Properties Of Aluminum Doped Zinc Oxide Research Articles

Effect of transparent conductive layers on the functionality of liquid crystal devices: Comparison of AZO, FTO and ITO

The integration of highly transparent and highly conductive layers plays a crucial role in the advancement of various next-generation optoelectronic technologies. Here, we demonstrate a comparison of optical, electrical and wettability properties of Aluminum-doped Zinc Oxide (AZO) deposited by Atomic Layer Deposition Technique (ALD) with commercially available Fluorine-doped Tin Oxide (FTO) and Indium-doped Tin Oxide (ITO) Transparent Conductive Oxide (TCO) layers. Their impact on the electro-optical modulation behavior when applied in Liquid Crystal (LC) device assemblies are compared and discussed. The AZO layers performance prove that are fully competitive to the commercial FTO and ITO layers and verify the high demand for the next generation indium tin oxide (ITO)-free technology.

Systematic investigations on morphological properties of aluminum-doped zinc oxide transparent electrode prepared from pulsed laser deposition and its electrochromic application

Transparent electrode (TE) is considered as one of the fundamental components in the optoelectronics. The surface of TE layer plays a crucial role in the charge-transport characteristics. Herein, a systematic investigation on the morphological properties of the laser-ablated aluminum-doped zinc oxide (AZO) films as a TE material prepared from various laser fluences is demonstrated. It is revealed that the electrical properties of AZO films are strongly associated with their surface properties rather than that of the bulk film. As the laser fluence increased, the concentration of Al-dopant in AZO films is decreased which directly impacts on the electrical properties. Such vanishment is originated from the bombardment of the incident particles/ions with excessive kinetic energy on film's surface during the deposition. Moreover, the optimized AZO film with low resistivity (1.13 × 10−3 Ω cm) and high optical transmittance (over 90%) achieved from controlling the laser fluence at 0.7 J/cm2 is employed as TE layer in the electrochromic device. Our results highlight that the surface properties of TE layer are very critical for electronic performance.

Improvement in structural, electrical, and optical properties of Al-doped ZnO nanolayers by sodium carbonate prepared via solgel method

The significant improvement in crystallinity, electrical, and optical properties of aluminum-doped zinc oxide (AZO) thin films was attained by Na doping. Both Al and Na contents were introduced into ZnO host via facile and cost-effective solgel method. Ultra-thin films of Na-doped AZO (NAZO), with thickness of about 40 nm, were deposited on glass substrates via spin-coating technique. The obtained results showed low sodium incorporation reduces the crystal strain which in turn leads to increase crystallite size from 31 nm for AZO to 49 nm for 2 at% Na-doped AZO layer. In addition, 2 at.% of Na doping, that was determined as an optimum level of doping concentration, decreased the macroscopic surface roughness (MRs) without notable changes in surface micro-cracks, leading to remarkable enhancement of the layer conductivity (about 54%). On the other hand, high concentration of sodium content (10 at%) increased the crystal strain and reduced the crystallinity order of AZO layer which resulted in high MRs and also high electrical sheet resistance. Optical dispersion curve and real and imaginary parts of dielectric constant were obtained using our precise method. More interestingly, 2 at% of Na doping led to an increase in transparency of AZO layer in the visible range, while its extinction coefficient (light power absorption) was enhanced which can be regarded as advantage for such thin films. Therefore, the optimum Na content can provide higher optical absorption even with higher transparency by reducing the light scattering and reflection. This finding provides a useful procedure to prepare transparent oxide semiconductor layers with noticeable light absorption, which is very interesting for various applications such as solar cells and anti-reflection coatings.

Three-level system for numerical modeling of ultraviolet and visible photoluminescence of aluminum-doped zinc oxide

The emission properties of aluminum-doped zinc oxide are numerically investigated. A complete model for photoluminescence, based on the set of rate equations for electron–hole recombination, is used to study the influence of carrier concentration (1017–1021 cm−3) on visible and ultraviolet (UV) emission. The set of coupled rate equations is solved numerically using the fourth-order Runge–Kutta technique for various optical pump intensities. The results for low carrier concentration (∼1017 cm−3) show that at low pump intensity (0.01 mJ/cm2), visible emission is dominant in the emission spectrum, and as the pump intensity increases (∼1 mJ/cm2), the UV emission becomes dominant. The study of ultrafast dynamics shows that for pump pulse durations of less than ∼1 ns, the intensity of UV emission is an order of magnitude larger compared to the visible intensity for aluminum-doped zinc oxide samples with carrier concentration ∼1018 cm−3.

Characteristics of low-resistivity aluminum-doped zinc oxide films deposited at room temperature by off-axis radio-frequency sputtering on flexible plastic substrates

The crystalline structure, morphology, composition, electrical transport, and optical properties of aluminum-doped zinc oxide (AZO) films are studied for applications in transparent electronics and optoelectronic devices. AZO thin films of c-axis-oriented growth and with different thickness were deposited on PET flexible plastic substrates at room temperature by rf magnetron sputtering. A larger grain size with a decreased strain e value is observed in a thicker film, while changes in composition for films with different thicknesses are insignificant. Moreover, the resistivity of film decreases with increasing thickness, and the low-temperature electrical transport properties can be described by the scenario of quantum corrections to conductivity. With the room-temperature growth conditions, the resistivity of 4.5 × 10−4 Ω cm, carrier concentration of 6.4 × 1020 cm−3, and transmittance of 80 % for the 1100-nm-thick film are obtained. In addition, the optical bandgap energy decreases with increasing film thickness, which can be attributed to the bandgap renormalization and crystallite size effects.

Approach using the electrical structure and optical properties of aluminium-doped zinc oxide for solar cells

Aluminium-doped zinc oxide (AZO) is attracting a continuously increasing amount of attention because of its potential as a solar cell material.

Depositing High-Performance Conductive Thin Films by Using Atomic Layer Deposition

This work characterizes the mechanical and opto-electric properties of Aluminum-doped zinc oxide (AZO) thin films deposited by atomic layer deposition (ALD), where various depositing temperature, 100, 125, 150, 175, and 200 °C are considered. The transmittance, microstructure, electric resistivity, adhesion, hardness, and Young’s modulus of the deposited thin films are tested by using spectrophotometer, X-ray diffraction, Hall effect analyzer, micro scratch, and nanoindentation, respectively. The results show that the AZO thin film deposited at 200 °C behaves the best electric properties, where its resistance, Carrier Concentration and mobility reach 4.3×10-4 Ωcm, 2.4×1020 cm-3, and 60.4 cm2V-1s-1, respectively. Furthermore, microstructure of the AZO films deposited by ALD is much better than those deposited by sputtering.

退火时间对AZO薄膜结构及光学性质的影响

退火时间对AZO薄膜结构及光学性质的影响

Optical and structural properties of Al-ZnO nanocomposites.

The optical and structural properties of aluminium-doped zinc oxide (AZO) films were investigated by photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy. Pure zinc oxide (ZnO) and AZO composite films were deposited using vacuum evaporation method. The films exhibited different morphologies and crystallinity depending on the Al-doping. The SEM micrographs showed that a granular and compact structure could be seen for the ZnO film, while a nanoleaf structure with relatively porous nature was observed for the AZO composite film. The XRD patterns indicated that the crystalline growth orientation would be significantly affected by addition of Al. Compared with pure ZnO, the XRD peak intensity of the AZO composite was stronger and the line-width was narrower. Two-probe resistivity measurements showed that the AZO composites could be used as transparent conducting materials. The PL spectra revealed that the PL intensities of the AZO composites were stronger than that of the pure ZnO. The PL enhancement might be ascribed to the surface plasmon resonance of metal nanoclusters within the composite. Another possible reason of the PL enhancement would be the metal-induced crystallization caused by doping Al to ZnO matrix.

The effect of substrate temperature on Al-doped ZnO characteristics for organic thin film transistor applications

The influence of substrate temperature on the structural, electrical, and optical properties of aluminum-doped zinc oxide (AZO) films fabricated by radio frequency (RF) magnetron sputtering was investigated. The AZO films were deposited at various substrate temperatures, and the effect of AZO gate electrode conductivity on organic thin film transistor (OTFT) performance was examined. While an increase in the substrate temperature from 100°C to 300°C led to an improvement in crystallinity, substrate temperatures over 300°C caused degradation of the electrical and surface properties. We fabricated OTFTs using AZO films prepared at various substrate temperatures and obtained good device performance. Thus, the performance of an OTFT can be determined by the conductivity of the AZO gate electrode.

Evaluation of the microstructural and photocatalytic properties of aluminum-doped zinc oxide coatings deposited by plasma spraying

Aluminum-doped zinc oxide (AZO) material produced from a nanopowder agglomerate was deposited as a plasma-sprayed coating, and the resulting microstructural and photocatalytic properties of these coatings were investigated. The microstructure of the AZO coatings was analyzed by X-ray diffraction and scanning electron microscopy. Additionally, the photocatalytic degradation of methylene blue caused by the AZO coatings was estimated via ultraviolet–visible spectroscopy. The results of this study demonstrate that the AZO coatings deposited by plasma spraying can influence the photocatalytic degradation of methylene blue.

Relation between synthesis conditions, dopant position and charge carriers in aluminium-doped ZnO nanoparticles

The ability to achieve an understanding of the correlations between chemical synthesis, doping mechanism and properties of aluminium-doped zinc oxide (ZnO:Al) nanocrystals is of great importance to evaluate the potential of ZnO:Al nanocrystals as optimal building blocks for solution deposited transparent conductive oxide layers. Two series of Al-doped ZnO nanoparticles were synthesized by solution-based methods under different conditions yielding phase-pure wurtzite ZnO:Al nanocrystals with different morphologies (quasispheres and rods). In both series 80% of the input Al is incorporated in the ZnO:Al crystals. Furthermore, 27Al nuclear magnetic resonance demonstrated a 5 times higher tetrahedral Al content for the quasispheres, which can be directly linked to the presence of free charge carriers, as showed with Fourier transform infrared spectroscopy. XPS data show the Zn2+ and O2− chemical state of the constituting ions. It is demonstrated that an efficient Al doping, creating charge carriers in the ZnO, can be achieved by controlling the chemical synthesis parameters of the nanoparticles.

Analysis on the interfacial properties of transparent conducting oxide and hydrogenated p-type amorphous silicon carbide layers in p–i–n amorphous silicon thin film solar cell structure

Quantitative estimation of the specific contact resistivity and energy barrier at the interface between transparent conducting oxide (TCO) and hydrogenated p-type amorphous silicon carbide (a-Si1−xCx:H(p)) was carried out by inserting an interfacial buffer layer of hydrogenated p-type microcrystalline silicon (μc-Si:H(p)) or hydrogenated p-type amorphous silicon (a-Si:H(p)). In addition, superstrate configuration p–i–n hydrogenated amorphous silicon (a-Si:H) solar cells were fabricated by plasma enhanced chemical vapor deposition to investigate the effect of the inserted buffer layer on the solar cell device. Ultraviolet photoelectron spectroscopy was employed to measure the work functions of the TCO and a-Si1−xCx:H(p) layers and to allow direct calculations of the energy barriers at the interfaces. Especially interface structures were compared with/without a buffer which is either highly doped μc-Si:H(p) layer or low doped a-Si:H(p) layer, to improve the contact properties of aluminum-doped zinc oxide and a-Si1−xCx:H(p). Out of the two buffers, the superior contact properties of μc-Si:H(p) buffer could be expected due to its higher conductivity and slightly lower specific contact resistivity. However, the overall solar cell conversion efficiencies were almost the same for both of the buffered structures and the resultant similar efficiencies were attributed to the difference between the fill factors of the solar cells. The effects of the energy barrier heights of the two buffered structures and their influence on solar cell device performances were intensively investigated and discussed with comparisons.

Influence of various thickness metallic interlayers on opto-electric and mechanical properties of AZO thin films on PET substrates

Various thickness metallic interlayers to improve the opto-electric and mechanical properties of aluminum-doped zinc oxide (AZO) thin films deposited on flexible polyethylene terephtalate (PET) substrates are studied. The effects of the interlayers on the resistance and transmittance of the AZO thin films are discussed. The result shows that the metallic interlayers effectively improve the electric resistance but reduce the optical transmittance of the AZO thin films. These phenomena become more obvious as the interlayer thickness increases. However, the AZO with an aluminum interlayer still behaves an acceptable transmittance. Moreover, mechanical tests indicate that the aluminum interlayer increases the hardness and modulus, and reduce the residual stress of the AZO thin films. In contrast, the silver and copper interlayers decrease the AZO's mechanical properties. Comparing to those without any interlayer, the results show that the best interlayer is the 6nm thick aluminum film.

Low Pressure Chemical Vapor Deposition of Aluminum-Doped Zinc Oxide for Transparent Conducting Electrodes

We carried out comprehensive studies on structural, optical, and electrical properties of aluminum-doped zinc oxide (AZO) films deposited by low pressure chemical vapor deposition (LP-CVD). The growth rates of LP-CVD AZO films increased slightly with Al doping. In addition, the resistivity was strongly dependent on the carrier electron concentration, also correlated with optical band gap and work function. All the AZO films exhibited high optical transmittance of >80% in the visible range of 400–700 nm and high work function of >4.6 eV regardless of the Al content. For the comparative studies on the electrical properties as gate electrodes, metal-oxide-semiconductor (MOS) capacitors were prepared by LP-CVD AZO and sputtered ITO as gates. The AZO gate showed higher dielectric constant (k = 8.8), lower interface state (Dit = 1.5 × 1011 cm−2eV−1), effective oxide charge (Qeff = 4.8 × 1011), and leakage current density (2.3 × 10−8 A/cm2 at −1 MV/cm) than the ITO gate (k = 8.5, Dit = 3 × 1011 cm−2eV−1, Qeff = 1.4 × 1012 cm−2 and leakage current density = 5.7 × 10−8 A/cm2 at −1 MV/cm, respectively).

Influence of different plasma treatments on electrical and optical properties on sputtered AZO and ITO films

In this paper, the influence of hydrogen and argon plasma treatment on the electro-optical and structural properties of aluminum-doped zinc oxide (AZO) and indium tin oxide (ITO) films were studied. The films were exposed for different times and at various plasma powers. AZO films did not reduce for all plasma conditions, while ITO films were deteriorated when exposed to hydrogen plasma for even a short treatment time. The argon plasma has little effect on the properties of AZO and ITO films. When the ITO films were exposed to Ar plasma for a long time, however, the optical properties of ITO films were strongly influenced.

The characteristics of chemical and heat stability properties of chromium–vanadium–aluminum co-doped zinc oxide films for dye-sensitized solar cells

Transparent conducting oxide thin films are used as front contact material for dye-sensitized solar cells. This study investigated the effects of chromium (Cr) and vanadium (V) contents on the chemical and heat stability properties of aluminum-doped zinc oxide (AZO) thin films using pulsed direct current magnetic sputtering on Corning 1737F glass substrates. The experimental results show that Cr and V doping is useful for improving the chemical and thermal stability of AZO films. The energy gap for AZO thin films is between 3.65 and 3.69 eV. The resistivity of the AZO:Cr:V thin film was 4.23 × 10 – 4 Ω cm at a Cr/V ratio of 0.30/0.23 wt.%, deposition power of 150 W, working distance of 5.5 cm, substrate temperature of 473 K, working pressure of 0.4 Pa, and frequency of 10 kHz. This value is lesser than (and therefore superior to) the resistivity of SnO 2:F (FTO) films (6.5 × 10 – 4 Ω cm), but greater than that of SnO 2:In (ITO) thin films (1.2 × 10 – 4 Ω cm). The resistivity increased by about 0.27% after electrolyte etching, which is similar to the 0.16% increase observed for the ITO thin film. After a thermal cycle test at 673 K, the resistivity of the AZO:Cr:V film increased to 5.42 × 10 – 4 Ω cm, which is better than the resistivity of the ITO and FTO films after the same thermal cycle.

Structural, optical, and electrical properties of AZO films by tilted angle sputtering method

We investigate the structural, optical, and electrical properties of aluminum-doped zinc oxide (AZO) films on Si substrate by a tilted angle sputtering method. The substrate holder is tilted by varying the angle from θ sh = 0 ° to θ sh = 80 ° during the sputtering process. As the tilted angle is increased, the deposition rate is increased due to the decreased distance between the substrate and the target. Without substrate rotation, the deposited AZO films exhibit apparently the inclined nanocolumnar structures, depending on the tilted angle. The refractive index, which is related to the porosity within films, is reduced for the larger inclined nanocolumnar structure while the extinction coefficient remains almost the same in the visible wavelength range. The inclination of nanocolumns disappears when the substrate is rotated. On glass substrate, the electrical properties as well as optical transmittance of AZO films are also dependant on the tilted angle.

Electrical properties of aluminum-doped zinc oxide (AZO) nanoparticles synthesized bychemical vapor synthesis

Aluminum-doped zinc oxide nanoparticles have been prepared by chemical vapor synthesis,which facilitates the incorporation of a higher percentage of dopant atoms, farabove the thermodynamic solubility limit of aluminum. The electrical propertiesof aluminum-doped and undoped zinc oxide nanoparticles were investigated byimpedance spectroscopy. The impedance is measured under hydrogen and syntheticair between 323 and 673 K. The measurements under hydrogen as well as undersynthetic air show transport properties depending on temperature and doping level.Under hydrogen atmosphere, a decreasing conductivity with increasing dopantcontent is observed, which can be explained by enhanced scattering processesdue to an increasing disorder in the nanocrystalline material. The temperaturecoefficient for the doped samples switches from positive temperature coefficientbehavior to negative temperature coefficient behavior with increasing dopantconcentration. In the presence of synthetic air, the conductivity firstly increases withincreasing dopant content by six orders of magnitude. The origin of the increasingconductivity is the generation of free charge carriers upon dopant incorporation. Itreaches its maximum at a concentration of 7.7% of aluminum, and drops forhigher doping levels. In all cases, the conductivity under hydrogen is higher thanunder synthetic air and can be changed reversibly by changing the atmosphere.

Characterization of Monolayer Formation on Aluminum-Doped Zinc Oxide Thin Films

The optical and electronic properties of aluminum-doped zinc oxide (AZO) thin films on a glass substrate are investigated experimentally and theoretically. Optical studies with coupling in the Kretschmann configuration reveal an angle-dependent plasma frequency in the mid-IR for p-polarized radiation, suggestive of the detection of a Drude plasma frequency. These studies are complemented by oxygen depletion density functional theory studies for the calculation of the charge carrier concentration and plasma frequency for bulk AZO. In addition, we report on the optical and physical properties of thin film adlayers of n-hexadecanethiol (HDT) and n-octadecanethiol (ODT) self-assembled monolayers (SAMs) on AZO surfaces using reflectance FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Our characterization of the SAM deposition onto the AZO thin film reveals a range of possible applications for this conducting metal oxide.