Properties Of Zinc Oxide Thin Films Research Articles

ZnO thin films as propane sensors: Band structure models to explicate the dependence between the structural and morphological properties on gas sensitivity

Pure Zinc oxide (ZnO) thin films were deposited on soda-lime glass substrates by utilizing ultrasonic spray pyrolysis technique (USP) and tested them as propane sensors. Propane sensitivity increased with decrease in the substrate temperature and water content in the feedstock solution. XRD analysis confirms that, the (002) directional ZnO which correspond to the hexagonal wurzite structure. Also, formations of rose like and spherical structures were confirmed by the SEM analysis. X-ray photoelectron spectroscopy (XPS) confirms the presence of loosely bound oxygen atoms on the surface of the low water content substrates. Two energy band structure models were proposed and explicated in detail for analyzing the effect of structural, morphological and optical properties of ZnO thin films on propane sensing properties. Highest sensitivity (~10) was obtained for ZnO films deposited with the lowest water content, at a deposition temperature of 400°C and operated at 200°C.

Effect of silver doping on optical properties of nanoflower ZnO thin films prepared by spray pyrolysis technique

Silver doped zinc oxide (ZnO) thin films have been synthesized by spray pyrolysis method on the substrate at a temperature of 450 °C. The aqueous Zinc acetylacetonate (ZnC10H14O5) and silver nitrate (AgNO3) dissolved in ethanol were used as a starting material. The effect of sliver doping on the structural, surface morphological, electrical as well as optical properties of Ag: Zno thin films were studied. It is confirmed by the X-ray diffractogram that the Ag: ZnO thin films was polycrystalline nature with the preferential orientation along (002) plane in wurtzite structure. The Scanning Electron Microscope exhibited the surface formation of nanoflower shaped grains with an addition of silver (Ag) and compositional analysis by Energy Dispersive Spectroscopy confirmed the presence of Zinc (Zn), Oxigen (O) and silver (Ag). Atomic force microscopy revealed that surface roughness of the films was decreased with the increase of silver concentration. The films were found to exhibit high transmittance and low absorbance in the visible /new infrared region.

Regulations of aging time on optical properties of nano-crystalline ZnO thin films fabricated by sol–gel method

Nano-crystalline Zinc oxide (ZnO) thin films on glass substrates have been fabricated by sol–gel method for different aging times. The thermal curve of the dried gel was examined and it was found that evaporation of solvent and the decomposition of the organics have completed before 250[Formula: see text]C. X-ray diffraction patterns and Atomic Force Microscope images of samples only have a small difference of microstructure. The transmittance spectra revealed high transmittance in visible region. The optical band gap of the samples remined stable (3.28[Formula: see text]eV). Also, the Urbach energy was calculated to explain the defect concentration. The Photoluminescence spectra in ultraviolet and visible regions were studied, and the decreased intensity of peaks at 387[Formula: see text]nm and the increased emissions in visible range were found. The results showed that excessive aging time can cause degeneration of optical properties of thin films.

Low temperature simple aqueous phase chemical synthesis and characterization of ZnO thin films

Zinc oxide (ZnO) nanorods were successfully deposited on the glass and fluorine doped tin oxide coated glass substrate in an aqueous alkaline medium using zinc acetate, ethylene diamine, hexamethylene tetraamine and ethanol by simple chemical reflux method at low temperature. An Optical, structural, morphological compositional and photoelectrochemical (PEC) properties of ZnO thin films were investigated. Optical absorption study of the sample shows band gap value 3.24 eV. The X-ray diffraction (XRD) pattern indicates that the deposited material is nanocrystalline and nanorods formation takes place along (002) plane having hexagonal wurtzite crystal structure. The scanning electron microscopy (SEM) images demonstrate existence of hexagonal nanorods with average50nm lengths and 10 nm diamete.The X-ray photoelectron spectroscopy (XPS) study confirms well composed thin film formation. The PEC study revel that material exhibit photo conversion efficiency 1.84% for solar cell application.

Impact of Post- Deposition Heat Treatment on the Morphology and Optical Properties of Zinc Oxide (ZnO) Thin Film Prepared by Spin-Coating Technique

This research work examines the structural and optical properties of ZnO thin films. Deposition were done by spin coating of solution of Zinc oxide onto pre-cleaned glass substrate at 4000 rpm for 30 sec using spin-coater under ambient condition at room temperature in order to form desired thickness of the film on the substrate. Post- deposition thermal annealing at different range of temperatures from 150°C to 600°C with steps of 50°C was carried out on the samples. The impact of thermal annealing on optical properties of the deposited thin film was investigated using UV-VIS spectrophotometer and scanning Electron Microscope for the morphology. The optical transmittance, reflectance, absorbance were recorded which was used to evaluate the optical band gap of Zinc oxide. Observation shows that band gap energy reduces as annealing temperature is increased from 150°C to 600°C. Observation made on the morphology using SEM model ASPEX 3020 showed that as the temperature increases the surface of the sample roughness increases. It was deduced that as the annealing temperature is increased the surface roughness increases. This may be due to increase in grain size with increase in annealing temperature. The band gap energy decreases as the annealing temperature increases.

Effect of the Nozzle-Substrate Distance on the Structural and Optical Properties of ZnO Thin Films Deposited by Spray Pyrolysis Technique

In the present work, zinc oxide (ZnO) thin films were deposited by pyrolysis spray technique on glass substrate temperature 350°C, using the zinc acetate with a molarity of 0.1M. Our interest is on the investigation of the nozzle-substrate distance on the structural and optical properties of the films. Structural analysis by X-ray diffraction showed that the deposited films have a preferred orientation along the direction (002) and are relatively uniform. The spectrophotometer UV-Visible confirms that it is possible to get good transparent ZnO films with a transmission of 80 to 95% in the visible. The values of optical gaps Eg deduced from the spectra of UV-Visible transmissions vary between 3.21 and 3.25 eV.

Structural and optical properties of Cr-doped ZnO thin films

In the present work, chromium (Cr)-doped zinc oxide (ZnO) thin films were prepared on silicon and glass substrates by using the sol–gel spin-coating technique. The influence of chromium doping on the structural and optical properties of zinc oxide films was investigated. The X-ray diffraction results reveal that the films are polycrystalline in nature with hexagonal wurtzite structure. The absence of secondary diffraction peaks other than those for zinc oxide suggests that the chromium ions successfully replaced zinc (Zn) ions and were incorporated into the crystal-lattice positions. The average grain size and the strain arising due to the introduction of chromium ions in the lattice were obtained by using Williamson–Hall analysis. The surface morphology of the films was observed by field emission scanning electron microscopy. The Raman spectra of the films show a peak at 434 cm−1 corresponding to E2 (high) mode of crystalline zinc oxide wurtzite structure, and the intensity of this mode decreases with increase in chromium doping. The films are highly transparent (∼90%) in the visible region, which reduces with chromium doping.

Morphological, Structural and Optical Properties of ZnO Thin Films Deposited by Dip Coating Method

Zinc oxide (ZnO) thin films were deposited on glass substrat by dip coating technique. The effects of sol aging time on the deposition of ZnO films was studied by using the field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and optical transmission techniques. The morphology of the films strongly depends on preparation route and deposition technique. It is noteworthy that films deposited from the freshly prepared solution feature indistinct characteristics; had relatively poor crystalline quality and low optical transmittance in the visible region. The increase in sol aging time resulted in a gradual improvement in crystallinity (in terms of peak sharpness and peak intensity) of the hexagonal phase for all diffraction peaks. Effect of sol aging on optical transparency is quite obvious through increased transmission with prolonged sol aging time. Interestingly, 72-168 h sol aging time was found to be optimal to achieve smooth surface morphology, good crystallinity and high optical transmittance which were attributed to an ideal stability of solution. These findings present a better-defined and more versatile procedure for production of clean ZnO sols of readily adjustable nanocrystalline size.

Low cerium doping investigation on structural and photoluminescence properties of sol-gel ZnO thin films

Undoped and cerium (Ce)-doped zinc oxide (ZnO) thin films with various doping concentrations of cerium (0.1–0.9 at.%) were prepared on glass substrates by the sol-gel dip-coating process. The effects of Ce doping on the structural, morphological and optical properties were studied by X-ray diffraction, energy-dispersive X-rays, atomic force microscopy, UV–visible spectrophotometry and photoluminescence spectroscopy. The diffraction patterns showed that all the samples are characterized by a hexagonal wurtzite crystalline ZnO structure with (0002) preferred orientation. The crystal quality and crystallite size were found to decrease with the Ce doping level. From the atomic force microscopy images analysis it was revealed that both of the grain size and the surface roughness decrease with the increasing of the Ce concentrations. According to UV–visible measurements all the films are highly transparent with average visible transmittance values ranging from 79% to 82%, and the optical band gap is sensitive to the dopant concentration. Room temperature photoluminescence spectra put into evidence that UV and visible emissions decrease significantly as the Ce concentration increases from 0.1 to 0.9 at.%.

Fabrication of nanostructured ZnO thin films based NO2 gas sensor via SILAR technique

Zinc oxide (ZnO) thin films have been widely used as an effective gas sensor element. In the present study, nanostructured thin films of ZnO were prepared by using the simplistic and economical successive ion layer adsorption and reaction (SILAR) technique. The effects of SILAR cycles on the structural, optical, surface morphological and electrical properties of nanostructured ZnO thin films were investigated. Characterization techniques such as XRD, UV-vis, PL, FESEM, and Hall measurement were utilized to study the physical and chemical properties of the synthesized films. XRD confirms the formation of hexagonal phase structural ZnO thin films. FE-SEM analysis reveals the formation of well-dispersed ZnO nanoparticles having sizes of ∼18–40nm. The SILAR cycles play a key role in the synthesis of nanostructured ZnO thin films and it is found that, with increasing SILAR cycles, the grain size continues increasing. Optical studies confirm the presence of oxygen vacancies in synthesized ZnO thin films. Finally, the ZnO thin films were exposed to NO2 gas with a concentration of 100ppb–200ppm and the resulting resistance transient was recorded. The nanostructured ZnO thin films synthesized at 30 SILAR cycles displays an enhancement of gas sensing performance and exhibit significantly higher responses (∼5%per ppm). Moreover, our ZnO thin-film-based gas sensor is sensitive to very low concentrations of dangerous NO2 (100ppb). The sensitive gas sensor used to trace level NO2 detection, synthesized via simple SILAR route proves the novelty of our work. The present report provides a new direction in fabricating nanostructured ZnO thin films for low-cost and efficient gas sensing applications.

Optical and structural properties of ZnO thin films after laser treatment

abstractRecently, much work has been done to improve the optical and electrical properties of zinc oxide (ZnO) films. A comprehensive study of optical properties (transmittance and scattering), electrical properties (carrier mobility, carrier concentration, conductivity, and resistance), and surface topography allows to give recommendations for optimizing the process of obtaining layers with the parameters enabling their use in thin film solar modules. Parameters of the conductive layers can be changed by the method of doping with boron zinc oxide films, ion etching, and laser annealing.

Dependence of solution molarity on structural, optical and electrical properties of spin coated ZnO thin films

Zinc oxide (ZnO) thin films were deposited on glass substrates through spin coating technique. Zinc acetate dihydrate, monoethanolamine and 2-methoxyethanol were used as the starting material, stabilizer and solvent, respectively. The effect of precursor concentration on the structural, optical and electrical properties of ZnO thin films is investigated. The X-ray diffraction studies reveal that all the films are polycrystalline in nature with preferred (002) orientation with crystallite size ranging from ~25 to 32 nm. Atomic force microscopy images infer the columnar growth of the films. From the optical measurements it was found that there was a marginal decrease in the band gap energy with increase in molarity up to 0.7 M. Optical constants and thickness of the films were found with the help of Swanepoel envelope method and were verified through ellipsometric measurements. Electrical resistivity of the grown films was found to be in the range 29–244 Ω cm, with a lowest value obtained for the films grown at 0.7 M. Carrier concentration of the grown films has also followed a similar trend. On the other hand, the Hall effect mobility (~400 cm2/Vs) was highest for the films grown at 0.7 M. Such high values make these films potential candidates for photovoltaic and display applications.

Effect of Zr+F doping and vacuum annealing on the transparent conducting properties of ZnO thin films

Zr+F-doped zinc oxide (ZnO) thin films were prepared on preheated glass substrates (at a temperature of 200°C) by sol–gel spin coating method by keeping Zr doping level at 2 at.-% and varying the F doping level from 0 to 15 at.-% in steps of 5 at.-%. All the films were annealed in vacuum ambience at 350°C. The samples were characterised for their structural, optical, electrical, photoluminescence (PL) and surface morphological properties. The hexagonal wurtzite crystal structure of the films with the crystallites oriented along (002) plane was confirmed through X-ray diffraction profiles. The crystalline quality of the films is found to be deteriorated with the increase of F doping concentration but improved after vacuum annealing. The average optical transmittance is >85% in the visible region. The vacuum annealing reduced the resistivity of the films significantly and the lowest resistivity of 3.8 × 10− 3 Ω cm is obtained for 5 at.-% of F doping.

Preparation of Nanostructured ZnO Thin Films Using Magnetron Sputtering for the Gas Sensors Applications

ZnO is one of the most promising transparent conducting oxide materials, which widely used in thin film gas sensors. In this research, the dependence of the thermal oxidation time on structural, morphological and gas sensing properties of ZnO thin films is investigated. ZnO nanostructures are synthesized by using DC magnetron sputtering for deposition of pure zinc layers on glass substrates and then thermal oxidation of deposited zinc layers to produce zinc oxide (ZnO) thin films. Obtained results from X-ray diffraction revealed that the degree of crystallinity and the average grain size of the ZnO deposited thin films enhance with increasing the thermal oxidation time. Surface topography and growth behavior of ZnO thin films have important role in optimization of gas sensing properties of these films. In this study, scanning electron microscopy and atomic force microscopy have been used to investigate the effective parameters related to the surface topography of the films. Obtained results from these analyzes revealed that the surface topography of ZnO deposited samples strongly depend on thermal oxidation time. Also the effect of thermal oxidation time on the performance of ZnO gas sensors is investigated. The results indicated that the ethanol gas sensing properties of ZnO samples improve with decreasing the size of grains.

Electric properties of ZnO thin films by RF Magnetron sputtering technique

The Zinc Oxide (ZnO) thin film deposited on n-type silicon (Si) by radio frequency magnetron sputtering at room temperature. During the Radio Frequency (RF) power, argon/oxygen gas pressure at different Standard Cubic Centimeters per Minute (SCCM), substrate temperature was varied, optimized for crystal structure, surface morphology, roughness, and optical electrical studies. The deposited films were examined crystalline structures and investigated by X-Ray Diffraction (XRD), surface morphology by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM), optical studies by UV-Vis, electrical studies by IV characteristic. The film post deposition annealed was improving the quality of the film properties

Deposition and characterisation of shear-mode ZnO sensor and micro-cantilever for contact sensing and nanoactuation

Integrated sensors in fitness and sports equipment have been developed in the last two decades. A zinc oxide (ZnO) thin film could be a suitable material for such applications due to its excellent physical and piezoelectric properties. In this paper, nanocrystalline ZnO films were deposited on silicon (Si) wafers with different substrate tilt angles (30° to 75°) and sputtering durations (2 to 4h) using RF magnetron sputtering at room temperature. ZnO thin film topographical properties, film thickness (0.8 to 3.7μm) and columnar inclined angle (14° to 34°) on the different locations of specimens were characterised by scanning electron microscope (SEM). Simulation and experimental results from the sensor arrays were also fabricated using fabrication techniques compatible with a standard micromachining process. The simulation and experiments for sensor arrays proved that sensor arrays were capable of distinguishing the differences of contact force values, contact locations and directions. Moreover, ZnO thin film micro-cantilevers were fabricated and tested by an AC impedance technique and a laser doppler vibrometer (LDV). The results exhibited good piezoelectric properties of shear-mode ZnO thin film driven cantilevers.

Chemical bath deposited ZnO thin film based UV photoconductive detector

Ag/ZnO/Ag metal-semiconductor-metal (MSM) Ultraviolet (UV) photodetectors based on Zinc oxide (ZnO) thin films are successfully fabricated on the glass substrate by using chemical bath deposition (CBD), which shows the good ohmic contact behavior between metal-semiconductor junctions. The devices are characterized to investigate the effect of deposition time and thickness on the photoconductive properties of ZnO thin films. The physiochemical properties of ZnO thin films are carried out. Thin films exhibit hexagonal crystal structure with the preferential orientation along (002) plane. With the applied bias of 5 V, the ZnO based photodetector shows low dark current and high photocurrent of 113.83 μA. The device exhibits relatively high photoresponse with rise time about 9 s and fall time about 21 s. It suggests that ZnO thin films are potential candidates for the UV photodetector application using easy and low-cost fabrication method.

Fabrication of Si/ZnO vertical n–n+ and p–p+ isotype junction devices by pulsed laser deposition

Device development and electrical characterization of high quality zinc oxide (ZnO) thin films grown on silicon (100) substrates are presented in this paper. Thin films of ZnO are grown at an optimized growth temperature of 300°C and two oxygen overpressure regimes on n and p-type Si substrates by pulsed laser deposition technique. Current–voltage characteristics of four devices are investigated by deposition of silver contacts on ZnO films and back gating the substrates. Rectifying properties are observed for two devices: one, for the n-Si substrate device with the film grown at low (6.66×10−4Pa) oxygen overpressure and two, for the p-Si device with ZnO grown at high (3.33×10−2Pa) oxygen. For the other two devices, namely the devices with the films grown on n-Si at high oxygen and p-Si at low oxygen pressure less pronounced rectifications are observed. Forward bias currents follow a quadratic current–voltage (IV) relationship, and this is in agreement with space-charge-limited current transport theory. Our results confirm the effects of the growth conditions including oxygen overpressure and growth substrate on intrinsic carrier concentrations and, hence, electrical properties of ZnO thin films. We conclude that output characteristics of Si/ZnO junction devices can be adjusted by modifications of growth conditions to create p–n equivalent junctions. The results have significant contributions to the development of future ZnO-based devices.

Growth-temperature-dependent optical and acetone detection properties of ZnO thin films**Project supported by the Dong-Eui University Grant (No. 2014AA342).

Zinc oxide (ZnO) thin films were prepared onto glass substrates at moderately low growth temperature by two-stage spray pyrolysis technique. The effects of growth temperature on structural, optical and acetone detection properties were investigated with X-ray diffractometry, a UV–visible spectrophotometer, photoluminescence (PL) spectroscopy and a homemade gas sensor testing unit, respectively. All the films are polycrystalline with a hexagonal wurtzite phase and exhibit a preferential orientation along [002] direction. The film crystallinity is gradually enhanced with an increase in growth temperature. The optical measurements show that all the films are physically highly transparent with a transmittance greater than 82% in the visible range. The band gap of the film is observed to exhibit a slight red shift with an increasing growth temperature. The PL studies on the films show UV/violet PL band at ∼ 395 nm. Among all the films investigated, the film deposited at 250 °C demonstrates a maximum sensitivity of 13% towards 20 ppm of acetone vapors at 300 °C operating temperature.

Properties of antimony doped ZnO thin films deposited by spray pyrolysis technique

Antimony (Sb) doped zinc oxide (ZnO) thin films were deposited on the glass substrate at 450°C using spray pyrolysis technique. Effect of Sb doping on surface morphology structural, optical and electrical properties were studied. X-ray diffraction (XRD) analysis showed that both the undoped and doped ZnO thin films are polycrystalline in nature with (101) preferred orientation. SEM analysis showed a change in surface morphology of Sb doped ZnO thin films. Doping results in a marked increase in conductivity without affecting the transmittance of the films. ZnO films prepared with 3 at % Sb shows the lowest resistivity of 0.185 Ohm cm with a Hall mobility of 54.05 cm2 V–1 s–1, and a hole concentration of 6.25 × 1017 cm–3.