Thin ZnO Layer Research Articles

Temperature dependent dielectric properties of Au/ZnO/n-Si heterojuntion

Owing to importance of ZnO in electronics, Au/ZnO/n-type Si device was fabricated to investigate its dielectric properties by aid of capacitance-conductance-voltage measurements. While the ZnO thin film layer on the n-type Si was formed by atomic layer deposition (ALD) technique, the rectifying and ohmic contacts were obtained by thermal evaporation. The surface morphology of ZnO thin film was characterized using atomic force microscopy (AFM) to show its compatibility as interfacial layer in the Au/ZnO/n-type Si device. The dielectric properties of the device were examined in terms of dielectric parameters such as dielectric constant (ε′), dielectric loss (ε″), loss tangent (tan δ), the real and imaginary parts of electric modulus (M′ and M″) and ac electrical conductivity (σ) depending on applied voltages (from −1 to 2 V) and temperatures (from 140 K to 360 K) ranges. The results have revealed that interfacial polarization and charge carriers are the important parameters to affect the dielectric properties of the device with changing temperature. The device can be used at wide range temperatures for diode applications.

Enhanced electrical properties of dual-layer channel ZnO thin film transistors prepared by atomic layer deposition

The thin film transistors (TFTs) with a dual-layer channel structure combing ZnO thin layer grown at 200 °C and ZnO film grown at 120 °C by atomic layer deposition are fabricated. The dual-layer channel TFT exhibits a low leakage current of 2.8 × 10−13 A, Ion/Ioff ratio of 3.4 × 109, saturation mobility μsat of 12 cm2 V−1 s−1, subthreshold swing (SS) of 0.25 V/decade. The SS value decreases to 0.18 V/decade after the annealing treatment in O2 due to the reduction of the trap states at the channel/dielectric interface and in the bulk channel layer. The enhanced performance obtained from the dual-layer channel TFTs is due to the ability of maintaining high mobility and suppressing the increase in the off-current at the same time.

Improved efficiency of ZnO hierarchical particle based dye sensitized solar cell by incorporating thin passivation layer in photo-anode

Present article describes the DSSC performances of photo-anodes prepared using hydrothermal route derived ZnO particles having dissimilar morphologies i.e. simple micro-rod and nano-tips decorated micro-rod. The surface of nano-tips decorated micro-rod is uneven and patterned which facilitate more dye adsorption and better scattering of the incident light resulting superior photo-conversion efficiency (PCE) (η ~ 1.09%) than micro-rod ZnO (η ~ 0.86%). To further improve the efficiency of nano-tips decorated micro-rod ZnO based DSSC, thin passivation layer of ZnO is introduced in the corresponding photo-anode and a higher PCE (η ~ 1.29%) is achieved. The compact thin passivation layer here expedites the transportation of photo-excited electrons, restricts the undesired recombination reactions and prevents the direct contact of electrolyte with conducting substrates. Attempt is made to understand the effect of passivation layer on the transportation kinetics of photo-excited electrons by analyzing the electrochemical impedance spectra of the developed cells.

Polypyrrole nanowires coated with a hollow shell for enhanced electrochemical performance

Conducting polymers are promising electrode materials for electrochemical capacitors, but are suffered from poor cycling stability and relatively low capacitance. Herein, a hollow shell coated on polypyrrole (Ppy) nanowires is designed and constructed with the assistance of atomic layer deposition (ALD). Ppy nanowires are firstly deposited on flexible carbon cloth by electrodeposition, then a thin sacrificial layer of ZnO and a thin shell of TiO2 are deposited uniformly on the surfaces of the nanowires. After removing the ZnO layer, a nanogap between the Ppy core and TiO2 shell is formed thus generate a hollow core-shell Ppy-TiO2 (noted as PpyʘTiO2) nanoarray. When tested as supercapacitor electrodes, the hollow core-shell nanostructure shows apparent higher capacitance and better cycling stability than the bare nanowires. Such enhancement is ascribed to the rational hollow structure design that provides enlarged surface areas and enhanced structure stability. Such hollow structure can be extended to other conducting polymers and electrodes for various electrochemical applications.

Optical properties of the plasma hydrogenated ZnO thin films

Abstract We have optimized the deposition of the highly electrically resistive undoped (intrinsic) polycrystalline ZnO thin layers on fused silica substrates by the DC reactive magnetron sputtering of metallic zinc target in argonne/oxide atmosphere and we introduced the post-deposition hydrogen plasma doping. The thickness of thin film was evaluated by reflectance interferometry using the metallographic optical microscope fiber coupled to the CCD spectrometer operating in 400-1000 nm spectral range. The optical absorption was measured by photothermal deflection spectroscopy operating in 300-1600 nm spectral range. The change of the optical absorption edge and the increase of the infrared optical absorption was detected in hydrogenated ZnO. The increase of the infrared optical absorption goes with the increase of the electrical conductivity. We conclude that the plasma hydrogenation of the intrinsic ZnO thin films is related to increase of the free carrier concentration.

Preparation and Characterization of ZnO Thin Layers with Various Percentages of Gallium Impurities

In this study, thin films of pure ZnO and doped ZnO with different percentages of gallium (0.5, 1, 2 and 4vt. %) on the glass substrates were deposited by using sol-gel method via spin coating technique at 2500 rpm, and all layers were annealed at 200°C for 1h and then Were examined their electrical, optical and structural properties. Concentration of all solution was 0.1M. The results show that the optimized layer is 0.5% GZO. By examining the transmittance spectrums we find that by doping the transparency of samples were improved and all samples in the visible areas 400-800nm are transparent. The electrical conductivity of all samples has been measured by four-point probe technique. The electrical conductivitys of pure ZnO sample and 0.5% GZO are 910-5 S/cm and 110-4 S/cm respectively. It can be a good choice for optoelectronic applications. Also X-ray diffraction results showed that diffraction peaks of 0.5% GZO sample have a small changes towards lower angles compared to the diffraction peaks of ZnO.

Performance Enhancement via Incorporation of ZnO Nanolayers in Energetic Al/CuO Multilayers.

Al/CuO energetic structure are attractive materials due to their high thermal output and propensity to produce gas. They are widely used to bond components or as next generation of MEMS igniters. In such systems, the reaction process is largely dominated by the outward migration of oxygen atoms from the CuO matrix toward the aluminum layers, and many recent studies have already demonstrated that the interfacial nanolayer between the two reactive layers plays a major role in the material properties. Here we demonstrate that the ALD deposition of a thin ZnO layer on the CuO prior to Al deposition (by sputtering) leads to a substantial increase in the efficiency of the overall reaction. The CuO/ZnO/Al foils generate 98% of their theoretical enthalpy within a single reaction at 900 °C, whereas conventional ZnO-free CuO/Al foils produce only 78% of their theoretical enthalpy, distributed over two distinct reaction steps at 550 °C and 850 °C. Combining high-resolution transmission electron microscopy, X-ray diffraction, and differential scanning calorimetry, we characterized the successive formation of a thin zinc aluminate (ZnAl2O4) and zinc oxide interfacial layers, which act as an effective barrier layer against oxygen diffusion at low temperature.

Interface phenomena in magnetron sputtered Cu2O/ZnO heterostructures

The interface between ZnO and Cu2O has been predicted to be a good candidate for use in thin film solar cells. However, the high predicted conversion efficiency has yet to be fully realized experimentally. To explore the underlying causes of this we investigate the interface between ZnO and Cu2O in magnetron sputtered samples. Two different sample geometries were made: In the first set thin layers of ZnO were deposited on Cu2O (type A), while in the second set the order was reversed (type B). Using x-ray photoelectron spectroscopy (XPS), an intermediate CuO layer was identified regardless of the order in which the Cu2O and ZnO layers were deposited. The presence of a CuO layer was supported by transmission electron microscopy (TEM) results. Changes in the electron hole screening conditions were observed in CuO near the interface with ZnO, manifested as changes in the relative peak-to-satellite ratio and the degree of asymmetric broadness in the Cu 2p peak. The suppression of the Cu 2p satellite characteristic of CuO may cause the CuO presence to be overlooked and cause errors in determinations of valence band offsets (VBOs). For the type A samples, we compare four different approaches to XPS-based determination of VBO and find that the most reliable results are obtained when the thin CuO layer and the altered screening conditions at the interface were taken into account. The VBOs were found to range between 2.5 eV and 2.8 eV. For the B type samples a reduction of the Cu 2p-LMM Auger parameter was found as compared to bulk Cu2O, indicative of quantum confinement in the Cu2O overlayer.

Corrigendum: Chemical Activity of Thin Oxide Layers: Strong Interactions with the Support Yield a New Thin-Film Phase of ZnO.

Small Cu particles supported on and most likely activated by a ZnO substrate are the active component in the industrial catalyst used to convert syngas (H2, CO, CO2) into methanol, the third most important chemical product worldwide. Although a topic of intense research, the nature of the active site is still under debate. Recently, it has been pointed out that Zn atoms present at the surfaces of the Cu particles exhibit pronounced chemical activity and could explain some of the experimental findings. Another interesting suggestion is the presence of a thin layer of ZnOx species which forms on the surface of the Cu particles under reaction conditions. The importance of such thin oxide layers on the surface of metals under reaction conditions has already been pointed out in other contexts, where it was found that their chemical properties may differ substantially from those of the corresponding bulk oxides. In the case of ZnO this question is particularly interesting, since strong interactions between ZnO and the supporting metal have been reported for ZnO/ Cu and in recent work thin layers of ZnO have been shown to adopt a depolarized, graphitic structure, ZnO(gr), different from the wurtzite-type bulk. The properties of oxide thin films supported on metal substrates have been successfully studied in a number of cases, for example, for thin aluminum oxide films grown by oxidation of Ni/Al alloys. In contrast, the chemical activity of ZnO thin films supported on Cu single crystals has been investigated in a few cases only. Maroie et al. have investigated the adsorption and oxidation processes for single-crystal brass(110), brass(100), and brass(111) surfaces by X-ray photoelectron spectroscopy (XPS). Brass(110) and brass(111) show the same behavior with regard to the interaction with oxygen: the dissociative adsorption of oxygen on the surface is followed by the growth of thin ZnO layers. Wiame et al. reported that after oxidation of (111)-oriented Cu0.7Zn0.3 samples at room temperature the surface is covered by ZnO islands; it was suggested that these islands have (0001) and (0001) surface terminations. A more detailed characterization of the chemical properties of the thin ZnO layers was not carried out in this early work. In the present paper we report a detailed multitechnique investigation of a brass(111) single-crystal substrate (Cu/Zn ratio 9:1) subjected to different oxidation procedures using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) under ultrahigh vacuum (UHV) conditions. The experimental findings are then interpreted by comparison with the results of a rather extensive set of density functional theory (DFT) calculations. Our results reveal the growth of thin ZnO adlayers with chemical properties that are markedly different from those of normal, wurtzite-type ZnO substrates. XPS data recorded for the brass(111) surface before and after different oxidation procedures for two different exit angles of the photoelectrons are shown in Figure 1. Since it is difficult to discriminate between Cu and Cu on the basis of XPS data, also the corresponding results from Auger electron spectroscopy (AES) are shown. For the clean brass(111) substrate the data indicate a Zn atom concentration of 5%, clearly lower than the 10% expected based on the bulk Cu/Zn ratio. Upon oxidation, the XPS data reveal an increase of the surface Zn concentration. Since it is a crucial question whether, in addition to Zn, also Cu or Cu is present, we have carefully analyzed the XPS and AES data. Neither in the Cu2p XPS data nor in the Cu L3M45M45 Auger data were the characteristic signatures of Cu or Cu species resulting from an oxidation of copper atoms detected. Cu exhibits a L3M45M45 peak at electron kinetic energies of 915 eV– 917 eV, which is clearly absent in the present data (see Figure 1). This observation, which agrees with the conclusions presented in a previous study by Rameshan et al., is expected, since in the presence of the less noble Zn one would expect the formation of ZnO to precede that of CuxO. Oxidation at elevated temperatures results in a substantial increase of the Zn signal, revealing the formation of thicker ZnO adlayers. The thickness of these thin ZnO layers was determined from the intensity of the Zn2p3/2 and Cu2p3/2 XPS signals. Exposure of the samples to 500 L of O2 at room temperature yields a ZnO adlayer with an average thickness of about 1.7 , consistent with the presence of a monolayer. More extended exposures to oxygen at room temperature did not result in a significant further increase of the thickness of the ZnO layer. Even the oxidation of the brass substrate at [*] Dr. V. Schott, Dr. A. Birkner, Dr. M. Xu, Dr. Y. Wang Chair of Physical Chemistry Ruhr-University Bochum (Germany)

Electrosprayed BiVO4 nanopillars coated with atomic-layer-deposited ZnO/TiO2 as highly efficient photoanodes for solar water splitting

We report the fabrication and the performance in photoelectrochemical water splitting of thin films of electrostatically sprayed nanotextured bismuth vanadate (BiVO4) pillars coated with thin ZnO/TiO2 passivation layers formed by atomic layer deposition. The thin ZnO and TiO2 layers deposited on the BiVO4 nanopillars formed a heterostructure that promoted electron–hole separation and the migration of electrons toward the ITO substrate. The photocurrent density (PCD) of the ZnO/TiO2 coated BiVO4 was 2.5 times higher (2.25mA/cm2 at 1.2V (versus Ag/AgCl)) than that of pristine BiVO4 (0.9mA/cm2 at 1.2V (versus Ag/AgCl)). We present incident/absorbed photon-to-current efficiency and electrochemical impedance measurements confirming that this improvement is a result of the heterojunction produced by the conformal ZnO/TiO2 coating and discuss the mechanism of this dramatic enhancement of PCD.

Growth dynamics of ZnO nanowire on a fiber-tip air bubble

We demonstrate a novel method of online monitoring of ZnO nanowire growth by an optical method. Nanowires were grown on the surface of an optical fiber tip and their effect on the spectral characteristics of a fiber-tip Fabry-Perot interferometer (FPI) was investigated. The interference fringe of the fiber tip yielded a linear red shift against the ZnO nanowire growth. Results also indicated that the ZnO thin layer has a stronger correlation with the reflection spectra variation of the FPI than the ZnO nanowires. The growth rate of the ZnO thin layer was measured by monitoring the free spectral range (FSR) of the reflection spectra, which achieved growth rates of 2 nm/min from 40 to 100 min and approximately 1.1 nm/min from 100 to 120 min in a 0.01-M growth solution, and 6.8 nm/min from 40 to 90 min in a 0.05-M growth solution. The proposed method is simple and cost effective, and has potential for wider applications in nanostructure manufacturing.

Current–voltage characteristics of Au/ZnO/n-Si device in a wide range temperature

Au/ZnO/n-Si device was obtained by using atomic layer deposition (ALD) technique, and it was characterized by I–V measurement in a wide temperature from 100 to 380 K with 20 K steps. XRD measurements were performed on ZnO thin film layer, and (002) and (201) peaks were seen in XRD pattern of the film. Surface morphology and cross section of the device were taken by SEM and discussed in the details. Some device parameters such as barrier height, ideality factor, series resistance were calculated by thermionic emission theory (TE), using Cheung’s and Norde’s functions. The Calculation results revealed that all device parameters strongly depended on temperature changing. In addition, interface states (N ss ) graphs were plotted and discussed according to energy levels and measurement temperatures. It can be concluded that this device can be used in various technological applications in wide range temperatures in industry.

Retraction Note to: A new approach on preparation and characterization of zinc oxide deposited carbon nanotubes based materials applicable for electronic and optoelectronic devices

ZnO is a wide-band-gap semiconductor material that is now being developed for many applications, including ultraviolet (UV) light-emitting diodes, UV photodetectors, transparent thin-film transistors, and gas sensors. It can be grown as boules, as thin films, or as nanostructures of many types and shapes. However, as with any useful semiconductor material, its electrical and optical properties are controlled by impurities and defects. We have reviewed the growth and analysis of carbon molecular crystals by the plasma enhanced chemical vapour deposition method. The three main synthesis methods of Carbon Nanocrystals (CNCs) are the arc discharge, the laser ablation and the chemical vapour deposition with a special regard to the later one. By two different methods ZnO layers were coated on the tubes. RF sputtering was one of the ways to directly deposit ZnO thin layer on the MWCNCs. On the other hand, we used thermally physical vapour deposition for making thin Zn film to oxidize it later. Scanning electron microscopy and also Raman spectroscopy measurements of the prepared samples confirmed the presence of ZnO nanolayers on the CNC bodies.

Preferential orientation growth of ITO thin film on quartz substrate with ZnO buffer layer by magnetron sputtering technique

In order to improve the photoelectric transformation efficiency of thin-film solar cells, one plausible method was to improve the transparent conductive oxides (TCO) material property. In-doped tin oxide (ITO) was an important TCO material which was used as a front contact layer in thin-film solar cell. Using magnetron sputtering deposition technique, we prepared preferential orientation ITO thin films on quartz substrate. XRD and SEM measurements were used to characterize the crystalline structure and morphology of ITO thin films. The key step was adding a ZnO thin film buffer layer before ITO deposition. ZnO thin film buffer layer increases the nucleation center numbers and results in the (222) preferential orientation growth of ITO thin films.

Preparation and Characterization of ZnO Thin Layers with Various Percentages of Gallium Impurities

Preparation and Characterization of ZnO Thin Layers with Various Percentages of Gallium Impurities

Electrical and gas sensing investigations on the sprayed ZnO:Cu thin films

The electrical and gas sensing properties of the sprayed Cu doped ZnO thin layers were investigated. The main study is an analysis of the conduction mechanism based on the measurement results of the frequency dispersion of the conductivity at different temperatures performed by impedance spectroscopy. It emerges from this study that the transport mechanism of charge carriers in such thin films is a thermally activated hopping mechanism. This process is confirmed by the obtained values of the maximum barrier height Wm deduced from the study of the frequency power law of the ac conductivity. Otherwise, we have studied the response evolution of ZnO: Cu sensors ethanol versus time, working temperature and relative doping. From the measurement results of gas sensing properties of ZnO:Cu thin film, we find that a good stability and response was observed for a doping of 2%.

Sifat Optik Lapisan Tipis ZnO

The aim of this research is to manufacture and characterize optical properties of ZnO thin layer which is deposited on glass substrate by sol-gel spin-coating method, through the process of growing ZnO thin layer of zinc acetate dehydrate (ZnAc) precursor on glass substrate with spin speed 2000 rpm for 30 minutes on a spin coater plate. The growth of layers by the sol-gel method of spin-coating is determined by the length of time of spin rotation which is related to the thickness of the thin layer. The Samples on the substrate in anneling at 400 oC and 500 oC for 1.5 hours to obtain a thin layer of ZnO. The obtained layer was characterized by UV-Vis test to determine the optical properties of the coating which include absorbance, transmittance, and bandgap energy. UV-Vis testing states that, the higher concentration of ZnO solution then the layer looks increasingly not transparent so that the transmittance value is smaller, otherwise the absorbance value of the layer becomes higher. This is indicated by the results obtained, at 1 M molarity concentration obtained the value of transmittance (50. 40%), while at a concentration of 0.7 M obtained greater transmittance value (75.24%) at the same heating temperature 500 oC. The gap energy is a forbidden area where electrons are located between the valence bands filled by the electrons and the empty conduction bands of the electrons. With respect to the photon energy to excite the electrons, the annealing treatment will affect the magnitude of the gap energy. High annearance temperature obtained a smaller gap energy compared with lower anneling temperatures. The obtained energy gap of 2.1 eV at 400 °C annealing temperature is greater than 0.1 eV compared to the heating temperature of 500 oC at 2.0 eV.

Low-Temperature Synthesis of Vertically Align ZnO Layer on ITO Glass: The Role of Seed Layer and Hydrothermal Process

ZnO thin layer has a broad potential application in optoelectronic devices. In the present study, vertically align ZnO layers on ITO glass were synthesized using wet chemical method. The seed layers were prepared using electrodeposition method at 3°C. After that, the growing process was carried out using chemical bath deposition (CBD) at 90°C. To improve the structural property of the ZnO layers, hydrothermal technique was used subsequently. Results showed that seeding layer has a great influence on the physical properties of the ZnO layers. Moreover, hydrothermal process conducted after the ZnO growth can enhance the morphological property of the layers. From the experiments, it is found that the ZnO layers has diameter of ∼60 nm with increasing thickness from ∼0.8 to 1.2 μm and band-gap energies of ∼3.2 eV.

Free-Standing Atomically Thin ZnO Layers via Oxidation of Zinc Chalcogenide Nanosheets.

Monolayer ZnO represents a class of new two-dimensional (2D) materials that are expected to exhibit unique optoelectronic properties and applications. Here we report a novel strategy to synthesize free-standing atomically thin ZnO layers via the oxidation of hydrothermally grown ultrathin zinc chalcogenide nanosheets. With micrometer-scaled lateral size, the obtained ultrathin ZnO layer has a thickness of ∼2 nm, and the layered structure still maintained well after high temperature oxidation. The thermal treatment strongly improves the crystal quality as well without inducing cracks or pinholes in the ultrathin layers. The atomically thin ZnO layers are highly luminescent with dominant green emission. High quality white light is obtained from the mixed phosphors containing the ZnO layers, exhibiting their potential as compelling ultraviolet-excited phosphors.

ZnO wide bandgap semiconductors preparation for optoelectronic devices

ZnO nanoparticles were successfully synthesized by sol-gel method. According to unique structural and optical properties of ZnO semiconductor material, there are many potential important applications based on that material, including as an anti-reflection coating (ARC) in solar cells. Antireflective coatings (ARC) made of ZnO on top to improve the optical properties of the coating. TiO2 layer have been coated on a ZnO nanoparticle layer. ZnO nanoparticle was characterized by X-ray diffraction (XRD), Scanning electron Microscopy (SEM) and UV-Vis spectroscopy. ZnO annealed at a temperature of 600 °C have the greatest crystalinity and crystal size than that at a temperature of 400 °C and 500 °C. SEM images of ZnO shown agglomeration and grain size increases with increasing annealed temperature. While, the optical properties of ZnO increase with increasing annealed temperature. The optical transmittance spectra of the ZnO are shown that the increasing annealing temperature had effectively improved the optical transmittance of the films. While, reflectance (%R) properties shows that, the higher annealing temperature of ZnO preparations can decrease of %R value of ZnO thin layer. The difference properties of ZnO are due to differences of light scattering resulting from the crystal size effect. The ZnO prepared by annealed at 600 °C gain a good performance of the lowest reflectance value and highest size crystal. By the addition of ARC ZnO 600 °C we have been capable improve cell performance so that that cells achieve an efficiency of 0.27%.