Growth Of Zinc Oxide Thin Films Research Articles

Importance of substrate rotation speed on the growth of homogeneous ZnO thin films by reactive sputtering

Undoped zinc oxide (ZnO) thin films were reactively deposited on soda-lime glass substrates by radio frequency (rf) sputtering at room temperature. We have studied the importance of substrate rotation speed on the structural, optical and morphological properties. The rotation speeds used were 0, 20, 40, 60, and 80rpm. The XRD measurements confirmed that films were grown with (002) plane preferential orientation. The average transmittance was above 90% in the UV–vis region. The SEM images revealed that films deposited with substrate rotation are more homogeneous than the films deposited without rotation.

Structural and Optical Properties of Nitrogen‐doped Zinc Oxide Thin Films Grown on Muscovite Mica Substrates Using Sol–Gel Process

Nitrogen (N)‐doped zinc oxide (NZO) thin films were grown on muscovite mica substrates by sol–gel spin‐coating and their structural and optical properties were investigated for various N concentrations (0, 3, 6, 9, and 12 at. %). The surface morphologies of all the films exhibited granular structures consisting of spherical nano‐sized crystallites. The (1 0 0) and (0 0 2) diffraction peaks were observed at 0, 3, and 6 at. % N concentration, while the (1 0 0) peak could not be distinguished and the (0 0 2) peak intensities decreased gradually at the higher concentrations. The near‐band‐edge to deep‐level emission intensity ratio increased significantly with increasing N concentration up to 6 at. %. All the films exhibited an average transmittance of more than 75% in the visible region. The optical band gap and Urbach energy determined by the measured transmittance were obviously dependent on the N concentration.

Enhancement of thermoelectric properties of MBE grown un-doped ZnO by thermal annealing

In this paper, we have reported an enhancement in thermoelectric properties of un-doped zinc oxide (ZnO) grown by molecular beam epitaxy (MBE) on silicon (001) substrate by annealing treatment. The grown ZnO thin films were annealed in oxygen environment at <TEX>$500^{\circ}C-800^{\circ}C$</TEX>, keeping a step of <TEX>$100^{\circ}C$</TEX> for one hour. Room temperature Seekbeck measurements showed that Seebeck coefficient and power factor increased from 222 to <TEX>$510{\mu}V/K$</TEX> and <TEX>$8.8{\times}10^{-6}$</TEX> to <TEX>$2.6{\times}10^{-4}Wm^{-1}K^{-2}$</TEX> as annealing temperature increased from 500 to <TEX>$800^{\circ}C$</TEX> respectively. This observation was related with the improvement of crystal structure of grown films with annealing temperature. X-ray diffraction (XRD) results demonstrated that full width half maximum (FWHM) of ZnO (002) plane decreased and crystalline size increased as the annealing temperature increased. Photoluminescence study revealed that the intensity of band edge emission increased and defect emission decreased as annealing temperature increased because the density of oxygen vacancy related donor defects decreased with annealing temperature. This argument was further justified by the Hall measurements which showed a decreasing trend of carrier concentration with annealing temperature.

Study of post annealing effects on structural and optical properties of sol-gel derived ZnO thin films grown on n-Si substrate

Zinc oxide (ZnO) thin films were grown on n-type silicon (100) substrates by sol- gel spin coating technique. The prepared thin films were annealed in the presence of Ar at three different temperatures (at 450°C, 550°C and 650°C) to study the impact of annealing temperature on the structural and optical properties of the ZnO thin films. The structural, surface morphology and optical properties of the thin film were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) measurements respectively. The grown ZnO thin films are polycrystalline in nature with wurtzite hexagonal structure as evident from the XRD and SEM analyses. It further indicates that the crystalline size increases with increasing annealing temperature. The post annealing is also found to influence the optical properties in the terms of band gap energy of the ZnO thin films. The optical energy band gap was found to be decreased from 3.205 to 3.13eV as the annealing temperature is increased from 450°C to 650°C. However, our results concerning the growth of ZnO thin films on Si substrates suggest that there is an intermediate growth temperature allowing for the optimization of the ZnO film growth. The results of the study can be used as a guideline for growing ZnO thin films on n-Si substrates with a homogenous surface morphology, high surface to volume ratio and desired particle size, which are suited for optoelectronic/ gas sensing applications.

High electron mobility and low carrier concentration of hydrothermally grown ZnO thin films on seeded a-plane sapphire at low temperature.

Hydrothermal zinc oxide (ZnO) thick films were successfully grown on the chemical vapor deposition (CVD)-grown thick ZnO seed layers on a-plane sapphire substrates using the aqueous solution of zinc nitrate dehydrate (Zn(NO3)2). The use of the CVD ZnO seed layers with the flat surfaces seems to be a key technique for obtaining thick films instead of vertically aligned nanostructures as reported in many literatures. All the hydrothermal ZnO layers showed the large grains with hexagonal end facets and were highly oriented towards the c-axis direction. Photoluminescence (PL) spectra of the hydrothermal layers were composed of the ultraviolet (UV) emission (370 to 380 nm) and the visible emission (481 to 491 nm), and the intensity ratio of the former emission (IUV) to the latter emission (IVIS) changed, depending on both the molarity of the solution and temperature. It is surprising that all the Hall mobilities for the hydrothermal ZnO layers were significantly larger than those for their corresponding CVD seed films. It was also found that, for the hydrothermal films grown at 70°C to 90°C, the molarity dependences of IUV/IVIS resembled those of mobilities, implying that the mobility in the film is affected by the structural defects. The highest mobility of 166 cm2/Vs was achieved on the hydrothermal film with the carrier concentration of 1.65 × 1017 cm−3 grown from the aqueous solution of 40 mM at 70°C.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-014-0715-0) contains supplementary material, which is available to authorized users.

Growth of non-polar ZnO thin films with different working pressures by plasma enhanced chemical vapor deposition

Non-polar coexisting m-plane () and a-plane () zinc oxide (ZnO) thin films have been synthesized onto commercial silicon (100) substrates by using plasma enhanced chemical vapor deposition (PECVD) system at different working pressures. The effects of the working pressure on crystal orientation, microstructure, surface morphology, and optical properties of the ZnO thin films were investigated. From the X-ray diffraction patterns, the non-polar ZnO thin films were successfully synthesized at the working pressures of 6 and 9 Torr, respectively. The non-polar ZnO thin films showed stripes-like surface morphology and with smooth surface roughness (∼3.53 nm) was performed by field emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM), respectively. All the ZnO films show a remarkable near-band-edge (NBE) emission peak located at ultraviolet (UV) band accompanying a negligible deep-level (DL) emission at visible region detected by photoluminescence (PL) spectra at room temperature. From the above systematic measurement analysis, indicating the better crystallinity and optical character of ZnO thin film was improved with reducing the working pressure. The wettability of non-polar ZnO thin films was also explored in this presented article.

Structural and Optical Prosperities of Nickel Doped Zinc Oxide Thin Films Grown by Low Cost Modified SILAR Method

The effect of annealing in Ni doped Zinc oxide (ZnO) semiconductor thin films grown by a modified SILAR method is presented in this study. The XRD diffraction patterns reveal good crystalline quality without any appreciable changes from pure ZnO films and are genuinely polycrystalline with a hexagonal wurtzite structure. Scanning electron microscopic (SEM) investigation suggested that both the shape of the crystals and the texture of the films were highly influenced by the SILAR method. The SEM morphology shows the formation of vertical nanorods and interestingly, Ni doped ZnO shows fiber-like structures with good uniformity. These nano thin films are promising candidate for solar cells, photo detectors, and gas sensors.

Characterization of ZnO Thin Films Grown by SILAR Method

Zinc oxide (ZnO) thin films have been deposited using a SILAR (Successive Ionic Layer Adsorption and Reaction) technique, which is based on the alternate dipping of substrate in the solution and distilled water. The thin films were grown on copper, silicon and glass substrates. The precursors for ZnO films were diluted aqueous solution ZnSO4 complexed with NH3. The films were investigated by X-ray diffraction, scanning electron microscopy, XPS spectroscopy and spectrophotometer. XRD measurement showed that the films were crystallized in the wurtzite phase type with preferred orientation (002). X-ray photoelectron spectroscopy (XPS) was used to monitor changes in oxidation state of ZnO thin films. The XPS peaks of the O1s, Zn2p3/2 and Zn2p1/2 were used for studding the ZnO film. The results of influence of different parameters of SILAR method on phase structure, surface morphology, and optical properties are studied and discussed.

Growth and Characterisation of Nanocrystalline ZnO Thin Films by Dip Coating Technique

Nanocrystalline zinc oxide (ZnO) thin films have been obtained by the sol gel process. A stable and homogeneous solution was prepared by dissolving zinc acetate dehydrate as a starting material in a solution of 2-methoxyethanol and monoethanolamine (MEA). The molar concentration of zinc acetate was fixed at 0.6 mol/L while the molar ratio of MEA to zinc acetate was kept at 1:1. The films were deposited by various deposition speeds by dip-coating on glass substrates, and subsequently transformed into nanocrystalline pure ZnO films after a thermal treatment. Various deposition speeds were selected as the parameter to optimize the thin films quality. The structural and optical properties of the ZnO films were studied by X-ray diffraction (XRD), UV-Vis-NIR spectroscopy, respectively. The electrical properties of the ZnO thin films were characterised by dc 2 probing system and power supply (Advantest R6243). It was found that the deposition speed affects the resultant properties of ZnO thin films.

A comparative study of physico-chemical properties of CBD and SILAR grown ZnO thin films

In the present work, nanocrystalline zinc oxide (ZnO) thin films have been successfully deposited onto glass substrates by simple and economical chemical bath deposition (CBD) and successive ionic layer adsorption reaction (SILAR) methods. These films were further characterized for their structural, optical, surface morphological and wettability properties. The X-ray diffraction (XRD) patterns for both CBD and SILAR deposited ZnO thin films reveal the highly crystalline hexagonal wurtzite structure. From optical studies, band gaps obtained are 2.9 and 3.0eV for CBD and SILAR deposited thin films, respectively. The scanning electron microscope (SEM) patterns show growth of well defined randomly oriented nanorods and nanograins on the CBD and SILAR deposited samples, respectively. The resistivity of CBD deposited films (102Ωcm) is lower than that of SILAR deposited films (105Ωcm). Surface wettability studies show hydrophobic nature for both films. From the above results it can be concluded that CBD grown ZnO thin films show better properties as compared to SILAR method.

Structure and Electrical Characteristics of Zinc Oxide Thin Films Grown on Si (111) by Metal-organic Chemical Vapor Deposition

ZnO thin films were grown on Si (111) substrates by low-pressure metal-organic chemical vapor deposition. The crystal structures and electrical properties of as-grown sample were investigated by scanning electron microscopy (SEM) and conductive atomic force microscopy (C-AFM). It can be seen that with increasing growth temperature, the surface morphology of ZnO thin films changed from flake-like to cobblestones-like structure. The current maps were simultaneously recorded with the topography, which was gained by C-AFM contact mode. Conductivity for the off-axis facet planes presented on ZnO grains enhanced. Measurement results indicate that the off-axis facet planes were more electrically active than the c-plane of ZnO flakes or particles probably due to lower Schottky barrier height of the off-axis facet planes.

Growth of multifunctional ZnO thin films by spray pyrolysis technique

Simple and economical spray pyrolysis technique (SPT) was employed for synthesis of multifunctional zinc oxide (ZnO) thin films onto glass substrates. The synthesized material was composed of Zn2p and O1s, as confirmed from X-ray photoelectron spectroscopy (XPS). Field emission scanning electron microscopy (FESEM) image revealed the uniform distribution of grains of about 80–90nm. The film shows superhydrophobic nature with contact angle (CA) value 154°. The deposited film was specular and highly transparent with average transmittance of about 85%. The optical transmittance spectrum shows sharp band edge at 381nm, corresponding to band gap energy of 3.25eV. Film exhibits room temperature photoluminescence (PL) with a strong ultraviolet emission at 398nm with weak green emission at 520nm, confirms the less defect density in the samples. The gas sensing performance of the spray deposited ZnO films toward to reducing gases like ethanol, propanol and acetone was also studied. We examined here the viability of SPT in order to deposit such multifunctional ZnO thin films on glass substrates, which can be useful for various applications.

Crystallinity improvement of ZnO thin film by hierarchical thermal annealing

Molecular beam epitaxy (MBE) was adopted to grow zinc oxide (ZnO) film on sapphire substrate and improve the quality of ZnO thin film epitaxy using a magnesium oxide (MgO) buffer layer and a two-segment temperature scheme for ZnO thin film growth. The influence of thermal annealing of different layers on the optical and crystalline features, stress expression, as well as surface morphology of ZnO thin film was examined. SEM images showed smooth surfaces were formed, and these surfaces allowed the low-temperature ZnO buffer layer to have better epitaxial environment at the very beginning. X-ray diffraction (XRD) analysis revealed that a lower thermal annealing temperature more effectively released the stress of materials. The thermally annealed MgO buffer layer had 26% less strain than the purely thermally annealed, high-temperature-grown ZnO (HT-ZnO), and 33% less strain than the unannealed samples. Atomic force microscopy results showed that the root-mean-square of surface roughness of thermally annealed MgO was 0.255 nm, which was 80% lower than that of thermally annealed HT-ZnO (1.241 nm). Photoluminescence measurement showed that the thermally annealed MgO buffer layer had the highest strength for near-band-edge emission because of improved crystalline quality. HRTEM results showed that the stress caused by the mismatch between the sapphire lattice was effectively released because the MgO buffer layer was annealed at a high temperature. The surface of the MgO buffer layer became smooth and the stress mismatching with the ZnO lattice did not obviously extend upwards. When MBE was used to grow ZnO thin film, a lower thermal annealing temperature for the MgO buffer layer more effectively controlled stress accumulation and produced high-quality ZnO thin film.

Effects of the Argon Pressure on the Optical Band Gap of Zinc Oxide Thin Films Grown by Nonreactive RF Sputtering

Zinc oxide (ZnO) thin films were grown by nonreactive RF sputtering at room temperature under varying argon pressures (PAr). Their optical band gap was found to increase from 3.58 to 4.34 eV when the argon pressure increases from 2.67 to 10.66 Pa. After annealing at 200°C and 500°C, optical band gaps decrease considerably. The observed widening of the band gap with increasingPArcan be understood as being a consequence of the poorer crystallinity of films grown at higher pressures. Measurements of morphological and electrical properties of these films correlate well with this picture. Our main aim is to understand the effects ofPAron several physical properties of the films, and most importantly on its optical band gap.

Effect of Substrates on the Properties of ZnO Thin Films Grown by Pulsed Laser Deposition

Polycrystalline zinc oxide (ZnO) thin films have been deposited at 450°C onto glass and silicon substrates by pulsed laser deposition technique (PLD). The used source was a KrF excimer laser (248 nm, 25 ns, 5 Hz, 2 J/cm2). The effects of glass and silicon substrates on structural and optical properties of ZnO films have been investigated. X-ray diffraction patterns showed that ZnO films are polycrystalline with a hexagonal wurtzite—type structure with a strong (103) orientation and have a good crystallinity on monocrystalline Si(100) substrate. The thickness and compositional depth profile were studied by Rutherford Backscattering spectrometry (RBS). The average transmittance of ZnO films deposited on glass substrate in the visible range is 70%.

Structural and optical properties of ZnO thin films grown by using atomic layer deposition on O2-plasma-treated flexible PES substrates

Zinc oxide (ZnO) thin films have been grown by using atomic layer deposition (ALD) on O2-plasma-treated polyethersulfone (PES) substrates. We investigated the effects of the duration of O2 plasma pretreatment from 0 to 60 min on the characteristics of ZnO thin films grown on the substrates. When the duration of the plasma treatment increases, the surface roughness of the PES substrate increases. X-ray diffraction (XRD) measurements reveal an increasing tendency toward preferential c-axis orientation of the grains in the ZnO thin films with increasing duration of plasma pretreatment, which probably results from the improved crystallinity of the ZnO thin films grown on the roughened PES substrates after O2 plasma pretreatment. The roughened surfaces of PES substrates promote many nucleation sites, leading to perpendicular c-axis growth of ZnO thin films and, therefore, improved crystallinity of the ZnO thin films. The peak intensity of the NBE emission around 3.0 eV decreases with increasing duration of O2 plasma pretreatment up to 30 min. Then, it rapidly increases up to 60 min. The variations of the PL intensity and the NBE peak position strongly depend on the crystallinity of the ZnO thin films.

Influence of Annealing Temperature on the Properties of ZnO Thin Films Grown by Sputtering

Zinc oxide (ZnO) thin films were deposited by RF magnetron sputtering onto ITO coated soda-lime glass substrates. The effects of annealing in temperature range of 250 to 450°C on the structural and optical properties of the ZnO films have been studied. The crystalline structure, surface topology, morphology, optical properties of the films were determined using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV–Visible Spectrometry, respectively. X-ray diffraction measurement showed that the annealed ZnO films were polycrystalline in nature with (002), (101) and (001) oriented crystallites of hexagonal wurtzite structure. Crystalline property and grain size of the films were found to increase after annealing. The optical band gap of ZnO films initially blue shifted (3.1–3.23eV) when annealed at 400°C and further red shifted in the range of 3.23 to 3.1eV being annealed at 250 to 450°C range. From the UV spectroscopy, the films showed transmittance over 85% in the optical bandgap spectrum. All these results indicate that post deposition annealing improves the film quality with reduced roughness and better crystalline properties that can be utilised as buffer layer in the CIGS or CdTe thin film solar cells.

Evaluation of Acceptor Binding Energy of Nitrogen-Doped Zinc Oxide Thin Films Grown by Dielectric Barrier Discharge in Pulsed Laser Deposition

In this research, nitrogen (N)-doped zinc oxide (ZnO) thin films have been grown on a sapphire substrate by dielectric barrier discharge (DBD) in pulsed laser deposition (PLD). DBD has been used as an effective way for massive in-situ generation of N-plasma under conventional PLD process conditions. Low-temperature photoluminescence spectra of N-doped ZnO thin films provided near-band-edge emission after a thermal annealing process. The emission peak was resolved by Gaussian fitting and showed a dominant acceptor-bound excitation peak () that indicated acceptor doping of ZnO with N. The acceptor binding energy of the N acceptor was estimated to be approximately 145 MeV based on the results of temperature-dependent photoluminescence (PL) measurements.

Structural Characterization of Bismuth Zinc Oxide Thin Films Grown by Plasma-Assisted Molecular Beam Epitaxy

We report the structural characterization of thin films grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. By increasing the Bi flux during the growth process, thin films with various Bi contents (x

Zinc Oxide Thin Films Grown on Nanostructured Al Thin Layer/Glass Substrate by RF Magnetron Sputtering

ZnO films were deposited on nanostructured Al (n-Al) /glass substrate by RF magnetron sputtering. The results shows that the relation (I (002) /I (100) ≈ I annealed (002)/I annealed (100) ≈1.1) shows the rough n-Al surface is suitable for the growth of a-axis orientation. Meanwhile, the influences of substrate roughness, crystallinity and (101) plane of ZnO film deposited on n-Al layer have been discussed. XPS implies more oxygen atoms are bound to Aluminum atoms, which result in the increase of high metallic Zn in the film.