C-axis Oriented ZnO Thin Films Research Articles

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.

Low temperature photoluminescence and infrared dielectric functions of pulsed laser deposited ZnO thin films on silicon

Abstract C-axis oriented ZnO thin films were grown on silicon (100) and (111) substrates by pulsed laser deposition. Low temperature photoluminescence spectra show besides the peaks of free excitons, of defect bound excitons, and of a donor–acceptor pair transition a new doublet at 3.328/3.332 eV. The doublet seems to originate from the columnar textured ZnO film structure. A corresponding structural dependence of the broadening parameter of the infrared dielectric functions was derived from spectroscopic ellipsometry in the spectral range from 380 to 1200 cm− 1. The wave numbers of the E1 transverse optical and A1 longitudinal optical phonon modes of the ZnO films on silicon are determined to be 406 and 573 cm− 1, respectively. These values are slightly smaller than those of single-crystalline ZnO thin films on sapphire.

Catalyst growth of single crystal aligned ZnO nanorods on ZnO thin films

One dimensional ZnO nanorods were successfully fabricated on Si substrates via a simple physical vapor-phase transport method at 950 °C. A ZnO shell covered Au/Zn alloy is assumed as the nucleation site, then ZnO nanorods grow following a vapor-solid (VS) process. In order to guide the nanorod growth a c-axis oriented ZnO thin film and Au catalyst were first deposited on Si (100) surface. SEM images show nanorods grown on this substrate are vertical to the substrate surface. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

FBAR 소자제작을 위한 ZnO 박막 증착 및 특성

This paper gives characterization of ZnO thin film deposited by RF magnetron sputtering method, which is concerned in deposition process and device fabrication process, to fabricate solidly mounted resonator(SMR)-type film bulk acoustic resonator(FBAR). A piezoelectric layer of 1.1<TEX>${\mu}{\textrm}{m}$</TEX> thick ZnO thin films were grown on thermally oxidized SiO<TEX>$_2$</TEX>(3000 <TEX>$\AA$</TEX>)/Si substrate layers by RF magnetron sputtering at the room temperature. The highly c-axis oriented ZnO thin film was obtained at the conditions of 265 W of RF power, 10 mtorr of working pressure, and 50/50 of Ar/O<TEX>$_2$</TEX> gas ratio. The piezoelectric-active area was 50 <TEX>${\mu}{\textrm}{m}$</TEX><TEX>${\times}$</TEX>50<TEX>${\mu}{\textrm}{m}$</TEX>, and the thickness of ZnO film and Al-3 % Cu electrode were 1.4 <TEX>${\mu}{\textrm}{m}$</TEX> and 180<TEX>${\mu}{\textrm}{m}$</TEX>, respectively. Its series and parallel frequencies appeared at 2.128 and 2.151 GHz, respectively, and the qualify factor of the resonator was as high as 401.8<TEX>$\pm$</TEX>8.5.

Formation mechanism of preferential c-axis oriented ZnO thin films grown on p-Si substrates

Formation mechanism of preferential c-axis oriented ZnO thin films grown on p-Si substrates

Al-doped ZnO thin films by sol–gel method

Transparent and conductive high preferential c-axis oriented ZnO thin films doped with Al have been prepared by sol–gel method using zinc acetate and aluminium chloride as cations source, 2-methoxiethanol as solvent and monoethanolamine as sol stabilizer. Film deposition was performed by dip-coating technique at a withdrawal rate of 1.5 cm min −1 on Corning 1737 glass substrate. The effect of dopant concentration, heating treatment and annealing in reducing atmosphere on the microstructure as well as on the electrical and optical properties of the thin films is discussed. The optical transmittance spectra of the films showed a very good transmittance, between 85 and 95%, within the visible wavelength region. The minimum resistivity of 1.3×10 −3 Ω cm was obtained for the film doped with 2 wt.% Al, preheated at 400 °C and post-heated at 600 °C, after annealing under a reduced atmosphere of forming gas.

ZnO thin films produced by filtered cathodic vacuum arc technique

High quality c-axis oriented ZnO thin films have been successfully deposited on silicon substrates using filtered cathodic vacuum arc (FCVA) technique. Two deposition temperatures, namely room temperature and 420 °C, were studied. The films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD revealed that the ZnO films exhibited (0 0 2) orientation. An amorphous layer between the substrate and the ZnO film was observed in both samples using TEM. Both samples showed c-axis oriented ZnO columns. However, for the ZnO thin film deposited at room temperature, the c-axis oriented ZnO columns were observed to grow on a layer of randomly oriented nanocrystals.

Effect of growth temperature on ZnO thin film deposited on SiO 2 substrate

We investigated the effect of deposition temperature on the growth and structural quality of ZnO films on SiO 2 substrate in the range of 100–250 °C using the metal organic chemical vapor deposition (MOCVD) technique. We revealed that highly c-axis oriented ZnO thin films were obtained at the temperature of 200–250 °C and the ZnO thin film was successfully deposited at the lower temperature of 100–150 °C. The c-axis orientation of the film improved and the grain size increased by increasing growth temperature.

Temperature effect on ZnO/Si thin film grown using metal organic chemical vapor deposition

We investigated the effect of deposition temperature on the growth and structural quality of ZnO films on Si (100) substrate using the metal organic chemical vapor deposition (MOCVD) technique. We revealed that highly c-axis oriented ZnO thin films were obtained at the temperature of 400°C. The film crystallinity improved and the surface smoothness decreased with increasing growth temperature.

Preparation and characterization of ZnO thin films on InP by laser-molecular beam epitaxy technique for solar cells

Highly c-axis oriented ZnO thin films were epitaxially grown on semi-insulating 〈1 0 0〉 oriented InP substrates (SI-InP) held at room temperature (RT), 200°C and 300°C by laser molecular beam epitaxy (L-MBE) i.e., pulsed laser deposition. Through X-ray diffraction analysis, the material, the crystalline quality and the epitaxial lattice matching of the film were confirmed. The obtained high intense peak shows that the most preferential orientation was (0 0 2), i.e; along the ‘ c-axis’. Results obtained from the optical studies indicated that the deposited film showed nearly 95% transparency and acts as anti-reflection medium. Photoluminescence (PL) study confirms the high electrical conductivity of the film and the obtained low-intensity PL spectrum indicates high O/Zn ratio. Further, the elemental peaks for Zn, O, In and P were identified by EDAX and the spectrum shows the stoichiometry of the ZnO thin films. From the optical absorption spectrum, the optical band gap and the thickness were calculated. The sheet resistance of the deposited ZnO thin films was measured for various deposition temperatures. Structural, compositional, surface morphological, optical and photoluminescence characterization results are discussed.

The dielectric properties and optical propagation loss of c-axis oriented ZnO thin films deposited by sol–gel process

The c-axis oriented ZnO thin films were prepared on various substrates by sol–gel processes. The stability of solution was examined through solvent and stabilizer. The c-axis orientation and grain size of films were increased with increasing of heat treatment temperature. The optical propogation losses of ZnO films deposited SiO 2/Si(111) substrates were measured using end-coupling method. The losses result in the scattering of the interface of ZnO/SiO 2, and the ZnO grain. Dielectric constant and resistivity of thin films deposited on Pt/SiO 2/Si(111) substrates are, respectively, in the range of 7–13 and 1.7×10 4∼9.8×10 5Ω cm.

Sol-gel-derived c-axis oriented ZnO thin films

c-Axis oriented zinc oxide thin films were prepared by sol-gel process on fused quartz substrates. The structure, optical and electrical properties of ZnO films were investigated. Growth of the thin films strongly depends on heat-treatment conditions. The c-axis lattice constants of the thin films and the band gap are a little bigger than that of ZnO crystal. The differences between the thin film and crystal might be attributable to the grain boundaries and imperfections in thin films.

Preparation and microstructure of ZnO thin films by SOL-GEL process

Abstract Zinc oxide thin films were prepared from metallo-organic compounds through the sol-gel process. The crystal structure of ZnO films was investigated by XRD and SEM. Optical properties of the thin films were analyzed by using UV/visible spectroscopy. Strongly c-axis oriented ZnO thin films were obtained on fused quartz substrates; the surface of the thin films was smooth, homogeneous, crack-free, and dense. The growth of the thin films depends strongly on the heat-treatment conditions. The Crystal lattice constant of the thin films is a little larger than that of the ZnO crystal, the band gap is 3. 444 eV, and the absorption limit shifts to shorter wavelengths.

Preparation of c-axis oriented ZnO optical waveguiding films on fused silica by pulsed laser reactive ablation

c-axis oriented ZnO thin films have been deposited on fused silica by pulsed laser reactive ablation using a Zn target. The films are polycrystalline, transparent, smooth, dense and crackfree. The influence of the deposition parameters on film quality has been discussed. The fwhm of the (002) X-ray reflection peak reaches its minimum of 0.320 ° at substrate temperatures of 375–425 °C. The refractive index of the film versus wavelength has been determined. Favorable optical waveguiding property has been demonstrated by observation of sharp m-lines from the TE mode.

Effects of laser wavelength and fluence on the growth of ZnO thin films by pulsed laser deposition

Transparent, electrically conductive and c-axis oriented ZnO thin films have been grown by the pulsed laser deposition (PLD) technique on silicon and Corning glass substrates employing either a KrF excimer laser (λ = 248 nm) or a frequency-doubled Nd:YAG laser (λ = 532 nm). The crystalline structure, surface morphology, optical and electrical properties of the deposited films were found to depend not only on the substrate temperature and oxygen partial pressure, but also on the irradiation conditions. The quality of the ZnO layers grown by the shorter wavelength laser was always better than that of the layers grown by the longer wavelength, under otherwise identical deposition conditions. This behaviour was qualitatively accounted for by the results of the numerical solution of a one-dimensional heat diffusion equation which indicated a strong superheating effect of the melted target material for the case of frequency-doubled Nd:YAG laser irradiations. By optimizing the deposition conditions we have grown, employing the KrF laser, very smooth c-axis oriented ZnO films having a full-width at half-maximum value of the (002) X-ray diffraction value less than 0.16° and optical transmittance around 85% in the visible region of the spectrum at a substrate temperature of only 300°C.

Low temperature growth of highly transparent c-axis oriented ZnO thin films by pulsed laser deposition

The effects of the oxygen partial pressure, substrate temperature and laser wavelength on the structural and optical properties of thin films of ZnO grown on silicon and glass substrates by pulsed laser deposition have been studied. Regardless of thickness, all the grown layers are c-axis oriented and optically transparent. At substrate temperatures as low as 300°C, featureless layers with a FWHM value for the (002) XRD reflection less than 0.18° and exhibiting an optical transmission higher than 80% in the visible region were produced. For otherwise identical deposition conditions, the KrF excimer laser (at 248 nm) was always found to produce better quality thin films than the frequency-doubled Nd: YAG laser (532 nm). This is explained by the large difference between the optical absorption coefficients of ZnO at the two wavelengths employed, which play a keu role in the laser-target interaction. SEM investigation of the target surface after deposition revealed very different surface morphologies for the two wavelengths employed supporting this assumption.

Growth of c-axis oriented ZnO thin films with high deposition rate on silicon by CVD method

A highly c-axis oriented ZnO thin film with a high optical transparency is grown at a high growth rate of 90μm/h on a silicon substrate by a ZnO-H2-O2-H2O CVD system. Thin ZnO films are reproducibly obtained on silicon substrates only when an intermediately sputtered thin ZnO layer is present. In this CVD method, the intermediate thin ZnO layer provides a high density of nuclei and serves as a buffer layer in the succeeding CVD process. A ZnO film is selectively chemical-vapor-deposited on the part of the silicon substrate with a very thin sputter-deposited ZnO layer, with no chemical vapor deposition on the bare silicon substrate itself. The low resistivity, combined with optical transparency at visible to infrared, surface flatness, and good adherence to the silicon substrate of the ZnO film suggest the feasibility of ZnO/Si junction solar cells, which have shown a rather poor conversion efficiency of 0.92% so far.

Preparation of Highly C-Axis Oriented ZnO Thin Films by Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Thin-film ZnO with a high degree of c-axis orientation has been grown on glass substrate by plasma-enhanced metalorganic chemical vapor deposition at a substrate temperature of 200°C and rf input powers higher than 220W. In this system the ZnO films were fabricated by reacting diethylzinc with CO2 gas. The crystallographic properties and surface morphology of the films were greatly affected by the rf input power level, the substrate temperature and the growth rate.