Cadmium oxide, indium oxide and cadmium indate thin films obtained by the sol-gel technique

Thin films of the mixed CdO-In₂O₃ system were deposited on glass substrates by the sol-gel technique. The precursor solution was obtained starting from the mixture of two precursor solutions of CdO and In₂O₃ prepared separately at room temperature. The In atomic concentration percentages (X) in the precursor solution with respect to Cd (1 − X), were: 0, 16, 33, 50, 67, 84 and 100. The films were sintered at two different sintering temperatures (Ts) 450 and 550 °C, and after that, annealed in a 96:4 N₂/H₂ gas mixture at 350 °C. X-ray diffraction patterns showed three types of films, excluding those constituted only of CdO and In₂O₃ crystals: i) For X ≤ 50 at.%, the films were constituted of CdO + CdIn₂O₄ crystals, ii) For X = 67 at.%, the films were only formed of CdIn₂O₄ crystals and iii) For X = 84 at.% the films were constituted of In₂O₃ + CdIn₂O₄ crystals. In all films in the 0 < X < 100 range, the formation CdIn₂O₄ crystals of this material was prioritized with respect to the formation of CdO and In₂O₃ materials. All films showed high optical transmission and an increase of the direct band gap value from 2.4 (for CdO) to 3.6 eV (for In₂O₃), as the X value increases. The resistivity values obtained were in the interval of 8 × 10^− 4 Ω cm to 10⁶ Ω cm. The CdIn₂O₄ films had a resistivity value of 8 × 10^− 3 Ω cm and a band gap value of 3.3 eV.     

Lipase immobilized on nanostructured cerium oxide thin film coated on transparent conducting oxide electrode for butyrin sensing

Nanostructured cerium oxide (CeO₂) thin films were deposited on transparent conducting oxide (TCO) substrate using spray pyrolysis technique with cerium nitrate salt, Ce(NO₃)₃·6H₂O as precursor. Fluorine doped cadmium oxide (CdO:F) thin film prepared using spray pyrolysis technique acts as the TCO film and hence the bare electrode. The structural, morphological and elemental characterizations of the films were carried out using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) respectively. The diffraction peak positions in XRD confirmed the formation of highly crystalline ceria with cubic structure and FE-SEM images showed uniform adherent films with granular morphology. The band gaps of CeO₂ and TCO were found to be 3.2 eV and 2.6 eV respectively. Lipase enzyme was physisorbed on the surface of CeO₂/TCO film to form the lipase/nano-CeO₂/TCO bioelectrode. Sensing studies were carried out using cyclic voltammetry and amperometry, with lipase/nano-CeO₂/TCO as working electrode and tributyrin as substrate. The mediator-free biosensor with nanointerface exhibited excellent linearity (0.33–1.98 mM) with a lowest detection limit of 2 μM with sharp response time of 5 s and a shelf life of about 6 weeks.     

Some structural properties of CdO:F films produced by ultrasonic spray pyrolysis method

The fluorine doped cadmium oxide (CdO:F) samples have been deposited at 250 °C by ultrasonic spray pyrolysis method. Cadmiumacetat-dihydrat and ammonium fluoride have been taken as a source of cadmium and fluorine-dopant respectively. The thickness of the CdO:F samples was about 1.4 μm. X-ray diffraction pattern of the CdO:F samples has revealed that the samples are polycrystalline with cubic sodium chloride structure. There are shifts of the d values (interplanar spacing) for CdO:F samples with respect to standard CdO film. The lattice parameters for cubic structure have been calculated using the Bragg equation. The texture coefficients calculated for various planes at different fluorine concentrations indicate that the samples have exhibited (111) and (200) preferential orientations.     

Preparation and characterization of spray deposited NiMoO4 thin films for photovoltaic electrochemical studies

The preparation of nickel molybdate (NiMoO₄) thin film by spray pyrolysis with ammonical solution as a precursor is presented. The phase and surface morphology characterizations have been carried out by XRD and SEM analysis. The study of optical absorption spectrum in the wavelength range 350–850 nm shows direct as well as indirect optical transitions in the thin film material. The dc electrical conductivity measurements in the temperature range 310–500 K indicate semiconducting behavior of the thin film with high resistivity (10⁷ Ω cm) at room temperature. The thin films deposited on fluorine doped tin oxide (FTO) coated conducting glass substrates were used as a photoanode in photovoltaic electrochemical (PVEC) cell with configuration: NiMoO₄ |Ce⁴⁺, Ce³⁺| Pt; 0.1 M in 0.1N H₂SO₄. The PVEC characterization reveals the fill factor and power conversion efficiency to be 0.48 and 0.81%, respectively. The flat band potential is found to be −0.39 V (SCE).     

Transparent conducting properties of Ni doped zinc oxide thin films prepared by a facile spray pyrolysis technique using perfume atomizer

Undoped and Ni doped zinc oxide (Ni–ZnO) thin films were prepared by a facile spray pyrolysis technique using perfume atomizer from aqueous solution of anhydrous zinc acetate (Zn(CH₃COOH)₂ and hexahydrated nickel chloride (NiCl₂·6H₂O) as sources of zinc and nickel, respectively. The films were deposited onto the amorphous glass substrates kept at (450 °C). The effect of the [Ni]/[Zn] ratio on the structural, morphological, optical and electrical properties of Ni doped ZnO thin film was studied. It was found from X-ray diffraction (XRD) analysis that both the undoped and Ni doped ZnO films were crystallized in the hexagonal structure with a preferred orientation of the crystallites along the [002] direction perpendicular to the substrate. The scanning electron microscopy (SEM) images showed a relatively dense surface structure composed of crystallites in the spherical form whose average size decreases when the [Ni]/[Zn] ratio increases. The optical study showed that all the films were highly transparent. The optical transmittance in the visible region varied between 75 and 85%, depending on the dopant concentrations. The variation of the band gap versus the [Ni]/[Zn] ratio showed that the energy gap decreases from 2.95 to 2.72 eV as the [Ni]/[Zn] ratio increases from 0 to 0.02 and then increases to reach 3.22 eV for [Ni]/[Zn] = 0.04. The films obtained with the [Ni]/[Zn] ratio = 0.02 showed minimum resistivity of 2 × 10⁻³ Ω cm at room temperature.     

Some physical properties of Sn-doped CdO thin films prepared by chemical bath deposition

Undoped and Sn-doped CdO thin films were prepared by the chemical bath deposition method by means of a procedure that improves the deposition efficiency. All as-grown films were crystallized in the cubic structure of cadmium peroxide (CdO₂) and transformed into CdO with a cubic structure after an annealing process. The as-grown films have a high resistivity (> 10⁶ Ω cm) and an optical bandgap around 3.6 eV. Undoped CdO displays an optical bandgap around 2.32–2.54 eV and has an electrical conductivity of 8 × 10^− 4 Ω cm. The Sn incorporation into CdO produces a blue shift in the optical bandgap (from 2.55 to 2.84 eV) and a decrease in the electrical conductivity.The deposition procedure described here gives colloid-free surface thin films as indicated by the surface morphology analysis.     

Highly transparent and conducting In doped CdO synthesized by sol-gel solution processing

Cadmium oxide (CdO) is a much-studied wide gap semiconductor with an inherent high mobility of?>?100 cm²/Vs, high electron concentration of?>?10²¹ cm^?3 and a wide optical transparency window of?>?1800 nm. These unique properties make CdO a potential transparent conductor for full spectrum photovoltaics. However, in order to achieve optimum material properties for optoelectronic applications, CdO was grown by vacuum-based physical or chemical vapor deposition methods. In this work, we explored the application of a low-cost sol-gel spin coating method to achieve highly conducting and transparent CdO thin films doped with 0–10% In (CdO:In). We find that while as-grown CdO:In films are nanocrystalline/amorphous with a high resistivity of?~?1 Ω-cm, polycrystalline and highly conducting films can be obtained after optimized annealing at?≥?400 °C. However, the electron concentration n saturates at?~?5?×?10²⁰ cm^?3 for In concentration?>?5% (or N_In?~?1.9?×?10²¹ cm^?3). This low activation of In may be attributed to the high density of native defects and/or impurities incorporated in the sol-gel process. With 5% In doping, we obtained a low resistivity of ρ?~?2.5?×?10^–4 Ω-cm and a high mobility μ?~?50 cm²/Vs. These values of σ and µ are better than those reported for other TCOs synthesized by solution processes and comparable to conventional commercial TCOs grown by physical vapor deposition methods. Benefiting from their high mobility, these sol-gel CdO:In films are optically transparent over a wide spectral range up to λ?>?1800 nm, making them promising as transparent conductors for optoelectronic devices utilizing the infrared photons.

     

Fluorine doped gallium tin oxide composite films as transparent conductive oxides on polyethylene terephthalate film prepared by electron cyclotron resonance metal organic chemical vapor deposition

The undoped and fluorine doped gallium tin oxide composite films are prepared by an electron cyclotron resonance metal organic chemical vapor deposition. Characteristics of structural, optical and electrical properties of the fluorine doped gallium tin oxide composite thin films are investigated. The four point probe method, atomic force microscopy and X-ray photoelectron spectroscopy are employed to characterize the composite thin films. UV-visible, X-ray diffraction, scanning electron microscope and Hall measurement performed on fluorine doped gallium tin oxide composite are films deposited on polyethylene terephthalate substrates. The diffraction pattern shows the presence of tetragonal structure with (112) special orientation for fluorine doped gallium tin oxide composite films. The doped composite film on F/Ga + Sn mole ratio of 0.35 is observed the lowest electrical resistivity of 3.35 × 10^− 4 Ω cm.     

Atmospheric pressure chemical vapor deposition of transparent conducting films of fluorine doped zinc oxide and their application to amorphous silicon solar cells

Transparent conducting ZnO:F was deposited as thin films on soda lime glass substrates by atmospheric pressure chemical vapor deposition (CVD) deposition at substrate temperatures of 480–500 °C. The precursors diethylzinc, tetramethylethylenediamine and benzoyl fluoride were dissolved in xylene. The solution was nebulized ultrasonically and then flash vaporized by a carrier gas of nitrogen preheated to 150 °C. Ethanol was vaporized separately, and these vapors were then mixed to form a homogeneous vapor mixture. Good reproducibility was achieved using this new CVD method. Uniform thicknesses were obtained by moving the heated glass substrates through the deposition zone. The best electrical and optical properties were obtained when the precursor solution was aged for more than a week before use. The films were polycrystalline and highly oriented with the c-axis perpendicular to the substrate. The electrical resistivity of the films was as low as 5 × 10⁻⁴ Ωcm. The mobility was about 45 cm²/Vs. The electron concentration was up to 3 × 10²⁰/cm³. The optical absorption of the films was about 3–4% at a sheet resistance of 7 Ω/square. The diffuse transmittance was about 10% at a thickness of 650 nm. Amorphous silicon solar cells were deposited using the textured ZnO:F films as the front electrode. The short circuit current was increased over similar cells made with fluorine doped tin oxide, but the voltages and fill factors were reduced. The voltage was restored by overcoating the ZnO:F with a thin layer of SnO₂:F.     

Structural, electrical and optical studies of SILAR deposited cadmium oxide thin films: Annealing effect

Successive ionic layer adsorption and reaction (SILAR) method has been successfully employed for the deposition of cadmium oxide (CdO) thin films. The films were annealed at 623 K for 2 h in an air and changes in the structural, electrical and optical properties were studied. From the X-ray diffraction patterns, it was found that after annealing, H₂O vapors from as-deposited Cd(O₂)_0.88(OH)_0.24 were removed and pure cubic cadmium oxide was obtained. The as-deposited film consists of nanocrystalline grains of average diameter about 20-30 nm with uniform coverage of the substrate surface, whereas for the annealed film randomly oriented morphology with slight increase in the crystallite size has been observed. The electrical resistivity showed the semiconducting nature with room temperature electrical resistivity decreased from 10⁻² to 10⁻³ Ω cm after annealing. The decrease in the band gap energy from 3.3 to 2.7 eV was observed after the annealing.     

Effect of Li doping on the structural, optical and electrical properties of spray deposited SnO2 thin films

Studies on spray deposited transparent conducting Li doped SnO₂ thin films are scarce. Li (0 to 5 wt.%) doped SnO₂ thin films spray deposited onto glass substrates at 773 K in air from chloride precursors were studied for their structural, optical and temperature dependent electrical behaviors. X-ray diffraction patterns indicated single phase with polycrystalline nature. Systematic variation in surface morphology on Li doping was examined by scanning electron microscopy and atomic force microscopy. Film thickness, optical band gap (direct and indirect), sheet resistance and figure of merit were computed from spectral transmittance and temperature dependent resistivity data. Lithium doping was found to decrease the value of sheet resistance by an order in magnitude. Activation energy was computed from temperature dependent electrical resistivity data measured in the range 300 to 448 K. The 4 wt.% Li doped SnO₂ film was found to have a high value of figure of merit among other films. The results are discussed.     

Fabrication of Ta3N5-Ag nanocomposite thin films with high resistivity and near-zero temperature coefficient of resistance

In this study, we investigate as-deposited Ta₃N₅-Ag nanocomposite thin films with near-zero temperature coefficients of resistance (TCRs) that are fabricated by a reactive co-sputtering method; these films can be used in thin-film embedded resistors. In these films, the TCR approaches zero due to compensation between Ag (+TCR) and Ta-N (−TCR) at resistivities higher than 0.005 Ω-cm.Taking into account the fact that Ag counterbalances the resistivity of the Ta₃N₅-Ag thin film, we performed reactive co-sputtering at a nitrogen partial pressure of 55%, corresponding to a resistivity of 0.384 Ω-cm. The resistivity and power density changed, respectively, from 1.333 Ω-cm and 0.44 W/cm² for silver to 0.0059 Ω-cm and 0.94 W/cm² for the Ta₃N₅-Ag thin film. A near-zero TCR of + 34 ppm/K was obtained at 0.94 W/cm² in the Ta₃N₅-Ag thin film without heat treatment.     

Studies on micro-structural and electrical properties of spray-deposited fluorine-doped tin oxide thin films from low-cost precursor

Thin films of fluorine-doped tin oxide (SnO₂:F) on glass were prepared by spray pyrolysis technique using stannous chloride (SnCl₂) and ammonium fluoride (NH₄F) as precursors. The as-prepared films were characterized for their structural and electrical properties and are discussed in detail in this article. The surface morphology studies revealed that the films are grainy and the roughness of undoped films has been reduced on fluorine doping. X-ray diffraction (XRD) studies revealed that the films are polycrystalline. It further revealed that the undoped films grow along the preferred orientation of (211), whereas all the doped films grow along (200). The minimum sheet resistance 1.75 Ω/□ achieved in the present study for the films doped with 15 wt.% F is the lowest among the reported values for these materials prepared using SnCl₂ precursor. The electrical transport phenomenon has been analyzed in order to find out the possible scattering mechanism that limiting the mobility of charge carriers.     

Preparation and characterization of indium doped CdS0.2Se0.8 thin films by spray pyrolysis

The CdS_0.2Se_0.8 and indium doped CdS_0.2Se_0.8 thin films have been deposited onto the amorphous glass and fluorine doped tin oxide coated glass substrates by spray pyrolysis. The doping concentration of indium has been optimized by photoelectrochemical characterization technique. The structural, surface morphological, optical and electrical properties of CdS_0.2Se_0.8 and indium doped CdS_0.2Se_0.8 thin films have been studied. X-ray diffraction studies reveal that the films are polycrystalline in nature with hexagonal crystal structure. Scanning electron microscopy studies reveal that the grains are uniform with uneven spherically shaped, distributed over the entire substrate surface. The complete surface morphology has been changed after doping. In optical studies, the transition of the deposited films is found to be direct allowed with optical energy gaps decreasing from 1.91 to 1.67 eV with indium doping. Semiconducting behavior has been observed from resistivity measurements. The thermoelectric power measurements reveal that the films exhibit n-type conductivity.     

Atomic layer deposition of Ru thin film using N2/H2 plasma as a reactant

Ruthenium (Ru) thin films were grown by atomic layer deposition using IMBCHRu [(η6-1-Isopropyl-4-MethylBenzene)(η4-CycloHexa-1,3-diene)Ruthenium(0)] as a precursor and a nitrogen-hydrogen mixture (N₂/H₂) plasma as a reactant, at the substrate temperature of 270 °C. In the wide range of the ratios of N₂ and total gas flow rates (fN₂/N₂ + H₂) from 0.12 to 0.70, pure Ru films with negligible nitrogen incorporation of 0.5 at.% were obtained, with resistivities ranging from ~ 20 to ~ 30 μΩ cm. A growth rate of 0.057 nm/cycle and negligible incubation cycle for the growth on SiO₂ was observed, indicating the fast nucleation of Ru. The Ru films formed polycrystalline and columnar grain structures with a hexagonal-close-packed phase. Its resistivity was dependent on the crystallinity, which could be controlled by varying the deposition parameters such as plasma power and pulsing time. Cu was electroplated on a 10-nm-thick Ru film. Interestingly, it was found that the nitrogen could be incorporated into Ru at a higher reactant gas ratio of 0.86. The N-incorporated Ru film (~ 20 at.% of N) formed a nanocrystalline and non-columnar grain structure with the resistivity of ~ 340 μΩ cm.     

Visible light enhanced TiO2 thin film bilayer dye sensitized solar cells

Visible light enhanced nitrogen-sulfur (N-S) doped titanium dioxide (TiO₂) thin films were prepared by the sol-gel method using thiourea as a dopant. The physical and chemical properties of the TiO₂ thin films were greatly influenced by the amount of thiourea added to the sol-gel solution. The greatest shift to longer wavelengths for visible light absorption was observed with 0.6 g of thiourea in the precursor solution, while 0.4 g yielded the largest particle sizes. These single-cycle dip-deposited N-S doped TiO₂ thin films were used as visible light harvesters as well as blocking layers in dye sensitized solar cells. When deposited directly on conducting fluorine doped tin oxide electrodes, photo-conversion efficiencies were reduced. However, the opposite configuration, with N-S doped thin films on top of nanoporous TiO₂, yielded an increased open-circuit voltage of 0.84 V, a short-circuit current density of 9.86 mA cm⁻², and an overall conversion efficiency of 5.88% greater than that of a standard cell. The effectiveness of the blocking layer on the cell efficiencies was analyzed by electrochemical impedance spectroscopy.     

Optimization of n nc-Si:H and a-SiNx:H layers for their application in nc-Si:H TFT

The n-type doped silicon thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) technique at high and low H₂ dilutions. High H₂ dilution resulted in n⁺ nanocrystalline silicon films (n⁺ nc-Si:H) with the lower resistivity (ρ ∼0.7 Ω cm) compared to that of doped amorphous silicon films (∼900 Ω cm) grown at low H₂ dilution. The change of the lateral ρ of n⁺ nc-Si:H films was measured by reducing the film thickness via gradual reactive ion etching. The ρ values rise below a critical film thickness, indicating the presence of the disordered and less conductive incubation layer. The 45 nm thick n⁺ nc-Si:H films were deposited in the nc-Si:H thin film transistor (TFT) at different RF powers, and the optimum RF power for the lowest resistivity (∼92 Ω cm) and incubation layer was determined. On the other hand, several deposition parameters of PECVD grown amorphous silicon nitride (a-SiN_x:H) thin films were changed to optimize low leakage current through the TFT gate dielectric. Increase in NH₃/SiH₄ gas flow ratio was found to improve the insulating property and to change the optical/structural characteristics of a-SiN_x:H film. Having lowest leakage currents, two a-SiN_x:H films with NH₃/SiH₄ ratios of ∼19 and ∼28 were used as a gate dielectric in nc-Si:H TFTs. The TFT deposited with the NH₃/SiH₄∼19 ratio showed higher device performance than the TFT containing a-SiN_x:H with the NH₃/SiH₄∼28 ratio. This was correlated with the N−H/Si−H bond concentration ratio optimized for the TFT application.     

Percolation threshold for electrical resistivity of Ag-nanoparticle/titania composite thin films fabricated using molecular precursor method

To find the percolation threshold for the electrical resistivity of metallic Ag-nanoparticle/titania composite thin films, Ag-NP/titania composite thin films, with different volumetric fractions of silver (0.26 ≤ φ_Ag ≤ 0.68) to titania, were fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. Respective precursor solutions for Ag-nanoparticles and titania were prepared from Ag salt and a titanium complex. The resistivity of the films was of the order of 10⁻² to 10⁻⁵ Ω cm with film thicknesses in the range 100–260 nm. The percolation threshold was identified at a φ_Ag value of 0.30. The lowest electrical resistivity of 10⁻⁵ Ω cm at 25 °C was recorded for the composite with the Ag fraction, φ_Ag, of 0.55. X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and transmission electron microscopic (TEM) evaluation of the effect of the morphology and the nanostructures of the Ag nanoparticles in the composite thin films on the electrical resistivity of the film revealed that the films consist of rutile, anatase, and metallic Ag nanoparticles homogeneously distributed in the titania matrix. It could be deduced that the electrical resistivity of the thin films formed at 600 °C was unaffected by the anatase/rutile content within the thin film, whereas the shape, size, and separation distance of the Ag nanoparticles strongly influenced the electrical resistivity of the Ag-nanoparticle/titania composite thin films.     

Control of electrical resistivity of TaN thin films by reactive sputtering for embedded passive resistors

Tantalum nitride thin films were deposited by radio frequency (RF) reactive sputtering at various N₂/Ar gas flow ratios and working pressures to examine the change of their electrical resistivity. From the X-ray diffraction (XRD) and four-point probe sheet resistance measurements of the TaN_x films, it was found that the change of the crystalline structures of the TaN_x films as a function of the N₂ partial pressure caused an abrupt change of the electrical resistivity. When the hexagonal structure TaN thin films changed to an f.c.c. structure, the sheet resistance increased from 16 Ω/sq to 1396 Ω/sq. However, we were able to control the electrical resistivity of the TaN thin film in the range from 69 Ω/sq to 875 Ω/sq, with no change in crystalline structure, within a certain range of working pressures. The size of the grains in the scanning electron microscopy (SEM) images seemed to decrease with the increase of working pressure.     

New transparent conductive films: FTO coated ITO

New transparent conductive films, fluorine doped tin oxide (FTO) films coated on indium-tin-oxide (ITO) films, were developed. These transparent conductive films were prepared by the spray pyrolysis deposition method at a substrate temperature of 350 °C in ITO and 400 °C in FTO. For ITO deposition, an ethanol solution of indium(III) chloride, InCl₃·4H₂O, and tin(II) chloride, SnCl₂·2H₂O [Sn/(In+Sn), 5 at.%] was sprayed on a Corning #7059 glass substrate (100×100×1.1 mm³). After the deposition, FTO films were consecutively deposited for protecting oxidation of ITO films. FTO deposition was carried out by an ethanol solution of tin(IV) chloride, SnCl₄·5H₂O within the saturated water solution of NH₄F. These new transparent conductive films achieved the lowest resistivity of 1.4×10⁻⁴ Ω cm and the optical transmittance of more than 80% in the visible range of the spectrum. The electrical resistance of these new transparent conductive films increased by less than 10% even when exposed to high temperatures of 300-600 °C for 1 h in the air.