Abstract Aluminum-doped Zinc Oxide Research Articles

Mechanical Flexibility and Electrical Reliability of ZnO-Al Thin Films on Polymer Substrates Under Different External Deformation

Abstract Aluminum-doped zinc oxide (AZO) films have emerged as promising transparent electrodes for various optoelectronic applications due to their superior transparency, electrical conductivity, and cost-effectiveness compared to indium tin oxide (ITO). Despite their widespread use, investigations into the electromechanical properties of AZO films, especially under various mechanical deformations, remain limited. This study employs RF magnetron sputtering to deposit AZO films on polyethylene naphthalate (PEN) substrates and explores their mechanical behavior through uniaxial tensile fragmentation and bending tests, coupled with in-situ optical microscopy. Changes in electrical resistance of AZO films were monitored in situ during deformation. Fatigue behavior was examined to further understand mechanical failure, and SEM was used for surface characterization. A critical strain of about 3.1 percent was detected during uniaxial tensile testing, marking the onset of cracks in AZO-coated PEN. In contrast to thicker films, thinner films demonstrated improved stretchability beyond the initiation of crack onset strain. Tension and compression bending tests revealed that the material has excellent bendability, as shown by its critical radii of 5.4 mm and 3.9 mm, respectively. The bending reliability of AZO films under compression was found to be superior than that under tension. Bending fatigue experiments demonstrated that AZO films could withstand cyclic stress without experiencing no ticeable cracks after 100 cycles and with very minor resistance change. This study contributes to the creation of more reliable and optimized flexible optoelectronic devices by giving substantial quantitative data on the performance of AZO films when exposed to mechanical stress.

Stability under humidity, UV-light and bending of AZO films deposited by ALD on Kapton

Aluminium doped zinc oxide (AZO) films were grown by Atomic Layer Deposition (ALD) on yellow Kapton and transparent Kapton (type CS) substrates for large area flexible transparent thermoelectric applications, which performance relies on the thermoelectric properties of the transparent AZO films. Therefore, their adhesion to Kapton, environmental and bending stability were accessed. Plasma treatment on Kapton substrates improved films adhesion, reduced cracks formation, and enhanced electrical resistance stability over time, of importance for long term thermoelectric applications in external environment. While exposure to UV light intensity caused the films electrical resistance to vary, and therefore their maximum power density outputs (0.3–0.4 mW/cm3) for a constant temperature difference (∼10 °C), humidity exposure and consecutive bending up to a curvature radius above the critical one (∼18 mm) not. Testing whether the films can benefit from encapsulation revealed that this can provide extra bending stability and prevent contacts deterioration in the long term.

Preparation and Characterization of Sol-Gel Dip Coated Al: ZnO (AZO) Thin Film for Opto-electronic Application

AbstractAluminum doped zinc oxide (AZO) thin film was prepared by sol–gel dip coating method from methanol and monoethanolamine respectively, used as solvent and stabilizer agent. From the XRD study, it was confirmed that the aluminum was incorporated into the ZnO lattice. The prepared film have polycrystalline in nature and the film exhibit hexagonal wurtzite structure with (002) direction. SEM and AFM studies showed well defined smooth and uniformed wrinkle shaped grains distributed regularly on to the entire glass substrate without any pinholes and cracks. From the optical study, the observed highest transmittance was about 82% in the visible range and the band gap is 3.15 eV. Room temperature PL spectra exhibited a strong UV emission peak located at 390 nm for the deposited film. The electrical properties of the AZO thin film was studied by Hall-Effect measurement and found that it has n-type conductivity with low resistivity (ρ) of about 9.06 × 10^–3 Ω cm.

Al-doped ZnO films deposited by magnetron sputtering: effect of sputtering parameters on the electrical and optical properties

Abstract Aluminum-doped zinc oxide (AZO) thin films were prepared by magnetron sputtering method. The influences of deposition pressure, substrate temperature, Ar flow rate and film thickness on optical and electrical properties were investigated using ultraviolet-visible (UV-Vis) spectrometer and Hall measurements. The experimental results revealed that a low resistivity, smaller than 4 × 10-4 Ω·cm, was obtained when the deposition pressure was smaller than 0.67 Pa and substrate temperature about 200 °C. Ar flow rate had a small influence on the resistivity but a big influence on the transparency at near infrared range (NIR). We obtained optimized AZO thin films with high ponductivity and transparency at low deposition pressure, small Ar flow and appropriate temperature (around 200 °C). The etching behavior of the AZO thin films deposited at the different Ar flow rates was also studied in this paper. The results show that Ar flow rate is a very important factor affecting the etching behavior.

Optimization of Synthesis of ZnO:Al as n-Type Transparent Conductive Layer for Oxide-Semiconductor-Based Solar Cells

Aluminum-doped zinc oxide was deposited on silicon and glass substrates by magnetron sputtering methods with various conditions starting from conventional, then to oxygen reactive technique, and finally to cosputtering of aluminum and 2% Al2O3 in ZnO target. The results showed that the optical transmittance of the thin films in the visible range was above 80%. The direct bandgap of the aluminum-doped zinc oxide thin films, depending on the deposition conditions, was estimated to lie in the range between 3.2 eV and 4.2 eV. Good electrical properties with resistivity of about 2.5 × 10−3 Ω cm were also observed when doping more Al using the cosputtering method. Optimization of the synthesis conditions for aluminum-doped zinc oxide thin films was performed using a newly proposed dimensionless figure of merit based on analysis of the efficiency of solar cells. This study highlights that the optimized deposition condition was to cosputter aluminum during a total additional time of 2 min. The results show that such transparent conductive thin films could be applied in future low-cost heterojunction oxide-based solar cells with CuFeO2 delafossite p-type absorber.

Study of Large-Scale Aluminium-Doped Zinc Oxide Ceramic Targets Prepared by Slip Casting

Aluminium-doped zinc oxide (AZO) ceramic green compacts at a size of 170 × 340 × 17 mm have been prepared by slip casting. An AZO slurry with good fluidity and viscosity was obtained when 1.2 wt% of dispersant was added, which indicates that the slurry prepared with micrometre particles is more suitable for slip casting. The densification and electrical properties of the AZO targets prepared by particles with different sizes were investigated after sintering from 1380 to 1460°C. The results showed that the relative density of the AZO target prepared with 45 nm particles could reach nearly 98% at 1380°C; the resistivity of the AZO target prepared with nanometre particles could be as low as 1.6 × 10−3 Ω·cm at 1400°C; and the average transmittance of the AZO film prepared with nanometre particles could reach a maximum value of 93.73% in the visible region at 250 W. In this study, the correlation between the density, resistivity, and grain growth of AZO ceramic green compacts was studied.

Highly Oriented ZnO:Al Thin Films as an Alternative Transparent Conducting Oxide (TCO) for Windows Layer of Solar Cells

Aluminum doped zinc oxide (ZnO:Al) thin films were deposited on corning glass substrates using DC magnetron sputtering at various growth temperatures (27°C-400°C). X-rays diffraction spectroscopy (XRD) analysis showed the crystal structure of ZnO:Al thin films is wurtzite with c-axis orientation. By enhancing the growth temperature, the crystal size and the crystal stress are increase, while the resistivity of films decreases. Crystal size increase from 35 nm to 52 nm, the stress increase from -7.689 GPa to -5.126 GPa, while the resistivity decreases from 6.29 x 104 Ωcm to 4.05 x 103 Ωcm. Generally, the quality of crystal enhanced as the raising of growth temperature.

Influence of Thermal Annealing on the Properties of Sol-Gel-Derived Al:ZnO Thin Films

Aluminium doped zinc oxide (Al:ZnO) thin films were prepared by a sol-gel dip coating process. In particular, the case of change of thermal annealing temperature was studied. The characterisation of the films by various analytical methods shows a correlation between thermal annealing temperature and characteristic of the film. The influence of the thermal annealing temperature on the film growth can be clearly observed. At lower thermal annealing temperatures, granular structure dominates the films, while the films feature a bigger grain growth at higher annealing temperatures. All films exhibited an average transmittance of greater than 85% in the visible region, with absorption edges at ~380 nm.

Characterization of Aluminum Doped Zinc Oxide (Azo) Thin Films Prepared by Reactive Thermal Evaporation for Solar Cell Applications

Aluminium doped Zinc Oxide (AZO) thin films have been deposited using reactive thermal evaporation technique using an Edward Auto 306 Magnetron Sputtering System. Transmittance and reflectance data in the range 300 nm-2500 nm were obtained using UV-VIS NIR Spectrophotometer Solid State 3700 DUV for all the thin films samples that were prepared. Transmittance values of above 70% were observed. The optical measurements were simulated using SCOUT 98 software to determine optical constants and optical bad gap of the thin film. The optical properties in these films were varied by varying Aluminums doping percentages. It was observed that the transmission over the visible range decreased as the concentration of Aluminum increased. This is due to free carriers coupling to the electric field hence increasing the reflection. Optical band gap for various samples of Aluminum doped thin films show a direct allowed transition and a shift in the optical absorption edge as the Aluminums concentration increased. These results show values of band gap ranging between 3.2 eV and 3.5 eV. Between 0% - 3% the optical band gap reduces. This is followed with widening of the band gap for doping between 4%- 6%. Urbach energy gradually increased with increasing band gap. The band gap reduced due to formation of localized states near the conduction band corresponding to increase in Urbach energy.

Expanding Thermal Plasma Chemical Vapour Deposition of ZnO:Al Layers for CIGS Solar Cells

Aluminium-doped zinc oxide (ZnO:Al) grown by expanding thermal plasma chemical vapour deposition (ETP-CVD) has demonstrated excellent electrical and optical properties, which make it an attractive candidate as a transparent conductive oxide for photovoltaic applications. However, when depositing ZnO:Al on CIGS solar cell stacks, one should be aware that high substrate temperature processing (i.e., >200°C) can damage the crucial underlying layers/interfaces (such as CIGS/CdS and CdS/i-ZnO). In this paper, the potential of adopting ETP-CVD ZnO:Al in CIGS solar cells is assessed: the effect of substrate temperature during film deposition on both the electrical properties of the ZnO:Al and the eventual performance of the CIGS solar cells was investigated. For ZnO:Al films grown using the high thermal budget (HTB) condition, lower resistivities, ρ, were achievable (~5 × 10−4 Ω·cm) than those grown using the low thermal budget (LTB) conditions (~2 × 10−3 Ω·cm), whereas higher CIGS conversion efficiencies were obtained for the LTB condition (up to 10.9%) than for the HTB condition (up to 9.0%). Whereas such temperature-dependence of CIGS device parameters has previously been linked with chemical migration between individual layers, we demonstrate that in this case it is primarily attributed to the prevalence of shunt currents.

Influence of RF Power in the Growth of Aluminium Zinc Oxide (AZO) Thin Films by RF Sputtering

Aluminium doped zinc oxide (AZO) is fast becoming an important thin film material for applications as transparent conducting oxide (TCO) in several thin film solar cells, smart windows and many devices using touch screen displays. This is due to its good electrical and optical characteristics as well as lower cost and good abundance. Although sputtering is the general method for industrial fabrication of this material, but film characteristics depend strongly on fabrication processes. Thus, optimal films are obtained by optimization of the deposition conditions. In this work, we investigated the effects of RF deposition power on AZO thin films. Samples of similar thicknesses were grown under similar conditions in an RF sputtering chamber at different RF powers. The samples were then characterized using FESEM, AFM, UV-Vis, XRD and Hall effect measurement tools. Results indicate that the surface morphology is slightly affected with larger grain sizes obtained at higher RF powers. Also the surface roughness, average transmittance, conductivity and deposition rate all increase with the RF power. The lowest as-deposited resistivity of 15.3x10-3 Ω/cm was obtained, at the highest RF power of 100 W. This film also have the highest values of carrier concentration, mobility and figure of merit of 4.24x1020 cm-3, 0.96 cm2/V and 0.27x10-3 Ω respectively. This work highlights the significance of RF power in the fabrication of good quality AZO thin films.

The facile synthesis, properties and application of ZAO nanomaterials

Aluminium-doped zinc oxide (ZAO) nanocrystals with uniform size, high purity and good degree of crystallinity were prepared by an ultrasonic–microwave assisted method. The structure, optical properties and morphologies of ZAO nanocrystals were characterised by X-ray powder diffraction, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy, while the photocatalytic and anticorrosive effects of the product were studied by the degradation test of rhodamine B and salt spray corrosive test, respectively. The effects were quite satisfactory.

ZnO:Al films prepared by inline DC magnetron sputtering

Abstract Aluminum-doped zinc oxide (AZO) is one of the most promising transparent conductive oxide (TCO) materials that can substitute the high-quality but costly indium tin oxide (ITO). To ensure high-quality films as well as moderate production costs, inline DC magnetron sputtering was chosen to deposit thin AZO films. The influence of sputter gas pressure, substrate temperature, and film thickness on the electrical, optical, and structural properties was analyzed. The resistivity reaches a minimum of 1.3×10-5 Ωm at around 1 Pa for a substrate temperature of 90°C. A maximum conductivity was obtained by increasing the substrate temperature to 160°C. An annealing step after deposition led to a further decrease in resistivity to a value of 5.3×10-6 Ωm in a 200 nm thin film. At the same time, the optical performance could be improved. Additionally, simulations of the transmittance and reflectance spectra were carried out to compare carrier concentration and mobility determined by optical techniques with those from Hall measurements.

Investigation of Optical Properties of Aluminium Doped Zinc Oxide Thin Films Deposited by Magnetron Sputtering

Aluminium doped zinc oxide (AZO) thin films were prepared by magnetron-sputtering. The optical and structural properties of the films were investigated by optical transmission spectra and X-ray diffraction (XRD) measurements, respectively. The results indicate that the AZO films have hexagonal wurtzite structure with highly c-axis preferred orientation. The optical and structural properties of the films are observed to be subjected to the argon pressure. The AZO film prepared at the argon pressure of 0.5 Pa exhibits the largest crystallite size and the highest average visible transmittance. Also, the refractive index and optical energy-gap of the films were determined by optical characterization methods. The dispersion behavior of the refractive index was studied using the Sellmeier’s dispersion model.

Chemical Shift and Surface Characteristics of Al-Doped ZnO Thin Film on SiOC Dielectrics

Aluminum doped zinc oxide (AZO) films were fabricated on SiOC/p-Si wafer and SiOC film was prepared on a p-type Si substrate with the SiC target at oxygen ambient with the gas flow rate of 5-30 sccm by a RF magnetron sputter. C-V curve of SiOC/Si wafer was measured to observe the relationship between the polarity of SiOC dielectrics and the change of capacitance depending on oxygen gas flow rate. The SiOC film could be controlled to be polar or nonpolar, and their surface energy was changed depending on the polarity. Smooth surface is essential to improve the TFT performance. AZO-TFTs used smooth SiOC film with low polarity as a gate insulator was observed to show low leakage current (IL) and low subthreshold voltage swing. It is proposed that SiOC film with high degree amorphous structure as a gate insulator between AZO and Si wafer could solve problems of the mismatched interfaces, which was originated from the electron scattering due to the grain boundary.

Effect of Solvent Used in the Preparation of Aluminum-Doped ZnO as Electron Acceptor Layer on the Characteristic of its Hybrid Solar Cell

Aluminum doped Zinc Oxide (AZO) layer has been employed as electron acceptor in hybrid solar cell based on Poly(3-hexylthiophene) with inverted structure. AZO layers used in this work were prepared by sol-gel process using two different solvents, namely methanol and methoxyethanol. From X-ray diffraction measurements, AZO layer prepared using methanol solvent (AZO-me) indicates the formation of crystallines with the same (002) orientation, whereas AZO layer prepared using methoxyethanol (AZO-mx) indicates the formation of crystallines with (100), (002), and (101) orientations. The nanomorphology of those AZO layer surfaces was also remarkably different, which might be related to differences in crystal orientation. For both solvents, the photocurrent density-voltage (J-V) characteristics were also affected by the Al ion concentration in AZO layer. However, solar cell with AZO-mx shows better performances in comparison to that of AZO-me with the same Al ion concentration. The observation of performance variations in those fabricated solar cells are suggested to be strongly related with the crystal orientation and nanomorphology of AZO layer. These experimental results then suggest that charge carrier dissociation by AZO layer are significantly influenced by the crystal orientation and nanomorphology of AZO layer, which are affected by the solvent used for preparing the AZO layer.

Effects of sputtering pressure on properties of Al doped ZnO thin films dynamically deposited by rf magnetron sputtering

Aluminium doped zinc oxide (AZO) films were dynamically deposited by rf magnetron sputtering under various sputtering pressures in the range of 0·3–2·0 Pa. The effect of the Ar sputtering pressure on the structural, electrical and optical properties of the AZO films was systematically investigated by X-ray diffractometry, scanning electron microscope, four-point probe measurement and UV–vis spectrophotometer. As the sputtering pressures decrease, the crystallite sizes of the films became larger, while their deposition rate turns higher. Under the condition of lower sputtering pressures, a decrease in the resistivity was observed due to an increase in carrier concentration. The AZO film deposited at 0·5 Pa in the dynamic mode has shown the lowest resistivity of 9·5×10−4 Ω cm. This work was performed in a dynamic deposition system in order to produce a large area of AZO films, which is more important in practical fields to improve productivity.

Facile synthesis and photocatalytic activity of aluminium-doped zinc oxide materials with different shapes

Aluminium-doped zinc oxide (ZAO) with various shapes such as rod, particle and flake was prepared by the facile hydrothermal-template method. The morphologies and structures of the ZAO products were analysed by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and UV-vis spectroscopy and so on. The investigation of photocatalytic properties of ZAO products showed that ZAO products with large surface area and good crystallinity own better photocatalytic activity.

Investigations on properties of (ZnO:Al) films prepared by RF/DC co-sputtering

Aluminum doped zinc oxide (ZnO:Al) thin films with high conductivity, resistance to ion irradiation, high transparency in the visible range and moderate costs will be one of the most promising candidates for the present predominant transparent conducting materials. However, there are still some problems such as long preparation cycle and high surface resistance. In this paper, adding a certain amount of radio frequency (RF) power to the applied DC power, this technique known as RF-DC co-sputtering ionization is mainly driven by oscillating electrons in the bulk plasma, there is an enhanced substrate bombardment by plasma ions (mainly Ar+) of moderate energy to improve the optical and electrical properties of the film. The samples of crystal structure, surface morphology, electrical conductivity were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), four-probe meter, as well as visible spectrophotometer. The results show that the average transmittance in the visible was 89% and the resistivity was reduced by 80% compared to other single technique. When the radio frequency power makes up around 50% of the total, the resistivity reach a minimum of 1.5×10-3Ω•cm, improve the homogeneity of the film Effectively. DOI: http://dx.doi.org/10.11591/telkomnika.v10i5.1273

The enhanced conductivity and stability of AZO thin films with a TiO2 buffer layer

Abstract Aluminum doped zinc oxide (AZO) films were substitutes of the SnO2:F films on soda lime glass substrate in the amorphous thin-film solar cells due to good properties and low cost. In order to improve properties of AZO films, the TiO2 buffer layer had been introduced. AZO films with and without TiO2 buffer layer were deposited on soda lime glass substrates by r.f. magnetron sputtering. Subsequently, one group samples were annealed in vacuum (0.1 Pa) at 500 °C for 120 s using the RTA system, and the influence of TiO2 thickness on the properties of AZO films had been discussed. The XRD measurement results showed that all the films had a preferentially oriented (0 0 2) peak, and the intensity of (0 0 2) peak had been enhanced for the AZO films with TiO2 buffer layer. The resistivity of TiO2 (3.0 nm)/AZO double-layer film is 4.76×10−4 Ω cm with the maximum figure merit of 1.92×10−2 Ω−1, and the resistivity has a remarkable 28.7% decrease comparing with that of the single AZO film. The carrier scattering mechanism of TiO2 (3.0 nm)/AZO double-layer film had been described by Hall measurement in different temperatures. The average transmittance of all the films exceeded 92% in the visible spectrum. Another group samples were heat treated in the quartz tube in air atmosphere, and the effect of TiO2 thickness on thermal stability of AZO films had been discussed.