Thin ZnO Layer Research Articles

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%.

Temperature-dependent C-V characteristics of Au/ZnO/n-Si device obtained by atomic layer deposition technique

Since the importance of Schottkky devices, Au/ZnO/n-Si device were obtained, and the capacitance–voltage (C-V) and conductance-voltage (G-V) characteristics of Au/ZnO/n-Si device were studied using admittance spectroscopy at changing temperature from 160 to 340 K with 20 K intervals and −1 to +2 V bias voltage range. The interface thin film ZnO layer was deposited on the n-type Si wafer by atomic layer deposition technique (ALD) in order to obtain homogenous interface layer. The layer thickness of ZnO was taken as 10 nm by the resulting ZnO film growth rate at about 1.45 A per cycle. This thin film layer was characterized with XRD and AFM analyses. It can be seen from the C-V curves of the device that the capacitance values increased in depletion region with increasing temperature and exhibited peaks towards to forward biases after 240 K temperature. The changing of capacitance values confirmed re-ordering and re-structuring of charges in the interface of the device with changing temperature. The G-V curves of the device also increased with increasing temperature and towards to forward bias voltages due to increasing free charges in the interface. The series resistance (\({R}_{s}\)) of the device was taken into account to understand its effect on main electrical parameters, and it could be seen from these results that the \({R}_{s}\) strongly depends on the device temperature. The impedance (Z) values decreased with changing from −1 to +2 V bias voltages and increasing temperature. The barrier height which was obtained from the C −2 -V plots increased a slope of 0.00108 eV/K with a decrease in temperature from 160 to 340 K. It can be concluded that the Au/ZnO/n-Si device may be used and improved for next technological applications such as capacitor and memristor.

Novel synthesis of ZnO/PMMA nanocomposites for photocatalytic applications

The incorporation of nanostructured photocatalysts in polymers is a strategic way to obtain novel water purification systems. This approach takes the advantages of: (1) the presence of nanostructured photocatalyst; (2) the flexibility of polymer; (3) the immobilization of photocatalyst, that avoids the recovery of the nanoparticles after the water treatment. Here we present ZnO-polymer nanocomposites with high photocatalytic performance and stability. Poly (methyl methacrylate) (PMMA) powders were coated with a thin layer of ZnO (80 nm thick) by atomic layer deposition at low temperature (80 °C). Then the method of sonication and solution casting was performed so to obtain the ZnO/PMMA nanocomposites. A complete morphological, structural, and chemical characterization was made by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. The remarkable photocatalytic efficiency of the nanocomposites was demonstrated by the degradation of methylene blue (MB) dye and phenol in aqueous solution under UV light irradiation. The composites also resulted reusable and stable, since they maintained an unmodified photo-activity after several MB discoloration runs. Thus, these results demonstrate that the proposed ZnO/PMMA nanocomposite is a promising candidate for photocatalytic applications and, in particular, for novel water treatment.

Nanopore diameter-dependent properties of thin three-dimensional ZnO layers deposited onto nanoporous silicon substrates

In this paper, nanoporous silicon (NPSi) substrates with various pore diameters-ranging from 50nm to 100nm-were prepared by inductively coupled plasma (ICP) etching using anodic aluminum oxide (AAO) masks. Thin three-dimensional (3D) ZnO layers were deposited onto as-obtained NPSi substrates using atomic layer deposition (ALD). The results show that the silicon nanopore diameter has a large influence on the morphology, structure, and optical properties of thin 3D ZnO layers deposited onto NPSi substrate. A thin ZnO layer with optimal 3D morphology, crystallinity and luminescence performance is obtained when the silicon nanopore diameter is 90nm. The results also reveal that a silicon nanopore diameter increase greatly benefits thin 3D ZnO layer growth given that the NPSi substrate morphology is not destroyed. These investigations bring important guiding role for attaining AAO-assisted 3D semiconductor materials with nanoscale structure and high luminescence performance.

RETRACTED: Growth and characterization of carbon nanotubes and zinc oxide nanocomposite with the PECVD technique

Abstract In this research 50–100 nm Carbon Nanotube and Zinc Oxide (CNT-ZnO) Nanocomposite were synthesized. We have initially prepared Multi-walled Carbon Nanotubes (MWCNTs) by the Plasma Enhanced Chemical Vapour Deposition (PECVD) method. By two different methods, then, ZnO layers were coated on the tubes. Radio Frequency (RF) sputtering was one of the ways to directly deposit ZnO thin layer on the MWCNTs. Alternatively, we used thermally Physical Vapour Deposition (PVD) for making thin Zn film to oxidize it later. Results were analyzed and discussed.

Atomic layer deposition of semiconductor oxides on electric sail tethers

•This study shows that thin coating layers of semiconductor oxides, deposited by atomic layer deposition, can be successfully used to improve the performance of tethers used in space technology. Thin layers of ZnO, TiO2 and Ti-Zn mixed oxide with 25 to 100nm thickness were considered, and compared with native Al2O3 as reference. For this purpose, morphological, optical and electrochemical characterization was performed. As a result, deposited materials show very good adhesion and conformality. Coatings act as anti-reflective layers, increasing the absorbance of tethers. The presence of TiO2 thin layers and mixed oxide improves the corrosion resistance of tethers both in dark and under UV illumination conditions. Our results show that TiO2 has the best performance for space tether application followed by the mixed oxide.

Reinforcement role of GaP nanowires in a ZnO layer prepared by RF sputtering

This paper presents a thin nanocrystalline ZnO layer with embedded GaP nanowires (NWs). The NWs were grown in vapour-liquid-solid (VLS) mode by metal organic vapour phase epitaxy (MOVPE) at Au seeds formed from a very thin Au layer. The NWs were finally embedded in ZnO using deposition by RF sputtering combined with etching steps that resulted in a compact antireflection layer. We studied properties of such compact NWs structure by means of x-ray diffraction and atomic force microscopy. The study of mechanical properties was performed by nanoindentation measurements. The nanoindentation measurement showed that the incorporation of GaP nanowires into a ZnO layer led to increased hardness compared with that of a pure ZnO layer. The compact GaP NW/ZnO layer structure also exhibited some degree of pseudoelasticity. In addition, the mechanical properties of the compact nanowire layer are sufficiently robust to allow the thermo-compression bonding on the top of the structure.

Development of ZnO nanowire based CdTe thin film solar cells

This work reports on the development of CdTe thin film solar cells grown on ZnO nanowire arrays. The focus was placed on utilising ZnO nanowire arrays as a replacement to the conventional ZnO thin film buffer layer, thereby requiring minimal alteration to the existing solar cell structure. Incorporation of nanowires was found to alter subsequent film growth and processing, with the nanowire dimensions changing device performance significantly. Shorter, ~100nm, wires were found to produce particularly low device performance of <0.5% whilst longer wires in the range 250–2000nm were able to produce more functional cells. Working devices of up to 9.5% efficiency were achieved through the production of “embedded tip” nanowire solar cells. Variation of the nanowires length demonstrated that the nanowires were involved in carrier recombination and that this may be the performance limiting factor.

Evolution of Al:ZnO optical response as a function of doping level

ZnO and Al doped ZnO thin layers (<100nm) have been deposited through RF magnetron sputtering on quartz and Si substrates. Structural (XRD), compositional (SNMS), morphological (SEM) and optical/electrical (Spectroscopic Ellipsometry) characteristics of the samples have been studied in order to deduce the effect of dopant level variation. A combination of classical Tanguy+Drude+Sellmeier terms are used to analyze the dielectric function of ZnO and Al:ZnO. It has been found that increasing Al contents leads to smaller crystalline size, band gap shift and a gradual reduction of the refractive index and increase of the broadening of this transition. The electrical parameters extracted from the Drude model suggest a limit for the aluminium doping efficiency.

The effect of transparent conductive nanocrystalline oxide thin layer on performance of UV detectors fabricated on Fe-doped GaN

Two kinds of metal-semiconductor-metal (MSM) Schottky UV detectors with and without an insertion layer of transparent conductive nanocrystalline oxide were fabricated on Fe-doped semi-insulating GaN epilayers. It is found that the optical responsivity of the detectors can be significantly improved by two orders of magnitude by inserting a thin layer of Ga-doped nanocrystalline ZnO (GZO) between metal electrode and Fe-doped GaN. Such improvement is suggested to be associated with the valence-band discontinuities and efficient suppression recombination of traps induced by Fe impurities in GaN due to the insertion of a thin layer of GZO.

RETRACTED ARTICLE: 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.

Nanotextured cupric oxide nanofibers coated with atomic layer deposited ZnO-TiO2 as highly efficient photocathodes

We report the fabrication and performance of a CuO/ZnO/TiO2 nanofiber photocathode that achieved a photocurrent density (PCD) of −4.1mA/cm2, which is among the highest PCD values reported for a copper oxide based photocathode without a co-catalyst. To prepare this photocathode, we coated electrospun nanofibers with copper by electroplating, then dried them in air to produce cuprous oxide (Cu2O) nanofibers. Further annealing in air converted them to cupric oxide (CuO). The CuO nanofibers exhibit nanotextured surfaces, resembling the skin of the “thorny-devil” lizard of Australia, providing high accessible surface area for photocatalysis. These CuO nanofibers were uniformly coated with thin ZnO and TiO2 layers by atomic layer deposition (ALD) to promote electron migration from CuO to TiO2 and protect the CuO from corrosion. The nanofibrous photocathode films were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy, as well as by incident photon-to-electron conversion efficiency measurements.

Fabrication and Characterization of ZnO Langmuir-Blodgett Film and Its Use in Metal-Insulator-Metal Tunnel Diode.

Metal-insulator-metal tunnel diodes have great potential for use in infrared detection and energy harvesting applications. The quantum based tunneling mechanism of electrons in MIM (metal-insulator-metal) or MIIM (metal-insulator-insulator-metal) diodes can facilitate rectification at THz frequencies. In this study, the required nanometer thin insulating layer (I) in the MIM diode structure was fabricated using the Langmuir-Blodgett technique. The zinc stearate LB film was deposited on Au/Cr coated quartz, FTO, and silicon substrates, and then heat treated by varying the temperature from 100 to 550 °C to obtain nanometer thin ZnO layers. The thin films were characterized by XRD, AFM, FTIR, and cyclic voltammetry methods. The final MIM structure was fabricated by depositing chromium/nickel over the ZnO on Au/Cr film. The current voltage (I-V) characteristics of the diode showed that the conduction mechanism is electron tunneling through the thin insulating layer. The sensitivity of the diodes was as high as 32 V(-1). The diode resistance was ∼80 Ω (at a bias voltage of 0.78 V), and the rectification ratio at that bias point was about 12 (for a voltage swing of ±200 mV). The diode response exhibited significant nonlinearity and high asymmetry at the bias point, very desirable diode performance parameters for IR detection applications.

Formation of a compact Ga-doped ZnO layer over vertical free-standing GaP nanowires

We studied the process of deposition of a thin nanocrystalline ZnO layer on vertical free-standing GaP nanowires (NWs). The paper presents the preparation of a new type of composite antireflection coating based on a compact GaP NW/ZnO layer structure. The NWs were prepared using metal organic vapour phase epitaxy. They were grown at Au seeds created from a ∼0.3nm thick Au layer, which was deposited on GaP substrate by evaporation. RF sputtering was used to cover the NWs and substrate with a ZnO layer with a nominal thickness between 50 and 250nm. While thinner ZnO layers wrapped the NWs and covered the substrate, thicker ones also filled the volume between the NWs and the ZnO wrapping acquired a shape that resembled that of cotton swabs. A compact and planarized GaP NW/ZnO layer structure was achieved by altering ZnO deposition with ZnO etching by Ar ions. GaP NW/ZnO layer structures, which differed in the degree of ZnO filling, exhibited antireflection behaviour that was superioir to that of GaP substrate with GaP NWs.

Modulation of light absorption by optical spacer in perovskite solar cells

Lead halide perovskite solar cells with planar heterojunction configuration have recently attracted tremendous attention because of their excellent power conversion efficiencies. The modulation of optical absorption by using an optical spacer layer is a unique method to enhance the device efficiency. Here, we demonstrate the application of thin ZnO layer that act as an optical spacer that enhance the power conversion efficiency perovskite devices from 8.92% to 10.7%, which is mainly due to increment in short‐circuit current density by 16% compared to the reference solar cell. The simulation data revealed that ZnO acts as an optical spacer layer that shifts length (average) of electric field |E|2 distribution from 500 nm to 750 nm wavelength is 25 nm in the perovskite layer. Which represents that exciton generation region is moved to near the hole transport layer that enhances the exciton dissociation efficiency and device efficiency.

Effect of initial stress on the propagation behavior of SAW in a layered piezoelectric structure of ZnO/Al2O3

Theoretical analysis of surface acoustic wave (SAW) propagation in a pre-stressed layered piezoelectric structure basing on the modified ordinary differential equation (ODE) is described. Numerical calculations involve a thin piezoelectric layer of ZnO bonded perfectly to an elastic substrate of Al2O3. ZnO thin films are deposited on Al2O3 substrates using plasma assisted molecular beam epitaxial (MBE). The crystallographic orientation of ZnO thin films and the surface morphology are analyzed by X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. The density and the thickness of the ZnO films are determined by X-ray reflectivity. The initial stress and strain of ZnO films are measured by X-ray diffraction method. The effect of initial stress on the propagation behavior of Rayleigh and Love waves and on the coupled electromechanical factor is discussed.

Investigations of rapid thermal annealing induced structural evolution of ZnO: Ge nanocomposite thin films via GISAXS

In this work, we present in depth structural investigations of nanocomposite ZnO: Ge thin films by utilizing a state of the art grazing incidence small angle x-ray spectroscopy (GISAXS) technique. The samples have been deposited by sequential r.f. and d.c. sputtering of ZnO and Ge thin film layers, respectively, on single crystal Si(100) substrates. Transformation of Ge layers into Ge nanoparticles (Ge-np) has been initiated by ex-situ rapid thermal annealing of asprepared thin film samples at 600 °C for 30, 60, and 90 s under forming gas atmosphere. A special attention has been paid on the effects of reactive and nonreactive growth of ZnO layers on the structural evolution of Ge-np. GISAXS analyses have been performed via cylindrical and spherical form factor calculations for different nanostructure types. Variations of the size, shape, and distributions of both ZnO and Ge nanostructures have been determined. It has been realized that GISAXS results are not only remarkably consistent with the electron microscopy observations but also provide additional information on the large scale size and shape distribution of the nanostructured components.

Three-dimensional deposition of ZnO thin layer on nanopatterned silicon substrate

Three-dimensional deposition of 15nm thick ZnO thin layer can be achieved successfully on nanopatterned silicon substrate. The nanopatterned silicon (NPSi) substrate was prepared by two-step ICP etching using anodic aluminum oxide (AAO) film as etching mask. The average diameter and depth for the silicon nanopore arrays are approximately 60nm and 300nm, respectively. Also, the NPSi substrate was entirely covered by ZnO thin layer grown by atomic layer deposition. It is believed that the above-mentioned process may provide a good alternative for the preparation of three-dimensional ZnO film and device.

RETRACTED ARTICLE: Increase of the Surface Mobility of Carbon Molecular Crystals (CMCs) Using the PECVD Technique

Large-area boron doped multi-layer carbon is synthesized by the plasma enhanced chemical vapour deposition (PECVD) using boron oxide powder and ethanol vapor. We have reviewed the carbon molecular crystals preparation by the PECVD 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.

Application of Thin ZnO ALD Layers in Fiber-Optic Fabry-Pérot Sensing Interferometers.

In this paper we investigated the response of a fiber-optic Fabry-Pérot sensing interferometer with thin ZnO layers deposited on the end faces of the optical fibers forming the cavity. Standard telecommunication single-mode optical fiber (SMF-28) segments were used with the thin ZnO layers deposited by Atomic Layer Deposition (ALD). Measurements were performed with the interferometer illuminated by two broadband sources operating at 1300 nm and 1550 nm. Reflected interference signal was acquired by an optical spectrum analyzer while the length of the air cavity was varied. Thickness of the ZnO layers used in the experiments was 50 nm, 100 nm, and 200 nm. Uncoated SMF-28 fiber was also used as a reference. Based on the results of measurements, the thickness of the ZnO layers and the length of the cavity were selected in order to achieve good visibility. Following, the interferometer was used to determine the refractive index of selected liquids.