Close-spaced Sublimation Method Research Articles

Enhancement of detection performances of cadmium zinc telluride (CdZnTe) radiation detectors through sapphire substrates

Cadmium zinc telluride (CdZnTe) is a highly effective semiconductor material, renowned for its exceptional properties. In this study, we employed the close-spaced sublimation method to grow high-quality CdZnTe thick films on sapphire substrates. The effects of growth temperature on the composition, surface defects, and structural and electrical properties of CdZnTe films were examined. The investigation identified the optimal temperature conditions for the production of thick CdZnTe films of high quality. These were found to be a sublimation temperature of 675°C and a substrate temperature of 450°C. Furthermore, we have produced CdZnTe thick-film radiation detectors based on sapphire substrates. The detectors demonstrated an energy resolution of 18.9% when subjected to 59.54keV 241 Am γ-ray irradiation. The results of our investigation suggest that these CdZnTe thick film detectors have the potential to be employed in future low-cost, large-area imaging applications.

Interface-enhanced germanium selenide solar cells comprising an ultrathin and uniform antimony selenide buffer layer via hydrothermal approach

Germanium selenide (GeSe) is a promising thin film photovoltaic absorber material owing to its excellent optoelectronic properties, high stability, and low toxicity. Interface engineering by introducing an ultrathin antimony selenide (Sb2Se3) buffer layer between the CdS electron transport layer and GeSe absorber layer is an effective technique for enhancing solar cell performance. However, the key to this technique is the fabrication of a uniform and smooth Sb2Se3 buffer layer with minimal thickness. In this study, instead of the conventional closed-space sublimation method, a hydrothermal method was employed to slowly grow an Sb2Se3 buffer layer with a thickness of approximately 8 nm. The Se/Na2SO3 molar ratio in the selenium source during the hydrothermal synthesis was adjusted; a molar ratio of 1:2 led to an uneven Sb2Se3 buffer layer thickness, whereas a molar ratio of 1:10 resulted in the formation of Sb2O3 particles on the buffer layer surface. When the Se/Na2SO3 molar ratio was 1:6, a smooth, uniform, dense, and impurity-free Sb2Se3 buffer layer was obtained, achieving the highest efficiency of 3.33 % in a GeSe solar cell. Moreover, GeSe solar cells with hydrothermally grown Sb2Se3 buffer layers demonstrated superior device interface properties and efficiency comparable with those using Sb2Se3 buffer layers deposited via closed-space sublimation. This technique offers an effective method for steadily improving the performance of GeSe solar cells.

Enhanced photoelectrochemistry properties of CdZnTeSe thin films

CdZnTe (CZT), as an optimum absorption layer, has many attractive characteristics for photoelectrochemical (PEC) water splitting, such as tunable band gaps (1.45–2.26 eV) and high absorption coefficient (≥104 cm−1). The addition of Se into CZT was found to be very effective in arresting the formation of sub-grain boundaries, improving compositional homogeneity. In this paper, CZT films were deposited on fluorine-doped tin oxide-coated (FTO) substrates by close-spaced sublimation method. The influence of selenization process to the structural, morphological, and optical properties of CZT films was studied. The phase purity properties of CdZnTeSe (CZTS) films were analyzed by X-ray diffraction (XRD), energy disperse spectroscopy (EDS) and Raman spectra measurements. The morphological characteristics of CZTS films were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The PEC properties of CZTS films were also investigated, which indicated that the photocurrents of CZTS films were greatly increased than that of as-deposited CZT films. The mechanism of PEC enhancement of CZTS films were studied detailedly.

DC current–voltage and impedance spectroscopy characterization of nCdS/pZnTe HJ

This paper describes the electrical and dielectric behavior of the nCdS/pZnTe HJ by current–voltage, capacitance–voltage characteristics, and impedance spectroscopy in a temperature interval 220–350 K. A microcrystalline p-ZnTe layer and n-CdS were grown on glass/ZnO substrate by closed space sublimation method. As frontal contact to CdS, the transparent ZnO and as a back contact to ZnTe, silver conductive paste (Ag) treated at 50 °C in vacuum were used. The current–voltage results of nCdS/pZnTe HJ show a rectifying behavior. The junction ideality factor, barrier height, and series resistance values were extracted from the rectifying curves at different temperatures. The built-in voltage, carrier concentration and depletion width were obtained from the capacitance–voltage measurements. Analysis of the J–V–T and C–V–T characteristics shows that the thermionic emission and recombination current flow mechanisms dominate in the nCdS/pZnTe HJ. The dielectric study reveals that the experimental values of the AC conductivity, dielectric constant, dielectric loss, the imaginary part of the electric modulus are found to be very sensitive to frequency and temperature. The dielectric constant and dielectric loss are observed to be high at the low frequency region. The increase in the values of electric modulus with the frequency implies an increase in the interfacial polarization at the interface of nCdS/pZnTe HJ. Jonscher’s universal power law shows that with increasing frequency, AC conductivity increased. The results conductivity show that the ionic conductivity and interfacial polarization are the main parameters affecting the dielectric properties of the device when the temperature changes.

Fabrication of homogenous Sb2(S,Se)3 solar cells by close space sublimation using a single alloyed powder source

Sulfoselenide Sb2(S,Se)3, as a potential light-harvester, possesses a flexibly tunable bandgap of 1.1–1.7 eV to match solar radiation spectrum. However, the preparation of a homogenous Sb2(S,Se)3 film is still challenging due to the different growth kinetics in sulfide and selenide compound, which consequentially leads to phase separation, lattice disorder and unfavored band level. This dilemma also occurs in the simple and well-established close space sublimation (CSS) method, and poses a devastating carrier recombination in Sb2(S,Se)3 solar cells. Herein, alloyed powders of Sb2(S,Se)3 are exquisitely synthesized by a thorough gas-solid reaction, delivering a uniform and single phase composition distribution as well as finely-tunable S/Se ratio. Compared with a physically mixed powder source (Sb2S3/Sb2Se3), this alloyed Sb2(S,Se)3 source allows for the fabrication of a homogeneous Sb2(S,Se)3 thin film by CSS, rendering improved (hk1) orientation, dense morphology, a more consistent longitudinal S/Se ratio, and enhanced energy level arrangement. These advancements contribute to enhance carrier transport and reduce carrier recombination. As a result, the efficiency of the solar cell is remarkably boosted from 2.59% to 5.46%, which is among of the highest PCE of full-inorganic Sb2(S,Se)3 devices fabricated through the CSS method.

Chitosan Coatings Modified with Nanostructured ZnO for the Preservation of Strawberries.

Strawberries are highly consumed around the world; however, the post-harvest shelf life is a market challenge to mitigate. It is necessary to guarantee the taste, color, and nutritional value of the fruit for a prolonged period of time. In this work, a nanocoating based on chitosan and ZnO nanoparticles for the preservation of strawberries was developed and examined. The chitosan was obtained from residual shrimp skeletons using the chemical method, and the ZnO nanoparticles were synthesized by the close-spaced sublimation method. X-ray diffraction, scanning electron microscopy, electron dispersion analysis, transmission electron microscopy, and infrared spectroscopy were used to characterize the hybrid coating. The spaghetti-like ZnO nanoparticles presented the typical wurtzite structure, which was uniformly distributed into the chitosan matrix, as observed by the elemental mapping. Measurements of color, texture, pH, titratable acidity, humidity content, and microbiological tests were performed for the strawberries coated with the Chitosan/ZnO hybrid coating, which was uniformly impregnated on the strawberries' surface. After eight days of storage, the fruit maintained a fresh appearance. The microbial load was reduced because of the synergistic effect between chitosan and ZnO nanoparticles. Global results confirm that coated strawberries are suitable for human consumption.

Photodetector properties of CdSe thin films grown by close space sublimation method

Photodetector properties of CdSe thin films grown by close space sublimation method

Growth of CdZnTe (2 1 1) epilayers on GaAs by close spaced sublimation as an alternative substrate for HgCdTe growth

Cd0.96Zn0.04Te crystals are perfect substrates for epitaxial growth of HgCdTe films due to good lattice matching, but they are limited by cost factors. To grow a replacement substrate for the subsequent growth of low-cost, high-yield HgCdTe IR materials, CdZnTe epitaxial films have been fabricated by close-spaced sublimation on GaAs substrates, and the effect of substrate temperature on the crystalline quality of CdZnTe films has been investigated. The results of EBSD and TEM indicate that the surface is oriented in (211) and the low temperatures enhance the crystalline quality of the film. The results of dislocation density (average etch pit density ∼3.6 × 105 cm−2) and energy dispersive spectrometer (Zn content ∼5 %) indicate that CdZnTe films with appropriate Zn content and excellent crystal quality can be obtained by the close spaced sublimation method, which is expected to be applied for molecular beam epitaxy growth of HgCdTe films.

The effect of SbCl3 treatment on CdTe produced by close space sublimation method

In this study, influence of SbCl3 treatment on CdTe films deposited by the close space sublimation method was investigated. SbCl3 treatment was compared with conventional CdCl2 treated and untreated samples. It was determined that CdTe grew as Cd-rich and there was a slight decrease in Cd-amount after SbCl3 and CdCl2 treatments. In addition, a significant amount of Sb was detected in the SbCl3 treated sample. The samples crystallized in the cubic structure of CdTe. However, graded structures such as phase-I and phase-II with different structural parameters were formed. In the SbCl3 sample, it was revealed that the presence of Sb- caused a slight increase in the lattice parameter, compared to the other samples. Morphological analyses of the samples showed facet and large-small grain structures. CdCl2 treatment caused a slight decrease in grain size, while SbCl3 treatment resulted in a coarser and rougher grain structure. CdCl2 treatment increased transmittance, whereas SbCl3 treatment caused a decrease in transmittance (hence, an increase in absorbance). It was observed that the bandgaps were ∼1.49 eV in all samples, and annealing, as well as CdCl2 and SbCl3 heat treatments did not cause a sharp change in the bandgaps. Photoluminescence spectra revealed the presence of band-edge and shallow-level defect transitions (except CdCl2 treated) in the samples. All results suggest that SbCl3 heat treatment has a significant effect on CdTe and may be an alternative to CdCl2.

Preparation and characterization of Sb2S3 thin films for planar solar cells via close space sublimation method

Sb2S3 has a unique one-dimensional structure-composed (Sb4S6) n ribbons leads to strong anisotropic carrier transport characteristic: carrier transport along the (Sb4S6) n ribbon is more efficient than other ribbons. Therefore, it's crucial to control the direction of grain growth along the (hk1) orientation. In this work, the close space sublimation method was utilized to fabricate Sb2S3 thin films with a systematical regulation of substrate temperature. The results demonstrate that optimized Sb2S3 thin film presented preferred orientation at the direction of (hk1). The champion device based on Au and Ni electrodes achieved a power conversion efficiency (PCE) of 3.06% and 1.69%, respectively.

Copper-related defects in ZnTe thin films grown by the close space sublimation method

Low-temperature photoluminescence (PL) is used to study defects evolution via immersion technique and annealing in vacuum of ZnTe thin films. In this paper we studied how copper doping from solutions of different molar concentrations affects PL of ZnTe thin films grown by close space sublimation (CSS) method. Undoped ZnTe thin films showed PL emission in the (520-680) nm wavelength region. The incorporation of copper in ZnTe produce a number of broad emission bands that correspond to an electron transition from the conduction band to spin-orbit states of the localized level of Cu2+ ions. All the studied samples had variable concentrations of oxygen and the possibility of the formation of auxiliary oxides is discussed.

The effect of Te-doping and heat treatment on the structural properties of CdTe absorber layer for CdS/CdTe solar cell

Te rich CdTe thin films for absorber layer in CdS/CdTe solar cell were fabricated by the closed space sublimation method. Te enriched CdTe source materials with different Te rich contents were prepared before the deposition process of thin film. The properties of Te rich CdTe thin film were studied on the basis of the theoretical consideration of stoichiometric defect and self-doping. Here, we have considered the structural properties of CdTe with Te rich contents of 0, 1, 3, 5, 7, 10wt% by using scanning electron microscopy and X-ray diffraction. XRD measurements revealed that CdTe thin film had the largest lattice constant and the best crystallinity with less defects and stress at doping condition of 5%. Annealing in air represented more preferential orientation in (111) direction than the heat treatment in vacuum. We have analyzed the influence of Te doping and heat treatment on the structure and properties of CdTe:Te thin film to confirm more reasonable Te rich content and annealing atmosphere for CdTe thin film. Finally, we have determined Te rich content of the CdTe:Te thin film, 5%.

Microstructure and optical properties of CdTe thin films prepared by close spaced sublimation method at various growth temperatures

Cadmium telluride (CdTe) is an important Ⅱ-Ⅵ multifunctional semiconductor, often used as the light absorption layer in photovoltaic solar cells or the core layer in γ-ray detection. The deposition temperature has a great greatly influences on the microstructure and morphology of the thin films during their growth. Here, close spaced sublimation method is used for depositing CdTe thin films on glass substrate at various temperatures conditions. The microstructure, morphology, optical and luminescent properties of the CdTe thin films were systematically characterized. CdTe thin films with a high preferred crystal orientation, large grain size, low micro-stress, and strong luminescence performance were obtained. And the origin of luminescent peaks is analyzed in detail by low-temperature photoluminescence spectroscopy.

ACTIVATION METHOD OF CADMIUM TELLURIDE THIN FILMS FOR CREATION EFFECTIVE SOLAR CELLS

The influence of annealing in freon on the cadmium telluride films crystal structure obtained by closed space sublimation method and the output parameters and light diode characteristics of solar cells based on these films were studied. Annealing of structures was performed at a temperature of 400°С for different times. The studies of the crystal structure were performed by the X-ray diffraction analysis. These studies have shown that the annealing in freon leads to a recrystallization of cadmium telluride films, which reduces microstress. It is evidenced by the lattice period decrease after annealing from а = 6.491 Å to а = 6.488 Å. The study of the influence of annealing in freon on the output parameters and light diode characteristics of solar cells was performed. For this purpose the light current-voltage characteristics of ITO/SnO2/CdS/CdTe structures, annealed for 20‑40 minutes, were studied. It was found that the optimal annealing time in freon is 30 minutes. It is shown that the solar cells based on such films have the highest efficiency in 11.7% after annealing in freon for 30 minutes. A simulation of light diode characteristics influence on the efficiency showed that the solar cells efficiency increase due to the diode saturation current density decrease when the annealing time in freon increases to 30 minutes. When the annealing time increases to 40 minutes the efficiency decrease is associated with a shunt resistance decrease. It is also shown that the pre-irradiation of solar cells in the AM1.5 mode for 20 minutes leads to an additional efficiency increase to 12.2%. According to the simulation results, such efficiency increase is also due to the diode saturation current density decrease.

Effect of ultra-thin CdSexTe1−x interface layer on parameters of CdTe solar cells

Effects of an ultra-thin CdSexTe1-x junction interface layer on CdTe solar cell parameters were investigated employing a CdSexTe1-x/CdTe absorber structure. CdSexTe1-x thin films with varying composition were grown by vacuum evaporation and CdTe films were produced by the close spaced sublimation (CSS) method. XRD analysis showed that while the CdSexTe1-x layers with x values less than 0.39 crystallized in cubic structure, films that were richer in Se displayed a (cubic + hexagonal) mixed phase. SEM analysis demonstrated a morphology with compact grains for all films. However, the grain size decreased appreciably with increasing Se content. Optical measurements showed that the band gaps of the alloys reached the minimum value of 1.40 eV at x ∼ 0.32. CdS/CdSexTe1-x/CdTe solar cells were fabricated employing 100 nm thick CdSexTe1-x interlayers. The Grazing Incidence (GI)-XRD spectra of CdSexTe1-x used in the device structure showed that these inter-layers had graded alloy composition. The average Se-concentration within the graded alloy films were found to agree with the values obtained by EDS. Conversion efficiencies of 9.59% 11.69% and 10.13%, were obtained for x values of 0.24, 0.32 and 0.39, respectively. Spectral response showed enhanced long wavelength response for all devices due to the presence of the CdSexTe1-x interlayer. It was concluded that using an ultra-thin CdSexTe1-x inter-layer with optimum properties between CdS (junction partner) and CdTe improves the cell performance by increasing the current density of the device.

Deposition of CdZnTe Films with CSS Method on Different Substrates for Nuclear Radiation Detector Applications

CdZnTe (CZT) films were grown by closed space sublimation (CSS) method on (111)-oriented CZT wafers, non-oriented CZT wafers and FTO substrates. The compositional and morphological properties of CZT films on different substrates were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which indicated that CZT films grown on (111)-oriented CZT wafers had low dislocation density and high Zn composition. X-ray diffraction (XRD) measurements confirmed that CZT films grown on (111)-oriented CZT wafers had the best crystal quality. The I-V and DC photoconductivity measurements indicated that CZT films on (111)-oriented CZT wafer had good carrier transport performance. The energy spectra of CZT films grown on (111)-oriented CZT wafer presented that it had a good response to the nuclear radiation under 241Am.

Fabrication of closed-space sublimation Sb2(S1-xSex)3 thin-film based on a single mixed powder source for photovoltaic application

Because of favourable stability, facile fabrication, non-toxicity, tunable bandgap and high extinction coefficient, Sb 2 (S 1-x Se x ) 3 combined the advantages of Sb 2 S 3 and Sb 2 Se 3 have attracted extensive attention. Unlike previous studies using a preformed target or source of a single composition, our study offered a high‐throughput closed-space sublimation method based on a single mixed powder source of Sb 2 S 3 and Sb 2 Se 3 . We fabricated single-phase and highly crystalline Sb 2 (S 1-x Se x ) 3 films with strong (221) orientation, which is beneficial for the rapid transmission of photon-generated carriers. The bandgap of films evolved from 1.79 eV to 1.38 eV that accompany the varying x value of Se content from 0.14 to 0.85. The corresponding solar cells with the structure of FTO/CdS/Sb 2 (S 1-x Se x ) 3 /Au were fabricated, and then the relationship between performance, source temperature and alloy composition were investigated. The open-circuit voltage and short circuit current density showed opposite trends with increased Se content. Finally, the champion device with a PCE of 2.70% was obtained employing Sb 2 (S 0.25 Se 0.75 ) 3 absorber, which had optimal grain orientation, favourable surface morphology. The bandgap is 1.45 eV, which falls into the ideal bandgap in the Shockley–Queisser limit. A low reverse saturation current density (2.35 × 10 −5 mA/cm 2 ) and the relevant diode ideality factor (1.38) were obtained, which implies favourable junction quality. The CSS technique is expected to improve production efficiency and promote Sb 2 (S 1-x Se x ) 3 solar cell commercial applications, worth further optimization.

Microstructural evolution of oxygen incorporated CdTe thin films deposited by close-spaced sublimation

In this work, cadmium telluride (CdTe) thin film was deposited in vacuum (pure argon ambient) as well as different argon (Ar) and oxygen (O2) ambient conditions using close-spaced sublimation (CSS) method at the deposition pressure of 1 Torr. The deposited films were characterized via X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), UV–Vis spectrophotometer and Hall Effect measurement for the analysis of structural properties, morphology, optical properties and electrical properties, respectively. XRD patterns exhibited almost similar preferential orientation plane at (111) irrespective of the O2 concentration. SEM surface morphology microstructure revealed that O2 presence had a substantial effect on grain size reaching up to 7.19 µm. Optical properties also demonstrated insignificant changes in the direct band gap values of around 1.48 eV. Carrier concentration showed an upward trend in the order of 1013 cm−3, whereby resistivity and mobility did not change substantially either in vacuum (pure Ar ambient) or in Ar/O2 ambient.

Close-Spaced Sublimation of CdZnTe:In Films for Solar Energy Water Splitting

CdZnTe:In (CZT:In) films were deposited on fluorine-doped tin oxide-coated (FTO) substrates by close-spaced sublimation method, and the structural, morphological, and optical properties of CZT:In f...

Cracking mechanism of CdZnTe polycrystalline film deposited on TFT circuit board at high temperature by close-spaced sublimation method

In this paper, CdZnTe polycrystalline films are grown on TFT circuit boards and ITO/TFT substrates by using close-spaced sublimation (CSS) technique. The phase, morphology and structure of CZT polycrystalline film were characterized by XRD, SEM and EDS, and the cracking mechanism of CZT film deposited on TFT circuit board at high temperature was studied. The results show that the substrate temperature was too high during experiment, which released the stress between Al film and ITO film, produced small hills, and made the binding force of ITO and CZT film greater than that of ITO film and Mo/Al/Mo, resulting in CZT film falling off. The presence of SiNx on TFT circuit board can promote the rupture of CZT film.