Thickness Of ZnO Layer Research Articles

Controllable Synthesis, Magnetic Properties, and Enhanced Photocatalytic Activity of Spindlelike Mesoporous α-Fe2O3/ZnO Core–Shell Heterostructures

Mesoporous spindlelike iron oxide/ZnO core-shell heterostructures are successfully fabricated by a low-cost, surfactant-free, and environmentally friendly seed-mediate strategy with the help of postannealing treatment. The material composition and stoichiometry, as well as these magnetic and optical properties, have been examined and verified by means of high-resolution transmission electron microscopy and X-ray diffraction, the thickness of ZnO layer can be simply tailored by the concentration of zinc precursor. Considering that both α-Fe2O3 and ZnO are good photocatalytic materials, we have investigated the photodegradation performances of the core-shell heterostructures using organic dyes Rhodamin B (RhB). It is interesting to find that the as-obtained iron oxides/ZnO core-shell heterostructures exhibited enhanced visible light or UV photocatalytic abilities, remarkably superior to the as-used α-Fe2O3 seeds and commercial TiO2 products (P25), mainly owing to the synergistic effect between the narrow and wide bandgap semiconductors and effective electron-hole separation at the interfaces of iron oxides/ZnO.

Guided-wave acoustooptic Bragg diffraction in silica waveguides

A rigorous theoretical analysis of the optical guided-wave, surface acoustic wave and AO Bragg interaction between the optical guided-wave and surface acoustic wave in Si-based silica waveguide is presented. The mechanical displacement, strains and acoustic power of the SAW are studied for various SAW frequencies and ZnO layer thickness. The effects of SAW frequency, ZnO layer thickness, waveguide thickness, acoustic power and acoustic apertures on the AO Bragg interaction are provided as well.

ZnO/Cu/ZnO multilayer films: Structure optimization and investigation on photoelectric properties

A series of ZnO/Cu/ZnO multilayer films has been fabricated from zinc and copper metallic targets by simultaneous RF and DC magnetron sputtering. Numerical simulation of the optical properties of the multilayer films has been carried out in order to guide the experimental work. The influences of the ZnO and Cu layer thicknesses, and of O2/Ar ratio on the photoelectric and structural properties of the films were investigated. The optical and electrical properties of the multilayers were studied by optical spectrometry and four point probe measurements, respectively. The structural properties were investigated using X-ray diffraction. The performance of the multilayers as transparent conducting coatings was compared using a figure of merit. In experiments, the thickness of the ZnO layers was varied between 4 and 70nm and those of Cu were between 8 and 37nm. The O2/Ar ratios range from 1:5 to 2:1. Low sheet resistance and high transmittance were obtained when the film was prepared using an O2/Ar ratio of 1:4 and a thickness of ZnO (60nm)/Cu (15nm)/ZnO (60nm).

Texture‐etched ZnO as a versatile base for optical back reflectors with well‐designed surface morphologies for application in thin film solar cells

AbstractZnO layers with a wide range of surface morphologies were studied for applications in thin film silicon solar cells. The texture of ZnO layers, achieved by chemical etching, was measured by atomic force microscopy (AFM) and statistically analyzed in terms of the roughness, the crater depth, the crater diameter, and the crater opening angle. We present a method to independently tune the lateral and vertical dimensions of the etched crater structures by combined variations of ZnO layer thickness and etching time. The optical scattering properties of the textured ZnO layers are investigated. The effects of these morphologies on the performance of the solar cells, prepared in both p–i–n and n–i–p configurations are analyzed. For the latter cell type the roughness is introduced at the back side, thus the cell does not sense ZnO absorption and conductivity of the different morphologies. The link between the morphology, the optical properties of ZnO layers, and the solar cell performance is discussed.

A study of thin film encapsulation on polymer substrate using low temperature hybrid ZnO/Al2O3 layers atomic layer deposition

Hybrid ZnO/Al2O3 layers grown by atomic layer deposition (ALD) at extremely low temperature (60 °C) have been investigated as thin film encapsulations (crystalline ZnO and amorphous Al2O3 films) on polymer substrates. All single and laminated film thicknesses are approximately 60 nm. As the thickness of ZnO layer decreased from 60 nm to 0 nm, the physical properties of laminated structures were systematically manipulated such as film crystallinity, surface roughness, density, transmittance and stress. The multi-laminated structure with 10 nm thick ZnO and 10 nm thick Al2O3 layers exhibited very lower crystallinity, smoother surface (root mean square ∼ 0.2 nm), higher transmittance (over 90% at 550 nm wavelength) and similar film stress, to compare with these of a single ZnO film. As a transparent gas barrier layer, the multi-laminated structure with a thinner ZnO and Al2O3 had better barrier property than that of single ZnO and Al2O3 layers, showing that the water vapor transmission ratio of multi-laminated ZnO/Al2O3 layer was 10 times lower than that of the single layer.

THE OPTICAL AND ELECTRICAL PROPERTIES OF ZnO/Ag/ZnO FILMS ON FLEXIBLE SUBSTRATE

The deposition of ZnO / Ag / ZnO film on polyethylene terephthalate (PET) substrate was fabricated by DC magnetron sputtering method. The thicknesses of ZnO layers were 30 nm and Ag films' thicknesses were changed from 1 nm to 6 nm by controlled the sputtering time. This kind of film can be used as transparent conductive oxide (TCO) materials. The electrical and optical properties of composite layers were determined by Ag films. The optimum sputtering time of Ag thin films was found to be 20 s for the high optical transmittance with good electrical conductivity. The ZnO / Ag (20 s )/ ZnO layer, which has high optical transmittance of 73% at 550 nm, shows sheet resistance as low as 6.7 ohm/sq. These multilayer transparent films had low electrical resistance as the widely used transparent conductive oxide electrodes. SEM, XRD, the UV-Vis-NIR and Hall Effect measurement system were used to characterize properties of fabricated films. The reasons for the change of transmittance and resistance will also be interpreted.

Optimization of ZnO/Ag/ZnO multilayer electrodes obtained by Ion Beam Sputtering for optoelectronic devices

We investigated the electrical and optical properties of ZnO/Ag/ZnO multi-layer electrodes obtained by ion beam sputtering for flexible optoelectronic devices. This multi-layer structure has the advantage of adjusting the layer thickness to favor antireflection and the surface plasmon resonance of the metallic layer. Inserting a thin (Ag) metallic layer between two (ZnO) oxide layers decreases the sheet resistance while widening the optical transmittance window in the visible. We found that the optimal electrode is made up of a 10nm thin Ag layer between two 35nm and 20nm thick ZnO layers, which resulted in a low sheet resistance (Rsq = 6 Ω/square), a high transmittance (T≥80% in the visible) and the highest figure of merit of 1.65×10-2 square/Ω.

Impact of ZnO gate interfacial layer on piezoelectric response of AlGaN/GaN C-HEMT based ring gate capacitor

We report on a piezoelectric response investigation of AlGaN/GaN circular high electron mobility transistor (C-HEMT) based ring gate capacitor as a new stress sensor device to be potentially applied for dynamic high-pressure sensing. A ring gate capacitor of C-HEMT with an additional ZnO gate interfacial layer was used to measure the changes in the piezoelectric charge induced directly by the variation of piezoelectric polarization of both gate piezoelectric layers (AlGaN, ZnO) for harmonic loading at different excitation frequences. Our experimental results show that about 10 nm thick piezoelectric ZnO layer grown on ring gate/AlGaN interface of C-HEMT can yield almost a 60% increase in the piezoelectric detection sensitivity of the device due to its higher piezoelectric coefficient. A three-dimensional CoventorWare simulation is carried out to confirm the increase in the measured piezoelectric response of ZnO based ring gate capacitor of C-HEMT.

Thickness dependence of the resistive switching behavior of nonvolatile memory device structures based on undoped ZnO films

The resistive switching behavior of Al/ZnO/Al layered memory device structures was investigated in connection with varying ZnO layer thickness and related changes in crystallinity and concentration of oxygen-related defects. It was observed that, with increasing thickness, the crystallinity of the ZnO layer was improved and the concentration of oxygen-related defects within the layer increased. While the device showed unipolar switching characteristics, the current–voltage hysteresis was dependent on the thickness of the ZnO layer. In particular, the set voltage gradually increased with increasing layer thickness in the high resistive state whereas the reset voltage remained almost constant in the low resistive state. The observed operation characteristics of the device structures in relation to the crystallinity and oxygen-related defect concentration of the ZnO layer suggest that extended defects such as grain boundaries and dislocations play important roles in determining device performances.

The effect of Mg 0.1Zn 0.9O layer thickness on optical band gap of ZnO/Mg 0.1Zn 0.9O nano-scale multilayer thin films prepared by pulsed laser deposition method

Epitaxial ZnO/Mg 0.1Zn 0.9O (MZO) nano-scale multilayer thin films were prepared on Al 2O 3 (0001) substrates by pulsed laser deposition. The ZnO/MZO multilayer thin films were grown by stacking alternate layers of ZnO and Mg 0.1Zn 0.9O with a laser fluence, repetition rate, substrate temperature and oxygen partial pressure of 3 J/cm 2, 5 Hz, 600 °C and 3.8 × 10 − 7 Pa, respectively. The thickness of an individual ZnO layer was maintained at 3 nm, whereas that of the MZO layers was varied from 3 nm to 15 nm. Cross-sectional transmission electron microscopy revealed alternating layers of bright and dark contrast, indicating the formation of a ZnO/MZO multilayer. X-ray diffraction results showed that multilayer thin films were epitaxially grown as a hexagonal wurzite phase with orientation relationship of ( 0001 ) [ 10 1 ¯ 1 ] multilayer | | ( 0001 ) [ 10 1 ¯ 1 ] substrate . The 2θ value of the (0002) peak of the ZnO/MZO multilayer thin films increased from 34.30° to 34.71°, indicating that Mg is replaced with Zn in the hexagonal lattice in the MZO of ZnO/MZO multilayer. UV–visible spectroscopy showed a systematic increase in the band gap of the ZnO/MZO multilayer thin films from 3.34 eV to 3.70 eV with increasing MZO layer thickness, which suggests that the band gap energy of a ZnO/MZO multilayer thin film can be controlled by varying the thickness of each constituent layer.

Fabrication of the p-MgZnO/ZnO/n-MgZnO double-heterojunction by MOCVD

The p-MgZnO/i-ZnO/n-MgZnO double-heterojuntion was fabricated on GaAs (100) substrate by photon-assistant metal-organic chemical vapor deposition. We can found an obvious ultraviolet peak in the electroluminescence spectra and the causation has been discussed. The effects of the thickness of ZnO interlayer on the junctions properties was also analyzed. The conclusion indicated the intensity of the UV peak would increase by decreasing the thickness of ZnO interlayer. The thickness of ZnO layer had important impact on the optical qualities of the double-heterojunction.

Fabrication of ZnO/Zn1‐xMgxO heterostructure thin films by sol‐gel spin‐coating method

AbstractZnO/Zn0.85Mg0.15O heterostructure thin films were prepared by sol‐gel spin‐coating method on sapphire (0001) substrate with different thickness of ZnO layer. X‐ray diffraction patterns showed that all the samples were preferentially oriented in [0001] direction with no phase separation. Optical transmission spectra showed the clear band‐edge absorption of ZnO and Zn0.85Mg0.15O layer, and the thickness of each layer was roughly estimated. Also, two UV emission peaks originated from each layer at 3.2 eV and 3.55 eV were observed in photoluminescence measurement. And, the emission peak at 3.2 eV of ZnO layer shifted to higher energy side with decrease in the thickness of ZnO layer. This result indicates that Mg ions slightly diffused to the ZnO layer in several nanometers of ZnO/Zn0.85Mg0.15O interface by thermal treatment in growth process (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sensitivity Enhancement of Metal Oxide Thin Film Transistor with Back Gate Biasing

In this work, a room-temperature sensing device for detecting carbon monoxide using a ZnO thin film is presented. The ZnO layer (thickness close to the Debye length), which has a polycrystalline structure, is deposited with atomic- layer deposition (ALD) on an Al2O3/Si substrate. The operating principle of the sensor is based on measuring resistance change of the ZnO thin film upon exposure to CO in ambient environment. The ZnO-based sensor shows a large response to low CO concentrations ranging from 5 to 25ppm in air with 40% relative humidity at room temperature. Results show that the sensitivity of the sensor to CO at room temperature can be modulated with a back gate voltage.

Pulsed laser deposition of transparent ZnO/MgO multilayers

We report on the structural, optical and electrical properties of ZnO/MgO multilayers grown by pulsed laser deposition technique. The film thickness of ZnO sublayer ( t ZnO) was found to have great impact on the properties of ZnO/MgO multilayers. Investigations reveal the structural phase transition from wurtzite phase to cubic phase with corresponding decrease in ZnO thickness. The optical transmittance of the multilayers is over 80% in the visible region and there is a gradual shift of absorption edge towards a longer wavelength with corresponding increase in ZnO sublayer thickness. Two absorption bands at around 400 nm and 270 nm were observed in the transmission spectra of ZnO/MgO multilayers for similar ZnO and MgO layer thickness, which has been ascribed to phase separation to hexagonal and cubic phases. The calculated optical band gap E g shows a widening from 3.51 eV to 6.23 eV with corresponding decrease in ZnO sublayer thickness from 100 nm to 23 nm, which in turn leads to an increase in resistivity in ZnO/MgO multilayers. These results provide important information for the design and modeling of ZnO/MgO optoelectronic devices due to their adjustable bandgap energies.

Extended soft X-ray emission spectroscopy: quantitative assessment of emission intensities

Soft X-ray emission spectroscopy (SXES) in the energy range between 150 eV and 1500 eV has typical attenuation lengths between tens and a few hundred nanometres. In this work the transmission of soft X-rays in synchrotron-based SXES has been quantitatively analysed using specially prepared layer samples. The possibility of extending the standard qualitative analysis of SXES by exploiting the information underlying the emission intensity was examined for thin layer structures. Three different experiment series were accomplished with model layer systems based on different sulfur-containing substrates: (i) MoS(2), (ii) CuInS(2), (iii) Cu(In,Ga)(S,Se)(2). The absorption of the S L(2,3) emission line by ZnO cover layers of up to 80 nm thickness was monitored and compared with theoretical expectations. By comparison with a reference intensity recorded from a bare substrate, the attenuation of the S L(2,3) emission could be used to accurately determine the ZnO overlayer thickness up to a critical thickness, depending on the set-up and the net S L(2,3) emission intensity. The results from these local energy-resolved spot measurements were compared with spatially resolved scans of the integral S L(2,3) emission intensity over areas of several mm(2). In the scan images the attenuation of the S L(2,3) emission intensity clearly reflects the local ZnO layer thickness. From the attenuation the ZnO layer thicknesses were calculated and compared with ellipsometric measurements and were found to be in excellent agreement. These results demonstrate the benefits of a quantitative analysis of SXES, making it an even more powerful tool for examining buried interfaces and for monitoring lateral inhomogeneities.

AlN/ZnO/diamond waveguiding layer acoustic wave structure: Theoretical and experimental results

We present a theoretical calculation and experimental results for a waveguiding layer acoustic wave (WLAW). The experimental device is modeled by the finite element method (FEM) for the AlN/ZnO/diamond structure. It was found that the AlN thickness must be at least larger than 3lambda/2 to obtain negligible surface displacement. In the same way, the ZnO thickness for a fixed value of AlN thickness at 2lambda must be larger than lambda/4 to confine the acoustic wave. The electromechanical coupling of the wave presents an optimum around lambda/2 for the ZnO layer thickness. A first experimental AlN/ZnO/diamond device has been developed and shows the WLAW at 412 MHz.

Improved Performance of ZnO/n-Si Solar Cells

This research is intended to improve the performance of ZnO/n-Si solar cells. The structures were fabricated using thermal evaporation techniques. The indium dopant at suitable heat treatment is used to enhance the electrical characteristics of ZnO layer resulting in reducing atmospheric condition to change the stiochiometry of ZnO layer. The electric properties of the fabricated samples are dependent on many parameters such as annealing temperature, ZnO layer thickness, Indium layer thickness and temperature. The indium layer were deposited at different thickness (10-30) nm during the fabrication of the ZnO/n-Si solar cells. The resultant samples has been studied and the results obtained show an improvement in the efficiency of 0.4% compared with the standard ZnO/n-Si solar cell. Keyword: ZnO/n-Si, Indium, Thermal Evaporation

Effects of coating and thermal annealing on the photoluminescence properties of ZnS/ZnO one-dimensional radial heterostructures

Influence of the thermal annealing atmosphere and the ZnO layer thickness on the photoluminescence properties of ZnS-core/ZnO-shell one-dimensional (1D) radial heterostructures was investigated. ZnS nanowires were synthesized by thermal evaporation of ZnS powders and then coated with ZnO by using the sputter-deposition technique to form the nanostructures. TEM and XRD analysis results reveal that a crystalline ZnS phase with a zinc blende structure and a crystalline ZnS phase with an wurtzite structure coexist in the cores whereas amorphous ZnO exists in the shells. Photoluminescence (PL) measurements at room temperature show that the green emission of the ZnS/ZnO 1D radial heterostructures is enhanced by annealing in an oxygen atmosphere due to the decrease in the concentration of oxygen vacancies in the ZnO shells, which normally absorbs the light emitted from the core, during the annealing process. In contrast, the green emission is degraded by annealing in an argon atmosphere since the light emitted from the core is absorbed more efficiently by the defects in the shell due to the crystallization of the ZnO shells during annealing. The PL emission intensity of the ZnS/ZnO 1D radial heterostructures is decreased by increasing the thickness of the ZnO shell layers due to the absorption of the light emitted from the ZnS cores by the ZnO shells or some interfacial effects.

Quasi 2D-ZnO thin film for CO sensing at room temperature

In this work, a low-power sensing device for detecting carbon monoxide at room temperature using a quasi two-dimensional (Q2D) ZnO thin film is presented. The ZnO layer (thickness of 50 nm) used in this sensing device is realized with the atomiclayer deposition (ALD) technique on an Al2O3/Si substrate. The operating principle of the sensor is based on measuring resistance change of the ZnO thin film upon exposure to CO. The ZnO-based sensor shows a large response to CO in concentrations ranging from 10 to 150 ppm in air with 40% relative humidity at room temperature. The sensor is also tested in air with varied relative humidity from 0 to 60%. Results show that the sensitivity of the sensor to CO at room temperature is reduced with increasing the relative humidity.

Dye sensitized solar cells based on vertically-aligned ZnO nanorods: effect of UV light on power conversion efficiency and lifetime

Electrodes made of vertically-aligned ZnO nanorods (NRs) have been prepared and analyzed in dye sensitized solar cells (DSC). We report a ∼20% power conversion efficiency increase during the first hours of solar cell testing at 1000 W m−2 (AM 1.5). The latter has been attributed to the physisorption/chemisorption of the N-719 dye on the ZnO NRs induced by UV-light irradiation. The ZnO NRs were grown by the hydrothermal method for 6 h obtaining a ZnO layer thickness of about 1.8 μm. The highest solar cell efficiency obtained was 0.69% after UV light irradiation (at 72 °C, 0.63 V, 2.85 mA cm−2, 0.39 FF). The effect of UV light has been monitored by UV-VIS, IV-curves and IPCE analyses with time, and has been related to the solar cell performance.