Optical properties of chemical bath deposited CdS thin films

CdS thin films have been prepared by chemical bath deposition. As-deposited films are cubic and show a sulfur deficiency. From the transmittance and reflectance data analysis direct band gaps (E_g) ranging from 2.180 to 2.448 eV have been obtained. Air and vacuum annealed samples show a decrease in the band gap. The refractive index (n) lies in the range 1.61–2.34. A dependence of band gap on composition has been observed and the possible reasons are discussed.     

Thickness dependent physical properties of chemically deposited nanocrystalline MgSe thin films deposited at room temperature by solution growth method

Chemical bath deposition method has been employed to deposit nanocrystalline magnesium selenide thin films of thickness 104–292 nm onto glass substrates at room temperature. The deposition bath consists of magnesium chloride, triethanolamine (TEA) and selenium dioxide. The as deposited films were characterized by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), optical absorption, electrical resistivity and thermo-emf measurements. The X-ray diffraction (XRD) studies revealed that the crystallinity of the magnesium selenide thin film increases with thickness. SEM studies reveal that MgSe films exhibit uniform distribution of round shaped grains over the entire substrate surface.The optical band-gap and electrical resistivity of MgSe film decrease as the film thickness increases. Such type of dependence is attributed to the quantum size effect that is observed in nanocrystalline semiconductors.The thermo-emf measurement confirms its p-type conductivity.     

Growth mechanisms and their effects on the opto-electrical properties of CdS thin films prepared by chemical bath deposition

Chemically deposited CdS exhibits high sensitivity in the opto-electrical performance to the growth mechanisms. Hence it is of a great interest to study the effects of growth mechanisms on the opto-electrical performance in such films. Studies were carried out by the means of spectroscopic ellipsometry, and coupled with structural, optical, and electrical characterization. A range of bath temperatures (55 °C–95  °C) were used as the means to alter the growth mechanisms. Ion-by-ion process dominated deposition at lower bath temperatures throughout the length of the deposition. This mechanism produced films composed of single phase cubic crystals with corresponding opto-electrical properties inherent to such structures. Complex formations at higher bath temperatures supplement the sole ion-by-ion mechanisms with the cluster-by-cluster mechanism. This results in a mixed cubic/hexagonal structure, and deviation from stoichiometry. As a result, carrier concentrations and mobility increased nearly eight and four fold respectively. Resistivity decreased more than four times from 33.2 to 7.5 Ω cm. A noticeable decrease of, ~0.2 was observed in the refractive index and an increase of ~0.07 eV in the band gap is also reported. Nuclear magnetic resonance analysis confirms deviation from stoichiometry in the cluster-by-cluster mechanisms, resulting in interstitially trapped Cd⁺² and S⁻² ions. The trapped ions act as donors in the film enhancing its electrical performance.     

Identification of the impurity phase in chemically deposited CdS thin films

Identification of the impurity phase present in chemically deposited CdS thin films and in the precipitate used for screen printing CdS/CdTe solar cells is reported in this paper. X-ray diffraction (XRD) studies of the films and the precipitate showed that the impurity phase is a mixture of cadmium oxide sulphate (Cd₃O₂SO₄) and cadmium oxide (CdO). Analysis of the films and the powders obtained using thiourea (TU) and thioacetamide (TA) as sulphursing agents showed that the impurity phase is predominantly present when TU is used in the chemical bath. The high conductivity shown by chemically deposited CdS films (using TU) when annealed at higher temperatures in air is attributed to the predominance of the conducting CdO phase in the film.     

Solution flow rate influence on properties of copper oxide thin films deposited by ultrasonic spray pyrolysis

The present work is an investigation of the solution flow rate influence on copper oxide (CuO) thin film properties deposited by ultrasonic spray pyrolysis. A set of CuO thin films were deposited, with various solution flow rates, on glass substrate at 300 °C. The precursor solution is formed with copper salt dissolution in distilled water with 0.05 molarity. The solution flow rate was ranged from 10 to 30 ml/h. Films composition and structure were characterized by means of XRD (X Rays diffraction) and Raman scattering. The optical properties were studied using UV–visible spectroscopy. The electrical conductivity, carrier mobility and concentration were determined by Hall Effect measurements. The obtained results indicate that flow rate is a key parameter controlling CuO films growth mechanism and their physical properties. The prepared films are mainly composed with a CuO monophase, the crystallite size is reduced with increasing the flow rate. A ZnO/CuO heterojunction structure has been realized and its rectifying behavior is tested.     

Effect of temperature on structural and optical properties of ZnS thin films by chemical bath deposition without stirring the reaction bath

ZnS thin films were deposited at different temperatures on glass substrates by chemical bath deposition method without stirring the deposition bath. With deposition temperature increasing from 50 °C to 90 °C, pH decreases rapidly, homogeneous precipitation of ZnS, instead of Zn(OH)₂ easily forms in the bath. It means that higher temperature is favorable for the formation of relatively high stoichiometric film, due to the lower concentration of OH⁻. The thickness of the films deposited at 90 °C is much higher than that of the films deposited at 50 °C and 70 °C. Combining the film thickness with the change of pH, the growth of film, especially deposited at 90 °C mainly comes from the fluctuation region of pH. At the same time, with the increase of deposition temperature, the obtained films are transparent, homogeneous, reflecting, compact, and tightly adherent. The ZnS films deposited for 1.5 h, 2 h and 2.5 h at 70 °C and 90 °C have the cubic structure only after single deposition. The average transmission of all films, especially the thicker films deposited at 90 °C, is greater than 90% for wavelength values in the visible region. Comparing with the condition of stirring, the structural and optical properties of films are improved significantly. The direct band gaps range from 3.93 to 4.06 eV.     

Chemical bath deposition of nanocrystalline ZnS thin films: Influence of pH on the reaction solution

Zinc sulfide (ZnS) thin films were deposited onto glass substrates using chemical bath deposition technique (CBD). The deposition were carried out in a bath solution with pH ranged from 9 to 11. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to characterize the films structure and morphology respectively. The amorphous structure of as-deposited films is converted to a nanocrystalline one after a thermal annealing at 550 °C. The deposited ZnS films exhibit a high optical transmission in the UV–visible range (≥80%). They have a direct band gap. Using a solution with pH equal to 10 yields to films with larger optical band gap, smoother surface and lower electrical conductivity.     

Synthesis and characterization of CdSe nanocrystalline thin films deposited by chemical bath deposition

Cadmium selenide (CdSe) nanocrystalline thin films were prepared by chemical bath deposition (CBD) using ammonia and triethanolamine (TEA) as complexing agents, cadmium chloride and sodium selenosulphate as the sources of Cd²⁺ and Se^2? ions, respectively. The structural and optical properties of CdSe nanocrystalline thin films were investigated as a function of the sodium selenosulphate concentrations or ammonia concentrations in precursors using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) measurements, transmission electron microscopy (TEM) and UV–visible spectrophotometer measurements. The results reveal that the CdSe thin films are in the pure cubic phase, which composed of a large number of uniform spherical particles. Each spherical particle contains many nanocrystals 3–10 nm in crystallite size. An increase in both the average diameter of the spherical particles and the crystallite size of the nanocrystals occurs with an increase in ammonia concentrations. The Se/Cd atom ratios of CdSe thin films firstly increase and then decrease with an increase in ammonia concentration or sodium selenosulphate concentration. The optical band gap of CdSe thin films decrease with an increase in ammonia concentrations. The kinetics and reaction mechanism of the CdSe nanocrystalline thin films during deposition are discussed.     

CO2 detection with CNx thin films deposited on porous silicon

In recent years, porous silicon (PSi) has attracted a great deal of attention for sensing applications. However, the high reactivity of PSi surfaces causes serious problems of stability. In this work, we developed new thin films that can serve as stabilizer of PSi for CO₂ gas sensors development. PSi surface was coated with carbon nitride (CN_x) film which is one of the most important interfering to stabilize the PSi layer. CN_x film was deposited by pulsed laser ablation. The effect of CO₂ gas on the sensor response was investigated for different polarization voltages. The electrical properties of (Al/CN_x/PSi/Si) structure were modified in the presence of the gas. The device shows a high sensitivity against CO₂ gas. Furthermore, the current variation of the sensor as a function of time has been investigated. The results show that the Al/CN_x/PSi/Si structure becomes stable after the first two weeks.     

Elaboration and characterization of Co-doped ZnO thin films deposited by spray pyrolysis technique

The structure and the nature of magnetism of ZnO and Zn_1−xCo_xO (CZO) thin films (0?x?0.09) deposited on glass substrate at 450 °C by spray pyrolysis technique is investigated. All the CZO thin films have the ZnO wurtzite structure with a preferential orientation along the c-axis and had no impurity phase. This was also confirmed by transmission electron microscopy analysis. Transmission UV-visible spectroscopy showed that Co²⁺ was well substituted for the Zn²⁺ ions in the ZnO matrix. Magnetization measurements at low temperature show that CZO thin films present a paramagnetic behaviour and no sign of ferromagnetism.     

Effect of deposition time on lead selenide thermoelectric thin films prepared by chemical bath deposition technique

A series of lead selenide (PbSe) films was deposited at constant bath temperature with various deposition time (3–5 h) using simple chemical bath deposition techniques, to study the effect of deposition time on its structural and thermoelectric properties. The as-deposited film was analyzed through X-ray diffraction, SEM, Energy dispersive X-ray analysis, Raman spectroscopy and Seebeck coefficient measurement. The improvement of crystallinity of the PbSe films was studied using X-ray diffraction and Raman scattering. The structural parameters, such as the lattice constant (a), crystallite size (D), dislocation density (δ) and microstrain (ε) were evaluated from the XRD spectra. Average crystallite size was calculated from Scherrer׳s formula and it was found to be increased from 19.65 to 23.97 nm as the deposition time was varied from 3 h to 5 h. The dislocation density and microstrain were found to vary inversely with the crystallite size, whereas the lattice constant increases with an increase in crystallite size. SEM images show that the morphology of particles strongly depends on the deposition time. The possible growth mechanism for the variation in the morphology is discussed. The thermoelectric measurements have shown n-type conductivity in “as deposited films” and the magnitude of Seebeck coefficient is found to be increasing with an increase in deposition time.     

Structural, electrical and optical properties of ZnO thin films deposited by sol-gel method

Thin films of intrinsic and Al-doped ZnO were prepared by the sol-gel technique associated with spin coating onto glass substrates. Zinc acetate dehydrate, ethanol and monoethanolamine were used as a starting material, solvent and stabiliser, respectively. Structural, electrical and optical characterizations of the films have been carried out. All films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction 〈0 0 2〉. The four-points technique was used to characterize thin films electrically. All films exhibit a transmittance above 80-90% along the visible range up to 650 nm and a sharp absorption onset about 375 nm corresponding to the fundamental absorption edge 3.3 eV. Intense UV photoluminescence is observed for undoped and 1% Al-doped ZnO films.     

SnS thin films deposited by chemical bath deposition, dip coating and SILAR techniques

The SnS thin films were synthesized by chemical bath deposition (CBD), dip coating and successive ionic layer adsorption and reaction (SILAR) techniques. In them, the CBD thin films were deposited at two temperatures: ambient and 70 ℃. The energy dispersive analysis of X-rays (EDAX), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and optical spectroscopy techniques were used to characterize the thin films. The electrical transport properties studies on the as-deposited thin films were done by measuring the I-V characteristics, DC electrical resistivity variation with temperature and the room temperature Hall effect. The obtained results are deliberated in this paper.     

Surface morphology dependent tungsten oxide thin films as toxic gas sensor

Tungsten oxide (WO₃) films are of great importance in gas sensing technology due to its selectivity towards toxic gases. In this paper, structural, morphological and compositional properties of spray deposited and chemical vapor deposited WO₃ thin films were investigated using XRD, TEM, SEM, EDAX and Raman spectroscopy. These films have monoclinic crystal structure; and a filamentous network surface for spray deposited films whereas small flake-shaped microstructure was observed on the surface of chemical vapor deposited films. These films were studied for their gas sensing ability towards toxic gases like ammonia (NH₃) and sulphur dioxide (SO₂) as a function of temperature and concentration. Response-recovery characteristics were studied by varying gas concentration. The spray deposited films displayed higher gas response than the chemical vapor deposited films whereas the later exhibited lower optimum operating temperature as well as faster response and recovery. A correlation between the morphological, compositional, electrical and gas sensing properties of these films is also established.     

Sensing characteristics of zinc oxide thin films deposited by spray pyrolysis onto tubular Pyrex substrate

This paper presents NO₂ sensing properties of ZnO thin films grown onto tubular Pyrex substrate using the spray pyrolysis method. The sensor response was found to depend essentially on four parameters: chemical composition, structure, morphology and operating temperature. The crystallinity and morphology of the as-preapred films were analyzed using X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The sensing properties of ZnO toward NO₂ were investigated at different operating temperatures and NO₂ concentrations. Optimization of the preparation conditions show that ZnO thin film deposited during 15 min exhibit the highest sensitivity with fast response and recovery time.     

Enhanced photoluminescence properties of Cu-doped ZnO thin films deposited by simultaneous RF and DC magnetron sputtering

Copper (Cu)-doped ZnO thin films were grown on unheated glass substrates at various doping concentrations of Cu (0, 5.1, 6.2 and 7.5 at%) by simultaneous RF and DC magnetron sputtering technique. The influence of Cu atomic concentration on structural, electrical and optical properties of ZnO films was discussed in detail. Elemental composition from EDAX analysis confirmed the presence of Cu as a doping material in ZnO host lattice. XRD patterns show that the films were polycrystalline in nature with (002) as a predominant reflection of ZnO exhibited hexagonal wurtzite structure toward c-axis. From AFM analysis, films displayed needle-like shaped grains throughout the substrate surface. The electrical resistivity was found to be increased with increase of Cu content from 0 to 7.5 at%. Films have shown an average optical transmittance about 80% in the visible region and decreased optical band gap values from 3.2 to 3.01 eV with increasing of Cu doping content from 0 to 7.5 at% respectively. Furthermore, remarkably enhanced photoluminescence (PL) properties have been observed with prominent violet emission band corresponding to 3.06 eV (405 nm) in the visible region through the increase of Cu doping content in ZnO host lattice.     

Characteristics of GZO thin films deposited by sol–gel dip coating

Zinc oxide (ZnO) films were deposited by sol–gel dip coating using the acrylamide route. The films were doped with different concentrations of gallium in the range 250–1200 ppm. The films exhibited hexagonal structure. The grain size decreased from 100 to 10 nm as the dopant concentration increased. The resistivity of the doped samples decreased from 10³ to 3×10⁻³ Ω cm. The band gap value shifted towards the short-wavelength region as the dopant concentration increased. XPS studies indicated doping of Ga in ZnO     

衬底负偏压对Ni-Mn-Ga形状记忆薄膜成分及形貌的影响

采用能谱仪(EDS)和原子力显微镜(AFM)对不同衬底负偏压下射频磁控溅射法制备的Ni-Mn-Ga形状记忆薄膜进行了成分和形貌的分析.研究发现:当衬底负偏压在5～30V范围变化时,薄膜中的Ni含量随偏压的增加呈先减少后增加的趋势,在偏压为10V时,达到最小值52.84％(摩尔分数,下同).Ga含量的变化趋势恰好与Ni相...     

Indium doped zinc oxide thin films deposited by ultrasonic spray pyrolysis technique: Effect of the substrate temperature on the physical properties

Indium doped zinc oxide (ZnO:In) thin solid films were deposited on soda-lime glass substrates by the ultrasonic spray pyrolysis technique. The effect of the substrate temperature on the electrical, morphology, and optical characteristics of ZnO:In thin films was studied. It was found that, as the substrate temperature increases, the electrical resistivity decreases, reaching a minimum value in the order of 7.3×10⁻³ Ω cm, at 415 °C. Further increase in the substrate temperature results on an increment on the electrical resistivity of the thin solid films. All the samples were polycrystalline with a well-defined wurtzite structure. The preferred growth shows a switching from a random orientation at low substrates temperatures to (0 0 2) in the case of films deposited at the highest substrate temperature used. As the substrate temperature increases, the corresponding surface morphology changes from an almost faceted pyramidal to round-shaped form. The optical transmittance of the films in a interval of 400 to 700 nm is around 70%, with a band gap value in the order of 3.45 eV.     

Effect of deposition temperature on structural,optical properties and configuration of CdSe nanocrystalline thin films deposited by chemical bath deposition

CdSe nanoparticle thin films were deposited on glass substrates by the chemical bath deposition (CBD) method at low deposition temperature ranging from room temperature up to 50 °C while the pH of the bath was kept constant at 12.1. The structural and morphological variation were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) technique. The energy band gap and optical properties were characterized by the absorbance spectra. Rutherford backscattering spectroscopy (RBS) analysis reveals the excess of Cd rather than Se in depth profile along the thin film thickness. The prepared CdSe nanoparticles have cubic structure and by increasing the temperature the deposited films become continues, homogeneous and tightly adherent. The results also revealed that by increasing the deposition temperature from room temperature up to 50 °C, the band gap decreases from 3.52 eV up to 1.84 eV.