Deposited Al-doped ZnO Films Research Articles

Influence of unintentionally incorporated Ar atoms on the crystalline polarity of magnetron-sputtered Al-doped ZnO polycrystalline films on glass and sapphire substrates

The authors investigated the relationship between the content of incorporated Ar atoms and the crystalline polarity of polycrystalline Al-doped ZnO (AZO) films and examined the influence of this relationship on the resulting growth rate, crystallographic texture, and electrical properties. They deposited AZO films on glass and c-plane sapphire substrates via radio-frequency magnetron sputtering at substrate temperatures (Ts) of 100 or 200 °C using sintered AZO targets with an Al2O3 content of 2.0 wt. %. The incorporation of a large amount of Ar atoms induced a change in the crystalline polarity from Zn-polar to O-polar, the latter of which is associated with numerous obstacles, such as a lower deposition rate, large residual compressive stress, and increased electrical resistivity. The authors demonstrated that increasing the Ts led to a reduction in the amount of unintentionally retained Ar atoms, thereby affording Zn-polar AZO films with their associated advantages.

Work function of doped zinc oxide films deposited by ALD

Abstract

Effects of the erosion zone of magnetron sputtering targets on the spatial distribution of structural and electrical properties of transparent conductive Al-doped ZnO polycrystalline films

We investigated the effects of the erosion zone of magnetron sputtering (MS) targets on the deposition rates of magnetron-sputtered Al-doped ZnO (AZO) polycrystalline films and on the structural and electrical properties of the resulting AZO films. We deposited AZO films on glass substrates at a substrate temperature of 200 °C, which were placed parallel to the target surface, by radio frequency (RF), direct current (DC) or RF-superimposed DC (RF/DC) MS. Sintered AZO targets with an Al2O3 content of 2.0 wt. % were used. The structural and electrical properties were investigated by X-ray diffraction and Hall-effect measurements, respectively. For RF-magnetron-sputtered AZO films, the results of the electron probe microanalyzer and photo luminescence measurements show that the effects of the erosion zone of the targets on the properties were very small at any given substrate position, resulting in small differences in the structural and electrical properties among the AZO films grown at different substrate positions. In the case of DC-magnetron-sputtered AZO films, residual damage owing to recoiling Ar atoms was found, particularly for the films grown at substrate positions in the area opposite to the erosion zone of the targets. This gives rise to the formation of nonradiative recombination centers, low carrier concentration, and high contribution of grain boundary scattering to carrier transport owing to poor alignments between columnar grains, resulting in low Hall mobility. In this study, we prove that the use of the RF/DC MS technique is effective in reducing the amount of residual damage.

Highly transparent and conductive Al-doped ZnO films synthesized by pulsed laser co-ablation of Zn and Al targets assisted by oxygen plasma

Abstract Highly optically transparent and electrically conductive Al-doped ZnO (AZO) thin films were deposited by pulsed laser co-ablation of a Zn target and an Al target in an oxygen plasma. Zn ablation resulted in the reactive deposition of ZnO films assisted by the plasma, while Al ablation provided the growing ZnO films with Al dopants. The morphology, composition and structure as well as the optical and electrical properties were characterized and the effects of Al doping and annealing treatment were investigated. The deposited AZO films have a hexagonal wurtzite structure with deteriorated crystal quality which can be improved by annealing. The AZO films are highly transparent from ultraviolet up to 1450 nm and present an obvious blue shift in absorption edge and a widening of band gap compared with undoped ZnO. The electrical properties were also improved after annealing with the resistivity decreasing by over two orders of magnitude because of the increase of free carrier concentration. The variation in the carrier concentration also affects the absorption edge and the band gap of the films as well as the transparency in the infrared region. Meanwhile, this method offers an approach for in-situ doping preparation of other doped compound films with different dopant concentrations.

On the properties of aluminium doped zinc oxide thin films deposited on plastic substrates from ceramic targets

We report on the deposition of Al doped ZnO (AZO) thin films on unheated polyethylene terephthalate (PET) substrates by pulsed laser deposition technique using a UV excimer laser and Al2O3:ZnO ceramic targets (1.5 and 2wt% Al2O3). The deposited AZO films have been investigated by atomic force microscopy, scanning electron microscopy, X-ray diffraction, and optical spectrophotometry. Films present excellent optical and electrical properties (transmission in the visible range T>85%; resistivity at room temperature ρ=1.3×10−3Ωcm) as electrodes for plastic solar cells. A good correlation was found between deposition conditions (laser fluence) and structural, morphological, optical and electrical properties.

Thermophysical and electrical properties of Al-doped ZnO films

Thermal diffusivity of Al-doped ZnO (AZO) films with a thickness of 200 nm was quantitatively analyzed using a “rear heating/front detection type” nanosecond thermoreflectance system. AZO monolayer and Mo/AZO/Mo three-layered films were prepared on synthesized silica substrates by DC magnetron sputtering using high density ceramic ZnO–Al2O3 (Al2O3: 2.5 wt. %) and Mo metal targets. The thermal diffusivity and electrical resistivity of the deposited AZO films ranged 1.8 × 10−6 –2.4 × 10−6 m2 s−1 and 2.3 × 10−3–5.9 × 10−4 Ω cm, respectively. The thermal conductivity corresponding to the thermal diffusivity was one order of magnitude smaller than that of sintered AZO ceramics prepared from ZnO and Al2O3 powders. However, it was found to be larger than that of In2O3-based transparent conductive oxide (TCO) films with approximately the same electrical conductivity, thus implying that AZO can be considered an excellent material for diathermanous TCO circuits.

Plasma-aided hydrogenation and Al-doping: Increasing the conductivity and optical transparency of ZnO transparent conducting oxide

Plasma-assisted magnetron sputtering with varying ambient conditions has been utilised to deposit Al-doped ZnO (AZO) transparent conductive thin films directly onto a glass substrate at a low substrate temperature of 400°C. The effects of hydrogen addition on electrical, optical and structural properties of the deposited AZO films have been investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM), Hall effect measurements and UV–vis optical transmission spectroscopy. The results indicate that hydrogen addition has a remarkable effect on the film transparency and conductivity with the greatest effects observed with a hydrogen flux of approximately 3sccm. It has been demonstrated that the conductivity and the average transmittance in the visible range can increase simultaneously contrary to the effects observed by other authors. In addition, hydrogen incorporation further leads to the absorption edge shifting to a shorter wavelength due to the Burstein–Moss effect. These results are of particular relevance to the development of the next generation of optoelectronic and photovoltaic devices based on highly transparent conducting oxides with controllable electronic and optical properties.

Thickness Dependent Properties of Al-doped ZnO Film Prepared by Using the Pulsed DC Magnetron Sputtering with Cylindrical Target

Various thicknesses of Al-doped ZnO (AZO) films were deposited on glass substrate using pulsed dc magnetron sputtering with a cylindrical target designed for large-area high-speed deposition. The structural, electrical, and optical properties of the films of various thicknesses were characterized. All deposited AZO films have (0002) preferred orientation with the c-axis perpendicular to the substrate. Crystal quality and surface morphology of the films changed according to the film thickness. The samples with higher surface roughness exhibited lower Hall mobility. Analysis of the measured data of the optical band gap and the carrier concentration revealed that there were no changes for all the film thicknesses. The optical transmittances were more than 85% regardless of film thickness within the visible wavelength region. The lowest resistivity, was found in 750 nm films with an electron mobility of and a carrier concentration (n) of .

Mechanisms of lighting enhancement of Al nanoclusters-embedded Al-doped ZnO film in GaN-based light-emitting diodes

Aluminum (Al)-doped ZnO (AZO) films with embedded Al nanoclusters were proposed and utilized to enhance the light output power and maximum operation current of GaN-based light-emitting diodes (LEDs). The AZO films were sputtered using ZnO and Al targets in a magnetron cosputtering system. With Al dc power of 7 W and ZnO 100 W ac power, the electron concentration of 4.1×1020 cm−3, electron mobility of 16.2 cm2/V s, and resistivity of 7.2×10−4 Ω cm were obtained for the deposited AZO film annealed at 600 °C for 1 min in a N2 ambient. As verified by a high resolution transmission electron microscopy, the deposited AZO films with embedded Al nanoclusters were clearly observed. A 35% increase in light output power of the GaN-based LEDs with Al nanoclusters-embedded AZO films was realized compared with the conventional LEDs operated at 500 mA. It was verified experimentally that the various characteristics of GaN-based LEDs including the antireflection, light scattering, current spreading, and the light extraction efficiency in light emission could be significantly enhanced with the use of Al nanoclusters-embedded AZO films.