar CZTS detector. The spectra clearly showed all the expected gamma peaks with energy lower than 344.3 keV.

The FP-LAPW/GAM-MPW1K approach: a reliable abinitio method for calculating the band gap of II-VI semiconductors monochalcogenides.

The bandgap of metal monochalcogenides (MMCs) is a key property that governs their physical and chemical properties. Accurate measurement of the bandgap is essential for a range of applications, including optoelectronics and photovoltaics. However, many theoretical approximations fail to accurately calculate the bandgap for MMCs, making it difficult to obtain precise values. This study investigated the suitability of the FP-LAPW/GAM-MPW1K scheme for determining the bandgap of MMCs. The investigation included lattice parameters, bandgap, band structure, and density of states, which were compared against both previous theoretical calculations and available experimental data. The findings of the study indicate that the FP-LAPW/GAM-MPW1K approach accurately calculates the bandgap value of MMCs by efficiently treating d-state electrons. The results are consistent with prior studies, confirming the method's reliability in determining the bandgap of these semiconductors. our study used the GAM-MPW1K functional and the full potential linearized augmented plane wave method (FP-LAPW) in the ELK code to calculate the lattice parameters, electronic band structure, and bandgap of ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe compounds in the wurtzite structure. The crystallographic data were obtained from the COD database and the inputs were prepared by CIF2CELL code. The results were visualized using Xmgrace and VESTA software.

Tailoring the defects and resistivity in CdZnTe single crystal via one-step annealing with CdTe compound

Defects deteriorate the optical and electronic properties of the cadmium zinc telluride (CZT) single crystal. However, the growth of defects, such as vacancies and precipitation, could not be avoided in the industrial-grade preparation of CZT single crystal. Therefore, it is crucial to explore ways to eliminate defects after growth. This paper employs one-step heat treatment with the CdTe compound as an annealing atmosphere source. After annealing, some large-size Te inclusions are eliminated in CZT crystal, but nano Te precipitates still exist. At the same time, the crystal surface becomes rougher, caused by the thermal migration of Te droplets, dislocation proliferation, and aggregation. Increasing annealing time, dislocations migrate, decompose, and interact with each other to form dislocation walls, stacking faults or terminating at the surface, reducing dislocation etch pit density. In addition, a large number of ordered phases are still found in the crystal. Single annealing with CdTe significantly improved the crystal's optical and electrical properties. After 180 h annealing, the infrared (IR) transmittance of the as-grown wafer increased from 40% to 65%, and resistivity increased from 2.2 × 109 Ω cm to 1.7 × 1011 Ω cm. Compared to reducing the Te precipitation phase, these increasements were mainly dominated by replacing point defects, like Cd vacancies.

Optimization of threshold characteristics of Hg0·8Cd0·2Te -based laser under interband breakdown in a lateral electric field

HgCdTe is promising as a material to solve a problem of development of semiconductor sources in mid- and far-infrared range due to small direct band gap. Since the compound materials HgTe and CdTe are closely lattice matched, it is possible to design a wide variety of multilayer structures based on HgCdTe. In this paper we calculate and optimize the parameters of the Hg0·8Cd0·2Te/Cd0·7Hg0·3Te separate-confinement double heterostructure which are required for lasing. It is shown that lasing at a wavelength of 10 μm for the optimal active region thickness (∼90 nm) and resonator length (∼2 mm) occurs when a lateral electric field of more than 0.96 kV/cm is applied at a temperature of 77 K. This corresponds to a small voltage of ∼10 V at a distance between metal contacts of 100 μm and the threshold current of ∼30 A.

Evaluation of electron lifetime for Te inclusions free CdZnTe

Te secondary phase defects are known as major obstacle for improving charge carriers transport properties of CdTe compounds material. The enhanced detector performance was reported for Te inclusions free CZT detector implemented through two-step annealing (i.e., first in Cd and second in Te). We applied the time-of-flight (TOF) technique to measure the electron lifetime in as-grown and two-step annealed CZT material. TOF has several advantages over Hecht equation fitting such as independence of the electric field distribution, direct measurement of carrier lifetime, and high accuracy for high mobility-lifetime product CZT material. The detector performance improved drastically for the two-step annealed CZT detector except which containing inordinate number and size of prismatic punching defects. The average electron lifetime increased more than 10 times after successful two-step annealing.

Enhanced hole mobility-lifetime product in selenium-added CdTe compounds

An improved detector performance for 2% selenium-added CdZnTe(CZT) was observed and explained by the reduced concentration of a deep-level hole trap, which was confirmed by photoluminescence measurements of CdZnTeSe(CZTS) and CdTeSe(CTS). The hole lifetime in CZTS was found to be 2.18μs in the selenium-containing material, which is much longer than that typically measured by 10–100 times. The prolonged lifetime of hole carriers is likely caused by the disappearance of hole trapping at a specific binding energy of 1.1-eV below the conduction band. Also, the enhanced pulse height spectra of CZTS gamma-ray detectors were explained in terms of the ratio of electron and hole mobility-lifetime products. Cu-migrated patterns are used for the first time to reveal sub-grains and their networks in CZT and CZTS. Based on qualitative analysis, the Cu-migrated patterns in CZT and CZTS showed similar results.

Ellipsometry Characterisation for the Cd1-xZnxTe1-ySey Semiconductor Used in X-ray and Gamma Radiation Detectors

The study of the optical properties of the Cd1-xZnxTe1-ySey (CZTS) crystal provides a clear idea about its response to incident X-ray or gamma radiation. This is important for selecting a proper composition of CZTS to achieve superior quality and high-resolution X-ray and gamma radiation detectors at room temperature and reduce their production cost. This article’s novelty is in lowering the cost of the optical and compositional characterisation of CZTS using the ellipsometry technique. The most significant successes achieved are the composition ellipsometry model determination of CZTS based on the Effective Medium Approximation (EMA) substrate of the binary compound CdTe and ZnSe with an oxide layer of CdTe and the experimental verification that the bandgap moves to lower energies with the addition of Se.

First-principles study of the strain effect with half-metallic ferromagnetism in Cd 1−x V x Te alloys: supercell approaches

In this work, we study the effect of vanadium (V) dopantson the structural, electronic, and magnetic properties of the CdTe alloys using density functional theory (DFT). The calculations are performed as a function of the concentration of V in the host CdTe semiconductor using a 2 × 2 × 1 tetragonal supercell and a 2 × 2 × 2 cubic supercell. The lattice constants and bulk modulus of Cd 1−x V x Te alloys are determined. The analysis of the density of states shows that the Cd0.75 V0.25Te alloys in both supercells present a total polarization of 100% at the Fermi level, which confirms a stable half-metallic ferromagnetism phase in these materials, in contrast to the Cd 0.9375 V 0.0625 Te and Cd 0.875 V 0.125 Te alloys, which have a polarizability that does not reach 100%. In addition, the electronic band structures are used to estimate the s(p) − d exchange constants mainly resulting from the p − d hybridization between V- 3d and Te-p. Furthermore, the local magnetic moment of V of its free space charge value decreases, leading to the appearance of a small magnetic moment on the Cd and Te sites. Besides, the magnetic stability at different doping concentrations in the ferromagnetic (FM) and anti-ferromagnetic (AFM) states is examined, where the total energy of the systems is considered as a stability criterion. The robustness of the half-metallicity and the curie temperatures under the strain effect are also investigated. Finally, we rely on the binding energy to evaluate the energetic stability of the vanadium in the intrinsic compound CdTe under external deformations.

Cadmium Telluride (CdTe) Compound and Silicon (Si) Semiconductor Materials Detectors for X-Ray

There are different approaches and also materials to construct a detector for x-rays. the available semiconductor materials, Silicon (Si) is mainly used for charged particle detectors and soft X-ray detectors. Cadmium Telluride (CdTe) compound semiconductors for x-ray detectors have experienced a rather rapid development in the last few years, due to their appealing performance. In this paper we review the physical properties of semiconductor detectors for x-ray. In particular, we focus on compound semiconductor detectors. In addition, Si detector has better energy resolution achievement. However, it does not have good detection efficiency for higher energy above (40Kev). While CdTe detector supplies higher detection efficiency for x -rays about 100% for up to 100 keV in energy. The response functions of Si detector to reduce small x-ray, which has limited sensitivity for energy about 30keV. The XR-100T is high performance for x-ray and gamma ray detector by using 241Am (59.5keV), so the cooler are mounted the input FET a feedback components to the Amptek to charge sensitive preamplifier. Both the Si and CdTe detectors are connected to the PX2 combined amplifier and power supply, that was provide the voltage needed to operate XR-100T CdTe. The PX2 T CdTe amplifier has a Rise Time Discrimination circuit, measure the FWHM energy resolution of 55Fe (5.89) the peak in each spectrum hence a graph of energy resolution. Moreover, the Rise Time Discrimination So the escape peak of 55Fe was determined with Si detector was 11.66 keV, also k- sell x-ray energy was calculated to 5.77keV and the Rise Time Discrimination effect was studied on the spectrum when is it switched on and off. Its influence was found in decreasing the noise of the spectrum.

Specific features of microhardness and thermodynamic stability of the Cd1–xMnxTe solid solutions

The features of fusion and growth of Cd1–xMnxTe (0.02 x  0.55) solid solution crystals as well as the dependence of their microhardness on the composition have been studied. Local maxima of the microhardness at x = 0.14 and 0.46 have been experimentally found. Thermodynamics of Cd1–xMnxTe formation in the delta-lattice parameter model has been considered, and the phase diagram of spinodal decomposition in these solid solutions has been found. The empirical pseudopotential method was used to analyze the distribution of the valence charge density during formation of the Cd1–xMnxTe solid solution and its effect on the rearrangement of chemical bonds. It has been shown that the stability of the solid solutions is defined not only by the difference in the lattice constants of the CdTe and MnTe binary compounds but also by the charge exchange between bonds with the different degree of ionicity and the change in the nature of chemical bonds.

Evolution of Structural and Optical Properties of Cuprous Oxide Particles for Visible Light Absorption

Absorbent materials are being developed to replace semiconductor materials such as p‐type silicon, GaAs, CdTe, and quaternary compounds such as CIGS (copper indium gallium selenide). Cu2O is a potential candidate because it is non‐toxic, inexpensive, an abundant compound in the Earth’s crust, and has good optical properties, such as a high absorption coefficient. In this work, Cu2O was obtained simply by reducing Benedict’s solution with glucose in an alkaline medium (pH 10.2 ± 0.2) at 65°C. The samples were synthesized by varying glucose content from 1 g to 7 g. The results showed a phase proportion variation between 95.56% and 99.50% of the Cu2O phase. It was found that the changes in crystallite size, microstrains, particle size, and morphology are due to reaction times, which were influenced by the use of different glucose amounts. The use of a higher glucose amount in the synthesis favors a faster reaction, forming smaller crystallites with more microstrains. Lower glucose amount leads to a slower reaction giving the crystallites more time to grow, which relaxes the microstrains. When increasing glucose content, the obtained morphologies changed from cubes, irregular cubes, prismatic spheres, cauliflower‐like, to spherical shapes. The XPS spectra confirmed only the presence of chemical species such as Cu(I) and Cu(II), and chemical defects, such as oxygen vacancies (Vo), were detected in the samples. All samples presented a broad absorption range from 200 nm to 570 nm indistinctly of the morphology. The band gap showed an insignificant change from 2.04 eV to 2.09 eV when glucose was increased from 1 g to 7 g. The in-situ phase transformation study was analyzed from 25°C to 700°C. The results indicated a phase transition from Cu2O to Cu and CuO when the temperature was above 280°C.

Solar cells based on CdTe thin films

An analysis of the use of semiconductor solar cells based on thin-film cadmium telluride (CdTe) in power engineering is carried out. It is shown that the advantages of thin-film technology and CdTe itself as a direct-gap semiconductor open up the prospect of large-scale production of competitive CdTe solar modules. The physical and technical problems of increasing the efficiency of CdS/CdTe heterostructure solar cells, which are significantly inferior to the theoretically possible value in mass production, are discussed. The state of CdTe thin-film solar cells, which make CdTe a suitable material for ground-based photoelectric conversion of solar energy, the historical development of the CdTe compound, the application of CdTe thin films, the main methods and strategies of device production, device analysis and fundamental problems related to the future development of thin-film modules based on cadmium telluride.

REQUIREMENTS ANALYSIS AND DEVELOPMENT OF THE FLEXIBLE SOLAR CELLS OPTIMAL SOLUTION FOR USE IN COMBINED PV/T SYSTEMS

The article defines the requirements for photovoltaic converters designed to work as integrated power sources for combined PV/T systems: efficiently generate electricity at a temperature of 55 °С; provide the coefficient of absorption of solar energy at the level of not less than 90 % and to have the coefficient of reflection in the infrared part of the spectrum not more than 10 %; together with the cooling system cooling system, the design of the converter must provide a difference between the temperature of the converter and the temperature of the coolant not more than 5 °C. A study of the temperature dependence of efficiency for film photoelectric converters based on CdTe and CuInSe2 compounds, amorphous silicon and crystalline GaAs, showed that structures based on cadmium telluride base layers have the smallest decrease in efficiency with increasing operating temperature. When the temperature changes by 50 °С, the efficiency of such devices decreases by only 1 %, and the relative rate of decrease is –0.14 rel. %/C, which is significantly less than the same parameter for other types of converters: GaAs –0.16 rel. %/C, amorphous silicon –0.21 rel. %/C, CuInSe2 –0.36 rel. %/C. Analytical processing and analysis of the influence of light characteristics on the efficiency of cadmium-based transducers showed that the temperature stability of their efficiency is ensured by the density of the diode saturation current. With increasing temperature from 20 °С to 50 °С, the density of the diode saturation current increases by 50 % from 1.9·10-9 A to 2.7·10-9 A, which is less than for silicon devices, for which the diode saturation current increases by 300 %. Studies have shown that the absorption coefficient of solar energy of a flexible element based on cadmium telluride in the visible range is 94–96 %, and the reflection coefficient in the infrared region of the spectrum does not exceed 7–8 %, which allows the design of the collector to abandon the use of selective coating, since its function will be performed by a film photoelectric converter. A constructive-technological solution of a photovoltaic system with flexible photovoltaic converters based on cadmium telluride is proposed.

Elastic properties of CdTe1–xSex(x = 1/16) solid solution: First principles study

Elastic properties of the CdTe1–xSex (x = 1/16) solid solution in the framework of the density functional theory calculations have been investigated. The structure of the sample has been constructed using that of the original binary compound CdTe, which crystallizes in the cubic phase. The Young modulus, shear modulus, bulk modulus and Poisson ratio have been calculated theoretically. On the results for elastic coefficients, value of acoustic velocity and Debye temperature have been obtained. The obtained values are in good agreement with experimental data.

The History of the German Association for Crystal Growth

The History of the German Association for Crystal Growth

Electric field distribution around cadmium and tellurium inclusions within CdTe-based compounds

Abstract We examine two kinds of volume defects in CdTe-based compounds grown from the melt: cadmium and tellurium inclusions. We have determined their chemical composition by energy-dispersive X-ray spectroscopy and their internal morphology by infrared transmission microscopy. The tellurium inclusions are spheroidal/polyhedral, while the cadmium ones appear star-like. The core size of both the tellurium and the cadmium inclusions is 5–8 μm. Cadmium inclusions cause micro cracks so that they create star-like defects the size of which is about ten times bigger than the inclusions themselves. Each pair of branches in the star-shaped defect we associate with the three easy-cleavage planes (1 1 0) of the zinc blende structure. Using Pockels imaging we have investigated how tellurium and cadmium inclusions influence the electric field distribution in CdTe compounds, which is an important issue for nuclear detectors. Only tellurium inclusions distributed along a continuous plane have an impact on the internal electric field. Neither the separated tellurium inclusions nor the separated cadmium inclusions influence the internal electric field. Crystals of (Cd,Mn)(Te,Se) have a high concentration (104–105 cm−3) of both types of inclusions. In (Cd,Mg)Te there are numerous twin boundaries decorated with tellurium inclusions. Among the studied compounds, (Cd,Mn)Te has the highest quality.