Metallic Zinc Target Research Articles

Structural and optical properties of ZnO films obtained on mesoporous Si substrates by the method of HF magnetron sputtering

In the present work, ZnO films were obtained on mesoporous silicon substrates by the method of HF magnetron sputtering of a metallic zinc target in reaction oxygen and argon gas medium. The properties of the ZnO films obtained on mesoporous substrates were studied depending on the ratio of the partial pressures of the working gases (argon/oxygen). X-ray analysis showed that in the process of deposition, the ZnO films of a hexagonal structure were formed. The effect of the porous layer on the structural and luminescent properties of the thin ZnO films was studied. The results showed that the porous silicon substrate reduces residual stresses and can be used for obtaining high-quality ZnO films.

High performance piezoresistive response of nanostructured ZnO/Ag thin films for pressure sensing applications

This work reports on the preparation and characterization of zigzag nanostructured silver (Ag) doped zinc oxide (ZnO) films in order to improve piezoresistive response for pressure sensor applications. ZnO/Ag thin films were prepared by Glancing Angle Deposition (GLAD) from a metallic zinc (Zn) target DC sputtered in Ar + O2 atmosphere. The target was customized with different amounts of Ag pellets, symmetrically distributed along the preferential erosion area.It is shown that increasing the Ag content from 0 to 36 at.% in the ZnO/Ag system leads to a decrease of the electrical resistivity from 2.95 Ω cm to 1.52 × 10−5 Ω cm. The structural characterization of the thin films shows an evolution of the preferential growth, changing from a polycrystalline ZnO hexagonal-like structure, confirmed by the presence of dominant ZnO (002) and ZnO (101) diffraction peaks, to a Ag cubic (fcc)-like structure, as evidenced by the Ag (111), (200) and (220) diffraction peaks. The values of the gauge factor show a strong contribution both from Ag as well as from the zigzag nanostructure to the piezoresistive sensitivity of the films, in particular for Ag concentrations lower than 30 at.%. The tunneling distance between pairs of Ag conductive nanoregions was calculated for the different samples and in three different deformation regions, in order to evaluate its influence on the piezoresistive sensitivity. The results show that a longer distance between Ag particles, which varies from 0.1 to 10 nm, enhances the gauge factor, which ranges from 8 ± 1 to 120 ± 3, respectively.

Synthesis and Characterization of Self-Assembled ZnO Nanoparticles Embedded Within a SiO2 Matrix Deposited on (111) p-Type Silicon By Reactive RF Sputtering Using Metallic Zinc Target As Precursor

The results of the synthesis and characterization of self-assembled ZnO nanoparticles (NP) embedded within a SiO2 matrix deposited on (111) p-type silicon by reactive radio frequency sputtering are reported. Synthesis consists in a sequential deposit of SiO2/metallic-Zn/SiO2/SiO2 layers, using argon and oxygen as the working atmosphere at a substrate temperature of 400°C. ZnO NP were nucleated at valleys of the first rough SiO2 layer by the action of the reactive atmosphere and Zn atoms coming from the sputtered target. Three different deposition times for the zinc interlayer were studied. Scanning electron microscopy shows that films have uniform topography and transmission electron microscopy indicates the presence of NP with sizes around 10 nm. The successful production of ZnO is corroborated by x-ray photoemission spectroscopy studies. Secondary ion mass spectroscopy shows a spatial distribution of zinc depending on the thickness of the zinc interlayer, ZnO NP follow a similar distribution. Electrical transport studies have shown the formation of a rectifying structure between the layer and silicon substrate. Spectral response is observed with a wavelength distribution depending on the zinc interlayer thickness and probably due to the formation of ZnO NP of different sizes.

Optical properties of the plasma hydrogenated ZnO thin films

Abstract We have optimized the deposition of the highly electrically resistive undoped (intrinsic) polycrystalline ZnO thin layers on fused silica substrates by the DC reactive magnetron sputtering of metallic zinc target in argonne/oxide atmosphere and we introduced the post-deposition hydrogen plasma doping. The thickness of thin film was evaluated by reflectance interferometry using the metallographic optical microscope fiber coupled to the CCD spectrometer operating in 400-1000 nm spectral range. The optical absorption was measured by photothermal deflection spectroscopy operating in 300-1600 nm spectral range. The change of the optical absorption edge and the increase of the infrared optical absorption was detected in hydrogenated ZnO. The increase of the infrared optical absorption goes with the increase of the electrical conductivity. We conclude that the plasma hydrogenation of the intrinsic ZnO thin films is related to increase of the free carrier concentration.

Characterization of zinc oxide films deposited in helium–oxygen and argon–helium–oxygen atmospheres by sputtering

Zinc oxide (ZnO) thin films were deposited onto glass substrates by radio frequency (RF) magnetron sputtering using a metallic zinc target. Zinc oxide films were prepared in two different gas atmospheres; in the first set, helium and oxygen gas flow ratio (He:O2) was varied from 87.5% to 37.5%. In the second set of experiment, oxygen flow rate was kept constant at 2.5 sccm while argon and helium gas flow ratio (Ar:He) was varied from 9.0% to 87.5%. The structural, wettability, and optical properties of ZnO films were investigated by X-ray diffractometry (XRD), contact angle measuring system, and UV–vis–NIR spectrophotometer. The XRD results show increased preferred orientation along (002) plane for deposited ZnO films in both cases. The average crystallite size of ZnO films increases with increase in gas ratio for both set of experiments. The deposited films are hydrophobic by nature for water and ethylene glycol. Optical transmittances greater than 60% were observed in the wavelength interval from 450nm to 650nm for both cases.

Vertically aligned ZnO nanorods of high crystalline and optical quality grown by dc reactive sputtering

ZnO nanorods were grown on Si and quartz substrates by direct current reactive magnetron sputtering of metallic zinc target in argon–oxygen ambient, without the use of any seed layer or catalyst. A combination of top-down and cross-sectional scanning electron microscopy studies have shown that the substrate temperature critically controls the growth behavior and morphology of ZnO films, eventually resulting in the growth of well aligned and separated ZnO nanorods at substrate temperature of ∼750 °C. High resolution x-ray diffraction studies of ZnO nanorods grown at 750 °C have shown that the nanorods are highly c-axis oriented and vertically aligned perpendicular to both Si and quartz substrates, and display small values of tilt and micro-strain, particularly in the case of Si substrate (1.26° and 4 × 10−4, respectively). Cross-sectional transmission electron microscopy of ZnO nanorods demonstrates their single-crystalline nature and growth along [0002] direction. Room temperature photoluminescence spectra of ZnO nanorods display extremely high near-band-edge emission and weak defect emission due to point defects, compared to that of the ZnO films grown at lower substrate temperatures. The drastic enhancement of near-band-edge emission of ZnO nanorods (over two orders of magnitude) and strong suppression of defect emission are attributed to their high crystalline quality and absence of interface defects due to lateral coalescence.

Electron transport mechanism in rf‐sputtered amorphous zinc oxynitride thin films

AbstractAbstractauthoren We discuss the carrier transport mechanism in amorphous zinc oxynitride (ZnON) thin films fabricated by means of long‐throw magnetron sputtering. ZnON films were radio‐frequency sputtered from a metallic zinc target in a reactive atmosphere consisting of , , and Ar. The electrical conductivity of the films was controlled via variation of the deposition pressure and substrate temperature. Room temperature deposition yields amorphous, n‐type semiconducting ZnON thin films with a maximum Hall mobility of and carrier concentrations of . The mobility can be further increased up to the range by moderate substrate heating or annealing up to while maintaining the amorphous phase. From temperature‐dependent Hall effect measurements, we deduced that a percolation conduction model is most likely for the electron transport in the as‐grown ZnON thin films. For annealed samples, a quasi‐metallic behavior is observed.

P‐15: Self‐Aligned Top‐Gate Zinc Oxide Thin Film Transistors Fabricated by Reactive Sputtering of Metallic Zinc Target

Self‐aligned top‐gate zinc oxide (ZnO) thin film transistors (TFTs) was fabricated by reactive sputtering of metallic zinc target. By optimizing deposition conditions, high‐performance TFTs with a field effect mobility of 37.5 cm2/Vs and an on/off ratio of 3.8×108 was obtained.

English

We have grown ZnO thin films on glass substrate by R.F magnetron sputtering using metallic zinc target. The influences of some parameters on thin film optical properties were assessed. They exhibited extremely high resistivity of 1012 Ω.cm, an energy gap of 3.3 eV at room temperature. It was found that a R.F power of 50 W, a target to substrate distance of 70 mm, very low gas pressures of 3.35 x 10-3 Torr of argon and oxygen mixed gas atmosphere gave ZnO thin films with a good homogeneity and a high crystallinity. All the films are transparent in the visible region (400 to 800 nm) with average transmittance above 80 %. The optical transmittance and refractive index, calculated from the spectra of optical absorbance, show a significant dependence on the growth parameters. As for the sample grown at 100°C, the average transmittance is about 80% in the visible wavelength range and the refractive index is estimated to be 1.97.      key words: ZnO; R.F sputtering magnetron; X-ray diffraction; transmittance; refractive index.

Morphological and Photoluminescence analysis of Zinc Oxide thin films deposited by RF sputtering at different substrate temperatures

Zinc oxide (ZnO) thin films were prepared using reactive RF magnetron sputtering of a pure metallic zinc target onto n-type (100) silicon substrates. The evolution of the surface morphology and the optical properties of the films were studied as a function of the substrate temperature, which was varied from ambient to 300°C. X-ray diffraction pattern of ZnO thin film shows the appearance of c-axis oriented (002) peak for all samples shows varying degrees of crystallinity of films. Photoluminescence studies were also carried out (350-700 nm) to study the crystallinity and optically active defects in the films. PL spectra of the film shows UV emission peak depicts good crystallinity of ZnO film where as the intensity of deep level emission band decreases with increase in substrate temperature due to the formation of stoichiometric ZnO film which causes decrease in defect.

Structural transition of ZnO thin films produced by RF magnetron sputtering at low temperatures

Zinc oxide (ZnO) thin films were prepared using reactive radio-frequency magnetron sputtering of a pure metallic zinc target onto glass substrates. The evolution of the surface morphology and the optical properties of the films were studied as a function of the substrate temperature, which was varied from 50 to 250 °C. The surface topography of the samples was examined using atomic force microscopy (AFM), and their optical properties were studied via transmittance measurements in the UV–Vis–NIR region. DRX and AFM analyses showed that the surface morphology undergoes a structural transition at substrate temperatures of around 150 °C. Actually, at 50 °C the formation of small grains was observed while at 250 °C the grains observed were larger and had more irregular shapes. The optical gap remained constant at ~3.3 eV for all films. In the visible region, the average optical transmittance was 80 %. From these results, one can conclude that the morphological properties of the ZnO thin films were more greatly affected by the substrate temperature, due to mis-orientation of polycrystalline grains, than were the optical properties.

Effect of Zn Sputtering Rate on the Morphological and Optical Properties of ZnO Films

Zinc oxide (ZnO) thin films were deposited onto glass substrates by reactive radiofrequency (RF) magnetron sputtering using a metallic zinc target. Optical emission spectroscopy (OES) was used to monitor and control the Zn sputtering rate for the deposition of the ZnO films. Film thicknesses ranged from 350 to 750 nm. Optical transmittances greater than 80% were observed in the wavelength interval from 450 nm to 650 nm. The energy gap of the films remained constant at (3.28 ± 0.01) eV. The surface morphology was found to be homogeneous with well-distributed structures. Surface roughness was dependent on the Zn sputtering rate, indicating that greater densities of Zn atoms increase the surface diffusion. X-ray diffraction (XRD) analysis showed that the ZnO films were polycrystalline with a hexagonal wurtzite structure and preferential growth along the (002) plane.

Low-Temperature ZnO TFTs Fabricated by Reactive Sputtering of Metallic Zinc Target

A low-temperature metallic-zinc-target reactive sputtering technology is used to fabricate a ZnO thin-film transistor (TFT). The effect of the $\hbox{O}_{2}/\hbox{Ar}$ flow rate ratio on the performance of the resulting TFTs is investigated in detail. It is found that an $\hbox{O}_{2}/\hbox{Ar}$ ratio of 0.75–0.8 produces devices with the best performance. The maximum processing temperature used in this brief is 150 $^{\circ}\hbox{C}$ , and the fabricated TFTs have a saturation mobility of 7.4 $\hbox{cm}^{2}/(\hbox{V}\cdot \hbox{s})$ , an on–off current ratio of more than $\hbox{1} \times \hbox{10}^{7}$ , and a subthreshold swing of 0.58 V/dec. Experimental results also show that using $\hbox{SiO}_{x}$ as gate dielectric instead of $\hbox{SiN}_{x}$ can improve both carrier mobility and subthreshold.

Structural and optical properties of Zn3N2 films prepared by magnetron sputtering in NH3—Ar mixture gases

Zinc nitride films were prepared by RF magnetron sputtering a metallic zinc target in NH3—Ar mixture gases on glass substrate at room temperature. The effects of NH3 ratio on the structural and optical properties of the films were examined. X-ray diffraction (XRD) analysis indicates that the films are polycrystalline and have a preferred orientation of (321). An indirect optical band gap increased from 2.33 to 2.70 eV when the NH3 ratio varied from 5% to 25%. The photoluminescence (PL) spectrum shows two emission peaks; the peak located at 437 nm is attributed to the incorporation of oxygen, and the other at 459 nm corresponds to the intrinsic emission.

Transfer characteristic of zinc nitride based thin film transistors

AbstractPolycrystalline zinc nitride (Zn3N2) thin films were prepared on quartz and aluminum tin oxide/indium tin oxide (ATO/ITO) and SiO2‐covered crystalline silicon by reactive pulsed laser ablation (PLD) of a metallic zinc target using a pulsed Nd:YAG laser, assisted by a 13.56 MHz radio‐frequency (RF) nitrogen plasma. The microstructural, optical and electrical properties of the as‐deposited films were studied by Scanning Electron Microscopy (SEM), X‐ray diffraction (XRD), low‐temperature photoluminescence (PL), optical transmittance, and field effect transistor I‐V measurements. SEM revealed a compact and crack‐free film surface. XRD study indicated that the Zn3N2 films deposited at 673 K substrate temperature were cubic, with lattice constant a = 0.97 nm and having no preferred orientation. PL spectra taken at 4.2 K show a 7‐9 meV wide exciton‐related peak at 3.59 eV. The optical absorption coefficient, estimated from the transmission spectra using Beer's law, was utilized to determine the optical band gap of the films. The Zn3N2 showed a direct band gap of ∼3.2 eV at room temperature. Transparent field effect transistor structures with a 200 nm thick Zn3N2 film as active channel layer exhibited non‐linear I–V transfer characteristics, which is typical of devices having a large density of interface trap states (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Reactive Radiofrequency Sputtering-Deposited Nanocrystalline ZnO Thin-Film Transistors

The structural and electrical properties of ZnO films deposited by reactive radiofrequency sputtering with a metallic zinc target are systematically investigated. While the as-deposited ZnO film is in a poly-crystalline structure when the partial pressure of oxygen (pO2) is low, the grain size abruptly decreases to a few nanometers as pO2 increases to a critical value, and then becomes almost unchanged with a further increase in pO2. In addition, the resistivity of the ZnO films shows a non-monotonic dependence on pO2, including an abrupt transition of about seven orders of magnitude at the critical pO2. Thin-film transistors (TFTs) with the nanocrystalline ZnO films as channel layers have an on/off current ratio of more than 107, an off-current in the order of pA, a threshold voltage of about 4.5 V, and a carrier mobility of about 2cm2/(V·s). The results show that radiofrequency sputtered ZnO with a zinc target is a promising candidate for high-performance ZnO TFTs.

RF‐plasma assisted PLD growth of Zn3N2 thin films

AbstractPolycrystalline Zn3N2 films were prepared on sapphire and quartz substrates by reactive pulsed laser ablation of a metallic zinc target in a nitrogen plasma atmosphere using a frequency‐doubled Nd:YAG laser, assisted by a 13.56 MHz radio‐frequency (RF) plasma. The morphological, structural and optical properties are studied by Scanning Electron Microscopy, X‐ray diffraction, transmittance and ellipsometric spectroscopy. SEM revealed a very smooth and crack‐free film surface. X‐ray diffraction indicates that the Zn3N2 films deposited at 400 °C substrate temperature are cubic in structure with no preferred orientation. The lattice constant has been estimated to be a = 0.97 nm. The absorption coefficient is deduced from the transmission spectra, and its dependence on photon energy is examined to determine the optical band gap. Refractive index and film thickness are deduced from spectroscopic ellipsometry measurements. Zn3N2 is determined to be a n‐type semiconductor with a direct band gap of 3.2 eV. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The microstructures and the electrical and optical properties of ZnO:N films prepared by thermal oxidation of [formula omitted] precursor

Samples of p-type ZnO:N films were prepared on glass substrates by thermal oxidation of Zn 3N 2 precursor, which was produced by reactive magnetron sputtering with a metallic zinc target in Ar/N 2 working gas. The microstructures and the electrical and optical properties of the samples were systematically investigated as a function of the annealing temperature. The results indicate that the annealing temperature has strong effects on the conductivity and photoluminescence (PL) properties of the obtained ZnO:N films. With an annealing temperature of 500 ∘C in oxygen flux, ZnO:N samples show the best p-type characteristics. The doping mechanism and the doping efficiency are briefly discussed based on the experimental results.

Synthesis of nanostructured ZnO and ZnO<SUB align=right>2 by laser ablation process using third harmonic of Nd:YAG laser

A laser-based method was developed for synthesis of nanostructured ZnO/ZnO2 using nanosecond pulsed laser ablation (PLA) on a metallic zinc target in water. Typical laser pulse energy for PLA process was between 40-130 milli-joules per pulse. The addition of an oxidising agent enhanced the nanoparticle yield by 100% and reduced the grain size drastically. A variety of analysis techniques were applied for the characterisation of products. To the best of our knowledge, this is the first time ZnO2 (zinc peroxide) having grain size of 5 nm are produced using laser ablation.

Transparent thin-film transistors with zinc oxide semiconductor fabricated by reactive sputtering using metallic zinc target

We have investigated transparent thin-film transistors (TTFTs) with active channel of zinc oxide (ZnO) films, reactively grown by RF magnetron sputtering using metallic zinc target. According to the ratio of oxygen to the total gas (O 2/(O 2 + Ar)), microstructures of the films changed drastically, and especially, ZnO films formed at 20% of O 2 had good crystallinity with larger grains. ZnO films showed above 84% transparency in the wavelength range from 400 nm to 750 nm. Our bottom-gate ZnO-TTFTs showed n-type character with field-effect mobility of about 1.5 cm 2/Vs, an on/off ratio> 10 6, subthreshold swing of 1.1 V/decade, and threshold voltage of 15.9 V, after annealing at 250 °C for 30 min in O 2 ambient.