Structural and functional properties of ZnO thin films grown on Si substrates by air assisted USP method from non-aqueous solutions at low-temperature

In this work, we deals with the processing and characterization of transparent conducting ZnO thin films on p-type Silicon substrates (1 0 0) by air assisted Ultrasonic Spray Pyrolysis (USP) method. The thin films from different Zn acetate precursor solution concentrations (0.1, 0.2, 0.3 and 0.4 M) were deposited at several temperatures (400, 450 and 500 °C) with thickness from ～100 to ～500 nm. The effects of precursor solution concentration, deposition time and temperature on the structural, morphological, optical, and electrical properties of ZnO films were studied by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), UV–Vis-NIR spectroscopy, and Hall Effect techniques, respectively. It has been shown that on the ZnO film surface, the preferred orientation, the average crystallite size, the electrical resistivity and the RMS surface roughness depend on the substrate temperature. The grown films have showed a good adhesion and an excellent optical transmission of about 80–95% within the visible range (400–800 nm) and a direct band gap from 3.35 to 3.23 eV with the increase of the substrate temperature and the deposition time. All the PL spectra have exhibited a typical green-yellow emission band. Additionally photovoltaic (PV) activities of n-ZnO/p-Si heterostructures fabricated are investigated.     

Fabrications of SnS thin films and SnS-based heterojunctions on flexible polyimide substrates

The flexible polyimide substrates were utilized to realize the flexibility of SnS thin films and SnS-based heterojunctions. The SnS thin films and ZnO/SnS heterojunctions were deposited on polyimide substrates by magnetron sputtering. The properties of SnS thin films and ZnO/SnS heterojunctions were studied. The experimental results show that the post annealing can enhance the degree of crystallinity of flexible SnS thin films. The annealed SnS thin films present polycrystalline structure with preferential orientation along the (040) plane and grain size of 18 nm. The compositions of as-deposited and annealed flexible SnS thin films are close to the stoichiometry of SnS. The direct band gaps are 1.48 and 1.32 eV for the as-deposited and annealed SnS thin films, respectively. The fabricated flexible ZnO/SnS heterojunctions show rectifying properties with the rectifying ratio of 6.85 and the diode ideal factor of 1.23. The experimental results indicate the feasibility of using polyimide as the substrates of SnS thin films and SnS-based heterojunctions.     

Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O₂) at high substrate temperature (T_s = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high T_s by inputting Ar + O₂. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high T_s by PLD is rarely reported. The influence of the Ar + O₂ gas pressure on thickness, structural performance, surface morphology, optical property and band gap (E_g) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O₂ gas pressure from 5 to 12 Torr, the deposition rate and the E_g of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm² were prepared successfully.     

Effects of annealing temperature on the structural,morphology, optical properties and resistivity of sputtered CCTO thin film

CaCu₃Ti₄O₁₂ (CCTO) thin films with a thickness of 200 nm were deposited on ITO substrates by RF magnetron sputtering using a pure CCTO target. After the deposition, thin films were annealed at 400, 450, 500 and 550?°C, respectively, for 1 h. The effects of annealing temperature on the structural, surface morphology, optical properties and resistivity of (CCTO) thin films were investigated. The X-ray diffractometer results show that the thin films are polycrystalline in nature and are assigned to body-centered cubic perovskite configuration with a space group of Im-3. The intensity of the peaks and crystallinity gradually increased with the increase in annealing temperature. Microstructural investigation through FESEM showed that the grain size increased with increase in annealing temperature from 32 to 85 nm. The root mean square and roughness (Ra) were also enhanced with higher annealing temperatures, from 3.8 to 6.2 nm and from 4.7 to 7.7 nm, respectively, as confirmed by AFM. Increase in annealing temperature also affected the optical transmittance values which decreased to almost 60% at the visible range (550–850), as well as the optical energy band gap which decreased from 3.86 to 3.39 eV. The relevance between resistance behaviors and film microstructure is discussed. Therefore, it can be concluded that the desirable crystallinity, surface roughness, energy band gap and resistivity for 200 nm thick CCTO thin films deposited by RF magnetron sputtering can be achieved through the annealing process.     

Structural and optical properties of Ag2SeTe nano thin films prepared by thermal evaporation

Semiconducting Ag₂SeTe thin films were prepared with different thicknesses onto glass substrates at room temperature using thermal evaporation technique. The structural properties were determined as a function of thickness by XRD exhibiting no preferential orientation along any plane, however the films are found to have peaks corresponding to mixed phase. The XRD studies were used to calculate the crystallite size and microstrain of the Ag₂SeTe films. The calculated microstructure parameters reveal that the crystallite size increases and micro strain decreases with increasing film thickness. The refractive index, dielectric constants and thereby the optical bandgap of the films were calculated from transmittance spectral data recorded in the range 400?C1200 nm by UV?CVIS-Spectrometer. The direct optical bandgap of the Ag₂SeTe thin films deposited on glass substrates with different thicknesses 50?C230 nm were found to be in the range 1.48?C1.59 eV. The carrier density value is estimated to be around 9.8 × 10²¹ cm^?1 for the film thickness of 150 nm. The compositions estimated from the optical band gap studies reveal a value of 0.75 for Tellurium concentration. These structural and optical parameters are found to be very sensitive to the thin film thickness.     

Structural,morphological, optical and gas sensing properties of pure and Ce doped SnO<Subscript>2</Subscript> thin films prepared by jet nebulizer spray pyrolysis (JNSP) technique

Pure and cerium (Ce) doped tin oxide (SnO₂) thin films are prepared on glass substrates by jet nebulizer spray pyrolysis technique at 450 °C. The synthesized films are characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive analysis X-ray, ultra violet visible spectrometer (UV–Vis) and stylus profilometer. Crystalline structure, crystallite size, lattice parameters, texture coefficient and stacking fault of the SnO₂ thin films have been determined using X-ray diffractometer. The XRD results indicate that the films are grown with (110) plane preferred orientation. The surface morphology, elemental analysis and film thickness of the SnO₂ films are analyzed and discussed. Optical band gap energy are calculated with transmittance data obtained from UV–Visible spectra. Optical characterization reveals that the band gap energy is found decreased from 3.49 to 2.68 eV. Pure and Ce doped SnO₂ thin film gas sensors are fabricated and their gas sensing properties are tested for various gases maintained at different temperature between 150 and 250 °C. The 10 wt% Ce doped SnO₂ sensor shows good selectivity towards ethanol (at operating temperature 250 °C). The influence of Ce concentration and operating temperature on the sensor performance is discussed. The better sensing ability for ethanol is observed compared with methanol, acetone, ammonia, and 2-methoxy ethanol gases.     

Physical properties of very thin SnS films deposited by thermal evaporation

SnS films with thicknesses of 20-65 nm have been deposited on glass substrates by thermal evaporation. The physical properties of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet-visible-near infrared spectroscopy at room temperature. The results from XRD, XPS and Raman spectroscopy analyses indicate that the deposited films mainly exhibit SnS phase, but they may contain a tiny amount of Sn₂S₃. The deposited SnS films are pinhole free, smooth and strongly adherent to the surfaces of the substrates. The color of the SnS films changes from pale yellow to brown with the increase of the film thickness from 20 nm to 65 nm. The very smooth surfaces of the thin films result in their high reflectance. The direct bandgap of the films is between 2.15 eV and 2.28 eV which is much larger than 1.3 eV of bulk SnS, this is deserving to be investigated further.     

Structural and plasmonic characteristics of sputtered SnO<Subscript>2</Subscript>:Sb and ZnO:Al thin films as a function of their thickness

Heavily doped metal oxide semiconductors are being developed as thin film transparent electrodes for many applications and their deposition at low substrate temperature can extend the use on heat sensitive devices. The structural and electro-optical characteristics of such metal oxide coatings are tightly related and depend on the specific deposition parameters apart from the material composition. In this work, SnO₂:Sb (ATO) and ZnO:Al (AZO) thin films have been prepared by sputtering at room temperature on glass substrates, changing the deposition time to obtain various layer thicknesses from 0.2 to 0.9 μm; and they have been analyzed by X-ray diffraction, spectrophotometry, and Hall-effect measurements. ATO samples crystallize in the tetragonal structure with mean crystallite size increasing from 8 to 20 nm when the film thickness grows. The comparison of Hall mobility and optical mobility values indicates a significant contribution of grain boundary scattering for these ATO layers. Otherwise, AZO films show larger crystallites (21–27 nm) and a strong preferential orientation for analogous thickness increment, resulting in a lower contribution of the grain boundary scattering to the overall Hall mobility. The in-grain mobility for each sample is also related to the respective crystallite size and carrier concentration values.     

Structural, photoluminescence and optical properties of chemically deposited (Cd1−xBix)S thin films as a function of dopant concentration

In this study, (Cd_1?xBi_x)S thin films were successfully deposited on suitably cleaned glass substrate at 60 °C temperature, using the chemical bath deposition technique. After deposition, the films were also annealed at 400 °C for 2 min in air. The structural properties of the deposited films were characterized using X-ray diffraction and AFM. Formation of cubic structure with preferential orientation along the (111) plane was confirmed together with BiS second phase from structural analysis. The interplanar spacing, lattice constant, and crystallite size of (Cd_1?xBi_x)S thin films were calculated by the XRD. The crystallite size of the un-doped CdS thin films was found to be 7.84 nm, which increased to 11.1 nm with increasing Bi content from 0 to 10 %. The surface roughness of the films was measured by AFM studies. The photoluminescence spectra were observed at red shifted band edge peak with increasing doping concentration of Bi from 0 to 5 % in the un-doped CdS thin films. The optical properties of the films are estimated using optical absorption and transmission spectra in the range of 400–800 nm using UV–VIS spectrophotometer. The optical band gap energy of the films was found to be decreased from 2.44 to 2.23 eV with the Bi content being from 0 to 5 %. After annealing, the band gap of these films further decreased.     

Synthesis and characterization of nanostructured nickel oxide thin films prepared with chemical spray pyrolysis

Nickel oxide thin films have been deposited in an open atmosphere onto glass substrates by chemical spray pyrolysis using aqueous nickel acetate solutions and air as driving gas. The films show a strong variation in the surface morphology depending on the substrate temperature and the precursor solution flux. At 350 °C substrate temperature, a reticular tissue-like film morphology is obtained, becoming the reticular nickel oxide fibres of the film thicker with increasing precursor solution flux. At 450 °C substrate temperature, the film growth rate is 4 times slower and a highly symmetric self-ordering of the material at nanometer length scale occurs. These films consist of interconnected grains separated by pores, both of about 100 nm in size. XRD and TEM revealed that the films are cubic NiO, being the crystallite size around 10 nm. The optical band gap of the films decreases strongly for increasing film thickness from 4.3 eV to 3.65 eV.     

Growth technology,X-ray and optical properties of CdSe thin films

An ammonia-free chemical-bath deposition was used to obtain CdSe thin films on glass substrate. The materials used in the chemical bath were cadmium chloride complexed with sodium citrate and sodium selenosulphate. The preparation conditions, especially the starting solution characteristics, such as concentration of dissolved materials, temperature, pH value as well as deposition time and immersion cycles were optimized to obtain homogeneous stoichiometric films with good adherence to the glass substrate. The films thickness was in the range of 400–500 nm with a growing time of 4 h. The material obtained was characterized by optical absorption, SEM with the energy dispersive X-ray analysis (EDS) and X-ray diffraction. The films obtained at bath temperatures of 70 and 80 °C had the hexagonal structure (of wurtzite type), with crystallite size of about 20 nm. Room temperature deposition results in films with the cubic structure and crystallite size of about 4 nm. From optical transmission data, an energy gap equal to 1.88 eV was found. The material is interesting for applications in hybrid systems for solar energy conversion.     

Formation and properties of cadmium sulfide buffer layer for CIGS solar cells grown using hot plate bath deposition

In the present study, cadmium sulfide (CdS) thin films were deposited on different substrates [soda glass, fluoride doped tin oxide, and tin doped indium oxide (ITO) coated glass] by a hot plate method. To control the thickness and the reproducibility of the sample production, the thin films were coated at different temperatures and deposition times. The CdS thin films were heated at 400 °C in air and forming gas (FG) atmosphere to investigate the effect of the annealing temperatures. The thickness of the samples, measured by ellipsometry, could be controlled by the deposition time and temperature of the hot plate. The phase formation and structural properties of CdS thin films were studied by X-ray diffraction and scanning electron microscopy, whereas the optical properties were obtained by UV–vis spectroscopy. A hexagonal crystal structure was observed for CdS thin films and the crystallinity improved upon annealing. The structural and optical properties of CdS thin films were also enhanced by annealing at 400 °C in FG atmosphere (95 % N₂, 5 % H₂). The optical band gap was changed from 2.25 to 2.40 eV at different annealing temperatures and gas atmospheres. A higher electrical conductivity, for the sample annealed at FG, was noticed. The samples deposited on ITO and annealed in FG atmosphere showed the best structural and electrical properties compared to the other samples. CdS thin films can be widely used for application as a buffer layer for copper–indium–gallium–selenide solar cells.     

Annealing effects on the structural and optical properties of growth ZnO thin films fabricated by pulsed laser deposition (PLD)

Annealed ZnO thin film at 300, 350, 400, 450 and 500 °C in air were deposited on glass substrate by using pulsed laser deposition. The effects of annealing temperature on the structural and optical properties of annealed ZnO thin films by grazing incident X-ray diffraction (GIXRD), transmittance spectra, and photoluminescence (PL) were investigated. The GIXRD reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye–Scherrer equation and the average grain size were found to be in the range 5.22–10.61 ± 0.01 nm. The transmittance spectra demonstrate highly transparent nature of the films in visible region (>70 %). The calculation of optical band gap energy is found to be in the range 2.95–3.32 ± 0.01 eV. The PL spectra shows that the amorphous film gives a UV emission only and the annealed films produce UV, violet, blue and green emissions this indicates that the point defects increased as the amorphous film was annealed.     

Structural and optical properties of nc-Si:H thin films deposited by layer-by-layer technique

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited on c-Si and quartz substrates by layer-by-layer (LBL) technique using radio-frequency plasma enhanced chemical vapour deposition system. The effects of rf power on the interlayer elemental profiling, structural and optical properties of the films were investigated by Auger electron spectroscopy, Fourier transform infrared spectroscopy, Raman scattering spectroscopy, X-ray diffraction and optical transmission and reflection spectroscopy. The results revealed that the LBL deposition leads to a formation of different ranges of crystallite sizes of nc-Si corresponds 3–6 and 8–26 nm respectively. LBL deposition also demonstrated a capability to increase the crystalline volume fraction of nc-Si up to 65.3 % with the crystallite size in between 5 and 6 nm, at the rf power in between 80 and 100 W. However, the crystalline volume fraction decreased for the rf power above 100 W due to the growth of nc-Si was suppressed by the formation of SiO₂. In addition, the onset of crystallization of the films deposited on c-Si and quartz substrates are different with increase in the rf power. The effects of rf power on the growth of nc-Si, and the hydrogen content, structural disorder, crystallite size of nc-Si and oxygen diffusion into the LBL layer with the change of optical energy gap under the variation of rf power are also discussed.     

Effect of ZnO buffer layer on AZO film properties and photovoltaic applications

Aluminum-doped ZnO (AZO) transparent conducting films were deposited on glass substrates with and without intrinsic ZnO (i-ZnO) buffer layers by a home made and low cost radio-frequency (RF) magnetron sputtering system at room temperature in pure argon ambient and under a low vacuum level. The films were examined and characterized for electrical, optical, and structural properties for the application of CIGS solar cells. The influence of sputter power, deposition pressure, film thickness and residual pressure on electrical and optical properties of layered films of AZO, i-ZnO and AZO/i-ZnO was investigated. The optimization of coating process parameters (RF power, sputtering pressure, thickness) was carried out. The effects of i-ZnO buffer layer on AZO films were investigated. By inserting thin i-ZnO layers with a thickness not greater than 125 nm under the AZO layers, both the carrier concentration and Hall mobility were increased. The resistivity of these layered films was lower than that of single layered AZO films. The related mechanisms and plasma physics were discussed. Copper indium gallium selenide (CIGS) thin film solar cells were fabricated by incorporating bi-layer ZnO films on CdS/CIGS/Mo/glass substrates. Efficiencies of the order of 7–8% were achieved for the manufactured CIGS solar cells (4–5 cm² in size) without antireflective films. The results demonstrated that RF sputtered layered AZO/i-ZnO films are suitable for application in low cost CIGS solar cells as transparent conductive electrodes.     

Effect of deposition time on structural, optical and photoluminescence properties of Cd0.9Zn0.1S thin films by chemical bath deposition method

The present work investigates the effect of deposition times on the structural, optical and photoluminescence properties of Cd_0.9Zn_0.1S thin films deposited on glass substrate by chemical bath deposition method. The deposition time was varied from 30 to 90 min. The deposited films were uniform and adherent to the glass substrates and amorphous in nature. Structural, optical and photoluminescence properties of Cd_0.9Zn_0.1S thin films were studied through X-ray diffraction, energy dispersive X-ray, scanning electron microscopy, UV–Vis absorption, fourier transform infra red spectroscopy and photoluminescence spectroscopy. The average crystal size was increased from ~1.3 to 2.5 nm with increase in deposition times. The absorption of the films was increased and the absorption peak shifted to lower wavelength side when deposition time increases. The increased energy gap from 2.4 to 2.49 eV with deposition time was due to quantum size effect and better crystallization. The presence of functional groups and chemical bonding were confirmed by FTIR. PL spectra showed two well distinct and strong bands; blue band around 407–415 nm and green band around 537–541 nm due to size effect.     

Influence of Fe dopant concentration and annealing temperature on the structural and optical properties of ZnO thin films deposited by sol–gel method

Nanostructured Fe doped ZnO thin films were deposited onto glass substrates by sol–gel spin coating method. Influence of Fe doping concentration and annealing temperature on the structural, compositional, morphological and optical properties were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–Vis spectroscopy and photoluminescence (PL) measurements. XRD analysis showed that all the films prepared in this work possessed a hexagonal wurtzite structure and were preferentially oriented along the c-axis. Pure ZnO thin films possessed extensive strain, whereas Fe doped films possessed compressive strain. In the doped films, least value of stress and strain was observed in the 0.5 at.% Fe doped thin film, annealed at 873 K. Average crystallite size was not significantly affected by Fe doping, but it increased from 15.57 to 17.79 nm with increase in annealing temperature from 673 to 873 K. Fe ions are present in +3 oxidation state as revealed by XPS analysis of the 0.5 at.% Fe doped film. Surface morphology is greatly affected by changes in Fe doping concentration and annealing temperature which is evident in the SEM images. The increase in optical band gap from 3.21 to 3.25 eV, with increase in dopant concentration was attributed to Moss–Burstein shift. But increase in annealing temperature from 673 to 873 K caused a decrease in band gap from 3.22 to 3.20 eV. PL spectra showed emissions due to excitonic combinations in the UV region and defect related emissions in the visible region in all the investigated films.     

Characterization of titania thin films grown by dip-coating technique

A dip-coating technique was employed to prepare anatase phase of titania thin films. Fluorine doped tin oxide substrates were used to prepare titania thin films. The samples were annealed at 550 °C for 18 h. X-ray diffraction results revealed the amorphous and anatase phases of TiO₂ for as-synthesized and annealed samples, respectively. The crystallite size of anatase TiO₂ thin films was almost 25 nm for annealed samples. UV–visible confirmed the energy band gap 3.86 and 3.64 eV for as-prepared and calcinated titania thin films. The reduction in the energy band gap could be due to the change in crystallization and agglomeration of small grains after calcination. The morphology of the prepared films was investigated by field emission scanning electron microscopy which demonstrated the agglomeration of spherical particles of TiO₂ with average particle size of about 30 nm. The molecular properties (chemical bonding) of the samples were investigated by means of Fourier Transform Infrared (FTIR) spectroscopy. FTIR analysis exhibited the formation of titania, functional group OH, hydroxyl stretching vibrations of the C–OH groups, bending vibration mode of H–O–H, alkyl C–H stretch, stretching band of Ti–OH, CN asymmetric band stretching, and C=O saturated aldehyde.     

Band gap engineering in PbSe thin films from near-infrared to visible region by photochemical deposition method

Lead selenide (PbSe) thin films have been synthesized by the established photochemical deposition technique using lead nitrate and lead acetate as sources for the metal ions and sodium seleno sulphate as the selenium source along with triethanolamine, ammonia and hydrazine hydrate as complexing agents. A comprehensive study of the effect of substrate materials on physical properties of as deposited PbSe thin films is reported in this work. Two substrates were used in this investigation, namely soda lime glass slides and gold coin corning glass slides. The solution is irradiated with UV light and the photochemical reactions in the aqueous solution resulted in highly adherent metallic thin films. X-ray diffraction (XRD), scanning electron microscopy, optical and electrical measurement techniques were used for film characterization. The XRD analysis confirmed that all films were cubic, regardless of the cationic precursors and substrates used. The scanning electron microscope micrographs showed variations in morphology. The optical studies revealed that the films have good absorption in the visible region. The remarkable success of our effort was that we have been able to modify optical band gap of PbSe thin films over a wide spectral range by a cost effective route. The band gaps estimated from the transmission spectra were in the range 1.32–1.40 eV for films deposited on soda lime glass substrates and 1.46–1.55 eV for corning glass substrates. The room temperature conductivity of the PbSe films were in the range of 3.71 × 10^?7–513 × 10^?7 (Ω cm)^?1. The as deposited PbSe thin films with low transmittance in the visible region coupled with an appreciable reflectance in infrared region were found to satisfy the basic requirements for solar control coatings for window glazing applications in warm climates. Through this work we established that irrespective of metal salts, soda lime glass substrate was superior to corning glass substrate.     

Quantum dot sensitized aluminium doped and copper doped ZnO nanostructure based solar cells

Aluminium doped and copper doped ZnO nanostructured thin films have been prepared using simple solgel dip coating method. The X-ray diffraction pattern results revealed that the prepared Al and Cu doped ZnO sample exhibits hexagonal structure. The average crystallite size of pure ZnO, Al doped ZnO and Cu doped ZnO samples were found to be 29, 26 and 15 nm, respectively. The optical band gap of ZnO, Al doped ZnO and Cu doped ZnO thin films was found to be 3.27, 3.29, and 3.20 eV respectively. Solar cells have been fabricated using CdS quantum dots sensitized ZnO nanostructured thin films and the efficiency of the fabricated Al doped and Cu doped ZnO solar cells were 1.37 and 1.29 % respectively.