Kasimayan Uma

Structural properties of pulsed laser deposited zinc oxide thin films annealed at various temperatures

Abstract Zinc oxide (ZnO) thin films were prepared by pulsed laser deposition (PLD) technique using XeCl excimer laser with a wavelength of 308 nm at room temperature on quartz and single crystal silicon (100) substrates. The oxygen gas pressure was set at 6 torr during the deposition. The deposited films were post-heat treated (HT) in air at different annealing temperatures (ATs) for 30 min. The X-ray diffraction (XRD), optical and electrical properties were measured to study the properties of the films as a function of AT. XRD analysis showed that the strength of (002) peak increases and full width at the half maximum (FWHM) value decreases as the AT increases from 200 to 600°C. The films HT at higher AT of ∼600°C showed dominant c axis oriented hexagonal wurtize crystal structure. The films HT at 600°C exhibit high average transmittance of ∼85% in the visible region and very sharp absorption edge at 376 nm with energy band gap of ∼3·46 eV. Electrical measurement indicates that the resistivity of films decreases with the AT up to 600°C, after which there is an increase at higher AT. The complex of hydrogen defect and oxygen vacancy in the ZnO films may be the reason for low conductivity in undoped ZnO films.

Effects of Al content on Zn0.95Mg0.05O Thin Films Deposited by Sol?Gel Spin Coating

Al-doped Zn0.95Mg0.05O films were deposited on glass and silicon substrates by a sol–gel spin coating and the coated samples were dried at 350 to 450 °C and annealed at 550, 650, and 750 °C. The effects of Al content and annealing temperature on the structural and optical properties of Al-doped Zn0.95Mg0.05O thin films were studied. Al-doped Zn0.95Mg0.05O alloy films have a preferred orientation in the (002) direction. By increasing Al content, crystallinity as well as transmittance was decreased. An X-ray photoelectron spectroscopy (XPS) analysis of Al-doped Zn0.95Mg0.05O thin films was performed to determine the chemical state on the surface of the thin films. The resistivities of the thin films were found to increase with increasing Al content and decrease with increasing annealing temperature. For an Al (0.5 wt %)-doped Zn0.95Mg0.05O thin film with a low resistivity of 3.15×10-2 Ω cm dried at 450 °C and annealed at 750 °C, optical band gap increased from 3.08 to 3.32 eV.

Properties of zinc oxide thin films prepared on silicon (100) and glass substrates by pulsed laser deposition technique with different oxygen gas pressures

Abstract Nanostructured zinc oxide (ZnO) thin films were prepared on silicon (100) and Corning glass substrates by pulsed laser deposition (PLD) technique with different oxygen gas pressures. The microstructure, crystallinity and resistivity of the ZnO films are found to be dependant on the oxygen gas pressure. The X-ray diffraction (XRD) analysis showed that the growth of grains occurred along the c-axis of ZnO films obtained under high oxygen gas pressures. The ZnO films were oriented preferentially along the (002) direction, which is responsible for good electrical and optical properties. Pulsed laser deposited ZnO films, with the c-axis orientation (except for the ZnO films grown at room temperatures), show low structural defects. By applying higher oxygen gas pressures, the grain size of the films is found to increase, the electrical resistivity tends to decrease and the optical transmittance in the visible region becomes higher. The surface morphology of the films measured by scanning electron microscopy (SEM) showed nanostructures with surface which is smooth and without any cracks.

SCANNING ELECTRON MICROSCOPE AND X-RAY DIFFRACTION STUDIES ON THE LATTICE CONSTANT OF SPIN-COATED Zn1-xMgxO THIN FILMS OF SOL-GEL METHOD

ZnO and Zn1-xMgxO thin films were prepared on glass and silicon substrates by spin coating method using 2-methoxyethanol solution of zinc acetate dihydrate and magnesium acetate dihydrate stabilized by monoethanolamine. The effects of drying and annealing condition of structural and optical properties of the films were studied. It was found that the samples annealed at 650°C improves the crystallographic orientation of the ZnO films grown by the sol-gel process significantly. Two types of substrates were used to examine the substrate effects of the growth of Zn1-xMgxO thin films. In corning glass substrates, the lattice constant decreased by a little with increasing concentration of Mg, whereas in the case of silicon substrates, the lattice constant decreased rapidly with x when compared to the glass substrates. The optical band energy gaps of Zn1-xMgxO thin films were slightly increased with increasing concentration of Mg.

OPTICAL AND ELECTRICAL PROPERTIES OF ZINC OXIDE THIN FILMS DIP-COATED OF SOL–GEL METHOD

The transparent c-axis oriented ZnO thin films have been prepared by sol–gel method using zinc acetate as cations source, 2-mrthoxiethanol as solvent and monoethanolamine as sol stabilizer. Film deposition was performed by dip coating technique at a withdrawal rate of 10 mm/min on quartz and silicon substrates. The effect of annealing temperature in air ambient from 100 to 800°C on the structural, optical and electrical properties of the films is discussed. ZnO films annealed with higher temperature showed an extremely sharp (002) peak in the XRD patterns, indicates increased crystallization. The optical transmittance spectra of the films is found to change with annealing temperature and showed a very good transmittance (between 80 to 90%) with the films prepared at 600°C showed highest optical transparency within the visible wavelength region. The absorption edge analysis revealed that the optical band gap is found to increase with annealing temperature up to 3.5 eV at 600°C and decreased with higher temperature. Electronic transition was found to be direct transition type. The minimum electrical resistivity of 55 Ω-cm was obtained for the films annealed at 600°C.

Bulk ZnO nanorod assemblies fabricated by spin coating of organo-precursor gels on CuO nanowires

Bulk ZnO nanorod assemblies have been successfully fabricated on CuO nanowires through spin coating of organoprecursor gels. A thin film of CuO nanowires was first generated by direct heating of a metallic Cu-foil at 500 °C in an air atmosphere. A stable colloidal organo-precursor sol synthesized by dissolving equimolar zinc acetate dihydrate and monoethanolamine in 2-methoxyethanol was subsequently repeatedly deposited onto the CuO nanowires by spin coating. The formation of ZnO nanorod assemblies was controlled by varying the number of coatings. The average diameter of the ZnO rods was determined to be ∼600 nm.

TRANSPARENT ZINC OXIDE THIN FILMS PREPARED BY PLD WITH DIFFERENT OXYGEN PRESSURES

ZnO thin films were prepared on silicon (001) and corning glass substrates using Pulsed laser deposition (PLD) technique with different oxygen pressures. The microstructure, crystallinity, and resistivity of the films depend on the oxygen pressure used. The effects of the films grown at room temperature and at 500°C with different oxygen pressures have been investigated by analyzing the optical and electrical properties of the film. The XRD analysis showed that the high intensity of c-axis orientation of ZnO thin films was obtained under high oxygen pressure and this leads to greater electrical and optical properties. By applying high pressure oxygen, the resistivity value was decreased and optical transmittance became higher in the visible region. The surface morphology of the films showed that the smooth surface was observed without any cracks.