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.     

Influence of working pressure on the structural,optical and electrical properties of sputter deposited AZO thin films

Highly oriented crystalline aluminum doped zinc oxide (AZO) films were sputter deposited on glass substrates and a systematic investigation on the as deposited and etched films was reported for its further application in silicon thin film solar cell. Influence of the deposition pressure (from 2 to 8 mTorr) and post-annealing temperature (at 400 °C for 5 min) on the structural, optical and electrical properties of the as-deposited and etched samples were analyzed. The optimum condition for its reproducibility and large area deposition is determined and found that the depositions made at 8 mTorr at 200 W having the distance from source to substrate of 9 cm. All the AZO films exhibited a c-axis preferred orientation perpendicular to the substrate and their crystallinity was improved after annealing. From the XRD pattern the grain size, stress and strain of the films were evaluated and there is no drastic variation. Optical transmittance, resistivity, Hall mobility and carrier concentration for the as deposited and etched-annealed films were found to improve from 79 to 82%; 2.97 to 3.14×10⁻⁴ Ω cm; 25 to 38 cm²/V s; 8.39 to 5.96×10²⁰/cm³ respectively. Based on the triangle diagram between figure of merit and Hall mobility, we obtained a balance of point between the electrical and optical properties to select the deposition condition of film for device application.     

Influence of In doping on the structural,optical and acetone sensing properties of ZnO nanoparticulate thin films

Indium-doped zinc oxide (ZnO) nanoparticle thin films were deposited on cleaned glass substrates by spray pyrolysis technique using zinc acetate dihydrate [Zn(CH₃COO)₂ 2H₂O] as a host precursor and indium chloride (InCl₃) as a dopant precursor. X-ray diffraction results show that all films are polycrystalline zinc oxide having hexagonal wurtzite structure. Upon In doping, the films exhibit reduced crystallinity as compared with the undoped film. The optical studies reveal that the samples have an optical band gap in the range 3.23–3.27 eV. Unlike the undoped film, the In-doped films have been found to have the normal dispersion for the wavelength range 450–550 nm. Among all the films investigated, the 1 at% In-doped film shows the maximum response 96.8% to 100 ppm of acetone in air at the operating temperature of 300 °C. Even at a lower concentration of 25 ppm, the response to acetone in this film has been found to be more than 90% at 300 °C, which is attributed to the smaller crystallite size of the film, leading to sufficient adsorption of the atmospheric oxygen on the film surface at the operating temperature of 300 °C. Furthermore, In-doped films show the faster response and recovery at higher operating temperatures. A possible reaction mechanism of acetone sensing has been explained.     

Effects of Sb,Zn doping on structural,electrical and optical properties of SnO2 thin films

Highly transparent, low resistive pure and Sb, Zn doped nanostructured SnO₂ thin films have been successfully prepared on glass substrates at 400° C by spray pyrolysis method. Structural, electrical and optical properties of pure and Sb, Zn doped SnO₂ thin films are studied in detail. Powder X-ray diffraction confirms the phase purity, increase in crystallinity, size of the grains (90–45 nm), polycrystalline nature and tetragonal rutile structure of thin films. The scanning electron microscopy reveals the continuous change in surface morphology of thin films and size of the grains decrease due to Sb, Zn doping in to SnO₂. The optical transmission spectra of SnO₂ films as a function of wavelength confirm that the optical transmission increases with Sb, Zn doping remarkably. The optical band gap of undoped film is found to be 4.27 eV and decreases with Sb, Zn doping to 4.19 eV, 4.07 eV respectively. The results of electrical measurements indicate that the sheet resistance of the deposited films improves with Sb, Zn doping. The Hall measurements confirm that the films are degenerate n-type semiconductors.     

Effect of processing parameter on structural,optical and electrical properties of photovoltaic chalcogenide nanostructured RF magnetron sputtered thin absorbing films

The aim of this work was to develop high quality of CuIn_1−xGa_xSe₂ thin absorbing films with x (Ga/In+Ga)<0.3 by sputtering without selenization process. CuIn_0.8Ga_0.2Se₂ (CIGS) thin absorbing films were deposited on soda lime glass substrate by RF magnetron sputtering using single quaternary chalcogenide (CIGS) target. The effect of substrate temperature, sputtering power & working pressure on structural, morphological, optical and electrical properties of deposited films were studied. CIGS thin films were characterised by X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), Energy dispersive X-ray spectroscopy (EDAX), Atomic force microscopy (AFM), UV–vis–NIR spectroscopy and four probe methods. It was observed that microstructure, surface morphology, elemental composition, transmittance as well as conductivity of thin films were strongly dependent on deposition parameters. The optimum parameters for CIGS thin films were obtained at a power 100 W, pressure 5 mT and substrate temperature 500 °C. XRD revealed that thin film deposited at above said parameters was polycrystalline in nature with larger crystallite size (32 nm) and low dislocation density (0.97×10¹⁵ lines m⁻²). The deposited film also showed preferred orientation along (112) plane. The morphology of the film depicted by FE-SEM was compact and uniform without any micro cracks and pits. The deposited film exhibited good stoichiometry (Ga/In+Ga=0.19 and In/In+Ga=0.8) with desired Cu/In+Ga ratio (0.92), which is essential for high efficiency solar cells. Transmittance of deposited film was found to be very low (1.09%). The absorption coefficient of film was ~10⁵ cm⁻¹ for high energy photon. The band gap of CIGS thin film evaluated from transmission data was found to be 1.13 eV which is optimum for solar cell application. The electrical conductivity (7.87 Ω⁻¹ cm⁻¹) of deposited CIGS thin film at optimum parameters was also high enough for practical purpose.     

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.     

Optimising conditions for the growth of nanocrystalline ZnS thin films from acidic chemical baths

The growth of nanocrystalline zinc sulfide thin films onto glass substrates by chemical bath deposition has been optimized at acidic pH. Powder X-ray diffraction (p-XRD) confirms the deposition of sphalerite, the cubic phase of ZnS. The crystallite size calculated by Scherrer equation was found to be 4.0 nm. Scanning Electron Microscopy (SEM) show clusters of spherical nanoparticles uniformly distributed over the surface of the glass substrates. Energy Dispersive X-ray (EDX) analysis of the deposited thin films show the zinc to sulfur ratio close to 1:1. The observed band gap (3.78 eV) of the deposited thin films is higher than that reported for cubic phase of bulk ZnS (3.54 eV) as expected due to nano-size crystallites. Binding energies calculated by X-ray Photoelectron Spectroscopy (XPS) confirm the material as ZnS and the photoluminescence measurements show the blue shift in emission maximum.     

Direct synthesis of quaternary Cd(Zn,S)Se thin films: Effects of composition

In the present communication, the binary CdSe and quaternary Cd_1-xZn_xSe_1-yS_y (0 ≤ x = y ≤ 0.35) thin films were synthesized using a chemical bath deposition. Thin film deposition was carried out at the optimized conditions (pH = 10 ± 0.1, deposition temperature = 70 ± 0.1 °C, deposition time = 100 min and substrate rotation speed = 65 ± 2 rpm). X-ray diffraction studies confirmed hexagonal-wurtzite crystal structure with the formation of quaternary Cd(Zn, S)Se phase along with binary CdSe, CdS, ZnS and ZnSe, phases of the as-grown Cd_1-xZn_xSe_1-yS_y thin films. Elemental analysis showed presence of Cd²⁺, Zn²⁺, S^2- and Se^2- in the deposited films. Fourier transform infrared spectroscopy shown the bands at 911.15 cm⁻¹ – 901.62 cm⁻¹ which are assigned to the stretching frequency of Cd–Se bond. Scanning electron microscopy show transformation of the microstructure from globular crystallites to a rhomboid flake like network. The electrical conductivity was typically ≈ 10⁻⁷ Ω⁻¹ cm⁻¹. At low temperatures, the conduction was by variable range hopping, and this changed to thermally activated grain boundary dominated conduction for T > 350 K.     

Spray pyrolysis deposition of Cu–Zn–In–S solid-solution thin films with tunable compositions and band gaps

Cu–Zn–In–S solid solution thin films with tunable compositions and band gaps were deposited on glass substrates using a chemical spray pyrolysis approach. XRD results reveal the cubic-structured Cu–Zn–In–S films without detectable impurities. The successive shift of XRD patterns toward high-angle side of ZnS with increasing ZnS molar fraction in products proves a formation of Cu–Zn–In–S solid solutions. SEM images and EDAX analyses demonstrate homogeneous surface morphologies and adjustable compositions of Cu–Zn–In–S films, which results in film band gaps broadly tunable from 1.54 eV to 3.61 eV. These sprayed Cu–Zn–In–S solid solution thin films may find potential uses in photovoltaics and photocatalysis.     

Structural,morphological, electrical and optical studies of Cr doped SnO2 thin films deposited by the spray pyrolysis technique

Tin oxide (SnO₂) and chromium (Cr) doped tin oxide (Cr:SnO₂) thin films were deposited on the preheated glass substrates at 673 K by spray pyrolysis. Concentration of Cr was varied in the solution by adding chromium (III) chloride hexahydrate from 0 to 3 at%. The effect of Cr doping on the structural, electrical and optical properties of tin oxide films is reported. X-ray diffraction pattern confirms the tetragonal crystal structure for undoped and Cr doped tin oxide films. Scanning electron microscopic photographs show the modification of surface morphology of tin oxide film due to varying concentration of Cr. X-ray photoelectron spectra of Cr:SnO₂ (3 at%) thin film revealed the presence of carbon, tin, oxygen, and chromium. Carrier concentration and mobility of the SnO₂ films decrease with increasing concentration of Cr and 0.5 at% Cr doped tin oxide film acquires a mobility of 70 cm²/V s. Average optical transmittance in the 550–850 nm range varies from 38% to 47% with varying Cr concentration in the solution.     

Effect of substrate temperature on structural,morphological, optical and electrical properties of MnIn2S4 thin films prepared by nebulizer spray pyrolysis technique

Manganese indium sulphide (MnIn₂S₄) thin films were deposited using an aqueous solution of MnCl₂, InCl₃ and (NH₂)₂CS in the molar ratio 1:2:4 by simple chemical spray pyrolysis technique. The thin film substrates were annealed in the temperature range between 250 and 350 °C to study their various physical properties. The structural properties as studied by X-ray diffraction showed that MnIn₂S₄ thin films have cubic spinel structure. The formation of cube and needle shaped grains was clearly observed from FE-SEM analysis. The energy dispersive spectrum (EDS) predicts the presence of Mn, In and S in the synthesized thin film. From the optical studies, it is analyzed that the maximum absorption co-efficient is in the order between 10⁴ and 10⁵ cm⁻¹ and the maximum transmittance (75%) was noted in the visible and infrared regions. It is noted that, the band gap energy decreases (from 3.20 to 2.77 eV) with an increase of substrate temperature (from 250 to 350 °C). The observations from photoluminescence studies confirm the emission of blue, green, yellow and red bands which corresponds to the wavelength range 370–680 nm. Moreover, from the electrical studies, it is observed that, as the substrate temperature increases the conductivity also increases in the range 0.29–0.41×10⁻⁴ Ω⁻¹ m⁻¹. This confirms the highly semiconducting nature of the film. The thickness of the films was also measured and the values ranged between 537 nm (250 °C) to 483 nm (350 °C). This indicates that, as the substrate temperature increases, the thickness of the film decreases. From the present study, it is reported that the MnIn₂S₄ thin films are polycrystalline in nature and can be used as a suitable ternary semiconductor material for photovoltaic applications.     

Composition,structure and electrical properties of DC reactive magnetron sputtered Al2O3 thin films

Thin films of alumina (Al₂O₃) were deposited over Si 〈1 0 0〉 substrates at room temperature at an oxygen gas pressure of 0.03 Pa and sputtering power of 60 W using DC reactive magnetron sputtering. The composition of the as-deposited film was analyzed by X-ray photoelectron spectroscopy and the O/Al atomic ratio was found to be 1.72. The films were then annealed in vacuum to 350, 550 and 750 °C and X-ray diffraction results revealed that both as-deposited and post deposition annealed films were amorphous. The surface morphology and topography of the films was studied using scanning electron microscopy and atomic force microscopy, respectively. A progressive decrease in the root mean square (RMS) roughness of the films from 1.53 nm to 0.7 nm was observed with increase in the annealing temperature. Al–Al₂O₃–Al thin film capacitors were then fabricated on p-type Si 〈1 0 0〉 substrate to study the effect of temperature and frequency on the dielectric property of the films and the results are discussed.     

Deposition of aluminum oxide-doped zinc oxide transparent nano-films on glass substrates for electrostatic discharge applications

Aluminum oxide-doped zinc oxide (ZnO:Al₂O₃) transparent thin films were deposited by DC magnetron sputtering on glass substrates; film thickness can be correlated with deposition time. The effect of ZnO:Al₂O₃ film thickness on electrical properties, ultraviolet (UV) transmission, surface morphology and structure, solvent resistance, and scratch hardness was investigated. The surface roughness and crystallite size of deposited films increased from 0.75 to 2.22 nm and from 14 to 57 nm, respectively, as the film thickness was increased from 18 to 112 nm. In contrast, the percent UV transmission (% T) of ZnO:Al₂O₃ deposited glass plates at a wavelength of 365 nm increased when the film thickness was decreased. The electrical properties of nano-film deposited glass plates such as electrical resistance, tribo-charge voltage, and decay time were in the range of electrostatic discharge (ESD) specifications. The ZnO:Al₂O₃ nano-film deposited glass substrate possessed good acetone and iso-propanol resistance as well as high scratch hardness. This work opens up the possibility of using the ZnO:Al₂O₃ transparent ultra-thin film on glass substrate in ESD applications based on their excellent properties in terms of the relatively thin and adjustable ZnO:Al₂O₃ film thickness needed.     

Investigation on post annealed copper sulfide thin films from photochemical deposition technique

Cu_xS thin films were deposited on glass substrates at room temperature by photochemical deposition after 1 h photo irradiation using the precursor solution containing copper sulphate pentahydrate (CuSO₄·5H₂O), sodium thiosulphate (Na₂S₂O₃) as a source material for Copper and Sulphur respectively and Di Sodium salt of EDTA as a chelating agent in acidic medium (pH~3.0). The as deposited and annealed Cu_xS thin films were investigated using XRD, UV–vis, AFM, SEM and Hall measurements. The deposited thin films were annealed at temperature up to 400 °C for 1 h. Above 200 °C the deposited film of Cu_xS changes from anilite phase (Cu_1.75S) to digenite (Cu_1.8S) phase. The reduction in sulphur content of the films is evident in the EDX analysis. From the Hall Effect results as deposited and annealed films show p-type conductivity with increasing bulk concentration. Analyses of the optical bandgap of the films indicate an indirect bandgap between 1.75 and 2.35 eV.     

Effect of the film thickness on the crystal structure and ferroelectric properties of (Hf0.5Zr0.5)O2 thin films deposited on various substrates

In this work, the effect of the film thickness on the crystal structure and ferroelectric properties of (Hf_0.5Zr_0.5)O₂ thin films was investigated. The thin films were deposited on (111) Pt-coated SiO₂, Si, and CaF₂ substrates with thermal expansion coefficients of 0.47, 4.5, and 22×10⁻⁶/°C, respectively. From the X-ray diffraction measurements, it was found that the (Hf_0.5Zr_0.5)O₂ thin films deposited on the SiO₂ and CaF₂ substrates experienced in-plane tensile and compressive strains, respectively, in comparison with the films deposited on the Si substrates. For films deposited on all three substrates, the volume fraction of the monoclinic phase increased with increasing film thickness, with the SiO₂ substrate having the lowest monoclinic phase volume fraction at all film thicknesses tested. The grain size of the films, which is an important factor for the formation of the ferroelectric phase, remained almost constant at about 10 nm in diameter regardless of the film thickness and type of substrate utilized. Ferroelectricity was observed for the 17 nm-thick films deposited on SiO₂ and Si substrates, and the maximum remanent polarization (P_r) value of 9.3 µC/cm² was obtained for films deposited on the SiO₂ substrate. In contrast, ferroelectricity with P_r=4.4 µC/cm² was observed only for film on SiO₂ substrate in case of 55 nm-thick films. These results suggest that the films under in-plane tensile strain results in the larger ferroelectricity for 17 nm-thick films and have a ferroelectricity up to 55 nm-thick films.     

Structural,surface morphology and optical properties of sputter-coated CaCu3Ti4O12 thin film: Influence of RF magnetron sputtering power

This study focusses on the investigation of RF power variations (100–300 W) effects on structural, morphological and optical properties of CaCu₃Ti₄O₁₂ thin film deposited on ITO/glass substrate in a non-reactive atmosphere (Ar). The increase of RF power from 100 W to 300 W led to evolution of (112), (022), (033), and (224) of CCTO XRD peaks. The results indicated that all the films were polycrystalline nature with cubic structure. The crystallite size increased from 20 nm to 25 nm with increasing RF power. FESEM revealed that the films deposited were uniform, porous with granular form, while the grain size increased from 30 to 50 nm. AFM analysis confirmed the increment in surface roughness from 1.6 to 2.3 nm with increasing film grain size. Besides, optical transmittance values decreased to minimum 70% with increasing RF power while optical energy bandgap increased from 3.20 eV to 3.44 eV. Therefore, favorable CCTO thin film properties can be possibly obtained for certain application by controlling RF magnetron sputtering power.     

Mixed phase silicon thin films grown at high rate using 60 MHz assisted VHF-PECVD technique

Mixed phase amorphous and nanocrystalline silicon (a-Si:H and nc-Si:H) thin films were deposited by VHF-PECVD (60 MHz) using Argon (Ar) as the diluent of silane. These amorphous and crystalline silicon thin films were deposited by varying the argon dilution (f_Ar) from 10–97.5% while keeping other process parameters constant. The effects of argon dilution on deposition rate, structural and optical properties of micro/nanocrystalline silicon thin films are studied. It has been observed that the films deposited from f_Ar 10–70% showed the deposition rate >20 Å/s with the highest deposition rate achieved of ~25 Å/s. Structural characterization has been performed by micro-Raman analysis and Atomic force microscopy. Raman shift towards higher wave number (515 cm⁻¹) with increase of f_Ar indicates variation in crystallinity of silicon films. HRTEM studies revealed the distribution of grain size and the degree of crystallinity. Optical absorption spectroscopy confirmed the increase in band gap of the materials from 1.5 to 2.1 eV.     

Influence of Sn content on properties of ZnO:SnO2 thin films deposited by ultrasonic spray pyrolysis

The present work is devoted to the preparation of zinc oxide (ZnO): tin oxide (SnO₂) thin films by ultrasonic spray technique. A set of films are deposited using a solution formed with zinc acetate and tin chloride salts mixture with varied weight ratio R=[Sn/(Zn+Sn)]. The ratio R is varied from 0 to 100% in order to investigate the influence of Sn concentration on the physical properties of ZnO:SnO₂ films. The X rays diffraction (XRD) analysis indicated that films are composed of ZnO and SnO₂ distinct phases without any alloys or spinnel phase formations. The average grain size of crystallites varies with the ratio R from 17 to 20 nm for SnO₂ and from 24 to 40 nm for ZnO. The obtained films are highly transparent with a transmission coefficient equal to 80%. An increase in Sn concentration increases both the effective band gap energy from 3.2 to 4.01 eV and the photoluminescence intensity peak assigned defects to SnO₂. The films electrical characterization indicated that films are resistive. Their resistivities vary between 1.2×10² and 3.3×10⁴ (Ω cm). The higher resistivity is measured in film deposited with a ratio R equal to 50%.     

Preparation and electrochemical capacitance of MnO2 thin films doped by CuBi2O4

Manganese dioxide (MnO₂) and CuBi₂O₄-doped MnO₂ thin films with different nanostructures were deposited on indium tin oxide (ITO) glass and Ti foil substrates by using a chemical bath deposition (CBD) technique. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron microscopy (XPS). The effects of doping and substrates on electrochemical properties of MnO₂ and CuBi₂O₄-doped MnO₂ thin films on ITO glass and Ti foil were investigated. Capacitive properties of MnO₂ and CuBi₂O₄-doped MnO₂ thin films electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy in a three-electrode experimental setup using 0.1 M Na₂SO₄ aqueous solution as electrolyte. Specific capacitance, obtained from electrochemical measurement for the CuBi₂O₄-doped MnO₂, exhibited a higher value of 338 F g⁻¹ compared to the MnO₂ exhibiting value of 135 F g⁻¹. In addition, CuBi₂O₄-doped MnO₂ thin films on an ITO electrode had a better and satisfactory specific capacitance value, and exhibited more excellent electrochemical stability and reversibility than Ti foil substrates.     

Study of sensitivity and selectivity of α-Fe2O3 thin films for different toxic gases and alcohols

This paper presents a detailed study on the sensitivity and selectivity of α-Fe₂O₃ thin films produced by deposition of Fe and post-deposition annealed at two temperatures of 600 °C and 800 °C with flow of oxygen for application as a sensor for toxic gases including CO, H₂S, NH₃ and NO₂ and alcohols such as C₃H₇OH, CH₃OH, and C₂H₅OH. The crystallographic structure of the samples was studied by X-ray diffraction (XRD) method while an atomic force microscope (AFM) was employed for surface morphology investigation. The electrical response of the films was measured while they were exposed to various toxic gases and alcohols in the temperature range of 50–300 °C. The sample annealed at higher temperature showed higher response for different gases and alcohols tested in this work which can be due to the higher resistance of this sample. Results also indicated that the α-Fe₂O₃ thin films show higher selectivity to NO₂ gas relative to the other gases and alcohols while the best sensitivity is obtained at 200 °C. The α-Fe₂O₃ thin film post-deposition annealed at 800 °C also showed a good stability and reproducibility and a detection limit of 10 ppm for NO₂ gas at the operating temperature of 200 °C.