Aluminum-doped Zinc Oxide Target Research Articles

Electrical, morphological, optical and mathematical simulations equations studies in CAZO, CZO, AZO and ZNO films

Purpose In this paper, it can be seen from AFM images of the as-deposited ZnO and CZO films, and the particle size and shape are not clear, while by increasing annealing temperature, they become distinguishable. By increasing temperature to 600°C, ZnO and CZO, CAZO and aluminum-doped zinc oxide (AZO) films particles became almost spherical. Due to high content of Cu in CZO target, and of Al in AZO target which was 5% weight ratio, doping plays a great role in the subject. Therefore, the annealing processing strongly affect the size and the shape of nanoparticles. Design/methodology/approach In this paper, the authors tried to study, in detail, nobel optical characterizations of ZnO films doped by transition metals in different annealing temperature. The authors found that the values of skin depth, optical density, electron–phonon interaction, steepness parameter, band tail width, direct and indirect carriers transitions and the dissipation factor, free carriers density and roughness of films affect the optical properties, especially the optical absorptions of ZnO films doped by transition metals. Also these properties were affected by annealing temperatures. The authors also found that topography characterizations strongly were affected by these parameters. Findings The CZO films have maximum value of coordination number ß, with considering NC = 4, Za = 2, Ne = 8. The CZO films annealed at 500 °C have maximum value of optical density. The as-deposited CAZO films have maximum value of steepness parameters in about of 0.13 eV. The as-deposited AZO films have maximum value of dispersion energy Ed in about of 5.75 eV. Optical gap and disordering energy plots of films can be fitted by linear relationships Eg = 0.49 + 0.2 EU and Eg = 0.52 + 0.5 EU, respectively. Originality/value With considering Nc = 4, Za = 2, Ne = 8 for ZnO films, coordination number ß has maximum value of 0.198. CZO nanocomposites films annealed at 500°C have maximum value of optical density. Different linear fitting of ln (α) for films were obtained as y = Ax + B where 5<A < 17 and 5<B < 12. As-deposited CAZO nanocomposites films have minimum value of electron phonon interaction in about of 4.91 eV. Optical gap and disordering energy plots can be fitted by linear relationships Eg = 0.49 + 0.2 EU and Eg = 0.52 + 0.5 EU for as-deposited films and films annealed at 500°C, respectively. Steepness parameters of as-deposited CAZO nanocomposites films have maximum value of 0.13 eV. Dispersion energy Ed for as-deposited AZO nanocomposites films has maximum value of 5.75 eV.

Effects of Al2O3 doping on the microstructural evolution and densification process of AZO targets

Aluminum-doped zinc oxide (AZO) and zinc oxide (ZnO) slurries with high solid content and low viscosity were prepared by milling, and a new pressure slip casting technology was used to produce green compacts. Based on the shrinkage data obtained from thermal expansion experiments, activation energies for the densification of AZO and ZnO at different heating rates were calculated by the master sintering curve (MSC) method, and activation energies for grain growth were separately calculated. The optimal sintering process of AZO targets was investigated by the two-step sintering method, and AZO targets with a relative density of 99.8% and a grain size of 3.89 μm were obtained.

A Study on Formation of Aluminum-Doped Zinc Oxide Films by Pulsed-Direct Current Sputtering for CIGS Solar Cells.

Considering the relationship between thin film thickness of transparent conductive oxide (TCO) materials and the reversed pulse time in pulsed-direct current (DC) sputtering, aluminum-doped zinc oxide (AZO) films were deposited on glass substrates at different reversed pulse times by changing oxygen/argon (O₂/Ar) gas ratios for window layers of large area CuIn1-xGaxSe₂ (CIGS) solar cells. As a result of the reduced sputtering time, the thickness of AZO film was decreased when the reversed pulsed time was increased. The higher resistance and resistivity of the AZO film was obtained at a higher reversed pulse time. From the structural investigations of AZO such as transmittance and X-ray diffraction (XRD), it was possible to observe the relationship between the crystallinity of AZO and transmittance. Even at the short reversed pulse time of 0.5 µs, it can be concluded that the accumulated charges on the AZO target are completely cleared and the AZO layers show the highest figure of merit (FOM) with low sheet resistance and high transmittance.

Zinc-oxide-deposited Carbon Nanowalls for Acetone Sensing

The acetone level in diabetic patients is double that in healthy people, and is important not only for biosensors but also for gas sensors. In this study, carbon nanowall (CNW) was grown on a substrate using a microwave-plasma-enhanced chemical vapor deposition system with a mixture of methane (CH4) and hydrogen (H2) gases for acetone sensing. Zinc oxide (ZnO) and aluminum-doped ZnO (AZO) were deposited on the CNW using a radio frequency magnetron sputtering system with 4-inch AZO and ZnO targets. The surface structures of the AZO/CNW and ZnO/CNW were confirmed through Raman spectroscopy and field emission scanning electron microscopy. The detection characteristics were then confirmed using a current multimeter. A 200 mV voltage was applied to the electrode corresponding to the source and drain of each sample, and the organic matter was evaporated to confirm the acetone gas selectivity through the electrical variation of the samples.

Spatially Resolved Optoelectronic Properties of Al-Doped Zinc Oxide Thin Films Deposited by Radio-Frequency Magnetron Plasma Sputtering Without Substrate Heating.

Transparent and conducting thin films were deposited on soda lime glass by RF magnetron sputtering without intentional substrate heating using an aluminum doped zinc oxide target of 2 inch in diameter. The sheet resistance, film thickness, resistivity, averaged transmittance and energy band gaps were measured with 2 mm spatial resolution for different target-to-substrate distances, discharge pressures and powers. Hall mobility, carrier concentration, SEM and XRD were performed with a 3 mm spatial resolution. The results reveal a very narrow range of parameters that can lead to reasonable resistivity values while the transmittance is much less sensitive and less correlated with the already well-documented negative effects caused by a higher concentration of oxygen negative ions and atomic oxygen at the erosion tracks. A possible route to improve the thin film properties requires the need to reduce the oxygen negative ion energy and investigate the growth mechanism in correlation with spatial distribution of thin film properties and plasma parameters.

Highly (0001)-oriented Al-doped ZnO polycrystalline films on amorphous glass substrates

Very thin aluminum-doped zinc oxide (AZO) films with a well-defined (0001) orientation and a surface roughness of 0.357 nm were deposited on amorphous glass substrates at a temperature of 200 °C by radio frequency magnetron sputtering, which are promising, particularly in terms of orientation evolution, surface roughness, and carrier transport, as buffer layers for the subsequent deposition of highly (0001)-oriented AZO polycrystalline films of 490 nm thickness by direct current (DC) magnetron sputtering. Sintered AZO targets with an Al2O3 content of 2.0 wt. % were used. DC magnetron sputtered AZO films on bare glass substrates showed a mixed (0001) and the others crystallographic orientation, and exhibited a high contribution of grain boundary scattering to carrier transport, resulting in reduced Hall mobility. Optimizing the thickness of the AZO buffer layers to 10 nm led to highly (0001)-oriented bulk AZO films with a marked reduction in the above contribution, resulting in AZO films with improved Hall mobility together with enhanced carrier concentration. The surface morphology and point defect density were also improved by applying the buffer layers, as shown by atomic force microscopy and Raman spectroscopy, respectively.

Preparation of AZO nanoparticles, ceramic targets and thin films by a Co-precipitaition method

We comprehensively study the co-precipitation preparation of aluminum doped zinc oxide (AZO) nanoparticles, ceramic target and thin film deposition. The When the calcination temperature exceeded 700 °C, ZnAl2O4 phase appeared. The resistivity and relative density of the AZO target pressed from nanoparticles were 3×10-3 Ω∙cm and 99.1%, respectively. The minimum resistivity of AZO thin films prepared by DC sputtering of the ceramic target reached 4.1×10–4 Ω∙cm with the mobility of 33 cm2/v∙s and the carrier concentration of 4.5 ×1020 cm-3. The average optical transmittance of the AZO thin films in the visible wavelength range (400-800 nm) was more than 80%.

Structural evolution, electrical and optical properties of AZO films deposited by sputtering ultra-high density target

Aluminum-doped zinc oxide (AZO) target was fabricated using AZO nanopowders synthesized by co-precipitation method and then the AZO films with different thicknesses were deposited on glass by d.c. magnetron sputtering at room temperature. AZO target is nodules free and shows homogeneous microstructure, ultra-high density and low resistivity. ZnAl2O4 phase appears in AZO target and disappears in AZO films. All AZO films show c-axis preferred orientation and hexagonal structure. With increasing film thickness from 153 to 1404 nm, the crystallinity was improved and the angle of (002) peak was close to 34.45°. The increase in grain size and surface roughness is due to the increase in film thickness. The decrease of resistivity is ascribed to the increases of carrier concentration and Hall mobility. The lowest resistivity is 9.6 × 10−4 Ω·cm. The average transmittance of AZO films exceeds 80%, and a sharp fundamental absorption edge with red-shifting is observed in the visible range. The bandgap decreases from 3.26 to 3.02 eV.

Enhanced omni-directional performance of copper zinc tin sulfide thin film solar cell by gradient index coating

Many types of thin-film solar cells have a top, transparent conducting oxide (TCO) coating (such as aluminum-doped zinc oxide (AZO)) through which light is transmitted and current collected. In this paper, we demonstrate an effective antireflective coating for TCO surfaces using a gradient index coating formed from co-sputtered AZO and silicon dioxide (SiO2) targets that reduces reflection loss from the TCO. When applied to an active solar device, the power conversion efficiency of the solar cell increased by >10% when measured at normal incidence and >20% at angles 10° or greater.

Electrical and optical properties of radio frequency magnetron-sputtered lightly aluminum-doped zinc oxide thin films deposited in hydrogen–argon gas

We studied the electrical and optical properties of lightly aluminum-doped zinc oxide (L-AZO) films, which were deposited on soda-lime glass substrates by radio frequency (RF) magnetron sputtering using a 0.2wt.% aluminum-doped zinc oxide target and a 0.3wt.% hydrogen-mixed argon (Ar/0.3% H2) gas. The L-AZO films were characterized in terms of structural, optical, and electrical properties by X-ray diffraction, ultraviolet–visible spectrophotometry, photoluminescence and Hall measurements at room temperature. The Al contents of the L-AZO film were analyzed with secondary ion mass spectroscopy. As the Ar/0.3%H2 gas flow was increased up to 200sccm, the transmittance and conductivity of the film simultaneously improved as a function of the increasing flow rate without additional thermal or gas treatment. The 40nm-thick L-AZO film, which was deposited by an Ar/0.3% H2 gas flow of 200sccm at a substrate temperature of 100°C, had a carrier concentration of 1.0×1020/cm3, resistivity of 5.5×10−3Ω-cm, and an average transmittance of 93% in the wavelength range from 300nm to 2000nm.

Two-step sintering of aluminum-doped zinc oxide sputtering target by using a submicrometer zinc oxide powder

Aluminum-doped zinc oxide (AZO) is a potential substitute for tin-doped indium oxide due to its versatility. The properties of AZO films are related to those of the AZO sputtering target. To improve the performances of AZO targets, two-step sintering was used to densify a submicrometer zinc oxide (ZnO) powder with a size of 0.4μm to produce both AZO and ZnO targets.The results showed that the submicrometer ZnO powder cannot be densified by two-step sintering due to its coarse particle size and hexagonal structure. However, a 2wt% additive of Al2O3 in ZnO can modify the kinetic window of two-step sintering and help in the densification. Using two-step sintering, the sintered density of the AZO target can be improved from 97.4% to 99.8%. The grain size is also reduced by 60%, from 9.1μm to 3.6μm.

The mechanisms of negative oxygen ion formation from Al-doped ZnO target and the improvements in electrical and optical properties of thin films using off-axis dc magnetron sputtering at low temperature

Transparent conducting aluminum-doped zinc oxide (AZO) films have been prepared on glass substrates by dc magnetron sputtering using ceramic ZnO with 2 wt% Al2O3 target. The mechanism of negative oxygen ion generation on an AZO target surface and its influence on the conductivity of films were discussed. The negative ion generation on an AZO target was contributed by the surface ionization leading to the spot emission from Al atoms adsorbed on the AZO target surface. The contribution of negative ions' current was mainly from the erosion area of the target due to its higher temperature. To reduce the damage caused by negative ion bombardment to film growth, an off-axis sputtering system was proposed, where the substrates were placed perpendicular to the target. The effects of distance (d) on the electrical properties of films were experimentally verified in detail. A low resistivity of 3.7 × 10−4 Ω cm, an average transmittance above 85% in the visible range (300–800 nm) and reflectance higher than 85% in the infrared range (2500–4000 nm) were obtained for the films deposited at d = 2.5 cm. The overall analysis revealed that the generation of negative ions on the AZO target has a great influence on film growth, especially in the ultra-low pressure deposition process. Our work demonstrates the feasibility of reducing the negative effects of ion bombardment on the quality of films, which would be of great merit for industrial applications.

Effects of post-annealing on structural, optical and electrical properties of Al-doped ZnO thin films

Aluminum-doped zinc oxide (AZO) films were deposited at 400 °C by radio-frequency magnetron sputtering using a compound AZO target. The effects of annealing atmospheres as well as hydrogen annealing temperatures on the structural, optical and electrical properties of the AZO films were investigated. It was found that the electrical resistivity varied depending on the atmospheres while annealing in air, nitrogen and hydrogen at 300 °C, respectively. Comparing with that for the un-annealed films, the resistivity of the films annealed in hydrogen decreased from 9.8 × 10 −4 Ω cm to 3.5 × 10 −4 Ω cm, while that of the films annealed in air and nitrogen increased. The variations in electrical properties are ascribed to both the changes in the concentration of oxygen vacancies and adsorbed oxygen at the grain boundaries. These results were clarified by the comparatively XPS analyzing about the states of oxygen on the surface of the AZO films. There was great increase in electrical resistivity due to the damage of the surfaces, when AZO films were annealed in hydrogen with a temperature higher than 500 °C, but high average optical transmittance of 80–90% in the range of 390–1100 nm were still obtained.

In situ analyses on negative ions in the sputtering process to deposit Al-doped ZnO films

The origin of high energy negative ions during deposition of aluminum doped zinc oxide (AZO) films by dc magnetron sputtering of an AZO (Al2O3: 2.0 wt %) target was investigated by in situ analyses using the quadrupole mass spectrometer combined with the electrostatic energy analyzer. High energy negative oxygen (O−) ions which possessed the kinetic energy corresponding to the cathode sheath voltage were detected. The maximum flux of the O− ions was clearly observed at the location opposite to the erosion track area on the target. The flux of the O− ions changed hardly with increasing O2 flow ratio [O2/(Ar+O2)] from 0% to 5%. The kinetic energy of the O− ions decreased with decreasing cathode sheath voltage from 403 to 337 V due to the enhancement of the vertical maximum magnetic field strength at the cathode surface from 0.025 to 0.100 T. The AZO films deposited with the lower O− bombardment energy showed the higher crystallinity and improved the electrical conductivity.

Electrical resistivity and transmittance properties of Al and Ga-codoped ZnO thin films

Films were deposited on glass substrates by sputtering gallium-doped zinc oxide (GZO) (Ga2O3: 90 wt%, ZnO: 10 wt%) and aluminum-doped zinc oxide (AZO) (Al2O3: 3 wt%, ZnO: 97 wt%) targets simultaneously using a direct-current (DC)/radio-frequency (RF) magnetron cosputtering system. The concentration of gallium (Ga) in the film was varied by using different RF powers for sputtering the GZO target with the DC power for sputtering the AZO target fixed. A minimum resistivitywas obtained at an RF sputtering power of 200 W for the GZO target when the DC sputtering power for the AZO target was fixed at 60 W. It was found that the resistivity of AZO thin films (6.40 × 10−3 Ω-cm for 0 W) could be lowered by more than one order by cosputtering AZO and GZO targets to make AGZO thin films (2.14 × 10−3Ω-cm for 200 W) without lowering their transmittance at all. In addition, the origin of the enhancement in the electrical property of the AZO by additional Ga doping is discussed.

ITO와 AZO 동시 증착법으로 제조된 투명전도막의 특성 연구

Transparent conducting thin films of indium tin oxide(ITO) co-sputtered with aluminum-doped zinc oxide(AZO) were deposited on glass substrate by dual magnetron sputtering. It was found that the electrical properties and structural characteristics of the films are significantly changed according to the sputtering power of the AZO target. The IAZTO film prepared with D.C power of ITO at 100 W and R.F power of AZO at 50 W shows an electrical resistivity of <TEX>$4.6{\times}10^{-4}{\Omega}{\cdot}cm$</TEX> and a sheet resistance of <TEX>$30{\Omega}/{\square}$</TEX> (for 150 nm thick). Besides of the improvement of the electrical properties, compared to the ITO films deposited at the same process conditions, the IAZTO films have very smooth surface, which is due to the amorphous nature of the films. However, the electrical conductivity of the IAZTO films was found to be deteriorated along with the crystallization in case of the high temperature deposition (above <TEX>$310^{\circ}C$</TEX>). In this work, high quality amorphous transparent conductive oxide layers could be obtained by mixing AZO with ITO, indicating possible use of IAZTO films as the transparent electrodes in OLED and flexible display devices.

Coating material innovation in conjunction with optimized deposition technologies

Concentrating on physical vapour deposition methods several examples of recently developed coating materials for optical applications were studied for film deposition with optimized coating technologies: mixed evaporation materials for ion assisted deposition with modern plasma ion sources, planar metal and oxide sputter targets for Direct Current (DC) and Mid-Frequency (MF) pulsed sputter deposition and planar and rotatable sputter targets of transparent conductive oxides (TCO) for large-area sputter deposition. Films from specially designed titania based mixed evaporation materials deposited with new plasma ion sources and possible operation with pure oxygen showed extended ranges of the ratio between refractive index and structural film stress, hence there is an increased potential for the reduction of the total coating stress in High–Low alternating stacks and for coating plastics. DC and MF-pulsed sputtering of niobium metal and suboxide targets for optical coatings yielded essential benefits of the suboxide targets in a range of practical coating conditions (for absent in-situ post-oxidation ability): higher refractive index and deposition rate, better reproducibility and easier process control, and the potential for co-deposition of several targets. Technological progress in the manufacture of rotatable indium tin oxide (ITO) targets with regard to higher wall-thickness and density was shown to be reflected in higher material stock and coater up-time, economical deposition rates and stable process behaviour. Both for the rotatable ITO targets and higher-dense aluminum-doped zinc oxide (AZO) planar targets values of film transmittance and resistivity were in the range of the best values industrially achieved for films from the respective planar targets. The results for the rotatable ITO and planar AZO targets point to equally optimized process and film properties for the optimized rotatable AZO targets currently in testing.

DC 마그네트론 스퍼터링에 의해 증착한 AZO 박막의 특성

Aluminum doped zinc oxide (AZO) films were deposited on non-alkali glass substrate by DC magnetron sputtering with 3 types of AZO targets (doped with 1.0 wt%, 2.0 wt%, 3.0 wt% <TEX>$Al_2O_3$</TEX>). Electrical, optical properties and microstructure of AZO films have been investigated by Hall effect measurements, UV/VIS/NIR spectrophotometer, and XRD, respectively. Crystallinity of AZO films increased with increasing substrate temperature (<TEX>$T_s$</TEX>) and doping ratio of Al. Resistivity and optical transmittance in visible light were <TEX>$8.8{\times}10^{-4}{\Omega}cm$</TEX> and above 85%, respectively, for the AZO film deposited using AZO target (doped with 3.0 wt% <TEX>$Al_2O_3$</TEX>) at <TEX>$T_s$</TEX> of <TEX>$300^{\circ}C$</TEX>. On the other hand, transmittance of AZO films in near-infrared region decreased with increasing <TEX>$T_s$</TEX> and doping ratio of Al, which could be attributed to the increase of carrier density.

A comparison of transmittance properties between ZnO: Al films for transparent conductors for solar cells deposited by sputtering of AZO and cosputtering of AZO/ZnO

Aluminum-doped zinc oxide (AZO) thin films were deposited on sapphire (002) and glass substrates by two different sputtering techniques radio frequency magnetron cosputtering of AZO and ZnO targets and sputtering of an AZO target. The dependence of the photoluminescence (PL) and transmittance properties of the AZO films deposited by cosputtering and sputtering on the AZO/ZnO target power ratio, R and the O 2/Ar flow ratio, r were investigated, respectively. Only a deep level emission peak appears in the PL spectra of cosputtered AZO films whereas both UV emission and deep level emission peaks are observed in the PL spectra of sputtered AZO films. The absorption edges in the transmittance spectra of the AZO films shift to the lower wavelength region as R and r increase. Effects of crystallinity, surface roughness, PL on the transmittance of the AZO films were also explained using the X-ray diffraction (XRD), atomic force microscopy (AFM), and PL analysis results.

Effects of starting material of aluminum doped zinc oxide underlayer on the electric properties of palladium doped silver film

Crystallographic and electric properties of a palladium doped silver (Ag–Pd) layer formed on an aluminum doped zinc oxide (AZO) film in the multilayer system of Ag–Pd(10.5 nm)/AZO(42 nm)/glass were investigated. All of the films in this study were deposited by dc magnetron sputtering. Two kinds of sputtering targets, aluminum doped zinc metal (AZ) and AZO, were used for the deposition of AZO films. The AZ target was sputtered in an oxygen or carbon dioxide atmosphere whereas the AZO target was sputtered in an argon or argon/oxygen atmosphere. The Ag–Pd layers were deposited under the fixed sputtering condition. From x-ray diffraction patterns it was found that the most developed Ag(111) peak appeared in the case of the Ag–Pd film on the AZO layer deposited from the AZ metal target with oxygen. Atomic force microscope observation revealed that the smallest surface roughness was obtained in this case. Electrical resistivity of the Ag–Pd layer changed by up to 17% depending on deposition conditions and the target materials of the underlayer. The Ag–Pd film deposited on the AZO layer from the AZ target in an oxygen atmosphere also showed the lowest resistivity of 7.1×10−6 Ω cm. The smallest refractive index of Ag–Pd film was shown by the same sample from an analysis using spectroscopic ellipsometry (SE). Deposition of a thin metal (Zn–Al) overlayer on Ag–Pd/AZO/glass increased the overall resistivity of the multilayer. This may imply the diffusion of zinc atoms into the Ag–Pd layer, however, the resistivity recovery was observed after some storage time, which suggests the effect of an electron scattering at the surface.