Structure Properties Of ZnO Films Research Articles

Physical properties of spray pyrolysed ZnO thin films obtained from nitrate, acetate and chloride precursors: Comparative study for Solar Cell Applications

ZnO thin films prepared using zinc chloride, zinc acetate and zinc nitrate precursors have been successfully synthesized by Spray Pyrolysis method. Films depositions were carried out on glass substrates at 350◦C. Structural properties of ZnO films were investigated by X-ray diffraction (XRD), confirming that all precursors have an Hexagonal Wurtzite structure. The obtained films were oriented along the preferential (002) crystallographic plane. The phase purity was also confirmed by X-ray photoelectron spectroscopy (XPS), Ultra Violet-Visible, and Energy Dispersive X-ray spectroscopy measurements (EDX). The optical measurement revealed that films have average transmittance of 58%, 78% and 65% for zinc chloride, zinc acetate and zinc nitrate, respectively. The band gap values obtained are 3.19, 3.17 and 3.23 eV for ZnO films using zinc acetate, zinc chloride and zinc nitrate precursors, respectively. Additionally, the refractive index and extinction coefficient of the ZnO films for all precursors have been explored.

Electrical and Structural Properties of Semi-Polar-ZnO/a-Al2O3 and Polar-ZnO/c-Al2O3 Films: A Comparative Study.

In this work, the properties of ZnO films of 100 nm thickness, grown using atomic layer deposition (ALD) on a-(100) and c-(001) oriented Al2O3 substrate are reported. The films were grown in the same growth conditions and parameters at six different growth temperatures (Tg) ranging from 100 °C to 300 °C. All as-grown and annealed films were found to be polycrystalline, highly (001) oriented for the c-Al2O3 and highly (101) oriented for the a-Al2O3 substrate. The manifestation of semi-polar-(101) and polar (001)-oriented ZnO films on the same substrate provided the opportunity for a comparative study in terms of the influence of polarization on the electrical and structural properties of ZnO films. It was found that the concentration of hydrogen, carbon, and nitrogen impurities in polar (001)-oriented films was considerably higher than in semi-polar (101)-oriented ZnO films. The study showed that when transparent conductive oxide applications were considered, the ZnO layers could be deposited at a temperature of about 160 °C, because, at this growth temperature, the high electrical conductivity was accompanied by surface smoothness in the nanometer scale. On the contrary, semi-polar (101)-oriented films might offer a perspective for obtaining p-type ZnO films, because the concentration of carbon and hydrogen impurities is considerably lower than in polar films.

ZnO Films Incorporation Study on Macroporous Silicon Structure.

In the present work, we developed hybrid nanostructures based on ZnO films deposited on macroporous silicon substrates using the sol–gel spin coating and ultrasonic spray pyrolysis (USP) techniques. The changes in the growth of ZnO films on macroporous silicon were studied using a UV-visible spectrometer, an X-ray diffractometer (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). XRD analysis revealed the beneficial influence of macroporous silicon on the structural properties of ZnO films. SEM micrographs showed the growth and coverage of ZnO granular and flake-like crystals inside the pores of the substrate. The root mean square roughness (RMS) measured by AFM in the ZnO grown on the macroporous silicon substrate was up to one order of magnitude higher than reference samples. These results prove that the methods used in this work are effective to cover porous and obtain nano-morphologies of ZnO. These morphologies could be useful for making highly sensitive gas sensors.

Influence of the thermal annealing on the morphological and structural properties of ZnO films deposited onto polyimide substrates by ink-jet printing

In this work, ZnO films were deposited onto flexible polyimide substrates by ink-jet printing nanoinks containing polyol-synthesized nanocrystals. ZnO films were annealed at 200–400 °C for 10 min and 60 min under the ambient atmosphere. The morphological (shape, size, size distribution, surface roughness), structural (phase composition, crystal structure), optical (band gap, transmission coefficients) properties and the chemical composition of the synthesized nanocrystals and the obtained films were studied. X-ray diffraction analysis, transmission and scanning electron microscopies, atomic force microscopy, Fourier-transform infrared (FTIR) and optical spectroscopies, and energy-dispersive X-ray spectroscopy (EDS) were used to study the properties of obtained ZnO materials. The films, annealed at Ta = 400 °C for ta = 60 min, and nanocrystals, synthesized for tg = 120 min, have the good fundamental characteristics for application in the microelectronic devices, especially in solar cells and thermoelectric generators.

Oxygen effect on structural and optical properties of zinc oxide

ABSTRACTThis article deals with an investigation of the effect of oxygen content on optical and structural properties of ZnO films. Zinc oxide films were deposited with the DC reactive magnetron sputtering process on Si(100) and glass substrates. ZnO films were elaborated at different oxygen flow rates from (O2) 12 to 35 sccm. The evolution of optical and structural properties as a function of O2 was investigated by X-ray diffraction, Profilometer, Field Emission Scanning Electron Microscopy (FESEM) and ultraviolet–visible. By increasing O2, the crystallite size increases from 20 to 27 nm, which leads to an enlargement in the ZnO band gap from 3.18 to 3.30 eV. At 30 sccm of O2, the films present a significant improvement in the band gap (3.30 eV). The results reveal that with increasing O2, all films show a high crystallinity in the wurtzite phase and present a (002)ZnO preferential orientation along the c-axis. ZnO exhibited a good self-texture.

Room Temperature Strong Emission and Excitonic Enhancement in Multiple‐Stacked Nano‐Porous ZnO Thin Film

Electronic and structural properties of ZnO films before and after H2 annealing treatment are studied. The initial system is smooth amorphous ZnO films that are intentionally grown at room temperature. A dramatic change is found in the crystallinity and the surface transforms to a multiple‐stacked nanoporous structure upon annealing as observed by scanning electron microscopy and X‐ray diffraction. Photoluminescence spectroscopy shows the presence of a new mid‐gap state below the first optical transition, and the annealing treatment transforms the ZnO system to more transparent film. Interestingly, it is found that the structural evolution changes the dielectric function measured by high‐resolution, angle‐dependent spectroscopic ellipsometry and this generates strong emission at ≈2.5 eV. These results show the importance of structural modification via H2 annealing to control the optical properties and electronic structure of ZnO films.

Effect of laser annealing on ZnO nanorods grown by chemical bath deposition on flexible substrate

Integration of nanostructures of semiconducting materials such as zinc oxide with flexible substrates represent a great opportunity to obtain unique sensing platform especially for the biomedical market. However, the attractive optical and electrical properties of ZnO are usually obtained by growing or annealing nanostructured films at relative high temperatures (>400 °C), which are not suitable to substrates made of polymeric materials.We demonstrate in this work that high quality ZnO nanostructures can be processed at relative low temperature (<100 °C) by combining low temperature deposition process and XeCl excimer laser (wavelength 308 nm), used to locally anneal and recrystallize ZnO without affecting the underlying polymeric substrate. We obtain unique post-annealed ZnO nanostructures, grown and processed both on rigid and flexible substrates, that show comparable optical and structural properties of ZnO films that are processed at high temperatures. We discuss the effect of the laser energy density on the nanostructure by analyzing the recrystallized ZnO films through photoluminescence and scanning electron microscopy.

Effect of Ti-doping on optical and structural properties of ZnO films grown by spin coating method

ABSTRACT ZnO films with and without Ti doping were deposited on the glass substrate by the spin coating method. Zn1-xTixO films have been investigated by the XRD, field emission scanning electron microscopy (FESEM), energy dispersive x- ray spectroscopy, UV-VIS spectroscopy and atomic force microscopy (AFM) analyses. FESEM images have shown that films surface morphology clearly altered with different Ti content. AFM measurements have shown that the root mean square roughness have increased from 6.18 nm to 12.3 nm by increasing Ti doping content. By increasing Ti concentration, the transparency of the ZnO films decreased while the optical band gap increased.

HYDROTHERMAL SYNTHESIS of ZnO FILMS and CHARACTERIZATION

In this study, ZnO films were produced by hydrothermal synthesis onto glass substrates. The structural properties of ZnO films were examined using X-ray diffraction (XRD) techniques. According to XRD results, the high quality polycrystalline ZnO films were achieved at low temperature. Spectroscopic ellipsometry (SE) technique and Cauchy-Urbach model were used to the important optic constants of films as the thickness ( d ), refractive index ( n ) and extinction coefficient ( k ). The transmittance, absorbance and reflectance spectra of films were obtained by Uv-vis spectrophotometer and optical properties were analyzed using these spectra. Also, the surface properties, roughness and electrical resistivity values were investigated by atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and four-probe technique, respectively. Finally, the characterization results of ZnO films showed that, hydrothermal synthesis allowed production of ZnO films which higher quality than other techniques at low temperature.

Comparative Study About the Structural Properties of ZnO Films Grown on Si, GaAs, And Al2O3 Substrates and a GaN Template

We report on the structural properties of ZnO films grown on (001) Si, (001) GaAs, (0001) Al 2 O 3 substrates and a (0001) GaN template by RF-sputtering. It is observed that all the ZnO films have textured structures with a preferred orientation of the c-axis, irrespective growth conditions, in terms of atomic-force microscope and wide-range X-ray diffractometer. However, it is found that the ZnO films in the ZnO-on-Si and ZnO-on-GaAs are consisted of various domains with different orientations, while the ZnO films in the ZnO-on-Al 2 O 3 and ZnO-on-GaN are consisted of a single domain with the same orientation in terms of the φ-scan of X-ray diffractometer. Moreover, it is found that the ZnO-on-GaN has smaller edge dislocation density and screw dislocation density than the ZnO-on-Al 2 O 3 , which seriously depends on substrate temperature, in terms of the ω-scan of X-ray diffractometer.

Controlled growth of c-axis oriented ZnO nanorod array films by electrodeposition method and characterization

ZnO nanorod array films were deposited from aqueous solution containing different concentrations (1×10−2M and 5×10−3M) Zn(NO3)2⋅6H2O and C6H12N4 and at different electrodeposition times (i.e., 15min, 30min, 60min, 120min and 180min) using chronoamperometry method on p-Si substrate. Surface morphology and crystal structural properties of ZnO films were investigated by XRD and FESEM to select ZnO films which have optimum properties. The highest TC(hkl) value was observed in (002) plane for the film, which is deposited at 1×10−2M and 120min. It is also observed that the highly oriented nanorods in this film are denser. Additionally, the conductivity type was determined by using Mott–Schottky which is electrochemical impedance spectroscopy method (EIS). On the other hand, to investigate the utility of obtained ZnO on p-Si (p-Si/n-ZnO) as supercapacitor electrode active material, the electrochemical storage properties of p-Si/ZnO was studied by electrochemical impedance spectroscopy and repeating chronopotentiometry methods. It is suggested from electrochemical tests results that p-Si/ZnO is a promising electrode materials for supercapacitor applications that required low voltage (<10V). Rectifiying behavior was observed from the I–V characteristic of nanorod array n-ZnO/p-Si heterojunction diode. The n value, Io and the ϕb were found to be 5.48, 1.93×10−8A and 0.75eV, respectively.

On the environmental stability of ZnO thin films by spatial atomic layer deposition

Undoped and indium-doped ZnO films have been deposited by atmospheric spatial atomic-layer-deposition (spatial-ALD). The stability of their electrical, optical, and structural properties has been investigated by a damp-heat test in an environment with 85% relative humidity at 85 °C. The resistivity of the ZnO films increased during damp-heat exposure mainly due to a sharp decrease in the carrier mobility, while the carrier density and transparency degraded only partially. The increase in resistivity can be ascribed to a degradation of the structural properties of ZnO films, resulting in a higher level of tensile stress, as indicated by x-ray diffraction analysis, and in a reduced near-ultravoilet emission level in their photoluminescence spectra. Al2O3 thin (25–75 nm) films grown by spatial-ALD at 0.2 nm/s are used as moisture barrier to effectively enhance the stability of the electrical and structural properties of the films.

The effects of solvents on the highly oriented ZnO films prepared using sol–gel method

The effects of solvents in ZnO precursor solutions on highly oriented ZnO films is studied in this work. Three different solvents, including ethanol, isopropanol and 2-methoxyethanol, are used for the preparation of ZnO film on fused quartz wafer substrates in this study. The structural properties of ZnO films are investigated by X-ray diffraction and scanning electron microscopy analysis. It is found that ZnO film formed using 2-methoxyethanol precursor solution shows a strong preferred orientation and has the smoothest surface among the films. The properties of ZnO sol solutions are also studied using the thermal gravimetric-differential thermal analysis and ultraviolet–visible spectroscopy. The absorbance spectrum of the sol using 2-methoxyethanol as solvent shows an apparent ZnO absorbance edge while the others do not, which means ZnO nano-particles are formed in the sol. The mechanism of the formation of highly oriented ZnO films using different solvents is also discussed in this paper.

Effects of substrates on the structural properties of ZnO films deposited by rf magnetron sputtering

Insulating films of silicon nitride (Si3N4) or aluminum oxide (Al2O3) were grown on dry-oxidized Si wafers, and then ZnO was deposited on the insulating films. The crystallographic properties of the films were studied by X-ray diffraction (XRD), and their surface morphologies were investigated by atomic force microscopy (AFM). A high-resolution micro-Raman spectrometer excited with a 514.5nm argon laser was used to evaluate the quality of the ZnO films. Next, leakage currents flowing through the insulating films were measured. Finally, Auger electron spectroscopy (AES) was employed to track the diffusion of zinc atoms through the insulating films.

Structural properties of ZnO films grown by picosecond pulsed-laser deposition

Zinc oxide thin films have been grown on c-cut (0001) and r-cut (1 1¯ 0 2) sapphire substrates by pulsed-laser deposition using a Nd:YAG laser operating at 355nm in picosecond regime (pulse duration: 42ps). The composition and the structural properties of the films have been investigated by scanning electron microscopy, Rutherford backscattering spectroscopy and X-ray diffraction according to different substrate temperatures. The RBS spectra show a Zn/O ratio close to 1.1 with a constant in-depth oxygen concentration. The XRD diagrams in Bragg–Brentano geometry display a preferred orientation depending on the used substrate. The large width of XRD peaks is indicative of a small coherence length. In addition, according to the pole figures recorded in asymmetric configuration, epitaxial relationships between substrate and film are evidenced. An increase in the substrate temperature leads to a film crystalline quality improvement. The results are discussed regarding the well-known properties of ZnO films obtained by nanosecond and femtosecond PLD.

The Optical and Structural Properties of ZnO Films Prepared by Spray Pyrolysis

The Optical and Structural Properties of ZnO Films Prepared by Spray Pyrolysis

Synthesis and structural properties of ZnO films grown by spray pyrolysis of zinc acetate solution

Synthesis and structural properties of ZnO films grown by spray pyrolysis of zinc acetate solution

Highly conductive and optically transparent GZO films grown under metal‐rich conditions by plasma assisted MBE

AbstractWe demonstrate a critical effect of a metal‐to‐oxygen ratio on the electrical, optical, and structural properties of ZnO films heavily doped with Ga (carrier concentration in the range of 1020–1021 cm–3) grown by plasma‐assisted molecular beam epitaxy. The as‐grown layers prepared under the metal‐rich conditions exhibited resistivities below 3 × 10–4 Ω cm and an optical transparency exceeding 90% in the visible spectral range as well as a large blue shift of the transmission/absorption edge attributed to the Burstein–Moss shift of the Fermi level deep into the conduction band, indicating high donor concentration. In contrast, the films grown under the oxygen‐rich conditions required thermal activation and showed inferior properties. Furthermore, electrical measurements point to the nonuniform depth distribution of free carriers. An oxygen‐pressure‐dependent surface disordering is suggested to be responsible for the drastic effect of the metal‐to‐oxygen ratio on the film properties. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Study of structural and optical properties of ZnO films grown by pulsed laser deposition

Wurtzite zinc oxides films (ZnO) were deposited on silicon (0 0 1) and corning glass substrates using the pulsed laser deposition technique. The laser fluence, target–substrate distance, substrate temperature of 300 °C were fixed while varying oxygen pressures from 2 to 500 Pa were used. It is observed that the structural properties of ZnO films depend strongly on the oxygen pressure and the substrate nature. The film crystallinity improves with decreasing oxygen pressure. At high oxygen pressure, the films are randomly oriented, whereas, at low oxygen pressures they are well oriented along [0 0 1] axis for Si substrates and along [1 0 3] axis for glass substrates. A honeycomb structure is obtained at low oxygen pressures, whereas microcrystalline structures were obtained at high oxygen pressures. The effect of oxygen pressure on film transparency, band gap E g and Urbach energies was investigated.

Growth and structural properties of ZnO films on (10−10) m-plane sapphire substrates by plasma-assisted molecular beam epitaxy

Growth and structural properties of ZnO films on (10−10) m-plane sapphire substrates by plasma-assisted molecular beam epitaxy were studied. The ZnO films were grown at a wide range of growth temperature of 100–800°C. From the x-ray diffraction θ-2θ measurements, overwhelming ZnO (10−10) reflection was confirmed in addition to the very weak (0002) and (10−13) reflections. The sample grown at 500°C showed the highest purity with the very weak (10−13) and the negligible (0002) reflections. The full widths at half maximum (FWHMs) for the (10−10) x-ray rocking curves (XRCs) with ϕ=0° is much higher than those for with ϕ=90°, which indicates that the films have an anisotropic structural property. The FWHMs for the off-axis (10−11) XRCs were larger than by about 0.1° than those for the (10−10) XRCs with ϕ=90°. Two distinct features of the striated surface morphology with the grains along the ZnO ⟨0001⟩ direction and the inhomogeneity with the appearance of islands on the surface were observed. Detailed investigation on the microstructure by transmission electron microscopy revealed that ZnO (10−13) inclusion was present above the ZnO∕Al2O3 interface not at the interface. The ZnO (10−13) inclusion did reach to the top surface, which is believed to the cause for the extra spots in the reflection high energy electron diffraction patterns and the inhomogeneous islands in the atomic force microscope images.