Optical Properties Of Zinc Oxide Films Research Articles

Effect of Carrier Gas Flow Rates on the Structural and Optical Properties of ZnO Films Deposited Using an Aerosol Deposition Technique

Aerosol deposition (AD) is a simple, dry raw-powder deposition process in which the targeted film is formed by direct bombardment of accelerated starting powder onto the substrate surface at room temperature. Despite the increased interest in AD film formation, no work has been completed to systematically investigate the formation of dense zinc oxide (ZnO) films using the AD method and their optical properties. Therefore, this study was carried out to investigate the effect of AD gas flow rate on the formation of AD films and the optical properties of aerosol-deposited ZnO films. ZnO films with nanosized (<40 nm) crystallites were successfully deposited on FTO substrates at room temperature. A dense and uniform layer of aerosol-deposited ZnO films with a roughened surface was obtained without subsequent heat treatment. With the increase in the AD gas flow rate, the crystal size and the AD film’s thickness were reduced. The Raman spectroscopy verified that the thin film was of a ZnO wurtzite structure. The room temperature photoluminescence of the ZnO thin film produced strong visible emissions. The findings of this work demonstrated that AD can be an alternative technique for the rapid deposition of dense and thick ZnO films for optoelectronic applications.

Optic properties of ZnO films grown by sol-gel technique

Background. Zinc oxide (ZnO) is a promising material for designing the semiconductor radiation sources and detectors in the region of short wavelengths of the optical range. Films based on ZnO are considered as possible elements of optoelectronic devices that can be used to influence their optical properties. Nowadays, the methods of making such films are quite diverse, however, obtaining high-quality and inexpensive ZnO films remains an actual scientific and engineering task that needs to be solved. Thus, the research in this direction and the development of recommendations on the synthesis of ZnO films is urgent. Purpose of Work. The aim of the work is to obtain ZnO films by the sol-gel technique, to evaluate their structure and optical properties and to estimate the affect of ultraviolet radiation on the structure and optical characteristics of the obtained films. Techniques and Methodology. The process of obtaining ZnO films is considered. The process of obtaining such films by sol-gel technique is described. A visual analysis of the experimentally obtained films has been carried out. The optical properties of ZnO films were experimentally examined. In particular, the influence of ultraviolet radiation used at the stage of obtaining films on the features of their ability to absorb radiation in the optical range is analyzed. Results. ZnO films were grown experimentally by sol-gel technique. ZnO films were formed on quartz substrates. The formation of ZnO nanoparticles is observed in the films obtained without the influence of radiation. The usage of ultraviolet radiation at the stage of the final heat treatment at a temperature of 480 °C leads to the formation of a higher quality ZnO film and a decrease in the size of the granules. Analysis of the chemical composition of the films using X-ray fluorescence analysis shows the presence of zinc and oxygen in the formed films, as well as insignificant carbon content, which is associated with the use of quartz as substrates. The dependencies of the transmission capacity of ZnO films on the wavelength of radiation incident on the film in the range of 200-450 nm are obtained. It is shown that in films exposed to ultraviolet radiation at the stage of heat treatment, there is a shift in the value of the cut-off wavelength corresponding to the absorption edge and, accordingly, a decrease in the band gap calculated from the results of the experiment. Conclusions: To summarize the results of the research we can highlight that the influence of ultraviolet radiation at the stage of the final heat treatment on ZnO films formed by sol-gel method leads to an improvement in the quality of the films and to a change in their optical properties, in particular, a decrease in the energy corresponding to the absorption threshold.

Study on fabrication of Sn-doped ZnO thin films oriented to the application for organic dye degradation catalysts in water environment

In this study, zinc oxide (ZnO) doped with Sn thin films were deposited on the glass substrate at 550 °C by dip-coating technique using the solution synthesized by sol-gel method. The structural, surface morphology, optical and photocatalytic property of thin films were studied. X-ray diffraction (XRD) analysis showed that the Sn-doping greatly changed the microstructure, morphology and optical properties of ZnO films, which may contribute to the enhancement of photocatalytic activity. Additionally, the photocatalytic activity was investigated using methylene blue dye under solar irradiation, with has high UV index from 7 to 8. The results indicated that Sn-doped ZnO had a higher photocatalytic activity and Sn dopant greatly increased the photocatalytic activity of ZnO thin film.

Effect of Deposition Temperature on the Physical Performance of n-ZnO/p-Si Heterojunction

Comparative study of the physical characteristics of n-ZnO/p-Si heterojunction diode has been done as a function of deposition temperature in the range of 300-600 °C. Transparent conducting (TC) Zinc Oxide (ZnO) thin films were deposited by atmospheric pressure chemical vapor deposition (APCVD) technique on the p-Si(100) and glass substrates. Also, the influences of different deposition temperature on the morphology and optical properties of ZnO films were studied. Both the average surface roughness (from 62.8 to 18.8 nm) and the root mean square (from 78.2 to 24 nm) of ZnO films were decreased with the increase in the deposition temperature. Optical transmittance measurement results exhibited good transparency within the visible wavelength range for the films prepared at a temperature above 400 C. The current-voltage (I-V) characteristics of the heterojunction diodes exhibited rectification behavior and depend on the deposition temperature. The electrical parameters of the n-ZnO/p-Si heterojunctions were also affected by the deposition temperature. The diodes prepared at a temperature above 400 C were possessed lower reverse saturation current and high rectification ratio compared to those fabricated at a relatively lower temperature such as 300 C or 400 °C. Such low a temperature grown n-ZnO/p-Si heterojunction diodes with lower reverse saturation current could be suitable for photo-detection applications.

Resistive Switching Behaviour of Dip Coated ZnO Films with the Changing with Drawal Speed

Zinc Oxide (ZnO) thin films were produced by the sol gel dip coating process on the p-type silicon substrate with various withdrawal speeds changing from 1 to 4 cm/min, respectively. The films were annealed at a temperature of 500 °C for an hour in air ambient. The thin film thickness was found to be raised with the rise in withdrawal speed. The uniform distribution of the grains was appeared for all the films. The evolution of c-axis oriented (002) peak was revealed from X-ray diffraction (XRD) studies. The microstructural and optical properties of ZnO films were investigated by Raman, FTIR and photoluminescence spectroscopy (PL). The resistive switching properties of ZnO based memristors were studied by performing the current-voltage (I-V) measurements, where the thin films coated with lower withdrawal speed, have shown better switching property with rapid rise and fall of current during SET and RESET process, respectively.

Effects of NH3 flow on structural and optical properties of ZnO films grown by atmospheric-pressure chemical vapor deposition

Structural and optical properties of zinc oxide (ZnO) films doped with nitrogen (N) grown on r-plane sapphire substrates by the atmospheric-pressure chemical vapor deposition using zinc, water, and ammonia (NH3) as source materials have been studied. The small amount of NH3 flow was found to be effective for improving the film orientation and surface morphology. Photoluminescence (PL) spectra of the as-grown undoped and N-doped ZnO films were composed of a near-band-edge emission with two peaks at ~376 and ~386 nm and a green band (GB) emission with a peak at ~540 nm. PL and PL excitation (PLE) measurements for the as-grown N-doped films grown at the different NH3 flow rates indicated the possibility of the contribution of the N and/or hydrogen (H) related defect to both the appearance of the peak at ~386 nm and the excitation process of the GB emission. The comparison between the PL and photoacoustic (PA) spectra showed that the N atom occupying oxygen site (NO) or its complex defect is the most conceivable candidate for the non-radiative center responsible for the intra-band-gap PA absorption. After post annealing under the different conditions, a red band (RB) emission appeared at ~720 nm besides the GB emission. Both the RB and GB emissions observed for the annealed films were found to be effectively excited by the band-to-band (inter-band-gap) and free exciton transitions. Regardless of the difference in annealing condition, all the PLE spectra for the RB emissions showed a weak excitation band extending from 460 nm to 680 nm, suggesting the formation of the deep impurity level probably due to the NO acceptor. It was also confirmed by X-ray photoelectron spectroscopy that the NO deep acceptors were formed in the films, but passivated by the H atoms and/or compensated by the H related donors and/or by the nitrogen molecule substituting oxygen site [(N2)O] double donors.

Structural and optical properties of ZnO films grown on ion-plated Ga doped ZnO buffer layers by atmospheric-pressure chemical vapor deposition using Zn and H2O as source materials

Zinc oxide (ZnO) films were grown on glass substrates with ion-platedGa-doped ZnO (GZO) buffer layers at various substrate temperatures by atmospheric-pressure chemical vapor deposition using Zn powder and water as precursors. All the X-ray diffraction patterns of the ZnO/GZO films were dominated by a ZnO(002) peak, indicating the successful growth of highly c-axis oriented films. The substrate temperature dependence of growth rate was divided into three regions with the different activation energies, i.e.re-evaporation, mass-transport controlled and surface-controlled regions. Scanning-electron-microscope observations revealed that the films grown at the substrate temperature in the mass-transport-controlled region exhibited the terrace-like surface morphology with rock-like structures. Photoluminescence spectra of the ZnO/GZO films were composed of a near-band-edge (NBE) emission at a wavelength of about 380 nm and a broad-band emission spreading over the visible wavelength region, as regardless of the substrate temperature. The visible-broad-band emissions observed on many samples could be decomposed into two or three peak emissions with the Lorentzian shapes. With increasing substrate temperature, the wavelength of the emission showing the strongest intensity, which was obtained by the decomposition of the visible-broad-band emission, shifted towards longer wavelengths together with the broadening of its width.

Influence of Annealing Time on the Structural, Morphological and Optical Properties of ZnO Films

Zinc oxide (ZnO) thin films have been synthesized by thermally oxidizing the direct current magnetron sputtered zinc (Zn) films at 500[Formula: see text]C for different annealing time periods (3–5[Formula: see text]h) in ambient air. Influence of annealing time on the structural, morphological, optical and electrical properties of ZnO films was studied using X-ray diffractometer, field emission-scanning electron microscopy (FE-SEM), UV–Vis spectrophotometer and two-probe method, respectively. ZnO films exhibited hexagonal crystal structure with (1 0 1) as preferential orientation plane, and the crystallite size of the films increased from 30[Formula: see text]nm to 83[Formula: see text]nm on increasing the annealing time. Pebble-like surface morphology was observed from the FE-SEM micrographs. Optical band gap of the films varied between 3[Formula: see text]eV and 3.5[Formula: see text]eV for different annealing times. Electrical resistance of the ZnO films was decreased with increase in the annealing time, which is due to the improvement in the crystallinity.

Structural, morphological and optical properties of ZnO films by thermal oxidation of ZnSe films

In this work, zinc oxide (ZnO) thin films were synthesized by thermal oxidation of zinc selenide films in oxygen atmosphere without introducing any catalysts or additives. According to the X-ray diffraction and morphology analysis, the ZnO films were hexagonal wurtzite structure, indicating the high crystalline quality. Strong emission peak at around 370nm (ultraviolet) and weak emission peak at 525nm (green) were observed in the photoluminescence spectra. The dependence of photoluminescence intensity on annealing conditions was investigated in the experiment. With the increase of annealing temperature and time, the photoluminescence intensity reached a peak at 450°C for 45min in oxygen, which was considered to be the optimal condition.

Annealing Effect on Structural and Optical Properties of ZnO Films Prepared by Ultrasonic Spray Pyrolysis

Zinc Oxide (ZnO) thin films were deposited on glass substrates via the ultrasonic spray pyrolysis technique. The films were subsequently annealed in ambient air from 350°C to 550°C for 3h. The morphology and structural properties of the thin films were studied by atomic force microscopy (AFM) and X-ray diffractometry (XRD) techniques. The X-ray diffraction studies revealed that the films are polycrystalline with the hexagonal structure and a preferred orientation along (002) directions. The optical properties of the films were characterized by UV-vis spectroscopy. The transmission values of the annealed ZnO films were average 80% within the visible range (400–700 nm). The optical band gap values of the films are between 3.27 and 3.23 eV. Electrical resistivity of the films was measured using four-probe measurement system. The electrical resistivity of the films decreased with the increasing annealing temperature. According to our investigation results, it can be seen that annealing treatment plays an important role on the some physical properties of ZnO films.

Characterization of zinc oxide films deposited in helium–oxygen and argon–helium–oxygen atmospheres by sputtering

Zinc oxide (ZnO) thin films were deposited onto glass substrates by radio frequency (RF) magnetron sputtering using a metallic zinc target. Zinc oxide films were prepared in two different gas atmospheres; in the first set, helium and oxygen gas flow ratio (He:O2) was varied from 87.5% to 37.5%. In the second set of experiment, oxygen flow rate was kept constant at 2.5 sccm while argon and helium gas flow ratio (Ar:He) was varied from 9.0% to 87.5%. The structural, wettability, and optical properties of ZnO films were investigated by X-ray diffractometry (XRD), contact angle measuring system, and UV–vis–NIR spectrophotometer. The XRD results show increased preferred orientation along (002) plane for deposited ZnO films in both cases. The average crystallite size of ZnO films increases with increase in gas ratio for both set of experiments. The deposited films are hydrophobic by nature for water and ethylene glycol. Optical transmittances greater than 60% were observed in the wavelength interval from 450nm to 650nm for both cases.

Effect of Flexible Substrates on the Structural and Optical Properties of ZnO Films Deposited by Sputtering Method

Zinc Oxide (ZnO) has attracted much attention because of its high optical transmittance approximately ~80 % with a wide band gap of (3.3 eV at 300 K) and a relatively low cost material. ZnO thin films were deposited on plastic substrate using RF powered magnetron sputtering method. The target used is ZnO disk with 99.99 % purity. The sputtering processes are carried out with argon gas that flow from 10-15 sccm. Argon is used to sputter the ZnO target because the ability of argon that can remove ZnO layer effectively by sputtering with argon plasma bombardment. The deposited ZnO thin films are characterized using X-Ray Diffraction (XRD) and UV-Vis Spectrometer. The analysis of X-ray diffraction show that good crystalline quality occurs at nominal thickness of 400 nm. The optical studies showed that all the thin films have high average transmittance of approximately 80 % and the estimated value of optical band gap is within 3.1 eV-3.3 eV range.

Electrical and optical properties of zinc-oxide films deposited by the ion-beam sputtering of an oxide target

The influence of the parameters of the deposition process on the stoichiometric composition and electrical and optical properties of ZnO films deposited by the ion-beam sputtering of a ZnO target is studied. It is established that, upon sputtering of a ZnO target with stoichiometric composition, there is a deficit of oxygen in the films deposited. Even for the case of target sputtering in a pure O2 atmosphere, the stoichiometry index of the films is no higher than 0.98. A decrease in the oxygen content in the films is accompanied by a sharp decrease in the resistivity to 35–40 Ω m, narrowing of the optical band gap, and a shift of the optical transmittance edge from 389 to 404 nm. All of the variations in the optical and electrical properties of the ZnO films can be attributed to variations in the concentration and mobility of free charge carriers in the films.

Influence of Sn Low Doping on the Morphological, Structural and Optical Properties of ZnO Films Deposited by Sol Gel Dip-Coating

In this work, Undoped Zinc Oxide (ZnO) and Sndoped Zinc Oxide (ZnO:Sn) films have been deposited by sol-gel dip coating method, where the Sn/Zn atomic ratio was 3% and 5% in the solution. The effects of Sn incorporation on morphological, structural and optical properties of ZnO films were investigated. The Scanning Electron Microscopy (SEM) showed that the morphological surface of the films was affected by Sn low doping. The X-Ray Diffraction (XRD) patterns showed that all films have polycrystalline structures, and the doping incorporation has not lead to substantial changes in the structural characteristics of ZnO films. The crystallite size was calculated using the well-known Scherrer’s formula and found to be in the range of 23 - 40 nm. The measurements from UV-Visible Spectrophotometer (U-Vis) indicated that the highest average optical transmittance in the visible region was related to Undoped ZnO film, then the optical band gap and Urbach energy values of thin films were calculated. The X-Ray Photoelectron Spectroscopy (XPS) has demonstrated that Sn is incorporated in ZnO lattice.

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%.

Effect of Zn Sputtering Rate on the Morphological and Optical Properties of ZnO Films

Zinc oxide (ZnO) thin films were deposited onto glass substrates by reactive radiofrequency (RF) magnetron sputtering using a metallic zinc target. Optical emission spectroscopy (OES) was used to monitor and control the Zn sputtering rate for the deposition of the ZnO films. Film thicknesses ranged from 350 to 750 nm. Optical transmittances greater than 80% were observed in the wavelength interval from 450 nm to 650 nm. The energy gap of the films remained constant at (3.28 ± 0.01) eV. The surface morphology was found to be homogeneous with well-distributed structures. Surface roughness was dependent on the Zn sputtering rate, indicating that greater densities of Zn atoms increase the surface diffusion. X-ray diffraction (XRD) analysis showed that the ZnO films were polycrystalline with a hexagonal wurtzite structure and preferential growth along the (002) plane.

Effect Of Film Thickness On The Structural Morphological And Optical Properties Of Nanocrystalline ZnO Films Formed By RF Magnetron Sputtering

Zinc oxide (ZnO) thin films were formed by RF reactive magnetron sputtering onto p-type silicon and glass substrates held at room temperature. The thickness of the films deposited was in the range 160 – 398 nm. The thickness dependence structural, morphological and optical properties of ZnO films were systematically investigated. The maximum crystallite size of 21 nm observed at films thickness of 231 nm by X- ray diffraction. Scanning electron microscopic analysis revealed that the growth of nanowires in all the films. The root mean square roughness of the films increased from 7.3 to 53 nm in the thickness range of investigation. Fourier transform infrared analysis confirmed the Zn-O bonding located at wavenumber of 413 cm -1 . The average optical transmittance of the films was about 89 % in the visible region. The optical band gap of the ZnO films decreased from 3.14 to 3.02 eV with increase of film thickness from 160 to 398 nm respectively. Copyright © 2012 VBRI Press.

Fabrication and characterization of ZnO thin film using sol–gel method

In this work, the sol–gel method used to fabricate zinc oxide (ZnO) thin film on silicon (Si) substrate. To this purpose, zinc acetate dihydrate and monoethanolamine were used as solvent and stabilizer materials respectively. Structural and optical properties of ZnO films were studied. X-ray diffraction (XRD) analysis of the films showed polycrystalline nature of the prepared films. Depend on XRD peak of ZnO film with orientation (100), therefore, Scherrer's formula was used to calculate crystallite size of prepared films. Scanning electron microscopy (SEM) used to describe the surface morphology and Photoluminescence (PL) measurements revealed the energy bandgap of the films was in UV emission at 380nm. Finally, thickness of the films was measured with Filmetric (F-20). The result showed that we successful to fabricate ZnO films in simple and low cost method with high quality.

Effects of oxygen/argon ratio and annealing on structural and optical properties of ZnO thin films

Zinc oxide (ZnO) thin films were prepared on quartz substrate using radio frequency magnetron sputtering at various oxygen/argon (O2/Ar) flow ratios. The structural and optical properties of ZnO films were investigated in dependence of O2/Ar ratio and annealing temperature by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman scattering spectroscopy, UV–visible spectroscopy and photoluminescence (PL) spectroscopy. XPS spectra showed that the peak positions of the O1s and Zn 2p shifted to opposite directions of binding energy with increasing O2/Ar flow ratio, and the as-deposited ZnO films changed from the Zn-rich to O-rich. Raman spectra revealed that ZnO films consisted of wurtzite structure exhibited high crystalline quality and c-axis preferred orientation after annealing at 420°C. The transmittance and energy band gap (Eg) of the as-deposited ZnO films increased with increasing O2/Ar flow ratio. As the films were annealed, the Eg decreased first and then increased with annealing temperature. The PL spectra indicated that all films exhibited a violet emission peak and the ZnO films prepared at O2/Ar=35/35 showed an additional green emission. The origin of both emission peaks and the change in the intensity with O2/Ar ratio and annealing temperature were discussed.

Structural and optical properties of copper doped ZnO films derived by sol–gel

Undoped and copper doped ZnO (ZnO:Cu) films were prepared by sol–gel spin coating technique. The effect of Cu incorporation on the structural, morphological and optical properties of the Zinc oxide (ZnO) film was investigated. The chemical composition of the Cu doped ZnO films was confirmed by XPS and XRD measurements. The structural disorder was observed in XRD spectra depending on the Cu incorporation and these results were confirmed by the increasing Urbach energy values. The refractive index dispersion was analyzed by single oscillator model developed by Wemple and DiDomenico. The oscillator energy and dispersion energy values for the films were determined. The oscillator energy value Eo for the ZnO film decreases with Cu incorporation due to increase in the probability of electronic transitions between electronic bands. It is evaluated that the structural and optical properties of ZnO films can be controlled with Cu doping.