Preparation and optical–electrical properties of Al-doped ZnO films

Among the various semiconducting metal oxide materials, ZnO thin films are highly attractive in the development of materials area. In this paper, Al-doped ZnO thin films were prepared by sol–gel dipping and drawing technology and their composition, structure and optical–electrical properties were investigated. XRD results shows that the Al-doped ZnO thin film is of polycrystalline hexagonal wurtzite structure, and the (002) face of the thin film has the strongest orientation at the annealing temperature of 550 °C. The surface resistance of Al-doped ZnO thin film firstly drops and then increases with the increase in annealing temperature. Al doping concentration is also an important factor for improving the conductivity of modified ZnO thin films, and the surface resistance has the tendency to drop at first and then to increase when the Al concentration is increasing. The surface resistance of modified ZnO thin films drops to the lowest point of 139 KΩ sq^?1 when the Al concentration is 1.6 at% and the annealing temperature is 500 °C. The light transmission measurements show that the doping concentration has little influence on light transmittance. The transmittance at the visible region of films is all over 80 %, and the highest value is up to 91 %.     

Preparation and characterization of transparent conducting ZnS:Al films

Al-doped ZnS films were deposited using close-spaced evaporation of the powders synthesized by chemical precipitation method. The films were prepared for different Al concentrations in the range 0–10 at.% on glass substrates kept at 300 °C. The effect of Al-doping on ZnS composition, microstructure and optoelectronic properties of as-grown ZnS layers was determined using appropriate techniques. The films were polycrystalline and showed (111) preferred orientation for all the doping concentrations in spite of an additional phase of Al₂S₃ observed at higher dopant levels. The surface morphological studies indicated that the Al incorporation had a considerable effect on the surface roughness of the films. The optical measurements indicated that the optical energy band gap decreased slightly with the increase of dopant concentration without affecting the optical transmittance characteristics significantly. The electrical analysis indicated that the resistivity of the layers changed significantly with the doping concentration in the layers. The change of photoluminescence behaviour of the as-grown ZnS:Al films with dopant concentration was also studied.     

An investigation of Zn/ZnO:Al/p-Si/Al heterojunction diode by sol–gel spin coating technique

Present study shows the structural, morphological, optical characterization of sol–gel spin coated ZnO:Al film and investigation of device efficiency of Zn/ZnO:Al/p-Si/Al heterojunction diode structure. X-ray diffraction study indicates that film has hexagonal polycrystalline structure with (002) preferential direction. Atomic force microscope and scanning electron microscope images exhibit that surface of ZnO:Al/p-Si consists of homogenously scattered nanoparticles. The surface roughness of ZnO:Al film is found to be 15.24 nm. The band gap value of ZnO:Al film deposited on glass substrate is calculated to be 3.34 eV. The electrical characterization of Zn/ZnO:Al/p-Si/Al heterojunction structure is made by current–voltage (I–V) and capacitance–voltage (C–V) measurements. From these measurements, the heterojunction structure shows a rectifying behavior under a dark condition. The ideality factor and barrier height of Zn/n-ZnO:Al/p-Si/Al structure are calculated as 3.23 and 0.68 eV. The heterojunction structure have diode characteristic with rectification ratio at 64.4 at +2.0 V in the dark. The results suggest that Zn/ZnO:Al/p-Si/Al heterojunction diode can be successfully used in many optoelectronic applications.     

Effect of annealing atmosphere on structural,optical and electrical properties of Al-doped Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O thin films

1 at.% Al-doped Zn_1−x Cd _x O (x = 0–8 at.%) thin films were prepared on glass substrates by sol–gel method. The codoping films retained the hexagonal wurtzite structure of ZnO, and showed preferential c-axis orientation. The effect of annealing ambient (in vacuum and nitrogen) on the optical and electrical properties of (Cd,Al)-codoped ZnO films were investigated using transmission spectra and electrical measurements. The transmittances of the codoping films were obviously degraded by vacuum annealing to 50–60 %, but enhanced to 70–80 % after nitrogen annealing. The carrier concentration and Hall mobility both increased, and resistivity decreased with narrowing band gap of Al-doped Zn_1−x Cd _x O, below different critical concentrations x = 4 % (in vacuum) and x = 6 % (in nitrogen). It is revealed that the conductivity is also improved by Cd doping along with band gap modification. The variations in optical and electrical properties are ascribed to both the changes of the crystallinity and concentration of oxygen vacancies under different ambient. In view of transmittance and conductivity, nitrogen annealing might be a more effective post-annealing way than vacuum annealing for our (Cd,Al)-codoped ZnO films to meet the requirements of transparent conducting oxide (TCO).     

Transparent conducting Sn:ZnO films deposited from nanoparticles

Homogeneous transparent conducting Sn:ZnO films on fused silica substrates were prepared by dip-coating from nanoparticle dispersions, while the nanocrystalline Sn:ZnO particles with different dopant concentrations were synthesized by microwave-assisted non-aqueous sol–gel process using Sn(IV) tert-butoxide and Zn(II) acetate as precursors and benzyl alcohol as solvent. The dopant concentration had a great impact on the electrical properties of the films. A minimum resistivity of 20.3 Ω cm was obtained for a porous Sn:ZnO film with initial Sn concentration of 7.5 mol% after annealing in air and post-annealing in N₂ at 600 °C. The resistivity of this porous film could further be reduced to 2.6 and 0.6 Ω cm after densified in Sn:ZnO and Al:ZnO reaction solution, respectively. The average optical transmittance of a 400-nm-thick Sn:ZnO film densified with Sn:ZnO after the two annealing steps was 91%.     

Indium and aluminium-doped ZnO thin films deposited onto FTO substrates: nanostructure,optical, photoluminescence and electrical properties

The microstructure, optical, photoluminescence and electrical properties of ZnO based films deposited onto FTO glass substrates by ultrasonic spray pyrolysis have been investigated. For comparison and a better understanding of physical properties of indium- and aluminum-doped ZnO and undoped ZnO thin films, X-ray diffraction analysis, photoluminescence spectra, optical, SEM texture and electrical conductivity analyses were performed. The AZO and IZO films exhibit the nanofiber structure with diameters 260 and 400 nm. X-ray diffraction showed all samples to be polycrystalline with hexagonal ZnO. The optical band gaps of the films were varied by Al and In dopants. The photoluminescence spectra of the films show a weak broad in the visible range and shifted to green emission for indium doping and to the green blue emission for aluminum as dopant. The width of the PL spectra for aluminum-doped films is too large compared to those of the indium-doped ones. The electrical conductivity of the ZnO film changes with Al and In dopants. The position of donor levels changes with In and Al dopants and approaches the conduction band level with the metal dopants. The obtained results suggest that the metal doping has a clear effect upon the growth, optical, photoluminescence and electrical conductivity properties of the ZnO films.     

Improvement of electrical properties of sol–gel derived ZnO:Ga films by infrared heating method

In this study, we investigated the influences of gallium concentration and a rapid thermal annealing process on the electrical and optical properties of ZnO:Ga (GZO) films prepared by sol–gel method. Experimental data indicated that the preferential growth directions of ZnO crystallites were the (002) and (103) axes. This phenomenon implied that the nucleation and growth behaviors of ZnO crystallites were changed by the infrared heating procedure and monoethanolamine. Furthermore, since the deposited sol films were heated simultaneously, evenly, and rapidly, dopant material Ga got the opportunity to replace Zn instead of forming oxides embedded in grain boundary areas. Thus, carrier concentration of the GZO films can be considerably enhanced while the mobility of the GZO films was not apparently affected in our experiments. It was also found that the carrier concentration was not sensitive to Ga/Zn ratio even though higher Ga concentration led to lower mobility. The best sample with a resistivity of 2.20 × 10⁻³ Ω cm and a transmittance of over 80% in visible region was achieved with 1.0 at.% Ga.     

Effect of Al doping on the conductivity type inversion and electro-optical properties of SnO2 thin films synthesized by sol-gel technique

Al doped SnO₂ thin films have been synthesized by a sol-gel dip coating technique with different percentages of Al on glass and silicon substrates. X-ray diffraction studies confirmed the proper phase formation in the films and atomic percentage of aluminium doping in the films was obtained by energy dispersive X-ray studies. SEM studies showed the particle sizes lying in the range 100–150 nm for the undoped films and it decreased with increase of Al doping. Optical transmittance spectra of the films showed high transparency (∼80%) in the visible region and the transparency increases with the increase of Al doping in the films. The direct allowed bandgap of the films have been measured for different Al concentration and they lie within the range of 3.87–4.21 eV. FTIR studies depicted the presence of Sn–O, Al–O, bonding within the films. The room temperature electrical conductivities of the films are obtained in the range of 0.21 S cm⁻¹ to 1.36 S cm⁻¹ for variation of Al doping in the films 2.31–18.56%. Room temperature Seebeck coefficients, S_RT of the films were found in the range +56.0 μVK⁻¹ to −23.3 μVK⁻¹ for variation of Al doping in the films 18.56–8.16%. It is observed that the Seebeck coefficient changes its sign at 12.05% of Al in the films indicating that below 12.05% of Al doping, SnO₂:Al behaves as an n-type material and above this percentage it is a p-type material.     

溶胶-凝胶方法制备ZnO:Al薄膜及其制备工艺条件研究

采用Sol-Gel工艺在玻璃基片上制备出C轴择优取向性、高可见光透过率以及高电导率的Al³⁺离子掺杂的ZnO透明导电薄膜ZnO:Al(ZAO薄膜).并研究了退火温度、Al掺杂量等对其光电性能的影响.结果表明,溶胶-凝胶法制备ZAO薄膜的最佳工艺条件为:溶胶浓度0.75 mol/L、掺杂量1.5 atm%,镀膜层数10层(厚度约为136 nm)、退火温度600℃.     

Solution derived Al-doped zinc oxide films: doping effect,microstructure and electrical property

This study investigates the influences of the microstructures and doping effect on electrical and optical properties of ZnO:Al films deposited by sol–gel method. Experimental results showed that aluminum concentration affected the crystallite size obviously and enhanced the relative intensity i ₍₀₀₂₎ faintly. Based on photoluminescence results, too much doping atoms generally can cause film crystallinity to deteriorate. Hall measurements indicated the carrier concentration rose only to a certain level after several coating processes. According to ellipsometric data, higher carrier mobility was mainly caused by the escalating density resulted by the increasing film thickness. However, the formation mechanism of charge carrier by doping technique in the sol–gel process is different from that of sputtering technique. The best sample having a sheet resistance of 182 Ω/sq and a transmittance of over 80% in visible region was obtained in aluminum concentration of 1.0 at.%.     

Improved optical and electrical properties of sol–gel-derived boron-doped zinc oxide thin films

Sol–gel spin-coating was used to grow zinc oxide (ZnO) thin films doped with 0–2.5 at.% B on quartz substrates. The structural, optical, and electrical properties of the thin films were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), ultraviolet–visible spectroscopy, and van der Pauw Hall-effect measurements. All the thin films had deposited well onto the quartz substrates and exhibited granular morphology. The average crystallite size, lattice constants, residual stress, and lengths of the bonds in the crystal lattice of the thin films were calculated from the XRD data. The PL spectra showed near-band-edge (NBE) and deep-level emissions, and B doping varied the PL properties and increased the efficiency of the NBE emission. The optical transmittance spectra for the undoped ZnO and boron-doped zinc oxide (BZO) thin films show that the optical transmittance of the BZO thin films was significantly higher than that of the undoped ZnO thin films in the visible region of the spectra and that the absorption edge of the BZO thin films was blue-shifted. In addition, doping the ZnO thin films with B significantly varied the absorption coefficient, optical band gap, Urbach energy, refractive index, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator strength, average oscillator wavelength, dielectric constant, and optical conductivity of the BZO thin films. The Hall-effect data suggested that B doping also improved the electrical properties such as the carrier concentration, mobility, and resistivity of the thin films.     

Electrical-optical properties of nanofiber ZnO film grown by sol gel method and fabrication of ZnO/p-Si heterojunction

Electrical and optical properties of the ZnO film prepared by sol-gel dip coating were investigated and ZnO film was deposited onto p-type silicon to obtain Ag/ZnO/p-Si heterojunction diode. Two dimensional atomic force microscopy images indicate that the ZnO film is formed from the fibers consisted from nanoparticles with grain size of 250-350 nm. The electrical conductivity mechanism of the ZnO film was varied from extrinsic to intrinsic conductivity. The calculated optical band gap of the ZnO film was found to be 3.22 eV. The Ag/ZnO/p-Si diode exhibit a non-linear behavior with ideality factor of n = 4.17 and barrier height of ?_B = 0.79 eV. The electrical properties of the Ag/ZnO/p-Si diode were investigated by current-voltage, capacitance-voltage-frequency and conductance-voltage-frequency measurements.     

Study of the effect of stress/strain of mesoporous Al-doped ZnO thin films on thermoelectric properties

In this study, effects of induced stress and strain on the thermoelectric properties of mesoporous ZnO thin films with various Al doping concentrations were investigated. With Al doping in ZnO structure, the hexagonal wurtzite structure of ZnO was distorted owing to an ionic size difference between Al and Zn. With an increase in Al concentration to 4 at%, thermal conductivity unexpectedly decreased from 1.70 to 1.24 W/mK owing to an increase in the tensile strain, and electrical conductivity increased from 4 S/cm to 15 S/cm owing to an increase in the carrier concentration. Based on this study, the relationship between the induced strain owing to lattice distortion and thermoelectric properties was investigated. Thus, 4 at% Al-doped mesoporous ZnO demonstrated best enhanced thermoelectric properties.     

Effects of In, Al and Sn dopants on the structural and optical properties of ZnO thin films

Effect of In, Al and Sn dopants on the optical and structural properties of ZnO thin films have been investigated by X-ray diffraction technique and optical characterization method. X-ray diffraction patterns confirm that the films have polycrystalline nature. The thin films have (002) as the preferred orientation. This (002) preferred orientation is due to the minimal surface energy which the hexagonal structure, c-plane to the ZnO crystallites, corresponds to the densest packed plane. The grain size values of the films are found to be 29.0, 35.2 and 39.5 nm for In, Al and Sn doped ZnO thin films, respectively. The optical band gaps of the films were calculated. The absorption edge shifts to the lower wavelengths with In, Al and Sn dopants. The inclusion of dopant into films expands also width of localized states as E(UIn)>E(UAl)>E(USn). The refractive index dispersion curves obey the single oscillator model. The dispersion parameters and optical constants of the films were determined. These parameters changed with In, Al and Sn dopants.     

Influence of Ga dopant on photoelectrochemical characteristic of Ga‐doped ZnO thin films deposited by sol–gel spin‐coating technique

In this study, Ga‐doped ZnO thin films were prepared using sol–gel technique via spin‐coating method. The effect of Ga‐doping dopant (0, 1, 2 and 3 at.%) on microstructural, optical, electrical and photoelectrochemical (PEC) characteristics have been investigated. The spin‐coating was repeated six times, and as‐obtained thin films were then annealed at 500 °C for 1 h in vacuum. After annealing, all samples revealed single phase of hexagonal ZnO polycrystalline structure with a main peak of (002) in X‐ray diffraction (XRD) pattern. Raman spectra show that the vibration strength of E₂ is highly decreased by Ga doping. Thicknesses of all samples were ~300 nm measured via scanning electron microscopy (SEM) cross‐section images and alpha‐step. The optical band gap and resistivity of samples were in the range of 3.24 to 3.28 eV and 102 to 9 Ohm cm, respectively. Resulting from PEC response, the 2 at.% Ga‐doped ZnO thin film has a better PEC performance with photocurrent density of ~0.14 mA/cm² at 0.5 V versus saturated calomel electrode (SCE) under illumination with the intensity of 100 mW/cm². This value was about seven times higher than the un‐doped film (reference sample). Observed higher photocurrent density was likely because of a suitable Ga‐doping concentration causing a lower resistivity. Copyright © 2016 John Wiley & Sons, Ltd.     

50 keV H+ ion beam irradiation of Al doped ZnO thin films: Studies of radiation stability for device applications

Thin films of Al doped ZnO (Al:ZnO) were deposited on two substrates (Si and glass) at room temperature and 300°C using DC magnetron sputtering. These films were bombarded with 50 keV H⁺ beam at several fluences. The pristine and ion beam irradiated films were analysed by X‐ray diffraction, Raman spectroscopy, scanning electron microscopy, and UV‐Vis spectroscopy. The X‐ray diffraction analysis, Hall measurements, Raman and UV‐Vis spectroscopy confirm that the structural and transport properties of Al:ZnO films do not change substantially with beam irradiation at chosen fluences. However, in comparison to film deposited at room temperature, the Al:ZnO thin film deposited at 300°C shows increased transmittance (from 70% to approximately 90%) with ion beam irradiation at highest fluence. The studies of surface morphology by scanning electron microscopy reveal that the ion irradiation yields smoothening of the films, which also increases with ion fluences. The films deposited at elevated temperature are smoother than those deposited at room temperature. In the paper, we discuss the interaction of 50 keV H⁺ ions with Al:ZnO films in terms of radiation stability in devices.     

Structural and optical properties of ZnO thin films by the spin coating Sol-Gel method

ZnO thin films were deposited onto glass subsrates by a Sol-gel spin coating method. The structural and optical properties of ZnO thin films were investigated. The molar ratios of the zinc acetate dihydrate to Monoethanolamine were maintained 1:1. The as-grown film was sintered 250 °C for 10 min, then annealed in air at 500 °C for 30 min. The XRD results indicate that ZnO films were strongly oriented to the c-axis of the hexagonal nature. Absorption measurements were carried out as a function of temperature with 10 K steps in the range 10–320 K. The band gap energy was measured 3.275 and 3.267 eV for 0.5 and 1.0 molarity (M) ZnO thin films at 300 K. The steepness parameters were observed between 10 and 320 K and their extrapolations converged at (E₀, α₀) = 3.65 eV, 172,819 cm⁻¹ and 3.70 eV, 653,436 cm⁻¹ for 0.5 and 1.0 M ZnO thin films, respectively.     

Effect of Al-doping on the structure and optical properties of electrospun zinc oxide nanofiber films

Electrospun ZnO precursor nanofibers of average diameters 122±64 nm, 117±44 nm and 110±39 nm were fabricated by controlling the Al concentration of a polymeric solution. The resulting nanofibers were characterized by the XRD, SEM, EDS, TEM, XPS and PL. The electrospun Al-doped ZnO nanofiber films were polycrystalline and composed of densely packed grains, with crystallite size ranging from 28.7 nm, 25.7 nm, 25.4 nm to 20.4 nm corresponding to the atomic concentration of aluminum from 0, 1.6, 2.5 to 5.8 at.%. The incorporation of aluminum resulted in a decrease trend in the grain size and lattice parameter of the ZnO nanofiber films. The room temperature PL spectra of all samples show three different emissions, including UV (ultraviolet) emission with an obvious blue shift, Vis (visible) emission and NIR (near infrared) emission, the intensity of which decreases monotonically as the doping concentration is increased except for the highest doping level. The impurity content correlates with changes in the PL spectra, and the appropriate Al doping can improve the optical properties of ZnO nanofibers. The small size effect and Al-doping or the impurity incorporation should be responsible for the blue shift observation in Al-doped ZnO nanofiber films.     

An investigation of the microstructure,optical and electrical properties of ZITO thin film using the sol–gel method

The multi-compound ZITO transparent conductive oxide (TCO) thin films were synthesized using the sol–gel method. The ZITO thin films with various volume ratios of ZnO to ITO (1:1, 2:1 and 9:1) were crystallized at different temperatures (600–700 °C). The results showed that the crystalline characteristics and optical transmittance were mainly dependent on ITO content and crystallization. Notably, the 650 °C Z₉ITO film not only had better conductivity but also possessed excellent optical transmittance. In addition, the surface roughness of the ZITO films and optoelectric properties of IZO (indium doped ZnO) films were analyzed to confirm the contribution of indium dopants on the optical transmittance. Also, the ZITO films were subjected to the effects of indium and tin dopants and this improved the related characteristics of ZnO films.     

V含量对ZnO薄膜结构及光学特性的影响

0引言氧化锌是一种六角纤锌矿结构的直接宽带隙半导体,其室温下禁带宽度为3.37eV。它具有多种优良的物理性能,在声表面波[1,2]、透明电极[3,4]、光电材料[5]、蓝光器件[6]等方面都有较大的应用潜力。氧化锌价格低廉,不仅能制成良好的半导体和压电薄膜,亦能够制成良好的透明导电薄膜。理论计算表明[7],氧化锌掺杂V、Cr、Fe、Co、N i元素能够产生自旋极化,形成高于室温的稀磁性透明半导体,是下一代微电子和光电子领域自旋电子学器件有重要价值的材料之一。根据理论计算,V掺杂的ZnO膜具有最高的居里温度。V yatkin实验小组[8]用钒离子注入…