Aluminum-doped Zinc Oxide Thin Films Research Articles

Atomic Layer-Deposited Al-Doped ZnO Thin Films for Display Applications

The integration of high uniformity, conformal and compact transparent conductive layers into next generation indium tin oxide (ITO)-free optoelectronics, including wearable and bendable structures, is a huge challenge. In this study, we demonstrate the transparent and conductive functionality of aluminum-doped zinc oxide (AZO) thin films deposited on glass as well as on polyethylene terephthalate (PET) flexible substrates by using an atomic layer deposition (ALD) technique. AZO thin films possess high optical transmittance at visible and near-infrared spectral range and electrical properties competitive to commercial ITO layers. AZO layers deposited on flexible PET substrates demonstrate stable sheet resistance over 1000 bending cycles. Based on the performed optical and electrical characterizations, several applications of ALD AZO as transparent conductive layers are shown—AZO/glass-supported liquid crystal (LC) display and AZO/PET-based flexible polymer-dispersed liquid crystal (PDLC) devices.

Effect of RF sputtering power and vacuum annealing on the properties of AZO thin films prepared from ceramic target in confocal configuration

Aluminum-doped zinc oxide (AZO) thin films are deposited on glass substrate by radio frequency (RF) magnetron sputtering method in confocal configuration at room temperature (RT). Several techniques are used to investigate the effects of sputtering power, from 50 to 300 W, on structural, optical and electrical properties. It is found, from Grazing Incidence X-Ray Diffraction (GIXRD) analysis, that the sputtering power has a great influence on the crystalline quality of AZO films. A preferential orientation along the c-axis is obtained at lower sputtering power of 50 W. XPS analysis confirms the existence of only Zn and Al in the oxidized state in accordance with the XRD results. SEM and AFM observations of AZO films reveal dense and homogenous distribution of small grains on the surface. Analysis by UV–Vis–NIR spectroscopy at RT reveals that the average optical transmittance in the visible range (400–800 nm) of the AZO thin films is higher than 75%. Hall-effect measurements put into evidence that the electrical resistivity of the films increases with the increase of the sputtering power. A low resistivity of 1.65 × 10−3 Ω cm is obtained for the lowest sputtering power (50W). Moreover, AZO thin film deposited at 50 W and annealed for 1h at 400 °C under vacuum shows a lower resistivity of 5.75 × 10−4 Ω cm, an average optical transmission above 86% and a high figure of merit (ФTC) value of 3.4 × 10−3 Ω−1sq which suggests that the fabricated AZO thin films are promising for optoelectronic devices in the UV region.

Aluminum doped zinc oxide coatings at low temperature by atmospheric pressure plasma jet

Pure and aluminum-doped zinc oxide thin films were produced with an atmospheric pressure plasma (APP) deposition process. Chemical, structural, morphological, electrical and optical analyses were carried out on samples coated with a plasma deposition process and with a spray pyrolysis process for comparison, respectively. The coatings were characterized by a compact layered structure of oxide islands, with a quite uniform distribution of Al in the network. Electrical measurements confirmed the active role and the dispersion of dopant in the zinc oxide network with an observed increase of conductivity even if high resistance values indicated a highly defective microstructure. In comparison to the spray pyrolysis coating the atmospheric pressure plasma coatings show a uniform substrate coverage and a higher chemical purity.

On the Structural, Optical and Electrical Characterization of Zinc Oxide and Aluminium doped Zinc Oxide for Optoelectronic Applications

Zinc Oxide (ZnO) and Aluminium doped Zinc Oxide (AZO) thin films are deposited on the glass slides by sol-gel spin coating technique. Zinc acetate dehydrate, 2 methoxyethanol, and diethanolamine are respectively used as a precursor, solvent, and stabilizer. Aluminium nitrate nonahydrate was used as the dopant source to obtain the atomic percentage of the dopant of 2%, 4%, 6% and 8%. The structural, optical, and electrical properties of the films were investigated using X-ray Diffraction (XRD), UV-visible spectrophotometry, and a Four-point probe technique respectively. The results from structural analyses show that the films are polycrystalline with a hexagonal wurtzite structure and a preferential orientation alongside the \(c\)-axis. The value obtained for the unit cell \(a=3.020\) A and \(c= 5.108\) A are in line with the reported literature. The transmittance of the films was observed within the visible region of the spectrum and the optical bandgap of the un-doped ZnO was established to be around 4.11 eV. However, the optical bandgap of the AZO films (4 and 6 at %) marginally decreases with doping concentration, which may be ascribed to the shrinkage of band effect due to the increase in carrier concentration. The lowest resistivity of \(3.53\times {10}^{-3}\,\Omega\) cm was observed for the doping concentration of 2% of Al. From the results, it was established that as the doping concentration increases, the thicknesses of the thin films were increased. Likewise, the increase in doping leads to a better uniformly distributed absorption spectra of the deposited AZO thin films.

Performance optimization of transparent and conductive Zn1-xAlxO thin films for opto-electronic devices: An experimental & first-principles investigation

In the present work, a combination of the experimental techniques with first principle density functional theory (DFT) based calculations has been employed to study the performance of the aluminum doped ZnO (AZO) thin films as transparent conducting oxide (TCO) material. The AZO thin films with varying doping concentration (0 wt% to 10 wt%) and having thickness (<100 nm) were deposited on silicon substrate using pulsed laser deposition. Various structural, optical and electrical properties of the films have been explored using a variety of the experimental techniques e.g. X-ray diffraction, X-ray reflectivity, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and current-voltage characteristic measurements. The different physical properties are observed following interesting trends where the characteristics property shows an optimum response at a particular doping concentration (5 wt%). These trends are correlated and explained based on the structural evolution in the nanostructured AZO thin films on varying doping concentration. Moreover, the prepared films are found to be having significantly high transmission and low resistivity making them useful for TCO application. The experimental findings for the Al-doped ZnO are supported by DFT calculations. Overall, our study provides important inputs to control the properties of Al doped ZnO films for their applications in optoelectronic devices.

Influence of sputtering conditions on the properties of aluminum-doped zinc oxide thin film fabricated using a facing target sputtering system

In this study, aluminum-doped zinc oxide thin films are deposited on a glass substrate using a facing target sputtering system, as a function of film thickness and input power, to study their crystallographic, optical, and electrical properties at various sputtering conditions. X-ray crystallography results revealed a (002) peak at approximately 34° with the highest intensity. The 200 nm film deposited at 100 W exhibited high crystallinity, the highest transmittance (92%), and lowest resistivity (1.4 × 10−3 Ω cm).

Laser-Assisted Spin Coating of Al-Doped ZnO thin Films

Undoped and aluminum-doped ZnO (AZO) thin films were prepared by the sol–gel process. Single thin layers were synthesized at room temperature by spin coating on glass and silicon substrates. The gel was laser irradiated (530 nm, 10 W) during the spinning process. We used Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) to characterize the chemical bonding configuration and surface morphology. UV–Vis spectroscopy was used to find optical transmittance, and energy-dispersive X-ray spectroscopy (EDS) was used to measure the surface chemical composition. Results of the EDS and FTIR analyses confirmed the successful preparation of ZnO and AZO through laser-assisted spin coating. SEM images showed that surface morphology and porosity were affected by the doping concentration. Al-doped samples showed high transmittance and possessed optical band gap values between 3.26 and 3.34 eV without laser irradiation and 3.3 – 3.341 eV with laser irradiation. Laser irradiation improved the structure and optical properties of the films.

Influence of aluminum-doped zinc oxide seeding film on morphological properties of hydrothermally-grown zinc oxide nanorods

The morphological properties, e.g. diameter, aspect ratio, and density, of zinc oxide nanorods (ZnO-NRs) can be achieved through the control of seeding film morphology in seed-assisted hydrothermal process. The different morphologies of seeding film made by aluminum-doped zinc oxide (AZO) thin films are obtained by varying the thickness of seeding film. The change of seeding morphology from small granules with (002) plane dominant to platelets with (103) plane dominant leads to the significant change in the morphological formation of ZnO-NRs successively grown on the seeding film. The seeding film containing the dominant plane of (002) and small granules offers vertical-aligned ZnO-NRs with high surface area (high density and respect ratio) attributed to high nucleating density as well as the limit of the lateral growth from the surrounding adjacent nanorods. This work provides the consideration of morphological properties of seeding film.

Influence of Zr50Cu50 thin film metallic glass as buffer layer on the structural and optoelectrical properties of AZO films**Project supported by the National Natural Science Foundation of China (Grant No. 51571085), the Key Science and Technology Program of Henan Province, China (Grant No. 19212210210), the Foundation of Henan Educational Committee, China (Grant No. 13B430019), and the Henan Postdoctoral Science Foundation,

Aluminum-doped ZnO (AZO) thin films with thin film metallic glass of Zr50Cu50 as buffer are prepared on glass substrates by the pulsed laser deposition. The influence of buffer thickness and substrate temperature on structural, optical, and electrical properties of AZO thin film are investigated. Increasing the thickness of buffer layer and substrate temperature can both promote the transformation of AZO from amorphous to crystalline structure, while they show (100) and (002) unique preferential orientations, respectively. After inserting Zr50Cu50 layer between the glass substrate and AZO film, the sheet resistance and visible transmittance decrease, but the infrared transmittance increases. With substrate temperature increasing from 25 °C to 520 °C, the sheet resistance of AZO(100 nm)/Zr50Cu50(4 nm) film first increases and then decreases, and the infrared transmittance is improved. The AZO(100 nm)/Zr50Cu50(4 nm) film deposited at a substrate temperature of 360 °C exhibits a low sheet resistance of 26.7 Ω/□, high transmittance of 82.1% in the visible light region, 81.6% in near-infrared region, and low surface roughness of 0.85 nm, which are useful properties for their potential applications in tandem solar cell and infrared technology.

Effect of picosecond-laser irradiation on the properties of nanostructured aluminium-doped zinc oxide thin films

Effect of picosecond-laser irradiation on the properties of nanostructured aluminium-doped zinc oxide thin films

Physical properties of indium zinc oxide and aluminium zinc oxide thin films deposited by radio-frequency magnetron sputtering

Indium-doped zinc oxide (IZO) and aluminium-doped zinc oxide (AZO) thin films were grown by radio-frequency (RF) magnetron sputtering onto optical glass substrates and their structural, morphological, and optical properties were discussed in terms of varying the sputtering power as 40 W, 60 W, 80 W, and 100 W. No heating substrate or any post-thermal treatment was performed. The structural features were analyzed by grazing incidence X-ray diffraction and revealed the amorphous phase for IZO samples, while the AZO thin films inherited the Wurtzite structure of zinc oxide. The morphological properties were investigated by atomic force microscopy (AFM), in tapping mode and scanning electron microscopy (SEM). The AFM images showed relatively uniform and smooth surfaces for all prepared structures. The optical transmission spectra proved the excellent theoretical values of transparency for metallic oxides in the visible region of the electromagnetic spectrum, i.e. ∼60% for IZO and ∼70% for AZO. The obtained results showed that even without any thermal treatment the structural, morphological, and optical properties of IZO and AZO thin films prepared by RF magnetron sputtering are similar with those for samples subjected to medium or high temperatures.

Structural, Optical, and Thermoelectric Properties of the ZnO:Al Films Synthesized by Atomic Layer Deposition

Aluminum-doped zinc oxide thin films have been grown by atomic layer deposition at a temperature of 200°C. Using X-ray diffraction, it has been established that the ZnO:Al thin films exhibits the reflections from the (100), (002), (110), and (201) ZnO hexagonal phase planes. The (101) and (102) planes have also been detected by electron diffraction. The ZnO:Al thin films grow smooth with a root-mean-square roughness of Rq = 0.33 nm and characteristic nanocrystallite sizes of ~70 and ~15 nm without additional aluminum or aluminum oxide phases. The transmission at a wavelength of 550 nm with regard to the substrate has been found to be 96%. The refractive indices and absorption coefficients of the ZnO:Al thin films in the wavelength range of 250–900 nm have been determined. The maximum refractive indices and absorption coefficients have been found to be 2.09 at a wavelength of 335 nm and 0.39 at a wavelength of 295 nm, respectively. The optical band gap is 3.56 eV. The resistivity, Seebeck coefficient, and power factor of the ZnO:Al thin films are ∼1.02 × 10–3 Ω cm, –60 μV/K, and 340 μW m–1 K–2 at room temperature, respectively. The maximum power factor attains 620 μW m–1 K–2 at a temperature of 200°C.

Lossy Mode Resonance Generation on Sputtered Aluminum-Doped Zinc Oxide Thin Films Deposited on Multimode Optical Fiber Structures for Sensing Applications in the 1.55 µm Wavelength Range

In this work, we demonstrated lossy mode resonance (LMR) generation in optical fiber structures based on multimode fibers coated with aluminum-doped zinc oxide (AZO) films. AZO thin films were deposited by using radio frequency magnetron sputtering. In order to exhibit the usefulness of the LMR effect for sensing applications in optical fiber based systems, the deposition conditions of the AZO film coatings were set to obtain the second LMR order within the 1.55 µm wavelength range. An optical transmission configuration setup was used to investigate the LMR effect on fiber structures based on the use of no-core and cladding-removed multimode fibers coated with AZO films synthesized from metallic sputtering targets with different proportions of Zn:Al, 92:8% and 98:2%, at atomic concentrations. The optical and electrical/chemical features of the AZO films were characterized with UV–vis and XPS spectroscopy, respectively. The optical response of the proposed sensing configuration to refractive index (RI) variations was experimentally demonstrated. For the best approach, the sensitivity of wavelength displacement to RI variations on the liquid surrounding media was found to be 1214.7 nm/RIU.

Preparation of highly transparent conductive aluminum-doped zinc oxide thin films using a low-temperature aqueous solution process for thin-film solar cells applications

In this work, we developed a facile route to fabricate highly transparent conductive AZO thin films by using an aqueous solution process followed by an ultraviolet (UV) exposure technique at an annealing temperature as low as 200 °C, where the aluminum citrate complex was used as the Al doping source. Various of deposition parameters in the AZO thin films fabrication process were studied and optimized. The mechanisms on UV exposure and heat treatment to the conductivity improvement and conductivity stability of the AZO films were analysed. Results showed that the AZO thin films under the best parameters conditions demonstrated an optical transmittance higher than 85% in the visible spectra region and a lowest electrical resistivity of 4.8 × 10−3 Ω cm, while exhibited densely oriented columnar grains and uniform surface morphology as well as uniform composition distribution. The UV exposure could remove carbon species from the surface of the AZO thin films to reduce oxygen-related defects and release free carriers at the boundaries and interfaces, thereby improving the conductivity of the AZO thin films. The simultaneous treatment of the AZO thin film by ultraviolet exposure and heat treatment could remove carbon species at a deeper thickness, thereby improving the conductive stability of the AZO thin films. Kesterite Cu2ZnSnS4 thin film solar cells incorporating the optimal AZO thin films as top electrodes demonstrated a best power conversion efficiency (PCE) of 7.15%, which was comparable to the PCE value obtained by using the sputtering deposited AZO thin films as top electrodes.

Effect of growth temperature on the key properties of aluminum-doped zinc oxide thin films prepared by atomic layer deposition

Abstract

Experimental and ab-initio investigation of the microstructure and optoelectronic properties of FCM–CVD-prepared Al-doped ZnO thin films

In this research, pure and aluminium-doped zinc oxide (ZnO) thin films (5–50%) have been synthesized by the fine-channel mist chemical vapor deposition (FCM-CVD) technique. The microstructure and optoelectronic properties of the films have been characterized with the help of scanning electron microscope (SEM), X-ray diffraction (XRD), and UV–visible absorption (UV–Vis), respectively. The critical-doping (Al) concentration of ZnO was found to be 10%. Below this concentration of Al, the preferential orientation of the films was found to be along (002). Moreover, the films are in tensile states and the optical bandgap values found to be decreasing. For heavy doping concentration, the films are found to be in the compression states, and the optical bandgap increased with the Al concentration. To validate our experimental results, DFT calculations were performed to show and explain the origin of the variation of bandgap, tensile, and compression states.

Growth and characterization of undoped and aluminium doped zinc oxide thin films for SO2 gas sensing below threshold value limit

The present work explores the capability of undoped and aluminium doped zinc oxide thin films for the detection of low concentration of Sulphur dioxide gas (SO2). Highly transparent undoped and aluminium-doped ZnO thin films were successfully deposited using sol-gel spin coating technique. The influence of various concentrations of aluminium (Al) doping on structural, morphological, optical and electrical properties has been studied. The Al doping affected the crystallinity of the films as evident from the X-ray diffraction (XRD) studies. The Atomic force microscope (AFM) and the Field emission scanning electron microscope (FESEM) studies depict the wrinkled structure of the thin films. The transparency of the deposited films was revealed by the UV–Visible characterization. Electrical characterization showed a variation in the conductivity with varying aluminium concentration which influences the gas sensing performance of the thin films. The 2 at.% aluminium doped ZnO thin films exhibited a higher sensitivity of 70% for 3 ppm of SO2 gas which is below the threshold value limit. For comparison, NH3 gas sensing of the grown films was also studied.

Z-scan measurements of nonlinear refraction and absorption for aluminum-doped zinc oxide thin film.

In this paper, we investigate third-order nonlinearities in aluminum-doped zinc oxide (AZO) thin film by the Z-scan method at a wavelength of 1064nm. We carried out experiments under different pulse widths (26ns, 62ns, and 101ns) and energy densities (5.3 J/cm2, 10.6 J/cm2, and 15.9 J/cm2) and obtained the nonlinear absorption coefficient, nonlinear refractive index, and third-order nonlinear susceptibility of AZO thin film. The Z-scan results show that AZO thin film exhibits a larger nonlinear refractive index (-5.48×10-13 m2/W) and third-order nonlinear susceptibility (1.97×10-6 esu) than those of some other semiconductor materials at the wavelength of 1064nm. This suggests that AZO thin film may be a very promising nonlinear medium for nonlinear photonics applications in the tens of nanoseconds regime.

Contour loop analysis of multi-affine nanostructure AZO rough surfaces

Morphology of multi-affine aluminum-doped zinc oxide (AZO) thin films during spray pyrolysis growth process is characterized by contour loop analysis. The results show that the fractal dimension of each contour loop, Df, is different for various level cuts (in contrast to monofractal structures). Averaging it on all levels leads to a value Df = 1.13 ± 0.02, which remains constant during the growth process. Furthermore, there is a crossover to percolation regime with the exponent . Fractal dimension d of all contour loops, calculated by the box-counting method, decreases with the thickness, while the decreasing behavior is not as the monofractal structures ( ) and is influenced by the whole values of h(q) spectrum. To find the distribution of crystalline grains in the AZO rough surfaces during the growth process, the area cumulative distribution of loops was investigated. The results indicate that the exponent, μ, decreases with enhancement of thickness during the growth process. The loops radius is linearly proportional to the grain size of deposited thin films, which could be introduced as a new numerical parameter for determining this experimental measure.

Multimode AFM analysis of aluminum-doped zinc oxide thin films sputtered under various substrate temperatures for optoelectronic applications

Here we present an in-depth atomic force microscopy study of aluminum-doped zinc oxide (AZO) thin films utilizing various modes (topology, phase and error signal) together with image processing techniques including skew, kurtosis, entropy, autocorrelation and fractal analysis. Fractal dimension has been calculated via cube counting, triangulation, power spectrum and partitioning methods. A correlation has been found between the micromorphological properties and the functional properties of the AZO transparent conducting oxide when annealed at different temperatures. Structural, electrical, morphological and optical properties of AZO thin films were investigated by XRD, 4-Point-probe, AFM and UV-VIS spectroscopy. The results indicate that the AZO thin film properties are affected by substrate temperature. An optimum figure of merit of 1.518×10−3Ω−1 is obtained for a substrate temperature of 150°C. It is expected that this work can provide a novel approach towards optimization of transparent conducting oxides, in particular with regards to plasmonics.