ZnO Ceramic Target Research Articles

Combined effect of the target composition and deposition temperature on the properties of ZnO:Ga transparent conductive oxide films in pulsed dc magnetron sputtering

Composition-dependent changes in the properties of Ga-doped ZnO (GZO) transparent conductive oxide (TCO) films were investigated by preparing a series of GZO films on glass substrates via pulsed dc magnetron sputtering with ZnO ceramic targets having various Ga2O3 concentrations at various temperatures. As the Ga2O3 content in the target increased, crystalline quality was improved as revealed in the intense ZnO (0 0 2) diffraction peaks, which accompanied increased carrier concentrations. When the Ga2O3 content was low, it was deduced from the crystallinity and carrier concentration that Ga or its oxide species functioned primarily as a crystal growth promoter, which was more distinctive at lower deposition temperatures. Meanwhile, formation of the secondary oxide phases, detrimental to the carrier mobility, was rather enhanced up to intermediate temperature and then suppressed by further increasing the deposition temperature. Consequently, improved crystallinity and enhanced doping efficiency and therefore the lowest electrical resistivity could be achieved with the combination of higher Ga2O3 content in the target and higher deposition temperature. Electrical resistivity and optical transmittance of the GZO films prepared by the pulsed dc magnetron sputtering in this study fulfilled requirements for TCO films.

Sintering Behavior of Nano‐ and Micro‐Sized ZnO Powder Targets for rf Magnetron Sputtering Applications

In this work, the nonisothermal sintering behavior of as‐received commercial high purity ZnO micrometric (m_ZnO), submicrometric (sm_ZnO) and nanometric (n_ZnO) powders was studied. The sintering behavior for sputtering target production was evaluated by changing the green density of samples from 62% of theoretical density (TD) to 35%. We observed that for n_ZnO powder, the maximum shrinkage rate (MSR) temperature (TMSR) was not affected by the green density, and that it was reached at lower temperatures (~710°C) compared with m_ZnO and sm_ZnO powders. For these powders, the temperature of MSR increased from 803°C to 934°C and from 719°C to 803°C as TD changed from 62% to 35% TD, respectively. Small grain size (~0.560 μm) and high density targets were obtained for n_ZnO when sintered at temperatures below the TMSR. Heating rate from 1°C to 15°C/min led to lower activation energy for n_ZnO (~201 ± 3 kJ/mol) than for the submicrometric (sm_ZnO) (~332 ± 20 kJ/mol) and micrometric (m_ZnO) (~273 ± 9 kJ/mol) powders. Using the model proposed by Bannister and Woolfrey, an n value of 0.75 was found, which was correlated with a combination of viscous flow and volume diffusion mechanisms that should control the initial stage of n_ZnO sintering. No significant differences were observed for n_ZnO powder in terms of density when the size of targets (scale‐up effect) was increased, while in the case of m_ZnO and sm_ZnO, a delay in the densification was observed, which was related to the higher sinterability of n_ZnO powder. Two inches ZnO ceramic targets with different particle sizes and final densities were used in an rf magnetron sputtering system to produce ZnO films under the same deposition conditions. Films with thickness around 100 nm and good uniformity were produced using those targets, and no variation was observed in the optical and morphological properties. However, low electrical resistivity (1.4 Ω·cm) films were obtained with n_ZnO targets, which could be explained in terms of a nonstoichiometric Zn:O composition of the started powders.

Preparation of Al-doped ZnO thin films as transparent conductive substrate in dye-sensitized solar cell

We have prepared aluminum-doped Zinc oxide (AZO) thin films on glass substrates by rf magnetron sputtering technique using ZnO ceramic target in pure argon gas with different aluminum concentrations. The bandgap of the ZnO films slightly widens with increase in Al content and the lowest sheet resistance of AZO films with Al concentration of 4.3 at.% was obtained. The effects of post-annealing treatment on structural, electrical and optical properties of the AZO thin films were investigated. Using AZO thin film with 4.3 at.% Al as the transparent substrate, a titanium dioxide based dye-sensitized solar cell was constructed and a solar to electrical energy conversion efficiency of 2.9% was achieved under AM 1.5 solar simulated sunlight.

Influence of Annealing and Europium-Doping on the Structure and Optical Properties of ZnO Thin Films Grown on Quartz Substrate by Magnetron Sputtering

ZnO and Eu-doped ZnO thin films were deposited on quartz substrates by reactive radio-frequency magnetron sputtering from a ZnO and Eu-doped ZnO ceramic target respectively. The properties of thin films were characterized by atom force microscope (AFM), X-ray diffraction (XRD), and photoluminescence spectra (PL). XRD reveals that the prepared thin films possess a single crystalline hexagonal wurtzite crystal structure with preferential c-axis orientation. Under above-bandgap excitation at room temperature, PL shows that ZnO films exhibit strong UV near-band-edge excitonic emission and Eu-doped ZnO thin films present UV emission and red emission from Eu3+ ions, demonstrating efficient energy transfer from the host to Eu3+ ions. The influence of annealing on the structure and optical properties of ZnO and Eu-doped ZnO thin films is studied. The efficient energy transfer from the host to Eu3+ and high luminous efficiency indicates that the prepared Eu-doped ZnO thin films are very promising materials for lighting and flat panel display application.

Preparation and characterization of solid-state sintered aluminum-doped zinc oxide with different alumina contents

Aluminum-doped zinc oxide (AZO) ceramics with 0− 2 ·5 wt.% alumina (Al2O3) content were prepared using a solid-state reaction technique. It was found that AZO grains became finer in size and more irregular in shape than undoped ZnO as the Al2O3 content increased. Addition of Al2O3 dopant caused the formation of phase transformation stacking faults in ZnO grains. The second phase, ZnAl2O4 spinel, was observed at the grain boundaries and triple junctions, and inside the grains. In this study, a 3-inch circular Al2O3 (2 wt.%)-doped ZnO ceramic target sintered at 1500°C for 6 h has a relative density of 99·8% with a resistivity of 1·8 × 10 − 3 Ω-cm. The AZO film exhibits optical transparency of 90·3% in the visible region and shows an electrical resistivity of 2·5 × 10 − 3 Ω-cm.

The formation of nanoparticles, ceramics, and thin films of ZnO in the environment of zinc vapor

The investigations of formation mechanisms of ZnO nanoparticles, ZnO ceramic materials sintering and synthesis of ZnO thin films in zinc vapor-containing atmosphere shown that increase in "zinc/oxygen" relation (PZn/PO2 ratio) leads to a significant change in the structure and formation mechanisms of ZnO ultrafine particles, thin films and bulk materials. We observed that ZnO whiskers growth occurs in the direction of the optimal ratio of partial pressures of Zn and O2. Growth of ZnO tetrapods during the ejection of Zn vapor in an oxygen atmosphere occurs in two stages: the formation of the ZnO1−x seed and subsequent growth of ZnO whiskers from it. It was also shown that the synthesis of ZnO films by magnetron sputtering in the Zn vapor excess environment can occur by the "vapor-liquid-solid" (VLS) mechanism. Also sintering of Ga-doped ZnO ceramic targets in the atmosphere containing desired pressure of Zn vapor leads to increase in target density and oxygen deficiency. These targets were used for deposit transparent conductive oxide (TCO) thin films onto glass substrate by direct current (dc) magnetron sputtering. The relationship between the structural perfection and electrical characteristics of Ga doped ZnO (GZO) films as a function of synthesis temperature and Ga content (3–6 at.%) were investigated.

Photoluminescence properties of thin nitrogen- and phosphorus-doped ZnO films fabricated using pulsed laser deposition

The production of n- and p-type high-quality film structures is a foreground task in tackling the problem of growing the light-emitting p-n junctions based on zinc oxide. The ZnO:N and ZnO:P thin-film samples are produced from ceramic targets using the pulsed laser deposition. Zn3N2, MgO, and Zn3P2 are introduced in the ZnO ceramic targets for the fabrication of the p-type ZnO films. Gases O2 and N2O are used as buffer gases. The thermal annealing of the ZnO films is employed. The resistance and photoluminescence (PL) spectra of the ZnO films are measured prior to and after annealing. The dependence of the ZnO PL peak amplitude and position prior to and after annealing on the level of doping with nitrogen and phosphorus is established. The PL characteristics of the films are studied at cw optical excitation using a He-Cd laser with a radiation wavelength of 325 nm. The PL spectra in the interval 300–700 nm are recorded by an HR4000 Ocean Optics spectrometer in the temperature range 10–400 K. The effect of the conditions for the film deposition on the PL spectra is analyzed. The effect of the N- and P-doping level of the ZnO films on the PL intensity of the films and the position of the PL bands in the UV region is investigated. The short-wavelength (250–400 nm) transmission spectra of the ZnO:P films are measured. The effect of the P-doping level on the band gap of the ZnO films is studied.

Structures and Properties of ZnO-Based Ceramic Films for Low-Voltage Varistors by the R.F. Magnetron Sputtering

ZnO-based ceramic targets with 50mm in diameter and 3mm in depth were prepared by the traditional solid-state sintering process. ZnO-based ceramic films were deposited on Au/Si substrates by R.F. magnetron sputtering using ZnO-based ceramic target. The films have been characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and scanning electron microscopy. The ZnO-based ceramic films, with thickness close to 1 μm, show a good c-axis orientation, corresponding to vertical growth with respect to the substrate. The surface of the films looks very smooth and dense, and the films are the same composition as the ZnO ceramic target composed of Zn, Bi, Sb, Co, Cr and Mn. The ZnO-based ceramic films with nonlinear coefficient of 6.4, nonlinear voltage of 1.6V and the leakage current density 0.3μA/mm2 could be achieved.

X-Ray diffraction and Raman spectroscopy for a better understanding of ZnO:Al growth process

ZnO:Al thin films were prepared on glass substrates by radio frequency RF magnetron sputtering from a ceramic ZnO target mixed with Al2O3 (1 wt%) in pure argon atmosphere with a power of 250 W. Two series of samples were deposited, the first one as a function of the substrate temperature (between 20 and 325 °C) at 0.12 Pa, the second one as a function of the working pressure (between 0.01 and 2.2 Pa) at room temperature. The influence of these deposition parameters was studied by a detailed microstructural analysis using X-Ray diffraction and Raman spectroscopy. Their electrical properties were characterized by Hall effect measurements. As the substrate temperature is increased, crystallite size increases while the strain and the electrical resistivity decrease. An improvement of the crystallinity is deduced from Raman spectra and X-Ray diffraction patterns. From the pressure series, an electrical optimum is observed at 0.12 Pa. Above 0.12 Pa, there is a degradation of the crystallinity, attributed to the low mobility of the adatoms and below 0.12 Pa, high-energy sputtered particles damage the growing films. The trends given by Thornton structure zone model are also consistent with X-Ray diffraction results.

Dynamics of ZnO laser produced plasma in high pressure argon

Pulsed laser deposition of ZnO in high pressure gas offers a route for the catalyst-free preparation of ZnO nanorods less than 10 nm in diameter. This paper describes the results of some experiments to investigate the laser plume dynamics in the high gas pressure (5 × 10 3–10 4 Pa) regime used for PLD of ZnO nanorods. In this regime the ablation plume is strongly coupled to the gas and the plume expansion is brought to a halt within about 1 cm from the target. A 248 nm excimer laser was used to ablate a ceramic ZnO target in various pressures of argon. Time- and space-resolved UV/vis emission spectroscopy and Langmuir probe measurements were used to diagnose the plasma and follow the plume dynamics. By measuring the spatial profiles of Zn I and Zn II spectral lines it was possible to follow the propagation of the external and internal shock waves associated with the interaction of the ablation plume with the gas. The Langmuir probe measurements showed that the electron density was 10 9–10 10 cm −3 and the electron temperature was several eV. At these conditions the ionization equilibrium is described by the collisional-radiative model. The plume dynamics was also studied for ZnO targets doped with elements which are lighter (Mg), comparable to (Ga), and heavier (Er) than Zn, to see if there is any elemental segregation in the plume.

Highly conductive alumina-added ZnO ceramic target prepared by reduction sintering and its effects on the properties of deposited thin films by direct current magnetron sputtering

To obtain a suitable sputtering target for depositing transparent conducting Al-doped ZnO (AZO) films by using direct current (DC) magnetron sputtering, this study investigates the possibility of using atmosphere controlled sintering of Al 2O 3 mixed ZnO powders to prepare highly conductive ceramic AZO targets. Experimental results show that a gas mixture of Ar and CO could produce a sintered target with resistivity in the range of 2.23 × 10 − 4 Ω cm. The fairly low resistivity was mainly achieved by the formation of both aluminum substitution (Al Zn) and oxygen vacancy (V O), thus greatly increasing the carrier concentration. Compared to usual air sintered target, the thin film deposited by the Ar + CO sintered target exhibited lower film resistivity and more uniform spatial distribution of resistivity. A film resistivity as low as 6.8 × 10 − 4 Ω cm was obtained under the sputtering conditions of this study.

Aluminum-Doped Zinc Oxide Thin Films for Opto-Electronic Applications

Transparent conducting aluminum-doped Zinc oxide (AZO) thin films were prepared on glass substrates by rf magnetron sputtering technique using ZnO ceramic target in pure argon gas with different aluminum concentrations. The bandgap of the ZnO films slightly widens with increase in Al content and the lowest sheet resistance of AZO films with Al concentration of 4.25 atomic % was obtained. The effects of post-annealing treatment on structural, electrical and optical properties of the AZO thin films were investigated. Using AZO film with 4.2 at. % Al as the transparent electrode, a titanium dioxide based dye-sensitized solar cell was constructed and a solar to electrical energy conversion efficiency of 2.9 % was achieved under AM 1.5 solar simulated sunlight.

High-Performance Transparent Conducting Ga-Doped ZnO Films Deposited by RF Magnetron Sputter Deposition

Ga-doped zinc oxide (GZO) films were deposited using rf magnetron sputter deposition and a Ga2O3(5 wt %)-doped ZnO ceramic target under various deposition conditions. The effects of each deposition condition on the electrical, structural, and optical properties of the GZO films were investigated to obtain a transparent conducting oxide (TCO) with a high transmittance and a low resistivity for a-Si:H thin-film solar cells. Resistivity showed a strong dependence on working pressure and rf power. The lowest resistivity of 1.9×10-4 Ω·cm was obtained at an rf power density of 2.47 W/cm2. The highest figure of merit for the use of TCO was achieved in the 800-nm-thick GZO film [ρ=2.1×10-4 Ω·cm, average transmittance (400–800 nm) = 92.1%] deposited at 10 mTorr and an rf power density of 1.85 W/cm2. These results indicate that the high-performance TCO fabricated in this work is suitable for use as a transparent electrode layer for thin-film solar cells.

Investigation of thin ZnO layers in view of laser desorption-ionization

Thin zinc oxide films (ZnO) were developed as a matrix-free platform for surface assisted laser desorption-ionization (SALDI) time-of-flight mass spectrometry. The ZnO films were deposited by RF magnetron sputtering of ZnO ceramic targets in Ar atmospheres on monocrystalline silicon. The generation under UV (355 nm) laser irradiation of positive ions of atenolol, reserpine and gramicidin S from the ZnO layers deposited was studied. All analytes tested were detected as protonated molecules with no or very structure-specific fragmentation. The mass spectra obtained showed low levels of chemical background noise. All ZnO films studied exhibited high stability and good reproducibility. The detection limits for test analytes are in the 10 femtomol range.

Effects of Al content on the properties of ZnO:Al films prepared by Al2O3 and ZnO co-sputtering

Aluminum doped zinc oxide (AZO) films were deposited on quartz substrates by radio-frequency magnetron co-sputtering method with ZnO and Al2O3 ceramic targets. The structural, optical and electrical properties of these films as a function of the Al content were investigated. XRD results reveal that the AZO films are wurtzite structure with (002) preferred orientation. The average transmittance of all the films is higher than 80% in a wide wavelength range from 400 to 1,500 nm. The band gap energy, calculated from their optical absorption spectra, is in the range of 3.50–3.66 eV depending on the Al content. Doping of Al3+ in the ZnO makes the film surface roughness decrease. The dopant Al3+ acts as electron donor by which the electrical conductivity and carrier concentration of the films are obviously increased until the Al3+ reaches its saturation content of about 4.50 at.%.

Development of textured back reflector for n–i–p flexible silicon thin film solar cells

For silicon thin film solar cells, light trapping strategies, to increase the path length of incoming light, play a decisive role for device performance. In this work, a new way to develop textured back reflectors for n–i–p flexible solar cells is studied. ZnO:Ga films are deposited by DC magnetron sputtering system using two facing Ga-doped ZnO ceramic targets at room temperature. The influence of distance between substrate and plasma on the structure and etching characteristic of ZnO:Ga is investigated. Polyimide/textured ZnO:Ga/Al structure is used as the back reflector, and the morphological and optical analyses indicate that it is suitable to be used in the silicon thin film solar cells.

ZnO 분말 타겟을 스퍼터링하여 Glass 기판위에 증착한 ZnO 박막의 구조적, 광학적 특성

본 논문은 ZnO 분말 타겟을 스퍼터링하여 glass 기판 위에 증착한 ZnO 박막의 구조적, 광학적 특성을 보고한다. 소결된 ZnO ceramic target을 사용하는 보통의 radio-frequency magnetron sputtering과 달리 본 연구에서는 전처리과정이 필요하지 않은 ZnO 분말 target을 사용하였다. ZnO 박막은 wurtzite (0002) 우선배향면으로 성장하였다. 초기의 ZnO 박막은 매우 평평한 층구조로 증착되었고, 두께가 증가함에 따라 섬구조로 전이하였다. 400-1000 nm 광원에 대하여 평균 88% 이상의 광투과도를 나타내었으며, 220 nm 시편의 경우, 3.23 eV의 near bandedge emission 흡수단을 측정하였다. This paper reports the structural and optical properties of ZnO/glass thin films grown by radio-frequency magnetron sputtering with a powder target. In contrast to ZnO ceramic target typically used, a ZnO raw powder target was sputtered in this study. ZnO grew with the (0002) preferred orientation along the surface normal direction. Initially, the surface of ZnO thin films was flat considerably and then it became rougher as the thickness increased. The optical transmittance was as high as 88% in the range of 400-1000 nm. The bandgap energy of 3.23 eV at the 220 nm thick sample was estimated.

Effects of substrate temperature on the properties of heavy Ga-doped ZnO transparent conductive film by RF magnetron sputtering

Gallium-doped zinc oxide (GZO) transparent conductive thin films were deposited on glass substrate by RF magnetron sputtering using a ceramic ZnO target with 10 wt. % Ga2O3 doped. The effects of substrate temperature on structural, electrical and optical properties of the films were investigated. X-ray diffraction (XRD) measurements indicated that GZO films were polycrystalline and strongly c-axis oriented. The surface roughness evaluated in terms of RRMS measured by atomic force microscope (AFM) was 1.8 nm for the smoothest surface obtained at 250 °C. The electrical resistivity decreases with increasing substrate temperature and the lowest resistivity obtained was 5.8×10-4 Ω·cm at 350 °C. The average transmittance in the visible region was over 90%. The carrier concentration increased with substrate temperature increasing, and the highest mobility value was 22.1 cm2v-1·s-1.

Sputter deposition of ZnO thin films at high substrate temperatures

ZnO thin films have been deposited on GaN and ZnO substrates at substrate temperatures up to 750 °C by radio-frequency sputtering using ZnO ceramic targets in pure argon or in a mixture of argon and oxygen. By optimizing the sputter parameters, such as sputtering power, Ar/O 2 sputtering gas ratio and temperature of the substrates high quality films were obtained as judged from the X-ray rocking curve half width and luminescence line width. The crystallinity of the ZnO films increases with increasing substrate temperature. Yet there are distinct differences between films grown on GaN templates and on O- and Zn-polar ZnO substrates .

Comparative study on structural and optical properties of ZnO thin films prepared by PLD using ZnO powder target and ceramic target

Zinc oxide thin films have been obtained in O 2 ambient at a pressure of 1.3 Pa by pulsed laser deposition (PLD) using ZnO powder target and ceramic target. The effect of temperature on structural and optical properties of ZnO thin films was investigated systematically by XRD, SEM, FTIR and PL spectra. The results show that the best structural and optical properties can be achieved for ZnO thin film fabricated at 700 °C using powder target and at 400 °C using ceramic target, respectively. The PL spectrum reveals that the efficiency of UV emission of ZnO thin film fabricated by using powder target is low, and the defect emission of ZnO thin film derived from Zn i and O i is high.