Surface Morphology Of ZnO Films Research Articles

Effect of molar concentration on the optical and structural properties of ZnO thin films prepared by chemical bath deposition method

This research included the preparation of (ZnO) thin films by CBD technique for the deposition of chemical bath thickness (150 ± 20nm). X-ray diffraction was analyzed and showed that the films crystallize in a polycrystalline hexagonal structure, with a preferred direction along the level (100). Increased volume of calculated crystals for deposited films was found by increasing molar concentration. The surface morphology of films was studied by SEM, and the surface morphology of ZnO films is a heterogeneous distribution. The optical properties of all deposited ZnO films contained a spectral permeability and absorption spectrum in the wavelength range (300-1100nm), and the transmittance decreased with increasing molar concentration, it was found that the value of the light energy gap (Eg) increases with increasing molecular concentration band gap between 3.1 and 3.2 eV.

Effects of sputtering gas pressure dependence of surface morphology of ZnO films fabricated via nitrogen mediated crystallization

ZnO films were fabricated by RF magnetron sputtering with nitrogen mediated crystallization (NMC) under various gas pressures. X-ray diffraction measurements show that the NMC-ZnO films are highly crystalline regardless of the gas pressure, and the full width at half maximum values of the (0002) rocking curves range from 0.032 to 0.044°. In contrast, atomic force microscopy (AFM) reveals that the gas pressure plays an important role in determining the surface morphology of the films. The root-mean-square (RMS) roughness decreases monotonically from 1.05 to 0.60 nm with increasing pressure from 0.2 to 0.7 Pa. However, the RMS roughness increases with further increases in the pressure, reaching 2.15 nm at 2.1 Pa. The height distribution of the NMC-ZnO films derived from the AFM images is narrowest at 0.7 Pa, indicating that the smooth surface obtained at 0.7 Pa can be attributed to spatially uniform nucleation occurring in a short time period. These results indicate that the sputtering gas pressure is a key parameter for controlling the surface morphology of NMC-ZnO films.

Preparation of ZnO electron transport layers by spray technology for perovskite solar cells

ZnO-based electron transport layers (ETLs) have caused wide public interest in flexible and wearable electronic devices owing to its higher electron mobility and crystalline without sintering processes. Here we describe a fast, inexpensive and low temperature spray method for the preparation of ZnO electron transport layers in CH3NH3PbI3-sensitized perovskite solar cells (PSCs) based on CuI holes transporter layers (HTL). The SEM results show that the surface morphology of ZnO films has an impact on the coverage rate of perovskite which is caused by the spray method. Optimization of the thickness of ZnO layers yielded highest power conversion efficiency of devices up to 3.47% with short-circuit current density Jsc, open-circuit voltage Voc and fill factor were 14.21 mA/cm2, 0.55 V and 44%, respectively. The factors that influence the performance of the cells have been analyzed by the impedance spectroscopy technique.

Enhancing the electrical parameters of ZnO films deposited using a low-cost chemical spray technique through Ta doping

Tantalum doped ZnO thin films (doping levels – 0, 1, 3 and 5 at %) were deposited onto glass substrates using a simplified spray pyrolysis technique by employing a perfume atomizer for the first time. The effects of Ta doping level on electrical, optical and structural properties along with surface morphology of ZnO films were studied. EDAX and FTIR studies confirm the presence of the dopant in the prepared film. The chemical states of the constituent elements were analysed through XPS studies. The average optical transmittance of the film is over 90%. Even though the intensity of (001) peak increases at the expense of (002) plane with Ta doping, the direction of preferential growth is unaltered. The FESEM analysis shows that the dopant alters the grain size of the films. A minimum electrical resistivity of 2.05 × 10−3 Ω cm was obtained at the doping level of 1 at%. The obtained good quality factor (1.584 × 10−4 (Ω/sq.) −1) of the film at 1 at% of Ta doping level makes it a potential candidate for several opto-electronic devices like transparent electrodes, thin film transistors and many other functional devices.

Influence of annealing temperature of ZnO film as the electron transport layer on the performance of polymer solar cells

The surface morphology of ZnO films at different annealing temperatures and the performance of polymer solar cells (PSCs) with ZnO as the electron transport layer are studied. The low temperature sol-gel processed ZnO film has smoother surface than that in higher temperature, which results in the best photovoltaic performance with a power conversion efficiency (PCE) of 3.66% for P3HT:PC61BM based solar cell. With increasing annealing temperature, the photovoltaic performance first deceases and then increases. It could be ascribed to the synergy effects of interface area, the conductivity and surface energy of ZnO film and series resistance of devices.

Growth of residual stress-free ZnO films on SiO2/Si substrate at room temperature for MEMS devices

ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2”-wafer of SiO2/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 109 to 11.28 x 109 dyne/cm2 with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ∼3.275 eV to ∼3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications.

The role of nanoscale etched Si surface in ZnO growth by continuous spray pyrolysis

This work reports deposition of various ZnO nanostructure layers by continuous spray pyrolysis reactor over seed layer assisted nanoscale etched Si surface. The study of various surface morphologies of ZnO nanostructure layers are supported by XRD, SEM, photoluminescence and reflectance measurements. The anisotropic etch pits surface energy profile has played an important role in deciding the ultimate surface morphology of ZnO film and may be helpful in generating vertically aligned ZnO nanorods. The 4 min etched Si surface show poor film quality which further improves with Si etching to 8 min. The 8 min etched Si is helping in ZnO growth and with the increase of deposition time shape, size and alignment of ZnO nanorods takes place. XRD pattern show fall of texture coefficient in ZnO growth with deposition time but it remains constant for 8 min etched Si. Photoluminescence study reveals presence of novel defect at 600 nm due to the Si etching and appreciable PL quenching is observed in ZnO growth for 8 min etched Si. Reflectance measurement show light reduction up to 40 and 47 % of existing reflectance in 400–800 nm wavelength regions due to the ZnO growth on 8 min and complete textured Si surface. The growth mechanisms for various ZnO growths are also proposed.

Growth of nonpolar ZnO Films on (100) β-LiGaO2 substrate by molecular beam epitaxy

Nonpolar m-plane (11̄00) ZnO epitaxial films were grown on (100) β-LiGaO2 (LGO) substrates by plasma assisted molecular beam epitaxy (PAMBE). The dependence of growth characteristics on the growth temperatures was investigated. The surface morphologies of ZnO films were characterized by scanning electron microscopy and atomic force microscopy. Furthermore, the structural properties characterized by high resolution X-ray diffraction (HRXRD) indicated that the ZnO epilayers were grown in the nonpolar [11̄00] orientation. Detailed structural characterization and defect analysis of nonpolar ZnO epilayer on β-LiGaO2 substrate were studied by transmission electron microscope (TEM). Optical properties of m-plane ZnO films were investigated by Raman spectroscopy and photoluminescence analyses.

Effects of Nitrogen on Crystal Growth of Sputter-Deposited ZnO Films for Transparent Conducting Oxide

We have studied the effects of the N2 gas flow rate on the surface morphology of ZnO films deposited by the sputtering of a ZnO target using Ar/N2. Height-height correlation function (HHCF) analysis indicates that introducing a small amount of N2 (<5 sccm) to the sputtering atmosphere enhances adatom migration, leading to a larger grain size in the ZnO films associated with an increase in the lateral correlation length. The HHCF analysis also reveals that films deposited with and without N2 exhibit a self-affine fractal surface structure. We demonstrate that utilizing such ZnO films deposited using Ar/N2 as buffer layers, the crystallinity of ZnO:Al (AZO) films on the buffer layers can be greatly improved. The electrical resistivity of 100-nm-thick AZO films decreases from 1.8×10-3 to 4.0×10-4 Ω·cm by utilizing a ZnO buffer layers prepared at N2 flow rate of 5 sccm.

Cluster-assembled ZnO films prepared by electrochemical deposition on copper substrate

Cluster-assembled ZnO films were synthesized by using electrochemical deposition technique with various reaction times. Zinc nitrate dissolved in de-ionized water was used as a precursor of ZnO film. The as-synthesized cluster-assembled ZnO films were performed on a copper plate used as a substrate at room temperature. The stabilized high electric field of 4 kV/m was applied in the process. Field emission scanning electron microscopy (FE-SEM) was used to characterize the film morphology. The FE-SEM micrographs showed that the surface morphologies of ZnO films are clustered-like structures with aggregated nascent particles when the reaction time was increased. An energy dispersive x-ray spectroscopy (EDS) was used to monitor the films composition, consists of Zn and O with contamination-free composition and an x-ray diffractometry (XRD) showed the x-ray signal patterns of ZnO film incorporating hexagonal wurtzite crystal structures. Key words: Cluster-assembled ZnO films, copper substrate, electrochemical deposition.

Effect of ambient temperature on electrical properties of nanostructure n-ZnO/p-Si heterojunction diode

The nanostructure n-ZnO/p-Si heterojunction diode was fabricated by sol–gel method. The structural and morphological properties of the nanostructure ZnO film have been investigated. The X-ray diffraction spectra indicated that the films are of polycrystalline nature. The scanning electron microscopy images indicate that the surface morphology of ZnO film is almost homogeneous and the ZnO film is consisted of the circular formed with coming together of the nanoparticles. The electrical characterization of nanostructure n-ZnO/p-Si heterojunction diode has been investigated by current–voltage characteristics. The ideality factor (n) of the diode was found for different ambient temperatures and the obtained 6.40 value for 296K is higher than unity due to the interface states between the two semiconductor materials and series resistance. The values of n increased with decreasing ambient temperature. The reverse current of the diode increased with illumination intensity of 100mWcm−2 and the diode gave a maximum open circuit voltage Voc of 0.19V and short-circuits current Isc of 8.03×10−8A.

The structural, electrical and optical properties of ZnO/Al2O3 multilayer deposited on PET substrates by RF sputtering

Abstract In this work ZnO/Al 2 O 3 multilayer is deposited on PET(polyethylene terephthalate) substrate by RF sputtering in argon atmosphere and the effect of Al 2 O 3 layer on optical, electrical and structural properties of ZnO is investigated. It is observed that the presence of Al 2 O 3 layer between ZnO and PET reduce the transmission of light from ZnO/Al 2 O 3 /PET structure 11% but if a thin layer of SiO 2 ∼100 nm is applied between Al 2 O 3 and PET it can be compensated. The XRD results show that the ZnO film had hexagonal wurtzite structure with (002) preferred orientation and the application of Al 2 O 3 and SiO 2 layers do not have any effect on its structure. The effect of Al 2 O 3 and SiO 2 layers on optical band gap of ZnO has been investigated, also the surface morphology of ZnO film is studied by scanning electron microscopy.

Sprayed lanthanum doped zinc oxide thin films

Lanthanum doped zinc oxide thin films were deposited on soda-lime glass substrates using a pneumatic spray pyrolysis technique. The films were prepared using different lanthanum concentrations at optimum deposition parameters. We studied the variations in structural, morphological and optical properties of the samples due to the change of doping concentration in precursor solutions. X-ray diffraction (XRD) patterns show that pure and La-doped ZnO thin films are highly textured along c-axis perpendicular to the surface of the substrate. Scanning electron micrographs show that surface morphology of ZnO films undergoes a significant change according to lanthanum doping. All films exhibit a transmittance higher than 80% in the visible region.

Mist-CVD Growth of High Quality ZnO Thin Films at Low Temperature for Inverted Organic Solar Cells

We report the deposition of ZnO thin films on indium-doped tin oxide (ITO)-coated glass substrates via Mist chemical vapor deposition (Mist-CVD) at a temperature range of 250, 300 and 350 °C, respectively. Surface morphology and crystalline quality were investigated by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD), respectively and optical property by transmission spectra. Further, we have optimized the surface morphology of ZnO films for inverted organic solar cells (IOSCs) by fabricating IOSCs on glass substrate, consisting of Au/MoO 3 /PCBM:P3HT/ZnO/ITO. It was found that the photovoltaic power conversion efficiency (PCE) of IOSCs is affected by the transmittance and crystallinity of ZnO thin films.

Influence of high-pressure hydrogen treatment on structural and electrical properties of ZnO thin films

ZnO thin films were treated by high-pressure hydrogen (H 2). Scanning electron microscope (SEM) images show that the surface morphology of ZnO films has been changed significantly by H 2 treatment. X-ray diffraction patterns show that the Zn(OH) 2 phases formed after H 2 treatment. The X-ray photoelectron spectroscopy results indicate that H atoms were doped into the surface of ZnO by forming H–O–Zn bond. The phenomenon shows that it is easy to form O–H bond in ZnO rather than H interstitial atom under high-pressure hydrogen circumstance.

Growth and characterizations of nonpolar [1 1 −2 0] ZnO on [1 0 0] (La,Sr)(Al,Ta)O 3 substrate by chemical vapor deposition

Nonpolar a-plane ZnO film with [1 1 −2 0] orientation was grown on a nearly lattice-matched [1 0 0] (La 0.3,Sr 0.7)(Al 0.65,Ta 0.35)O 3 (LSAT) substrate from a simple chemical vapor deposition method. LSAT single crystal was grown by the Czochralski method. The dependence of growth characteristics on the growth temperatures and reactor's pressures was investigated. The surface morphologies of ZnO films were studied by a scanning electron microscope. The sample orientations were identified by X-ray diffraction pattern and transmission electron microscope. Optical properties examined by room temperature photoluminescence spectra exhibit a strong near-band-edge emission peak at 378.6 nm and a negligible green band.

Microstructure of a-plane ZnO grown on LaAlO 3 (001)

The microstructure of a-plane ZnO grown on LaAlO 3 (LAO) (001) has been systematically investigated by employing X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Based on the results of XRD and TEM, only a-plane ZnO has been found to grow on LAO (001), and it consists of two types of domains perpendicular to each other. The crystal orientation relationships of a-plane ZnO domains with LAO have been verified to be [0001] ZnO//[110] LAO and [11̄00] ZnO//[11̄0] LAO. The domain boundaries in the a-plane ZnO are along the direction in a rotation angle of about 45° from the c-axes of ZnO. The surface morphology of ZnO films in SEM exhibits domain structure in stripe-like shape. The formation of two domains can be attributed to the cubic symmetry of the surface configuration of LAO (001).

Influence of deposition pressure on the adhesion of ZnO thin films deposited by cathodic vacuum arc deposition on polyimide foil substrates

ZnO thin films, used as polymer protection layers against ultraviolet radiation and atomic oxygen for space application, were deposited on polyimide foil substrates using a cathodic vacuum arc deposition technique. A fragmentation test was employed to investigate the influence of deposition pressure on the adhesion of ZnO thin films. It was found that all the samples have good adhesive properties. Low deposition pressure is beneficial to the adhesion of ZnO films and polyimide substrates. Scanning electron microscopy was also employed to investigate the surface morphology of ZnO films that had suffered from large strain. No large areas of film detachment were found.

Electrical Properties of Pulsed Laser Deposited ZnO Thin Films

Epitaxial Single-crystal ZnO thin films have been grown on c-plane (0001) sapphire by Pulsed Laser Deposition process at different substrate temperatures (300 – 800 °C) with 10-1 mbar oxygen pressure. The thicknesses of the films have been varied by varying number of pulses with a repetition rate of 10 pulse/sec. It is found that the sheet resistivity of ZnO thin films grown on c-plane sapphires are in the order of 10-2 Ω-cm and it increases with increasing substrate temperatures and film thickness. The carrier concentrations and Hall mobility are found to be in the order of 1017 cm-3 and ~195 cm2/V-s, respectively. The Hall mobility slightly decreases with increase of substrate temperature and thickness of the films. It is also found that the ZnO films are structurally uniform and well oriented with perfect wurtzite structure with c/a ratio 5.1. We have also deposited non-epitaxial ZnO films on (100) p-Silicon substrates at the same conditions. From HR FE-SEM micrographs, surface morphology of ZnO films grown at lower substrate temperature are found to be uniform compared to the films grown at higher temperatures showing non-uniformity and misoriented wurtzite structures. However, the surface morphology of ZnO flims grown epitaxially on (0001) sapphire are found to be more uniform and it does not change much with growth temperature. The resistivity of the films grown on p-Silicon at higher temperatures is in the order of 103 Ω-cm whereas films grown at lower substrate temperatures show comparatively lower resistivities (~ 102 Ω-cm). From the recorded UV-Visible absorption spectrum the band gap of the film has been estimated to be 3.38 eV.

EPITAXIAL GROWTH OF NON-POLAR A-PLANE ZNO ON R-PLANE SAPPHIRE SUBSTRATES BY MOCVD AND RF-SPUTTERING

Epitaxial growth of non-polar [Formula: see text] thin films (a-plane ZnO ) on [Formula: see text] sapphire ( r -plane sapphire) were successfully implemented through metal organic chemical vapor deposition (MOCVD) and radio-frequency sputtering, respectively. For ZnO film deposited by sputtering, the growth temperature and the flow ratios of argon to oxygen were shown to significantly influence the crystalline quality and surface morphology of ZnO films. Flat surface ZnO epitaxial film can be grown by MOCVD. The epitaxial relationship between ZnO and sapphire substrate is [Formula: see text] and [Formula: see text]. The full width at half maximum (FWHM) of X-ray rocking curve for [Formula: see text] reflection peak depends on the orientation of X-ray beam toward sample surface. SEM and AFM observations show the surface morphologies of ZnO epilayers exhibit a stripe-like pattern along ZnO [0001] direction. The higher growth rate along ZnO [0001] and in-plane anisotropic lattice mismatch between a -plane ZnO and r -plane sapphire might result in the formation of such stripes.