Bath Deposited CdS Films Research Articles

Effect of Ammonium Acetate on the Properties of Chemical Bath Deposited CdS Films

ABSTRACTThis investigation is a comprehensive study of the effect of ammonium acetate on the electrical, optical, morphology and microstructure of CdS thin films grown by Chemical Bath Deposition method (CBD). Two sets of CdS thin films (A and B) were deposited on glass substrates at 60°C for 60 min. The films were deposited using chemical bath solution that consists of cadmium acetate, ammonium hydroxide, and thiourea. However, ammonium acetate was added into the chemical bath used to deposit set (B), where ammonium acetate was eliminated from bath solution used to deposit set (A). The films’ morphology was examined by Field Emission Scanning Electron Microscopy (FE-SEM), whereas, the chemical composition was investigated by Electron Probe Micro-Analyzer (EPMA). The X-Ray Diffraction (XRD) θ/2θ technique was applied to study the structure of the films. Atomic Force Microscopy (AFM) was used to measure the average surface roughness of the films, and Dektak Profilometer was used to determine the CdS films thickness. The optical and electrical properties for the films were determined using UV-Vis-NIR Spectrometer, and the Hall Effect technique, respectively. The highest carrier mobility was obtained for the films deposited in an ammonium acetate free bath. However, both films were polycrystalline with hexagonal structure exhibiting a tendency toward <002> texture, that increase with increasing the pH value of the chemical bath.

Morphological evolution of CdS films prepared by chemical bath deposition

In this article, the growth process of chemical bath deposited CdS films was systematically investigated. The structural, optical, and morphological properties were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), UV–Vis spectrophotometer, scanning electron microscope (SEM), respectively. CdS nanocubes with size of less than 500 nm and nanocrystallites with diameter of less than 5 nm forming in reaction solution are observed. According to the TEM results and the SEM morphological evolution of CdS films, a crystallite-by-crystallite growth mechanism is proposed to elucidate the growth process of chemical bath deposited CdS films based on the present growth mechanism.

Morphological and stoichiometric study of chemical bath deposited CdS films by varying ammonia concentration

The influence of ammonia concentration on stoichiometric, surface morphological, and optical properties of chemical bath deposited cadmium sulphide thin films has been studied systemically. Chemical bath deposition (CBD) of CdS thin films was carried out via using cadmium acetate as the cadmium ion source, thiourea as the sulphur source and ammonia as the complexing agent. Ammonia concentration was changed from 0 to 2.5 M. At ammonia concentration greater than or equal to 0.1 M and lower than 0.6 M, nanowires or flake-like structures were obtained. At ammonia concentration ranging from 0.8 to 2.0 M, uniform, dense, and continuously coated films were obtained. The energy dispersive X-ray spectroscopy (EDXS) analysis revealed that as the ammonia concentration changed from 0.1 to 2.0 M, the Cd/S ratio in the obtained film increased from 0.24 to 2.61. Not only typical cadmium-poor but also unusual sulphur deficiency phenomena were observed for CBD CdS thin films. The films deposited with ammonia concentration of 1.0 M show the highest degree of crystallinity and closest stoichiometry Cd/S≅1, and have a preferred orientation. The direct band energy gaps of as-grown films were found to be 2.23–2.77 eV. The formation mechanism of the films with various morphologies and cadmium and sulphur deficiencies are discussed.

Thermal annealing effect on structural and electrical properties of chemical bath-deposited CdS films

X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrical investigations of CdCl 2–thiourea–ammonia bath-deposited (CBD) CdS films on glass before and after post-deposition annealing have been carried out. The thiourea (TU) concentration, temperature and H 2, vacuum and isothermal ambient have been varied at low concentration of cadmium 1 mM. Coverage on glass, resistivity of CdS and mobility of charge carriers could be controlled by temperature, time and ambient of heat-treatment, and by thiourea concentration in bath. It is concluded that sintering of CdS, slow diffusion, incorporation in lattice and vaporization of cadmium chloride are the main factors of the heat-treatment process, responsible for changes in resistivity of CBD CdS.

Effects of deposition time and temperature on the optical properties of air-annealed chemical bath deposited CdS films

CdS films of over 1-μm thickness were deposited onto glass substrates by chemical bath deposition (CBD). Deposition temperature and time were varied from 40 °C to 60 °C and from 30 min to 4 h, respectively. The highest deposition rate, 6.39 nm/min, was obtained with samples deposited for 90 min at 60 °C. The films deposited at 60 °C for 4 h were found to have the best adhesion and without defects. The optical properties, in particular the optical band gap, depended on film thickness, the deposition and annealing temperatures. Annealing in air resulted in a shift of the absorption edge towards higher wavelengths, i.e., a decrease in the gap value from 2.45 eV to 2.38 eV. The optical band edges of the films were not constant but depended on the annealing temperature. The refractive index, calculated by applying the envelope method on the transmission of the films in wavelengths from 550 nm to 850 nm, was in the range 1.95–2.26. The resistivity determined from dark conductivity measurement, as a function of the annealing temperature, was found to be in the order of 105 Ω cm for samples annealed in air at 250 °C, 3 h, and the activation energy was about 0.22 eV.

Chemical bath deposited CdS films using magnetic treated solutions

AbstractCdS thin films were obtained by chemical bath deposition onto corning glass slides using precursor solutions previously treated in a steady magnetic field. The kinetic growth was affected in dependence of the magnetic field intensity used in the solution treatments. The growth rate is slower when magnetized solutions are used; however, the reaction exhaustion is more delayed. The magnetic treatments improve the conversion of starting materials in thin films. Thus, the bath is more efficient and thicker films can be obtained. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and morphological studies of chemical bath-deposited nanocrystalline CdS films and its alloys

The microstructure and surface morphology of chemical bath-deposited (CBD) nanocrystalline CdS films, its alloys (CdS:Ag and CdS:Mn) and the influence of growth conditions on their properties have been investigated by means of X-ray diffraction (XRD), scanning electron microscopic (SEM) and transmission electron microscopic (TEM) studies, respectively. CBD nanocrystalline CdS films exhibit the co-existence of hexagonal and cubic phases. This is related to the polymorphic tendency of the CdS structure and indicates a strong influence of local parameters in the deposition conditions. Microscopic studies indicated that CdS films are formed from coalescence of individual crystallites with a high degree of crystallinity. The preferred orientation of CdS film is due to the controlled nucleation process associated with the low-formation rate of CdS. In CdS:Ag alloys, presence of Ag2S monoclinic species is indicated and presence of uniform, monodispersive and spherical crystallites is evident. In CdS:Mn alloys, presence of well-defined hexagonal structures with size distribution of the order of 0.2–2.0μm corresponding to monocrystalline MnS species is indicated.

Effects of complexing agent on CdS thin films prepared by chemical bath deposition

CdS films have been prepared by chemical bath deposition (CBD) without stirring using weak and strong complexing agents, i.e., ammonia and ethylenediaminetetraacetic acid (EDTA). The optical, structural, and morphological properties of chemical bath deposited CdS films have been investigated. When the complexing agent is ammonia, five peaks in the X-ray diffraction (XRD) patterns from the CdS film, respectively, correspond to the interplanar spacing of 3.5498, 3.3429, 3.1449, 2.0574, and 1.7487 Å, which are definitely ascribed to hexagonal structure; unfortunately, this hexagonal CdS film is with poor morphology and its optical property in the visible region is not desirable for the solar cells. While, when the complexing agent is EDTA, three diffraction peaks in the XRD patterns from the CdS film, respectively, correspond to the interplanar spacing of 3.1164, 2.6716, and 1.8507 Å, indicating that the film is of a cubic structure. Furthermore, the CdS film has good morphology and its optical property in the visible region is compliant to the requirements of solar cells.

PIXE and RBS investigation of growth phases of ultra-thin chemical bath deposited CdS films

Polycrystalline CdS films, with thicknesses typically 20–180 nm, have been chemically deposited on glass substrates using an ammonia–cadmium–thiourea reaction solution. Film elemental composition, thickness and microstructure have been examined using proton-induced X-ray emission, Rutherford backscattering and atomic force microscopy. Analysis indicates that the stability of the deposition temperature plays a critical role in CdS film growth and composition. Films deposited with high temperature stability ( 60±0.5 ° C) show a consistent 1:1 Cd:S atomic ratio for all stages of film growth, and have good substrate adhesion. Films deposited with lower temperature stability ( 60±4 ° C) show initial high S concentrations, followed by a rapid increase in Cd concentration, until a final 1.2:1 Cd:S ratio is achieved. A mechanism is proposed to explain this difference in film composition and properties.

Structure and morphology of chemical bath-deposited CdS films and clusters

Thin films of cadmium sulfide have been deposited on glass substrates and the structural properties of films have been investigated using scanning electron microscopy and X-ray diffraction techniques. The films consist of domains (groups of grains) and weakly bound grain clusters. The structural parameters of grains, domains and clusters and the effect of film thickness on these parameters are reported. From the measurement of lattice constants in CdS films and in free CdS clusters, it has become evident that the films on glass substrates have a tensile strain along their planes. The effect of thermal annealing on the partial relaxation of the strain is discussed.

Impurities in Chemical Bath Deposited CdS Films for Cu ( In , Ga ) Se2 Solar Cells and Their Stability

The highest efficiencies for ‐based thin film solar cells have been achieved with CdS films prepared by a solution growth method known as the chemical bath deposition (CBD) technique. The impurity content in such cadmium sulfide films has been examined. By means of secondary ion mass spectroscopy, Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, and x‐ray photoelectron spectroscopy, we conclude that CBD grown CdS films contain ∼11 atom percent (a/o) O, ∼5 a/o N as well as C and H. Unlike previously published results, cadmium carbonate and water are found to be the main oxygen‐containing compounds. No clear evidence of cadmium hydroxide and/or oxide (CdO) is found. Carbon‐nitrogen bonds originating from any pseudohalogenic ions [e.g., cyanamide ), thiocyanate , cyanate , cyanide ] are identified as the main nitrogen impurity. To investigate the stability of the impurities, the films were subjected to air annealing (200 to 350°C) as well as storage (1.5 month) in three different environments: desiccator, humidity of 79%, and at 100°C. Air annealing results in a decrease of the water content, which disappears at 350°C. On exposure to humidity, the water content increases somewhat. The CN bonds are very sensitive to all treatments, but do not totally decompose, not even at 350°C. In contrast, is much more stable.

Improvements on the electrical resistivity of chemical bath deposited CdS films by laser annealing

The dark resistivity of cw Ar+ ion laser annealed chemical bath deposited CdS films has been measured. A two-decade decrement of the electrical resistivity, as compared to the unannealed samples, is reported. A threshold laser power density for reproducible annealing has been found to be ≳50 W/cm2. Log ρ vs 1/T plots were used to calculate the mobility ratio b = μn/μp. This ratio shows a slight increment on laser annealed but it is not sufficient to explain the resistivity changes.

Solar energy conversion by photoelectrochemical cells using chemical-bath-deposited CdS films

A study of the direct conversion of solar energy into electricity by photoelectrochemical cells using chemical bath deposited CdS films on titanium and stainless steel substrates is reported.