Deposited Zinc Oxide Research Articles

Highly c-axis oriented deposition of zinc oxide on an ITO surface modified by layer-by-layer method

The easy method to construct c-axis oriented zinc oxide (ZnO) layer directly attached onto a transparent conducting substrate was studied. On the assumption that anionic organic functional groups serves as a directing group for Zn2+ ion, poly(sodium p-styrenesulfonate) (PSSNa) was immobilized onto ITO surface by layer-by-layer (LbL) process, and ZnO was electrodeposited onto the modified ITO surface. Nucleation of ZnO crystals was induced by LbL treatment and the nucleated crystals were aligned toward <001>. The ZnO crystals gradually formed a film as the electrolysis progressed maintaining the crystal alignment, resulted in (001)-oriented ZnO continuous film. The obtained ZnO film was more transparent and uniform, and exhibited more intense photoluminescence at UV region than those deposited on a bare ITO. Also, the present method for the orientation selective nucleation of ZnO crystals revealed to be utilized as a seed layer for well aligned ZnO nanopillar array.

Zinc Oxide Buffer Layer Insertion for Sensitivity Improvement in Aluminium-Doped Zinc Oxide-Based Humidity Sensors

The improvement of sensitivity toward humidity by insertion of buffer layer has been investigated. The insertion of hetero- or homo-buffer layer of zinc oxide (ZnO) thin film before deposition of high quality ZnO had been reported for the growth on highly mismatched substrate. Three samples are characterized with different properties which are as deposited ZnO thin film without buffer layer (as deposited ZnO thin film) , anneal ZnO thin film without buffer layer (ZnO thin film) and anneal ZnO thin film with buffer layer (ZnO/ AZO thin film). The structural properties of ZnO thin film has been characterized field emission scanning electron microscopy (FESEM) JEOL JSM 6701F, atomic force microscope AFM (Park System XE-100) and XRD (Rigaku Ultima IV). The electrical and optical properties has been characterized using 2 point probe I-V measurement (Keithley 2400) and UV-Vis spectrophotometer (JASCO 670) respectively. In this work, we have focused on investigating the humidity sensitivity of ZnO thin film deposited using RF magnetron sputtering (SNTEK RSP 5004-PVD) with and without the buffer layer (Aluminum-doped ZnO (AZO)) for humidity sensor application.

Atmospheric pressure based electrostatic spray deposition of transparent conductive ZnO and Al-doped ZnO (AZO) thin films: Effects of Al doping and annealing treatment

Zinc oxide (ZnO) and Al-doped ZnO (AZO) thin films were prepared by electrostatic spray deposition method at atmospheric pressure followed by annealing. The effects of annealing and Al doping on the structural, electrical and optical properties of the films were investigated. The results show that films have random orientation with compact hexagonal wurtzite structure. It also implies that the annealing and the Al doping help to improve the electrical conductivity and optical properties as well. The minimum value of resistivity was 1.10 × 10−4 Ω cm for 0.5 at. % AZO film and transmittance was greater than 96% in the visible region. The present value of resistivity is comparable to the lowest values for AZO films reported in open literatures. All the films prepared by this method have a good crystalline structure and homogenous surface. We proposed that the substitution of Al in the ZnO lattice has positive effects in terms of increasing the free electron concentration. At atmospheric pressure, the electrospraying method was confirmed to be suitable for the preparation of AZO films with low resistivity and high transmittance.

Effect of rapid thermal annealing on texture and properties of pulsed laser deposited zinc oxide thin films

A comparative study on the properties of pulsed laser deposited ZnO thin films as a function of rapid thermal annealing temperature (Ta) is presented. Grazing incidence x-ray diffraction pattern reveals that preferred orientation of the films changes from (002) to (103) as Ta varies from 500 to 800°C. A clear correlation between grain morphology and texture formation is noticed. Photoluminescence spectra of all films show a strong near-band-edge ultraviolet (UV) emission and the UV emission intensity increases with Ta. Simultaneously, a weak and broad green emission centered at 505nm corresponds to oxygen vacancies also emerged in the films annealed at Ta≥600°C. A significant hysteresis behavior is observed in current–voltage characteristics and attributed to trapping/de-trapping driven effect. It is shown that high resistance state is dominated by space charge limited currents and low resistance state is governed by both Pool–Frenkel (2–5V) and Schottky emission (0–2V).

Intrinsic photoluminescence from low temperature deposited zinc oxide thin films as a function of laser and thermal annealing

An investigation into the modification of low temperature deposited ZnO thin films by different annealing processes has been undertaken using laser, thermal and rapid thermal annealing of 60 nm ZnO films deposited by high-target-utilization sputtering. Single-pulse laser annealing using a KrF excimer laser (λ = 248 nm) over a range of fluences up to 318 mJ cm−2 demonstrates controlled in-depth modification of internal film microstructure and luminescence properties without the film degradation produced by high temperature thermal and RTA processes. Photoluminescence (PL) properties show that the ratio of defect related deep level emission (DLE, 450–750 nm, 2.76–1.65 eV) to excitonic near band-edge emission (NBE at 381 nm, 3.26 eV) is directly correlated to processing parameters. Thermal and rapid thermal processing results in the evolution of a strong visible orange/red DLE PL (with peaks at 590 nm, 2.10 eV and 670 nm, 1.85 eV) dominated by defects related to excess oxygen. At higher temperatures, the appearance of a green/yellow emission (530 nm, 2.34 eV) indicates a transition of the dominant radiative transfer mechanism. In contrast, laser processing removes defect related DLE and produces films with intense NBE luminescence, correlated to the observed formation of large grains (25–40 nm).

Integration of n-doped ZnO nanorod structures as novel light-trapping concept in amorphous thin film silicon solar cells

Commonly, wet etched transparent conductive oxide (TCO) is used as a textured window electrode of hydrogenated amorphous thin film silicon solar cells. This study demonstrates a novel light trapping solutions using electrochemically deposited zinc oxide nanorod arrays to replace standard light management concepts. Here we systematically investigate the influence of rod size and array geometries on the solar cell efficiency and correlate our experimental results to multidimensional solar cell simulations. Especially, the requirement is demonstrated to match the solar cell design to the nanorod geometry which strongly influences the electrical cell characteristic. The results clearly outline the potential of TCO nanorod technology regarding the light trapping effect in silicon based thin film solar cells.

Study of Zinc Oxide Films on SiO&lt;sub&gt;2&lt;/sub&gt;/Si Substrate by Sol–Gel Spin Coating Method for pH Measurement

This In this work, zinc oxide film was deposited onto the SiO2/Si substrate with low-cost sol-gel spin coating method. Zinc oxide thin film was deposited on the silver interdigit elctrodes for the pH measurement. The surface morphology and microstructures of the deposited zinc oxide films were analyzed by field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). Whereas the crystallinity and structure of the zinc oxide films were determined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The measurement at various pH values, which were ±1 above and below of the neutral pH had been conducted with a real time dielectric analyzer measurement. It was observed that the increase in pH would decrease the capacitance of the device.

Ethanol-enriched low-pressure chemical vapor deposition ZnO bilayers: Properties and growth—A potential electrode for thin film solar cells

Ethanol is used as a precursor during the growth of zinc oxide (ZnO) by low-pressure chemical vapor deposition (LPCVD). By adding ethanol, the surface of the deposited ZnO layer is flattened and its roughness is decreased about sevenfold. The layers become increasingly stressed and their resistivity grows significantly. We propose an explanation for the observed behavior based on the catalytic decomposition of ethanol at the ZnO surface and on the growth of selected crystal planes. By using ethanol for the last 10% of the total ZnO layer growth only, sheet resistance is maintained and roughness is slightly decreased. Our results indicate that such LPCVD ZnO bilayers could be a promising method to modify the ZnO surface morphology before cell deposition, thus, providing an alternative to argon plasma treatment, which is typically reported to improve solar cell parameters such as open-circuit voltage and fill factor.

Optimization of the Asymmetric Intermediate Reflector Morphology for High Stabilized Efficiency Thin n-i-p Micromorph Solar Cells

This paper focuses on our latest progress in n-i-p thin-micromorph solar-cell fabrication using textured back reflectors and asymmetric intermediate reflectors, both deposited by low-pressure chemical vapor deposition of zinc oxide. We then present microcrystalline bottom cells with high crystallinity, which yield excellent long wavelength response for relatively thin absorber thickness. In a 1.5-μm-thick μc-Si:H single-junction n-i-p solar cell, we thus obtain a short-circuit current density of 25.9 mA·cm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $^{-2}$</tex></formula> , resulting in an initial cell efficiency of 9.1%. Subsequently, the roughness of the intermediate reflector layer is adapted for the growth of high-performance amorphous silicon (a-Si:H) top cells. Combining bottom cells with high current, an optimal intermediate reflector morphology and a 0.22-μm-thick a-Si:H top cell, we reach high initial open-circuit voltages of 1.45 V, and we obtain a stabilized cell with an efficiency of 11.1%, which is our best stable efficiency for n-i-p solar cells.

Effect of Deposition Temperature on the FTIR Absorbance of Zinc Oxide Thin Films Produced by MOCVD

Metalorganic chemical vapour deposition (MOCVD) method was used to deposit zinc oxide thin films on soda-lime glass substrates at temperatures of 330°C, 360°C, 390°C and 420°C, using zinc acetate as the precursor. Compressed air was used as the carrier gas at a flow rate of 2.5 dm3 per minute. Each deposition was carried out for two hours under atmospheric pressure. FTIR measurements were subsequently made on the produced thin films to determine their struc ture and trend with deposition temperatures. The measurements showed the presence of lingering functional groups of organic, oxide and nitride origin, which prominently moderated the natural vibrational modes of the material within their respective affiliate wavenumbers, as well as three slight but evident trends in absorbance peaks, cut-off wave length, and the existence of the functional groups with temperature. The produced materials are expected to be useful for enhanced solar cells, triggering sensor devices, p-doped zinc oxide, etc.

Solvent-free synthesis of supported ZIF-8 films and patterns through transformation of deposited zinc oxide precursors

Film processing and patterning techniques are a prerequisite to fully exploit the potential of metal–organic frameworks (MOFs) in integrated applications. We report a solvent-free approach for the synthesis of ZIF-8 thin films and patterns through the reaction of ZnO films with melted 2-methylimidazole.

Influence of Annealing on Properties of Spray Deposited ZnO Thin Films

Zinc Oxide (ZnO) thin films were deposited on glass substrates via the spray pyrolysis technique. The films were subsequently annealed in ambient air from 300°C to 500°C. The morphology and structural properties of the thin films were studied by field emission scanning electron microscope (FESEM), atomic force microscopy (AFM), and X‐ray diffractometry (XRD) techniques. Electrical resistivity of the thin films was measured using a data acquisition unit. The optical properties of the films were characterized by UV‐vis spectroscopy and photoluminescence (PL) technique. X‐ray diffraction data showed that the films were grown in the (002) direction with a hexagonal wurtzite structure. The average grain size ranged from 15 to 27 nm. Increasing annealing temperatures resulted in larger grain sizes and higher crystallinity, with the surface roughness of annealed films being more than twice if compared to unannealed film. The electrical resistivity of the films decreased with the increasing annealing temperature. The UV and visible band emissions were observed in the photoluminescence spectra, due to exciton and defect‐related emissions, respectively. The transmission values of the films were as high as 90% within the visible range (400–700 nm).

Conductive zinc oxide thin film coatings by combustion chemical vapour deposition at atmospheric pressure

We have established a combustion chemical vapour deposition (C-CVD) system for the deposition of zinc oxide (ZnO) at atmospheric pressure. This C-CVD process has the advantage of a short exposure of the substrates to the flame. It is also potentially applicable as an inline coating system.Fundamental studies were performed on undoped ZnO. The specific resistivity of these layers strongly depends on the film thickness and decreases with increasing thickness. As the lowest resistivities, values of about 2.0·10−1Ωcm are achieved. Ultra-violet photoemission spectra show the valence band structure of the deposited ZnO. The work function and valence band edge were determined. UV–vis spectra were taken to investigate the transmission of the coated glass samples. From these spectra the band gap energy was obtained. Raman spectroscopy as well as infrared spectroscopy confirmed the presence of ordered ZnO crystallites. The X-ray diffraction verified this result and illustrates the hexagonal structure. In the mid-infrared range precursor deposits were detected for low substrate temperatures.

Aerosol assisted fabrication of carbon nanotube/zinc oxide arrays for a field emission device

Aerosol deposition of zinc oxide (ZnO) nanoparticles was used to catalyze a silicon substrate site-selectively for a carbon nanotube (CNT) growth. An ambient spark discharge was used to produce aerosol ZnO nanoparticles, and the particle deposition on the substrate through a shadow mask was enhanced by thermophoresis. The ZnO-deposited substrate was then loaded into a chemical vapor deposition chamber, resulting in the formation of CNT/ZnO arrays. The turn-on field of an emission device constructed with the CNT/ZnO arrays was 1.7Vμm−1 at a current of 2μA, which was lower than that of the common CNT arrays.

ZnO Nano/Microstructures Grown by Laser Assisted Flow Deposition

Nano/microstructures of zinc oxide (ZnO) were grown by the laser assisted flow deposition (LAFD) method. This new process has proved to be very efficient, allowing high yield ZnO deposits at high-rate applicable to large-scale substrates. Laser local heating promotes fast ZnO decomposition and recombination under a self-catalytic vapour–liquid-solid mechanism for the nucleation and growth. Three types of ZnO morphologies were obtained according to the temperature/oxygen availability inside the growth chamber. The morphology can also be controlled adding rare-earth elements to the initial composition. Particularly, tetrapod morphology was obtained by europium oxide addition to the precursors. The structural and microstructural characterizations confirm the good crystallinity of the wurtzite structure. The photoluminescence spectroscopy revealed high optical quality of the as-grown ZnO. Specifically, the free exciton recombination and a strong near band edge recombination due to donor bound exciton transitions can be clearly recognized, although deep level emission in the green spectral region is present.

Galvanostatic deposition of ZnO thin films

In this study we report on the galvanostatic deposition of zinc oxide (ZnO) thin films from an aqueous chloride based solution. The influence of the deposition conditions (bath temperature, supporting electrolyte (KCl) concentration and current density) on the properties of ZnO 2D layers is studied. It has been found that to obtain good quality films the bath temperature should be above 60°C. At lower deposition temperatures, porous-like layers formed by small grains of ZnO with poor optical properties are obtained. The supporting electrolyte concentration ([KCl]) influences the film composition, morphology and optical properties due to the change of species reparation in the solution. It is shown that the increased KCl concentration is the main cause for surface defects, which are accounted to the electrode passivation due to the Zn2+ ions complexation. The applied deposition current density is another parameter permitting to prepare 2D layers with desired surface morphology and thickness. ZnO thin films deposited at high temperature (70°C) and lower [KCl] are homogeneous and compact (without surface defects) which permits their integration in solar cells and other optoelectronic devices. ZnO nanowires were electrodeposited on these thin films. It has been found that the nanowire dimensions could be tailored by the seed layer thickness and morphology.

Active Layer Thickness Effects on the On-State Current and Pulse Measurement at Room Temperature on Deposited Zinc Oxide Thin-Film Transistors

This study reports on the fabrication of thin-film transistors (TFTs) with transparent zinc oxide (ZnO) semiconductors serving as the active channel and silicon dioxide (SiO2) serving as the gate insulator. The ZnO films were deposited by radiofrequency magnetron sputtering at room temperature. Moreover, the effects of channel thickness on the structural and pulse current–voltage characteristics of ZnO TFTs using a bottom gate configuration were investigated. As the channel thickness increased, the crystalline quality and the channel conductance were enhanced. The electrical characteristics of TFTs exhibited field-effect mobilities of 8.36 cm2/Vs to 16.40 cm2/Vs and on-to-off current ratios of 108 to 107 for ZnO layer thickness of 45 nm and 70 nm, respectively. The threshold voltage was in the range of 10 V to 31 V for ZnO layer thicknesses from 35 nm to 70 nm, respectively. The low deposition and processing temperatures make these TFTs suitable for fabrication on flexible substrates.

ZnO/ITO interface nanostructure films for the photocatalytic degradation of a textile dye

We have produced zinc oxide (ZnO) photocatalyst nanostructure films by the deposition of ZnO onto indium tin oxide (ITO) glass substrates. A polyethylene glycol (PEG) aided sol–gel route using zinc acetate, 2-methoxyethanol and monoethanolamine, followed by spin coating and heat treatment, was utilized to form these photocatalyst films. The obtained interface nanostructure films were characterized with X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The photocatalytic activity of the films were also investigated using Direct Sky Blue 5B (C. I. Direct Blue 15) as a model organic compound under UV light irradiation. The influence of operating parameters, including the pH of the solution and the number of ZnO layers on Direct Sky Blue 5B degradation, were examined. An interesting decolorization performance was observed in the ZnO/ITO thin films produced using 2 % PEG.

Improving the field emission of graphene by depositing zinc oxide nanorods on its surface

Zinc oxide (ZnO) nanorods were vertically grown on the surface of graphene sheets by chemical vapor deposition, and their use in a field emission device was demonstrated. In comparison with pristine graphene, the graphene/ZnO nanorod hybrid structure exhibited efficient field emission with low turn-on field, low threshold field, high emission spot density, high field enhancement factor and excellent emitting stability. It is proposed that the introduction of mid-density ZnO nanorods on the surface of graphene sheets can increase the number of emitters, enhance tunneling probability, and lead to optimized field emission for the hybrid emitters. The results showed that the field emission properties of graphene can be tailored by growing various ZnO nanostructures on its surface.

Zinc oxide-linen fibrous composites: morphological, structural, chemical and humidity adsorptive attributes

The main result and characterizing aspect of the research consists of the effectiveness of novel ZnO-linen fibrous composites synthesized by means of hydrothermal deposition of zinc oxide onto linen fibers, with the assistance of two surfactants. This has a direct implication on the relationship between the morphological, structural and chemical attributes and water vapor sorption-desorption behavior. Methodology consists of the hydrothermal synthesis of zinc oxide onto linen fibrous substrates previously grafted with MCT-β-CD (MonoChloroTriazinyl–β-CycloDextrin) via a hydrothermal process. The morphological, structural and chemical properties of the samples were examined, in terms of a co-assisted investigation system: SEM images for the morphology, EDX analysis for surface composition, FTIR spectroscopy and X-ray diffractometry for structural samples features. Dynamic vapor sorption (DVS) analysis will complete this study. According to the results provided by the characterization technique, the uniformity of the fabric coated with ZnO powder hydrothermally synthesized with assistance of CTAB (Cetyl TrimethylAmmonium Bromide) is better than that of ZnO powder hydrothermally synthesized in the presence of Pluronic P123 and possesses good washing fastness. X-ray diffraction results have indicated that the composites exhibited a more ordered structure and higher water vapor sorption-desorption capacity (obtained by DVS analysis) compared with those of the reference fibrous linen supports.