Sol–gel derived undoped and boron-doped ZnO semiconductor thin films: Preparation and characterization

We report the influence of boron doping concentration on the microstructure, electrical and optical properties of solution-processed zinc oxide (ZnO) thin films. The B doping concentration in the resultant solutions was varied from 0 to 5 at%, and the pH value of each synthetic solution was adjusted to 7.0. XRD measurements, SEM observations, and SPM examinations revealed that boron doping produced ZnO thin films consisting of a fine grain structure with a flat surface morphology. Moreover, ZnO thin films doped with B raised the texture coefficient along the (002) plane. All B-doped ZnO (ZnO:B) thin films exhibited higher transparency than that of the undoped ZnO thin film in the wavelengths between 350 and 650 nm. The optical band gap and Urbach energy of the ZnO:B thin films were higher than those of the undoped thin film. According to electrical transport characteristics, the 1% B-doped ZnO thin film exhibited the highest Hall mobility of 17.9 cm²/V s, the highest electron concentration of 1.2×10¹⁵ cm⁻³, and the lowest electrical resistivity of 2.2×10² Ω cm among all of the ZnO:B thin films.     

Effect of nickel doping on structural,optical, electrical and ethanol sensing properties of spray deposited nanostructured ZnO thin films

Undoped and nickel (Ni)-doped ZnO thin films were spray deposited on glass substrates at 523 K using 0.1 M of zinc acetate dihydrate and 0.002–0.01 M of nickel acetate tetrahydrate precursor solutions and subsequently annealed at 723 K. The effect of Ni doping in the structural, morphological, optical and electrical properties of nanostructured ZnO thin film was investigated using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV–vis Spectrophotometer and an Electrometer respectively. XRD patterns confirmed the polycrystalline nature of ZnO thin film with hexagonal wurtzite crystal structure and highly oriented along (002) plane. The crystallite size was found to be increased in the range of 15–31 nm as dopant concentration increased. The SEM image revealed the uniformly distributed compact spherical grains and denser in the case of doped ZnO thin films. All the films were highly transparent with average transmittance of 76%. The measured optical band gap was found to be varied from 3.21 to 3.09 eV. The influence of Ni doping in the room temperature ethanol sensing characteristics has also been reported.     

Effect of doping concentration on the properties of aluminium doped zinc oxide thin films prepared by spray pyrolysis for transparent electrode applications

Zinc oxide possesses many interesting properties, such as modifiable conductivity, wide band gap, high excitonic binding energy, piezo-electric polarisation and cathodoluminiscence. In this study transparent conducting aluminium doped zinc oxide (ZnO:Al) thin films were deposited on float glass substrates by tailor made spray pyrolysis with adaptation for measuring the actual temperature of the substrate surface during deposition. The films were characterised and the effect of aluminium doping concentration [Al/Zn] on their optical, electrical and structural properties was investigated as a function of aluminium doping between 0 and 10 at.%. There was widening of optical band gap with increasing doping concentration. ZnO:Al films with low resistivity of 2.8 × 10⁻² Ω cm and high transmittance of over 85% at 550 nm which are crucial for opto-electrical applications were obtained at a doping ratio of 2 at.%.     

Nanostructure silver-doped zinc oxide films coating on glass prepared by sol–gel and photochemical deposition process: Application for removal of mercaptan

Silver-doped zinc oxide (SDZO) films have been grown on glass substrate by a novel combination of sol–gel and photochemical deposition processes (SGPD). The effect of sintering on structural, electrical and optical properties was investigated. The films were characterized by UV–vis absorption spectroscopy (UV–vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The result of X-ray photoelectron spectroscopy (XPS) revealed that the binding energy of Ag 3d_5/2 for SDZO shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between silver and zinc oxide. The XRD spectra of the SDZO films indicate that silver was incorporated in the hexagonal crystal structure of zinc oxide. SEM micrographs show the uniform distribution of spherical grains of about 73 nm grain size for the pure zinc oxide thin films. The results indicated that silver doping photochemical deposition was a feasible method to tune the optical properties of zinc oxide nanostructures. SDZO films coated on glass were applied for the photodegradation of mercaptan in water. SDZO films were applied for degradation of mercaptobenzoxazole which reduced the mercaptan concentration to more than 98%.     

Synthesis and characterization of ZnO:Ni thin films grown by spray-deposition

In the present study, nickel-doped zinc oxide thin films (ZnO:Ni) at different percentages (0–10%) were deposited on glass substrates by using a chemical spray technique. The effect of Ni concentration on the structural and optical properties of the ZnO:Ni thin films was investigated. The effect of Ni contents on the crystalline structure and optical properties of the films was systematically investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), UV–vis, Photoluminescence spectra PL, and Raman spectrometry. The XRD analysis showed that both the undoped and Ni-doped ZnO films were crystallized in the hexagonal structure with a preferred orientation of the crystallites along the [002] direction perpendicular to the substrate. The XRD analysis also showed that the films were well crystallized in würtzite phase with the crystallites preferentially oriented towards (002) direction parallel to the c-axis. SEM study reveals the surface of NiZnO to be made of nanocrystalline particles. The SEM images showed a relatively dense surface structure composed of crystallites in the spherical form whose average size decreases when the [Ni]/[Zn] ratio increases. The optical study showed that all the films were highly transparent. The band gap decreased up to the 7 at% Ni doping level, but the band gap increased after 10 at% Ni doping level. All thin films exhibited approximately 80% and above transmittance in the visible region. PL spectra of undoped and Ni-doped ZnO thin films showed some marked peaks at 376, 389, 494, and 515 nm. The obtained results revealed that the structures and optical properties of the films were greatly affected by doping levels. These films are useful as conducting layers in electro chromic and photovoltaic devices. Finally, all results were discussed in terms of the nickel doping concentration.     

Ultra-rapid microwave-assisted synthesis of gallium doped zinc oxide for enhanced photocurrent generation

Ultra-rapid microwave-assisted hydrothermal synthesis was performed, zinc oxide nanoparticles were fabricated and doped with gallium. Different times (5, 15, and 30 min) and concentrations of doped Ga (1, 3, and 6%) were used to improve their characteristic properties. In addition, the relation between time/dopant was analyzed. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and UV–Vis diffuse reflectance spectroscopy. Photoluminescence (PL) to verify number of defects. SEM analysis showed the formation of nanorods morphology even with a short synthesis time. The X-ray diffractograms and Raman spectra suggest the successful insertion of Ga into the ZnO lattice. The crystallite size obtained by doping was between 36 and 50 nm. The lattice parameters determined by the Rietveld refinement confirmed the formation of a wurtzite hexagonal structure. The band gap range found was 3.12–3.22 eV, which increases the potential of ZnO for optical applications. The presence of defects as result of doping was confirmed by PL. The microstructural changes of the material are enhanced by doping, which causes the photocurrent to increase from 0,002 to 0.012 mA/cm² in doped ZnO. The synthesis time and Ga doping facilitated the production of ZnO nanoparticles with improved properties.     

High-quality c-axis oriented non-vacuum Er doped ZnO thin films

Preparation, growth, structure and optical properties of high-quality c-axis oriented non-vacuum Er doped ZnO thin films were studied. Zn_1−xEr_xO (x=0.0, 0.01, 0.02, 0.04, and 0.05) precursor solutions were prepared by sol–gel synthesis using Zn, and Er based alkoxide which were dissolved into solvent and chelating agent. Zn_1−xEr_xO thin films with different Er doping concentration were grown on glass substrate using sol–gel dip coating. Thin films were annealed at 600 °C for 30 min, and tried to observe the effect of doping ratio on structural and optical properties. The particle size, crystal structure, surface morphologies and microstructure of all samples were characterized by X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM). The UV–vis spectrometer measurements were carried out for the optical characterizations. The surface morphology of the Zn_1−xEr_xO films depend on substrate nature and sol–gel parameters such as withdrawal speed, drying, heat treatment, deep number (film thickness) and annealing condition. Surface morphologies of Er doped ZnO thin films were dense, without porosity, uniform, crack and pinhole free. XRD results showed that, all Er doped ZnO thin films have a hexagonal structure and (002) orientation. The optical transmittance of rare earth element (Er) doped ZnO thin films were increased. The Er doped ZnO thin films showed high transparency (>85) in the visible region (400–700 nm).     

Effect of the Growth Parameters on Nonlinear Optical Properties of Al‐Doped ZnO Nano Films

The objective of this research work is to provide a systematic method to perform test and evaluation on the nonlinear optical properties of Al‐doped ZnO nano thin film structure for designing a high‐performance optical‐electronic structure. Some different kinds of samples can be manufactured for testing. The samples are designed by changing technical parameters such as sputtering power of Al and ZnO, pressure and sputtering time and each parameter has three levels. The test results show that the main factor is the sputtering power of Al, which means the doping density of Al. In the meantime, the Maxwell–Garnett theory is used to investigate the optical prosperities of Al‐doped ZnO nano thin films in the visible range. The optical band gap of Al‐doped ZnO nano thin films increases with the increasing of Al doping density, but it becomes slowly when the doping density is more than 16.0%. The results and the investigation method are useful for designing and manufacturing for nano thin films.     

Sol–gel synthesis of novel cobalt doped zinc tin oxide composite for photocatalytic application

A novel photocatalyst based on cobalt doped zinc tin oxide is proposed. Cobalt doped zinc tin oxide thin films were deposited using a sol–gel deposition method and characterized by scanning electron microscopy (SEM), X-ray diffraction, Raman spectroscopy, photoluminescence emission measurement and UV–vis spectroscopy. It was found that the addition of Co into the zinc tin oxide does influence the structural and optical properties of the thin films and increases the overall photocatalytic degradation of methylene blue.     

Optical band gap modulation by Mg-doping in In2O3(ZnO)3 ceramics

In this study, different amounts of Mg were doped in In₂O₃(Zn_1−xMg_xO)₃ and their thin films were grown by using the RF magnetron sputtering method. The optical and electrical characteristics of the films revealed that the lattice constant decreased while the optical band gap increased as the Mg content increased, showing an inverse proportional relationship with each other. Therefore, it was found that Mg doping in indium zinc oxide (IZO) is also effective for band gap modulation as it was reported in a Mg-doped ZnO system. When IZO thin films were grown in a more reducing ambient, the carrier concentration increased which resulted in the increase of band gap energy. This was explained due to the Burstein–Moss effect.     

The role of TiO2 addition in ZnO nanocrystalline thin films: Variation of photoelectrochemical responsivity

In this study, the effects of TiO₂ addition on the physical and photoelectrochemical properties of ZnO thin films have been investigated. The (TiO₂)_x–(ZnO)_1−x nanocomposite thin films were dip-coated on both glass and indium tin oxide (ITO)-coated conducting glass substrates with various values of x, specifically 0, 0.05, 0.1, 0.25 and 0.5. Optical properties of the samples were studied by UV–vis spectrophotometry in the range of 300–1100 nm. The optical spectra of the nanocomposite thin films showed high transparency in the visible region. The optical bandgap energy of the (TiO₂)_x–(ZnO)_1−x films increased slightly with increasing values of x. The crystalline structure of the nanocomposite films was investigated by X-ray diffraction, which indicated the formation of ZnO nanocrystals in the thin films with x < 0.5. Moreover, the crystallinity of the films decreased with increasing values of x. The surface chemical composition of the samples was investigated by X-ray photoelectron spectroscopy (XPS), which revealed stoichiometric ZnO and TiO₂ on the surfaces of the films. The photoelectrochemical properties of the samples were also characterized using a high-pressure xenon light source and KOH electrolyte. The addition of 10 mol% (x = 0.1) TiO₂ to the ZnO thin films resulted in the best photoresponse in the visible region of the solar spectrum. In addition, the effect of TiO₂ concentration on the electrical properties and the flat-band potential of the (TiO₂)_x–(ZnO)_1−x system was studied by impedance spectroscopy; x = 0.1 exhibited the highest donor density and charge-transfer resistance.     

Characterization of low-temperature solution-processed indium–zinc oxide semiconductor thin films by KrF excimer laser annealing

We have employed KrF excimer laser annealing (ELA) treatment on sol–gel derived indium–zinc oxide (IZO) precursor films to develop a method of low thermal-budget processing. As-coated IZO sol–gel film was dried at 150 °C and then annealed using KrF excimer laser irradiation under ambient air. The laser irradiation energy density was adjusted to 150, 250, 350, and 450 mJ/cm² to investigate the effects of laser irradiation energy density on the microstructure, surface morphology, optical transmittance, and electrical properties of laser annealed IZO thin films. Results of GIXRD and TEM-SAED indicated that the ELA IZO thin films had an amorphous phase structure. The surface characteristics and electrical properties of laser annealed IZO thin films were significantly affected by the laser irradiation energy density. It was found that the dried IZO sol–gel films irradiated with a laser energy density of 350 mJ/cm² exhibited the flattest surface, the highest average optical transmittance in the visible region, and the best electrical properties among all ELA samples.     

Enhanced thermoelectric and optical response of Ag substituted Cu2O compositions for advanced applications

Cu₂O based semiconductor materials are promising candidates for modern electronic devices due to have excellent electronic and optical properties. In this work, pure and Ag doped Cu₂O structures were simulated using density functional theory in the framework of wien2k code with generalized-gradient-approximation under full potential linearized augmented plane wave approach. Experimentally, pure and Ag doped Cu₂O uniform thin films were successfully fabricated. The morphology and elemental compositions of thin films were investigated using field emission scanning electron microscopy and energy dispersive x-rays spectroscopy, respectively. X-ray diffraction analysis exhibited cubic phase having space-group 224-Pn-3m in all synthesized thin films. Total density of states spectra for Ag containing compositions present overlapping of states at Fermi level. Thermoelectric properties show a significant variation in various parameters with the change in temperature and Ag content in structure. The see-beck coefficient was observed to vary from 0.0002 to 0.00035 Vk⁻¹ for pure and Ag doped Cu₂O compositions. The optical parameters like extinction and absorption curves attains maximum values at higher photon energies. The refractive index presents an enhanced transmittance power with the increment in photon energy. The band gap was found to reduce from 2.33 eV to 1.99 eV with Ag doping attributed to the sharp increase in optical conductivity.     

Preparation and characterization of Al-doped ZnO piezoelectric thin films grown by pulsed laser deposition

Undoped and Al-doped ZnO (AZO) thin films (Al: 3, 5 at%) using a series of high quality ceramic targets have been deposited at 450 ºC onto glass substrates using PLD method. The used source was a KrF excimer laser (248 nm, 25 ns, 2 J/cm²). The study of the obtained thin films has been accomplished using X-ray diffraction (XRD), M-lines spectroscopy and Rutherford backscattering spectroscopy (RBS). XRD patterns have shown that the films crystallize in a hexagonal wurtzite type structure with a highly c-axis preferred (002) orientation, and the grain sizes decrease from 37 to 25 nm with increasing Al doping. The optical waveguiding properties of the films were characterized by means of the prism-coupling method. The distinct M-lines of the guided transverse magnetic (TM) and transverse electric (TE) modes of the ZnO films waveguide have been observed. The M-lines device has allowed determination of the accurate values of refractive index and thickness of the studied ZnO and AZO thin films. An evaluation of experimental uncertainty and calculation of the precision of the refractive index and thickness were developed on ZnO films. The RBS results agree with XRD and m-lines spectroscopy measurements.     

Highly Efficient Room Temperature Synthesis of Silver‐Doped Zinc Oxide (ZnO:Ag) Nanoparticles: Structural,Optical, and Photocatalytic Properties

Synthesis of silver‐doped zinc oxide (ZnO:Ag) nanoparticles through precipitation method has been reported. The synthesis was conducted at room temperature and no subsequent thermal treatment was applied. ZnO nanoparticles were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), fourier transmission infrared spectroscopy (FTIR), and ultraviolet‐visible (UV–Vis) spectroscopy. Detailed crystallographic investigation was accomplished through Rietveld refinement. The effect of silver content on structural and optical properties of resultant ZnO nanoparticles has been reported. It was found that silver doping results in positional shifts for the XRD peaks and the absorption band edge of ZnO. These were attributed to the substitutional incorporation of Ag⁺ ions into Zn²⁺ sites within the ZnO crystal. In addition, higher silver incorporation resulted in smaller size for ZnO nanoparticles. The photocatalytic activity of the ZnO:Ag nanoparticles was also determined by methylene orange (MO) degradation studies and compared to that of undoped ZnO. Improved photocatalytic activity was obtained for ZnO:Ag nanoparticles. It has been shown that an optimum amount of silver dopant is required to obtain maximum photocatalytic activity.     

Experimental and Numerical Evaluation on Optical Properties of Al‐Doped ZnO Film Materials

The aim of this article is to provide a systematic method to perform numerical and experimental evaluation on the optical properties of Al‐doped ZnO nano thin films. Some different doping density samples are deposited for testing the transmittance. The results show that the transmittance of Al‐doped ZnO has a nonlinear relation with the optical constants and Al‐doped quantity. The optical band gap of the Al‐doped ZnO decreases with the Al doping quantity increasing. Meanwhile, the Maxwell‐Garnett (MG) theory is used to investigate the optical properties of Al‐doped ZnO nano thin films in visible range. The comparison can illustrate the validity of both test and design method. It implies a potential design and evaluation method for developing a new type of ceramic nano thin film in engineering.     

Al3+ doping induced changes of structural,morphology, photoluminescence,optical and electrical properties of SnO2 thin films as alternative TCO for optoelectronic applications

Highly transparent and conductive pure (SnO₂) and aluminum doped tin oxide (Al:SnO₂) thin films were deposited on glass substrates by the sol-gel spin-coating method. The structural, morphological, optical and electrical properties of the prepared thin films at different doping rates have been studied. X-ray diffraction results revealed that all the films were polycrystalline in nature with a tetragonal rutile structure. SEM images of the analyzed films showed a homogeneous surface morphology, composed of nanocrystalline grains. The EDS results confirmed the presence of Sn and O elements in pure SnO₂ and Sn, O, Al in doped SnO₂ thin films. The optical results revealed a high transmittance greater than 85% in the visible and near infrared and a band gap varying between 3.82 and 3.89 eV. PL spectra at room temperature showed that the most dominant defects correspond to oxygen vacancies. A low resistivity of order varying between 10^?3 and 10^?4 Ω cm and a high figure of merits ranging between 10^?3 and 10^?2 Ω^?1 in the visible range were obtained. The best performances were obtained for samples containing 2 at. % Al, which could be used as an alternative TCO layer for future optoelectronic devices.     

Characterization of Pure and Al Doped ZnO Thin Films Prepared by Sol Gel Method for Solar Cell Applications

Pure and Al-doped Zin Oxide ZnO (AZO) thin films with different aluminum (Al) concentrations (0.5, 1, 2, and 3 at.%) were prepared on glass substrates by a dip-coating technique using different Zn and Al precursors. The structural, morphological, optical and electrical properties of these films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Atomic force electron microscopy, ultraviolet–visible spectrophotometry, photoluminescence (PL) spectroscopy and four-point probe technique. XRD results showed that the obtained AZO thin films were polycrystalline with a highly c-axis preferred (002) orientation, and the average crystallites size decreased from 29 to 25 nm with the increase in Al doping concentration. EDS microanalysis confirmed the presence of Zn, O and Al elements in the prepared films as expected. The optical study demonstrated that the ZnO thin film had a good transparency in the visible range with a maximum transmittance of 90% and the band gaps varied from 3.16 to 3.26 eV by Al doping. SEM micrographs showed a wrinkles-like morphology of the thin films that changed in density with the increase of Al concentrations. The PL emission spectra indicated that except the thin film doped with 1 at.%, other films exhibited high emission intensities under an excitation of 325 nm which allows to apply them as downconversion layers for solar cell applications.

     

UV photodetection properties of pulsed laser deposited Cu-doped ZnO thin film

Nanocrystalline undoped and 2 at% copper (Cu) doped zinc oxide (ZnO) thin films were successfully grown onto SiO₂/n-Si substrates at 600 °C by using pulsed laser deposition (PLD) technique. The influence of Cu incorporation on structural, surface morphological, elemental composition and UV detection properties of ZnO film was investigated. X-ray diffraction studies of thin films show that they are polycrystalline and have a hexagonal wurtzite structure; however, Cu doping improves the preferential orientation along c-axis. The chemical state of constituent elements was analysed by X-ray photoelectron spectroscopy (XPS). It indicates the presence of Cu ions in the doped film that exist in a mixed univalent and bivalent state. FE-SEM observations support the crystallographic results. The effective incorporation of Cu ions into the lattice of the ZnO nanostructure without changing its wurtzite structure was confirmed by an energy dispersive X-ray spectroscopic analysis (EDX). The UV photodetection characteristics of both films were further studied in metal-semiconductor-metal (MSM) planar configurations at room temperature and are found to be greatly influenced by Cu doping. The incorporation of Cu into ZnO lattice increases the resistivity of thin film; which leads to lower dark current. As a result, the Cu-doped ZnO film based UV PD demonstrates improved UV sensitivity of about 66.92 upon 2 mW/cm² UV illumination at 365 nm peak wavelengths and 5 V applied bias. The reproducible UV detection performance of MSM devices was also ensured by periodically switching UV light on and off at fixed time intervals.     

Effects of Ni doping on structural,optical and dielectric properties of ZnO

Structural, optical and dielectric properties of Ni doped ZnO samples prepared by the solid state route are presented. X-ray diffraction confirmed the substitution of Ni on Zn sites without changing the hexagonal structure of ZnO. NiO phase appeared for 6% Ni doping. Fourier transform infrared measurements were carried out to study phonon modes in Ni doped ZnO. Significant blueshift with Ni doping was observed in UV–visible studies, strongly supported by photoluminescence spectra that show a high intensity UV emission peak followed by the low intensity green emission band corresponding to oxygen vacancies and defects. The photoluminescence analysis suggest that doping of Ni can affect defects and oxygen vacancies in ZnO and give the possibility of band gap tuning for applications in optoelectronic devices. High values of dielectric constant at low frequency and a strong dielectric anomaly around 320 °C were observed.