Properties Of ZnO Thin Films Research Articles

The Effect of Sn Dopant on the Electrical and Optical Properties of ZnO Thin Films

We study the electrical and optical properties of Sn-doped ZnO (SZO) films grown by DC-unbalanced magnetron sputtering. To study the electrical properties of the films, we perform current-voltage (I-V) measurement by using metal-semiconductor-metal configuration with Ag as a metal contact. The measurement is performed in the dark and under UV exposure condition to study the photodetection properties of the films. From the I-V curve, it shows that the sensitivity of SZO is dramatically enhanced compared to the undoped film. This enhancement is due to the role of Sn dopant, which gives more electrons to the system. Furthermore, UV-Visible spectra reveal that the band gap increase by introducing the Sn dopant. Photoluminescence spectra show SZO film exhibits a higher green emission intensity compared to ZnO film, which is related to the presence of oxygen vacancy. Our result is important to improve the functionality of ZnO for optoelectronic devices applications.

Irradiation Effects on The Sensitivity of ZnO Thin Films Synthesized on Glass Substrate by Sol-gel Method

This work investigates the structural, optical, and surface properties of ZnO thin films prepared by sol-gel method. The effect on waveguide sensor was examined at different irradiation durations of alpha particles. The X-ray diffraction (XRD) measurements revealed that the crystalline phase of ZnO thin films does not change after irradiation and showed a hexagonal structure of wurtzite type with an orientation toward (002). Moreover, ZnO thin films absorbance was increased with increasing irradiation time, whereas the transmittance was decreased. Additionally, increasing the irradiation time of alpha particles caused an increase in the extinction coefficient and the imaginary part, while the optical energy gap of the ZnO samples was decreased. Finally, the maximum value of sensitivity was 42%, found at 6 min of irradiation duration.

Optical properties of Al-doped ZnO thin films obtained by the method of high-frequency magnetron sputtering

The optical constants and thickness of Al-doped ZnO (ZnO:Al(2.5 wt.%)) thin films prepared by high-frequency magnetron sputtering method are determined. ZnO:Al thin films are crystallized in the hexagonal structure from XRD studies. The optical constants and the bandgap of the films under study have been determined. Optical properties (refractive index [Formula: see text], absorption coefficient [Formula: see text], extinction coefficient [Formula: see text], dielectric functions [Formula: see text] and optical conductivity [Formula: see text]) of thin films and thickness [Formula: see text] can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. Single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models. The increasing value of dispersion parameter for polycrystalline thin films than for single crystals is observed. The fundamental absorption edge position (3.26 eV) in the transmittance spectrum of studied thin films corresponds to the values that are typical for ZnO:Al compound. No significant increase of the bandgap width was revealed by comparing ZnO:Al thin films with the known results of the optical studies of ZnO thin films. Possible reasons of such behavior were analyzed and the influence of bandgap increase on spectral behavior of optical functions are investigated. The material optical parameters such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio were also calculated.

Physical properties of graphene oxide GO-doped ZnO thin films for optoelectronic application

This paper highlights some physical investigations on GO-doped ZnO thin films synthesized using zinc acetate dehydrate isopropyl alcohol and graphene oxide (GO) as doping element in a starting solution using a mini-spray pyrolysis process. These films, with thicknesses less than 400 nm, crystallize in hexagonal wurtzite structure with a preferential orientation according to (002) direction. The morphological characterization revealed a good homogeneity at the surface with good dispersion of graphene nanoparticles over the entire surface, especially for 2% GO doping. The refractive index and thickness of ZnO:GO thin films have been calculated using the envelope method. A decrease in the refractive index with doping was observed which indicates an increase of free carriers. In addition, band gap and Urbach energies were also deducted from the absorption coefficient. Indeed, this layer provides an increase in the dielectric constant e2 in the IR range, which is a proof of creating free electrons. Finally, the 2% GO doping gives the best optoelectrical properties of ZnO thin films which can be used in a forthcoming application for future optoelectronics.

Tribological Behaviour of Sputter Coated ZnO Thin Films

The tribological properties of ZnO thin film coated on an aluminium work piece by RF magnetron sputtering were studied as a function of deposition power, substrate coating temperature, heat treatment and rotation speed. The variation in the coefficient of friction of ZnO films produced under various levels of coating parameters and conditions were experimentally determined using a pin-on-disk tribometer. The results showed that with change in deposition conditions and heat treatment, there are significant microstructural changes in ZnO films, which affect the coefficient of friction. The hardness of the prepared films was also tested using a Vickers Hardness testing machine. There was a consistent and considerable decrease in the friction coefficient of the aluminium working piece after ZnO coating. It is found that the ZnO can be used as a low friction coating material for components working under oxidative and high temperature environments.

Influence of the Substrate, Process Conditions, and Postannealing Temperature on the Properties of ZnO Thin Films Grown by the Successive Ionic Layer Adsorption and Reaction Method.

Here, we report the effect of the substrate, sonication process, and postannealing on the structural, morphological, and optical properties of ZnO thin films grown in the presence of isopropyl alcohol (IPA) at temperature 30–65 °C by the successive ionic layer adsorption and reaction (SILAR) method on both soda lime glass (SLG) and Cu foil. The X-ray diffraction (XRD) patterns confirmed the preferential growth thin films along (002) and (101) planes of the wurtzite ZnO structure when deposited on SLG and Cu foil substrates, respectively. Both XRD and Raman spectra confirmed the ZnO and Cu-oxide phases of the deposited films. The scanning electron microscopy image of the deposited films shows compact and uniformly distributed grains for samples grown without sonication while using IPA at temperatures 50 and 65 °C. The postannealing treatment improves the crystallinity of the films, further evident by XRD and transmission and reflection results. The estimated optical band gaps are in the range of 3.37–3.48 eV for the as-grown samples. Our experimental results revealed that high-quality ZnO thin films could be grown without sonication using an IPA dispersant at 50 °C, which is much lower than the reported results using the SILAR method. This study suggests that in the presence of IPA, the SLG substrate results in better c-axis-oriented ZnO thin films than that of deionized water, ethylene glycol, and propylene glycol at the optimum temperature of 50 °C. Air annealing of the samples grown on Cu foils induced the formation of CuxO/ZnO junctions, which is evident from the characteristic I–V curve including the structural and optical data.

Enhancement of optoelectronic properties of ZnO thin films by Al doping for photodetector applications

Abstract In the present study, pure and Al-doped ZnO thin films have been deposited on glass substrates using a cost-effective nebulizer spray technique. The structural, topographical, photoluminescence, and UV detector properties of ZnO thin films have been studied for various aluminium-doping concentrations. X-ray diffraction (XRD) studies confirmed the polycrystalline hexagonal structure plane with preferred orientation along (002) direction. The ZnO structural parameters like crystallite size, dislocation density, and strain showing considerable variation with aluminium doping. Atomic force microscope (AFM) images displaying spherical grains and the grain size is increasing with Al concentration. The energy dispersive X-ray (EDX) analysis displays the presence of Zn, Al, and O elements in the deposited thin films. The optical bandgap values are decreased with aluminium doping concentration and the lowest value was observed for the 1% Al doping. Photoluminescence (PL) spectra reveal a sharp emission peak at 390 nm and peak with the shoulder at 554 nm. The Responsivity, External quantum efficiency, and Detectivity of pure and doped samples are in the range of 0.22–0.38 AW-1, 70–123%, and 1.22 × 1010 to 1.70 × 1010 Jones, respectively. The better photodetection results are observed for the 1% Al-doped ZnO thin film which indicates it is a good candidate for photo-detector applications.

UV sensitivity enhancement in Fe-doped ZnO films grown by ultrafast spray pyrolysis

The effect of Fe dopant on structural and photosensitivity properties of ZnO thin films have been studied. The Fe-doped ZnO films were fabricated by ultrafast spray pyrolysis for 30 s. As a result, X-ray diffraction analysis demonstrates that the deposited films are polycrystalline with the hexagonal wurtzite structure. Fe doping in the ZnO system provokes not only the decrease of crystallinity and crystallite size (~50% for Fe concentration of 0.5%) but also the increase of interplanar spacing and strain. Surface morphology images show that the grain size of 3% Fe-doped ZnO (67 nm) is smaller than that of the pure ZnO (114 nm). Based on I–V characterizations, Fe doping increases photocurrent as well as UV sensitivity up to 21 times (1.5% Fe) and 70 times (3% Fe) than that of the undoped ZnO. This study is important to improve the functionality of ZnO as a UV photodetector. • ZnO thin films are fabricated using ultrafast spray pyrolysis for 30 s. • Fe doping decreases the crystallinity and crystallite size of ZnO. • Fe concentration of 3% has the highest UV sensitivity. • Lower dark current and higher photocurrent are found in Fe concentration of 3%.

Structural, Morphological and Optical Properties of Spray Deposited Multi-doped (Ba, Sr, Mn, Fe and Ni) Compositionally Complex ZnO Thin Films

Configurational disorder due to high level multi element doping has gained huge attention from research community because of its possibility of unique phase stability as well as unusual functional properties. Based on this context extensive researches performed in recent decades to establish a new horizon of materials i.e. high entropy alloy and ceramics. Of-late, compositionally complex ceramics (CCCs) has been released as an extended form of high entropy ceramics (HECs) where compositional space has been broadened by consideration of both non-equimolecular compositions and relatively low entropy regions. This report aims to stabilize ZnO wurtzite phase at room temperature replacing the Zn-site with five metallic elements i.e. Ba, Sr, Mn, Fe, Ni in equimolecular ratio to impose configurational disorder in the ZnO lattice. Therefore, (BaxSrxMnxFexNix) Zn1-5xO (where x=0, 0.01, 0.02 and 0.03; the films are denoted hereby as ZO, 5DZO, 10DZO and 15DZO respectively) thin films were deposited by low cost spray pyrolysis technique at 200°C. These high-level multi-element doping results in significant effects on the structural, morphological, optical properties of pure ZnO thin film. X-ray diffraction study demonstrated ZnO wurtzite phase stabilization for each deposited film. SEM micrographs revealed a noteworthy transition from original nanorod to well distributed homogeneous fine particles morphology. UV-vis spectroscopy disclosed a sharp rise in transparency (~98%) and band gap (4eV) doped films. At the end, correlations of structural and morphological parameters with tuned functional properties were demonstrated.

Comparison of Thermoelectric Properties of ZnO and ZnSnO Thin Films Grown on Si Substrate by Thermal Evaporation

In this manuscript, we compared the thermoelectric properties of ZnO and ZnSnO thin films grown on silicon (100) substrate. We have evaporated Zn and Sn+Zn metal powders were evaporated in vacuum tube furnace alternatively, under same experimental conditions for the growth of ZnO and ZTO respectively. After the deposition, these grown films were cut into pieces and post growth annealed at different annealing temperatures from 600oC to 800oC in the air using programmable muffle furnace. Seebeck and Hall data suggested that ZTO sample shows highest value of Seebeck coefficient, electrical conductivity and power factor as compared to the ZnO samples. It is also observed that the value of Seebeck coefficient showing an increasing trend for both of the samples as we increase the post growth annealing temperature. The higher thermoelectric properties for ZTO are due the presence of Sn atoms in ZnO structure. Tin dopants may generate secondary phases and/or enhanced the carrier mobility which might be the reason that ZTO has improved thermo-electric properties as compared to ZnO. XRD and Raman measurements were used to confirm the formation of ZTO. XRD data verified the hexagonal structure of ZnO but a slight red shift is observed for the case of ZTO samples. To further justify our argument, we have also performed Raman spectroscopy measurements which confirmed the presence of Sn elements in ZTO.

Mutual effect of solvent and Fe-In codoping on structural, optical and electronic properties of ZnO thin films prepared by spray pyrolysis technique

This work demonstrates a comparative analysis of structural, morphological, optical and electronic properties of ZnO thin films with respect to change in solvent composition as well as relative codoping concentration of Fe and In. Two different solvent compositions are used i.e. methanol mixed with de-ionized water (methanol-water) and only de-ionized water. X-ray diffraction analysis shows methanol-water solvent resulting preferred orientation along (002) plane. However, de-ionized water derived ZnO samples depicts the usual three most intense peaks along (100), (002) and (101) planes as in case of zincite. There is also observed a change in morphology of the films e.g. flake like nanoparticles are found in 1 at.% Fe and 3at.% In co-doped ZnO thin films synthesized using methanol-water only. Room temperature photoluminescence emission spectra show evolution of a strong emission at 415 nm in case of low doping concentration of Fe (1–3 at.%) in codoped ZnO samples.

Influence of number of deposited layers on the microstructure, hydrophobicity and electro-optical properties of electrospun Al-doped ZnO thin films

The present study focused on the electro-optical properties of mono and multilayer Al-doped ZnO (AZO) thin films (TFs) using the electrospinning method. The microstructures of 1, 3, and 5 layered TFs were studied using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) techniques. The results revealed that the monolayered TF was formed by attaching homogeneous nanoparticles (NPs) with a size of 21 nm. With increasing the number of layers, the agglomerates of AZO NPs covered the surface of TFs, the homogeneity decreased, the thickness of TFs increased from 340 nm to 1.8 µm, and the transparency decreased from 97.3% to 85.3%. With the deconvolution of photoluminescence spectra, it was found that the point defects between valence and conduction bands of AZO TFs did not change drastically. However, their optical band gap increased from 3.24 eV monolayered TFs to 3.32 in multilayered TFs. The sheet resistance of mono and multilayered TFs was 17.3 kΩ•sq−1 and 102.2 kΩ•sq−1, respectively. This study suggests electrospinning as a controllable method for the fabrication of transparent conductive oxides (TCOs).

Modification of the photoconducting properties of ZnO thin films via low-temperature annealing and air exposure

A simple thermal annealing at 150 °C followed by exposure to air ambient conditions in epitaxial ZnO thin films produces a photoconductivity enhancement and a reduction of the energy gap. The first effect is related to a release of carriers from bulk traps while the second is caused by a gradual adsorption of species on the film surface which increases the band bending, as x-ray photoemission spectroscopy (XPS) shows. An observed drift of the photoconductivity and the energy gap over the days is connected to this adsorption kinetics. These findings have a potential application in ZnO based optoelectronic devices.

Effect of tin doping on optical properties of ZnO thin films grown on glass substrate

The optical properties of synthesized zinc oxide films doped with tin in different concentrations (0-5 mol.%) were studied. X-ray diffraction revealed that the main phase of the obtained films is ZnO (wurzite). According to SEM data, the film consists of nanocrystallites, which are 10-20 nm in size. It was shown that the introduction of 0.5 mol.% tin ions leads to an increasing in the absorption of wavelengths (in the range of 300-370 nm) and a slight narrowing of the band gap.

Influence of magnetron configurations on the structure and properties of room temperature sputtered ZnO thin films

Under the unbalanced magnetron (UBM) sputtering process, not only the plasma is confined near the target like in the conventional balanced magnetron (BM) sputtering process, but also extends towards the substrate and support the ion-assisted deposition (surface of thin films is bombarded by energetic Ar+ ions during the sputtering process). Here, we report the influence of magnetron configurations on the structure and properties of room temperature sputtered ZnO thin films while keeping other process parameters fixed. The UBM configuration has significantly improved various properties of ZnO thin films in comparison to the BM configuration. The crystalline quality with dominant orientation (002) and uniform distribution of grains is observed while an increase in the band gap from 3.25 eV (BM) to 3.33 eV (UBM) is obtained. The lower defects as investigated from Zn2p and O1s core level XPS spectra, which is well supported by Photoluminescence measurements. In addition to that, surface hydrophobicity has been increased from 121.2° (BM) to 125.5° (UBM). Thus, the unbalanced magnetron configuration in the sputtering process significantly enhanced the structural, optical and surface properties of ZnO thin films even at room temperature and low plasma power without any post annealing treatments, which is highly desired for the device fabrication.

Synthesis, optical, and photoluminescence properties of undoped and Cu-doped ZnO thin films by colloidal solution route

The effects of pure ZnO and copper (Cu) dopant on the properties of ZnO thin films grown by chemical bath deposition (CBD) and dip coating method on glass substrates are investigated. For more comparison purpose, powder samples of pure ZnO and Cu-doped ZnO prepared at room temperature. Optical properties are investigated through UV–vis–NIR transmission spectroscopy. Raman spectroscopy from ZnO films has been investigated. Photoluminescence spectra of the samples shows prominent peaks corresponding to blue emission and defect-related green emission in the visible region at room temperature and their possible mechanism have also been discussed.

Effect of post irradiation of IR light on the structural, morphological and optical properties of ZnO thin film grown by CBD method

Abstract Zinc oxide thin film was synthesized on commercial microscopic glass slide by using chemical bath deposition (CBD) technique and the prepared film was post irradiated with IR light. We compared the structural, optical and morphological properties of as deposited and IR irradiated ZnO thin films. The XRD pattern of pure and IR irradiated ZnO confirms that both the films were polycrystalline in nature. The optical band gap was found to be 3.5 eV and 3.04 eV for as deposited and IR irradiated samples. The SEM studies reveals that IR irradiation effects ZnO thin films morphology. The films prepared by this method can be used in optoelectronic applications.

Influence of Bi3+ doping on microstructure and photoelectric properties of ZnO thin film

Bismuth (Bi) doped ZnO (BZO) thin films were successfully synthesized by sol-gel spin-coating technique. The effects of the concentration and photoelectric properties of the films were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED) techniques, photoluminescence (PL) studies. The results showed that the successful doping of Bi3+ into ZnO lattice could produce more photo-generated carriers. The grain size of the film was decreased with the increasing of doping ratio. The photocurrent of 1% Bi3+ doped BZO thin film is 25% higher than that of pure ZnO thin film.

Effect of pressure on the elemental composition and magnetic properties of lithium-doped ZnO thin films

The paper presents the results of a study of the effect of pressure in a vacuum chamber on magnetic characteristics of Zn1-xLixOy thin films obtained by pulsed laser deposition on sapphire substrates as well as the results of elemental analysis across thickness of the samples. Secondary ion mass spectrometry demonstrated that the method of pulsed laser deposition allows for the synthesis of zinc oxide based thin films characterized by a high uniformity of elemental composition across thickness. It was established that different pressure in the vacuum chamber affects the number of oxygen vacancies in thin films, but not the distribution of elements across thin film thickness. Weak room temperature ferromagnetism was observed in Zn1-xLixOy thin films synthesized at a pressure of 3.15·10−5 Torr; it increases upon the increase in lithium concentration. Interstitial lithium atoms are considered to play a important role in its occurrence. The results of the study allow for expansion of the body of knowledge about the nature of room temperature ferromagnetism in zinc oxide based thin film structures as well as for developing technologies for high-quality thin film materials for recording and storing information.

Effect of heavy metals (Ni, Cu, Pb) doped ZnO on the nonlinear optical properties

In this paper, the non-linear optical properties of undoped and doped ZnO thin films were investigated. The films were doped with Ni, Pb, and Cu. an increase in the refractive index against wavelength is apparent for all films up to a certain value of wavelength. Z scan technique is used for measuring the nonlinear optical parameters via open and closed aperture configurations. Third order nonlinear susceptibilities (χ (3)) of samples were calculated. The sign of nonlinear refractive index (n2) of ZnO was changed from positive (self-focus) to negative (de-focus) upon metal doping. Doping ZnO with heavy metals changes the sign of nonlinearity although the nonlinear absorption coefficient (β) is positive for all samples; the doped materials behave as optical limiters at high intensity. These materials are promising for optoelectronic devices and optical limiting applications.