xZnxS Thin Films Research Articles

Variation of ZnS deposition time on chemically prepared Cd1-xZnxS ternary compound from CdS/ZnS bilayers

Chemical bath deposition (CBD) was successfully used for the preparation of cadmium zinc sulphide (Cd1-xZnxS) ternary alloy thin film with × composition, in the range of 0 and 1, from post annealing treatment of bilayer cadmium sulphide (CdS)/zinc sulphide (ZnS) thin film. Increasing the ZnS layer deposition time leads to an increase in the overall thickness of the bilayer with an attendant increase in zinc ion concentration. From the XRD measurement, thin film samples presented hexagonal structure, with a shift in the peaks position to higher angles coupled with a decreasing crystalline size and lattice constants as zinc ion is continuously incorporated into the Cd1−xZnxS thin films. The continuous addition of the wider band gap energy ZnS into the ternary compound as the ZnS deposition time increases constantly brought about the widening of the band gap energy. Energy dispersive spectroscopy (EDS) measurement established the presence of the major elements Cd, Zn and S. The room temperature electrical resistivity determined from the point probe measurement ranges between 2.1 × 10-3 and 1.2 × 101 Ωm, and showed a decrease with increasing zinc ion contents. In this study, it was established that Cd1-xZnxS ternary compounds can be prepared starting with CdS/ZnS bilayer, and its post thermal annealing, with the band gap energy able to be accurately controlled by modifying the CdS/ZnS thickness ratio through variation of ZnS deposition time. The results from CdZnS thin film compounds prepared under this present condition established its superior effectiveness as a buffer layer in thin film solar cells.

Chemical Bath Deposition of Cd1−xZnxS as Buffer Layer in CIGS Solar Cell

Cd1−xZnxS thin films were deposited on glass substrates by chemical bathdeposition (CBD). The effect of ZnSO4 solution concentration on the prop-erties of the thin films was analyzed. The concentration of ZnSO4 solutionaffects the deposition rate of Cd1−xZnxS thin films. When the deposition rateis low, Cd1−xZnxS cubic crystal phase is formed. The surface morphology ofhexagonal Cd1−xZnxS thin films is denser than that of cubic phase, the latticemismatch rate of cubic phase Cd1−xZnxS thin films and CIGS is lower, only0.56%, the interfacial state density is lower. SCAPS software was used tosimulate the performance of the buffer layer and the conversion efficiencyof the cubic phase Cd1−xZnxS buffer layer in CIGS Solar Cell was up to23.50%. Based on the EDS results, the functional relationship between thecontents of Zn2+ and Cd2+ in the films and the bandgap content was deduced.

Simplified two-electrode electrochemical growth and characterization of Cd1−xZnxS thin films: Influence of electrolytic bath pH

Cd1−xZnxS thin films were prepared from an aqueous electrolytic solution using a simple low-cost two-electrode electrodeposition technique. Effect of pH on physico-chemical properties was studied at three different pH values of 1.8, 2.7 and 3.6. It was found as the pH is raised, intensity of the X-ray diffraction peaks of the films decreased gradually. Raman measurement also showed similar observation a decrease in intensity of peaks as pH is raised. Compositional characterization shows that more Zn is incorporated into the CdS lattice as pH increases and on the other hand deposition rate decreases due to formation of more OH− ions in the bath. SEM measurement reveals that the variation of pH significantly influences surface morphology of the films. The optical band gap ranges from 2.43 eV to 2.50 eV which indicate that, electrodeposited Cd1−xZnxS thin films can be used as good window/buffer layer for solar cell application in place of CdS.

Synthesis and characterization of high-efficiency low-cost solar cell thin film

Abstract Polycrystalline chalcogenide semiconductors play a vital role in solar cell applications due to their outstanding electrical and optical properties. Among the chalcogenide semi-conductors, CdZnS is one kind of such important material for applications in various modern solid state devices such as solar cells, light emitting diode, detector etc. Due to their applications in numerous electro-optic devices, group II-VI semiconductors have been studied extensively. In recent years, major attention has been given to the study of electrical and optical properties of CdZnS thin films. In this work, Cd1−xZnxS thin films were prepared by chemical bath deposition technique. Phase purity and surface morphology properties were analyzed using field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) studies. Chemical composition was studied using energy dispersive spectrophotometry (EDS). Optical band gap property was investigated using UV-Spectroscopy. Electrical conductivity studies were performed by two probe method and thermoelectric power setup (TEP) to determine the type of the material. This work reports the effect of Zn on structural, electrical, microstructural and optical properties of these films.

Physico-chemical studies of Cd1−xZnxS thin films produced by simple two-electrode electrodeposition system for solar cell application

Cd1−xZnxS thin films have been cathodically electrodeposited on glass/fluorine-doped tin oxide substrates using a low-cost two-electrode configuration with an electrolytic bath containing cadmium chloride, zinc chloride and sodium thiosulphate precursors. The deposition was carried out by varying zinc chloride concentration (0 M, 0.3 M, 0.6 M and 0.9 M) in the deposition electrolyte. The structural, compositional, phonon vibrational, morphological and optical properties of the resulting films have been characterized using glancing incidence X-ray diffraction, energy-dispersive X-ray (EDX) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM) and UV–Vis spectrophotometry respectively. The XRD result indicates the existence of hexagonal structure of Cd1−xZnxS with intensities of the diffraction peaks decreasing as more Zn is incorporated into the film as a result of decrease in deposition rate. EDX results show the presence of Cd, Zn and S in the deposited Cd1−xZnxS thin films. SEM images show uniform and densely packed surface morphology of the films with distinct shaped grains which gradually less distinct as more Zn is incorporated into the films. The optical measurements reveal a significant increase in energy band gap of the Cd1−xZnxS material as more zinc is incorporated into the films and a film thickness decreases with the energy band gap increasing from 2.40 eV for CdS to 2.62 eV for Cd1−xZnxS. These results show that Cd1−xZnxS material can be applied as a better window material for CdTe, CIG(S,Se) and CZTS-based solar cells than CdS.

Preparation of cadmium zinc sulfide (Cd1−xZnxS) thin films from acidic chemical baths

Ternary cadmium zinc sulfide (Cd1−xZnxS) thin films were deposited by chemical bath deposition method for the entire range of 0 ≤ x ≤ 1 from acidic chemical bath using tartaric acid and hydrazine as a complexing agents. The X-ray diffraction (XRD) studies revealed that the deposited thin films had hexagonal crystal structure in the range of 0 ≤ x ≤ 0.6 and pure cubic phase at x = 1, whereas, the thin films deposited in the range of 0.72 ≤ x ≤ 0.9 had a mixed cubic and hexagonal structures. Furthermore, the XRD results showed that the crystalline size and lattice constants were decreased linearly with the gradual incorporations of zinc ion in the Cd1−xZnxS thin films. The optical spectroscopy investigation established that the band gap of the deposited ternary thin films found in the range of 3.84 eV to 3.94 eV. The scanning electron microscope studies illustrated that the surface morphologies of the prepared thin films were formed from spherical grains. The presence of cadmium, sulfur and Zinc elements in the synthesized thin films were confirmed by the energy dispersive x-ray analyses. The unusual large band gap obtained for pure cadmium sulfide and ternary Cd1−xZnxS thin films deposited under the present deposition condition together with the preferred orientation along the (002) plane make these thin films useful as a buffer layer in thin film solar cells.

The deposition of thin films of cadmium zinc sulfide Cd1\u2212xZnxS at 250\xa0\xb0C from spin-coated xanthato complexes: a potential route to window layers for photovoltaic cells

Thin films of Cd1−xZnxS (CZS) were prepared by a novel spin coating/melt method from cadmium ethylxanthato [Cd(C2H5OCS2)2] and zinc ethylxanthato [Zn(C2H5OCS2)2] in x ratios of 0–0.15 and of 1. A solution of the precursor(s) in THF was spin coated onto a glass substrate and then heated at 250 °C for 1 h under N2. The thickness of the film formed can be controlled by varying the solution composition and/or the spin rate of the coating. A total metal precursor solution concentration of 50 mM was used in all cases. The films were characterized by p-XRD, SEM, EDX, ICP-AES, XPS, UV–Vis absorption spectroscopy, Raman spectroscopy and resistivity measurements. The band gaps of the films were between 2.35–2.58 and 3.75 eV (0 ≤ x ≤ 0.15 and at x = 1). The resistivity of Cd1−xZnxS films was found to vary linearly with zinc contents, and the properties of the films suggest potential application to photovoltaics as window layers. This work is the first study to demonstrate Cd1−xZnxS thin films by a spin coating/melt method from xanthato precursors.

Deposition and characterisation of spray-deposited nanocrystalline Cd1−XZnXS thin films for photovoltaic device applications

Nanocrystalline Cd1−XZnXS thin films (X = 0.2, 0.4, 0.6, 0.8) have been grown on glass substrate by spray pyrolysis technique using equimolar concentration aqueous solution of cadmium chloride, zinc acetate and thiourea. Prepared thin films have been characterised by UV–vis spectrophotometer, X-ray diffractometer, SEM/EDAX analysis and two-point probe set-up. The optical band gap of the films has been studied by transmission spectra in wavelength range 325–600 nm. It has been observed that optical band gap increases with increasing zinc concentration. The X-ray diffraction pattern of films indicated that the films are polycrystalline with hexagonal grain structure. The lattice parameters of prepared Cd1−XZnXS films decrease with increase in zinc content. SEM/ EDAX analysis consolidates the formation of ternary compound. The DC electrical conductivity and activation energy of the films has been measured in vacuum by a two-point probe set-up. It has been observed that the electrical conductivity decreases with increasing Zn concentration in films.

Annealing-induced effects on structural and optical properties of Cd1−xZnxS thin films for optoelectronic applications

AbstractCd1−xZnxS thin films of variable compositions (x = 0.2, 0.4, 0.6, 0.8) were deposited on glass at room temperature by thermal evaporation process. The prepared samples were annealed at two different temperatures (300 °C, 400 °C) for 1 hour in ambient air. The effects of post-annealing on the structural and optical characteristics were investigated using X-ray diffraction (XRD), spectrophotometry, and Raman spectroscopy (RS) methods. XRD studies suggested that the annealed and as-deposited samples belong to wurtzite structure for all Zn concentrations with a preferential orientation along (002) plane. Spectrophotometry analysis of the samples revealed that the energy band gap decreased with annealing temperature. RS investigated different phonon bands and crystalline phases. Two longitudinal optical phonon modes (1-LO, 2-LO) corresponding to monophase hexagonal structure were observed for all Cd1−xZnxS samples. The observed red-shift and anti-symmetrical nature of the 1-LO phonon mode can be associated with annealing, while the overall blue-shift, except for x ⩽ 0.6, was caused by the structural disorders in periodic Cd atomic sub-lattices and broken translational symmetry. The spectroscopic results were strengthened by the XRD studies and their results are consistent.

Effects of ammonia concentration on property of Cd1−xZnxS films by chemical bath deposition

Cd1−xZnxS thin films were grown on soda–lime glass substrates by chemical-bath deposition (CBD) at 80°C with stirring. All the samples were annealed at 200°C for 60min in the air. The crystal structure, surface morphology, thickness and optical properties of the films were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), step height measurement instrument and spectrophotometer respectively. The results revealed that Cd1−xZnxS thin films had cubic crystal structure and the intensity of the diffraction peak increased gradually as ammonia concentration rose and the grain size varied from 5.1 to 8.3nm. All of Cd1−xZnxS thin films had a granular surface with some smaller pores and the average granule sizes increased from 92 to 163nm with an increase in ammonia concentration. The Cd1−xZnxS thin films had the highest transmittance with ammonia concentration of 0.5ML−1, whose thickness was 50nm and band gap was 2.62eV.

Cd1 − xZnxS thin films with low Zn content obtained by an ammonia-free chemical bath deposition process

Cd1−xZnxS films with low Zn content were obtained on glass substrates by an ammonia-free chemical bath deposition process. Alkaline reaction solutions were prepared using cadmium chloride, zinc chloride, sodium citrate, thiourea and potassium hydroxide. As a result of varying the mixture ratio between Cd and Zn precursors, microstructural studies from X-ray diffraction reveal that the resulting films have hexagonal, wurzite type, crystalline structure with changes in the preferential growth orientation. Important changes on the surface morphology and thickness of the Cd1−xZnxS films were also observed as effects of adding Zn to the CdS lattice. Optical studies show that Cd1−xZnxS thin films with energy band gaps in the range from 2.48 to 2.65eV were obtained.

Preparation and characterization of Cd1−x Zn x S buffer layers for thin film solar cells

Cd1−x Zn x S (x = 0, 0.1, 0.2, 0.3, 1.0) thin films have been grown successfully on soda-lime glass substrates by chemical bath deposition technique as a very promising buffer layer material for optoelectronic device applications. The composition, structural properties, surface morphology, and optical properties of Cd1−x Zn x S thin films were characterized by energy dispersive analysis of X-ray technique (EDAX), X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectrophotometer techniques, respectively. The annealed films were observed to possess the deficient sulfur composition. The results of XRD show that the Cd1−x Zn x S (x = 0.1) thin film annealed at 450 °C forms hexagonal (wurtzite) structure with lattice parameters a = 0.408814 nm, c = 0.666059 nm, and its average grain size is 24.9902 nm. The diffraction peaks become strong with the increasing annealing temperatures. The surface of Cd1−x Zn x S (x = 0.1) thin film annealed at 450 °C is uninterrupted and homogenous as compared to other temperatures. From optical properties, it is observed that the presence of small amount of Zn results in marked changes in the optical band gap of CdS. The band gaps of the Cd1−x Zn x S thin films vary from 2.42 to 3.51 eV as composition varies from x = 0.0 to 1.0. The optical studies in figs reveal that Cd1−x Zn x S thin film annealed at 450 °C shows a high transmittance as a direct-gap semiconductor. The calculated band gap (E g) of the film is about 2.56 eV annealed at 450 °C. This is in close agreement with the reported value (2.49 eV) of Cd0.9Zn0.1S film. Compared to the E g value (2.42 eV) of CdS, the increased E g value is due to the entrance of the element of zinc.

Tunability of physical properties of (Cd:Zn)S thin film by Close Space Sublimation Process (CSSP)

The present paper reports on a systematic study of the influence of Zn alloying on the structural and optical properties of Cd1−xZnxS thin films. X-ray diffraction study for structural analysis reveals that the two binary compounds have been completely transformed into ternary compound with hexagonal (wurtzite) structure with preferred orientation along c-direction with (002) planes. The optical properties such as optical constants and band gap energy of the films were examined by using spectroscopic ellipsometer and Photospectrometery. It was found that the optical constants (n and k) decrease with the addition of Zn content in the alloy. It was also confirmed that the band gap increases with increasing Zn amount in the alloy and is attributed to quantum size effect in the grain size. Raman spectroscopy analysis shows one dominant phonon band at 326cm−1, the so-called longitudinal optical (LO) mode for all the alloy composition (x). The appearance of a single phonon band in the Raman spectra established the formation of single phase hexagonal structured Cd1−xZnxS thin film. The LO band is asymmetrically broaden and high frequency shifted due to potential fluctuation caused by the dopant material. The AFM results showed that the surface roughness was decreased with increasing Zn content.

Growth and characterization of chemical bath deposited Cd 1− xZn xS thin films

Cd 1− x Zn x S (0 ≤ x ≤ 1) thin films have been deposited by chemical bath deposition method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 80 ± 5 °C and after annealed at 350 °C. The structural, morphological, compositional and optical properties of the deposited Cd 1− x Zn x S thin films have been studied by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) and UV–vis spectrophotometer, respectively. X-ray diffraction analysis shows that for x < 0.8, the crystal structure of Cd 1− x Zn x S thin films was hexagonal structure. For x > 0.6, however, the Cd 1− x Zn x S films were grown with cubic structure. Annealing the samples at 350 °C in air for 45 min resulted in increase in intensity as well as a shift towards lower scattering angles. The parameters such as crystallite size, strain, dislocation density and texture coefficient are calculated from X-ray diffraction studies. SEM studies reveal the formation of Cd 1− x Zn x S films with uniformly distributed grains over the entire surface of the substrate. The EDX analysis shows the content of atomic percentage. Optical method was used to determine the band gap of the films. The photoluminescence spectra of films have been studied and the results are discussed.

Comparative Studies of CdZnS Thin Films at Low Zinc Content Prepared by Vacuum Evaporation and CBD

Cd1−xZnxS thin films at low Zn content were prepared both by chemical bath deposition (CBD) and vacuum co-evaporation. The X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS) analysis were performed to determine the composition of the films, while the structural properties were investigated by X-ray diffraction (XRD). As a probable window layer, the optical band gaps of Cd1−xZnxS thin films prepared by the dry and wet process were calculated. Finally, the surface morphologies of the thin films were survey by scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Structural and optical properties of Cd0.8Zn0.2S thin films

Cd1−xZnxS thin films were deposited on glass substrates by a vacuum coevaporation method. The structural, compositional, and optical properties of as-deposited Cd0.8Zn0.2S films were investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), and optical transmittance spectrum. The thin films are hexagonal in structure, with strong preferential orientation along the (002) planes. The composition of Cd1−xZnxS thin films monitored by a quartz crystal oscillator agrees well with that obtained from XRF and XPS measurements. The optical constants, such as refractive index, single-oscillator energy, dispersion energy, absorption coefficients, and the optical band gap, were deduced by the Swanepoel's method, in combination with the Wemple and DiDomenico single-oscillator model, from the transmission spectrum of Cd0.8Zn0.2S thin films.

Optical properties of Cd1−xZnxS thin films for CuInGaSe2 solar cell application

Abstract The photovoltaic Cd1−xZnxS thin films, fabricated by chemical bath deposition, were successfully used as n-type buffer layer in CuInGaSe2 (CIGS) solar cells. Comprehensive optical properties of the Cd1−xZnxS thin films were measured and modeled by spectroscopic ellipsometry (SE), which is proven to be an excellent and non-destructive technique to determine optical properties of thin films. The optical band gap of Cd1−xZnxS thin films can be tuned from 2.43 eV to 3.25 eV by controlling the Zn content (x) and deposition conditions. The wider-band-gap Cd1−xZnxS film was found to be favorable to improve the quantum efficiency in the wavelength range of 450–550 nm, resulting in an increase of short-circuits current for solar cells. From the characterization of quantum efficiency (QE) and current–voltage curve (J-V) of CIGS cells, the Cd1−xZnxS films (x = 0.32, 0.45) were demonstrated to significantly enhance the photovoltaic performance of CIGS solar cell. The highest efficiency (10.5%) of CIGS solar cell was obtained using a dense and homogenous Cd0.68Zn0.32S thin film as the buffer layer.

Growth, annealing and thermo-electrical properties of Cd1−xZnxS thin films for microbolometers

Cd1−xZnxS (0<x<0.14) nanocrystalline thin films were grown and tested for use as sensing elements in microbolometer-type uncooled infrared detectors instead of vanadium oxides. Films of thickness 80–700 nm were deposited on SixNy/silicon as well as on glass and SiO2/silicon wafers using both thermal evaporation and MOCVD. The films were characterized by AFM, SIMS and electrical measurements. CdS thin films showed good parameters for use in microbolometer-type infrared uncooled sensors. The thermal coefficient of resistance (TCR) was in the range of 1.1–3.6% for the different film thicknesses. The TCR and electrical resistance of CdS films were optimized using annealing in different environments (vacuum, nitrogen, hydrogen and NF3) and by using a capping silicon nitride layer. The correlations between grain size, grain boundaries structure and TCR were established. Owing to the nanoscale film structure and thickness, significant grain growth and grain-boundary reconstruction occurred during minute long annealing time at temperatures as low as 200 °C.

Formation of CdZnS thin films by Zn diffusion

The structural, composition and optical absorption properties of Cd1−xZnxS (CdZnS) thin films fabricated by the reactive diffusion of Zn in CdS have been investigated. These ternary compounds were characterized by x-ray diffraction (XRD), energy dispersive x-ray fluorescence and optical absorption measurements. It is established that thermal annealing of Zn/CdS structure at temperature (400 °C) lower than the melting point of Zn (418 °C) results in the concentration distribution of Zn in CdS film described by an erfc-curve (D = 5 × 10−14 cm2 s−1) and characterizing the free impurity diffusion from a constant source. In contrast to this, the concentration profile of Zn in CdS film at higher annealing temperature (570 °C) is not described by the erfc-curve and shows a nearly stepped form, which is characteristic of reactive diffusion. XRD patterns of Zn/CdS structures annealed at 570 °C showed diffraction peaks of ternary CdZnS compounds. Analysis of the absorption spectrum of such films indicates formation of CdZnS composition with the largest value of energy band gap up to 2.64 eV, exceeding the band gap of CdS (2.43 eV). It is concluded that interdiffusion in Zn/CdS structures at temperatures exceeding the melting point of Zn was accompanied by formation of Cd1−xZnxS ternary compounds. The band gap of this variable band structure changes from 2.64 eV in the near surface region to 2.43 eV (CdS) in the inner region of the film.

K shell fluorescence yield of Cd and Zn in Cd 1− xZn xS thin films

The K shell fluorescence yield ω K of Cd and Zn in Cd 1− x Zn x S semiconductors has been studied. Energy dispersive X-ray fluorescence (EDXRF) technique was used to measure K X-ray photons. Cd and Zn elements were excited by using 59.5 keV photons emitted by a 50 mCi 241Am radioactive source. The emitted characteristic K X-rays were detected by a Si (Li) detector having a resolution of 160 eV at 5.9 keV. It was found that the K shell fluorescence yield ω K changed in Cd 1− x Zn x S thin films for different compositions of x.