Housei Akazawa

Nippon Telegraph and Telephone, Edo, Tōkyō, Japan

Are you Housei Akazawa?

Claim your profile

Publications (88)184.73 Total impact

  • Housei Akazawa, Hiroyuki Shinojima
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated how the crystallinity of ZnO host films deposited on Si(1 0 0) substrates by electron cyclotron resonance (ECR) plasma sputtering affects the optical activity of Er3+ ions doped in them under resonant excitation with 532-nm laser light. Photoluminescence from ZnO:Er films deposited at room temperature (RT) exhibited a main emission peak at 1538 nm with a sub-peak at 1553 nm. The emission intensity reached a steady state at Er content between 0.6 and 3 at.%, and attenuated above 3 at.%. This concentration quenching correlates with derivation of X-ray diffraction angles from the Vegard's law. Deposition at RT produced non-equilibrium state of ZnO:Er films possibly stabilized with vacancies to maintain charge neutrality. After post annealing of ZnO:Er films with Er content less than 1 at.%, the emission intensities were markedly reduced as the crystalline lattice was rearranged. For films in the concentration quenching range, however, post annealing increased the emission peak width while maintaining emission intensity, indicating that Er3+ ions migrated and populated various emission-active sites. In this case, the main peak wavelength blue shifted to 1536 nm and produced a new sub peak at 1546 nm. When the deposition temperature exceeded 500 °C, emissions from Er3+ ions were greatly enhanced. This will result from improvement in crystallinity and fixing Er3+ ions at six-fold coordinated C4v symmetry sites.
    Materials Science and Engineering B 11/2014; · 2.12 Impact Factor
  • Housei Akazawa, Yuko Ueno
    [Show abstract] [Hide abstract]
    ABSTRACT: We report how the crystallinity and orientation of hydroxyapatite (HAp) films deposited on sapphire substrates depend on the crystallographic planes. Both solid-phase crystallization of amorphous HAp films and crystallization during sputter deposition at elevated temperatures were examined. The low-temperature epitaxial phase on C -plane sapphire substrates has c -axis orientated HAp crystals regardless of the crystallization route, whereas the preferred orientation switches to the (310) direction at higher temperatures. Only the symmetric stretching mode (ν 1) of PO43− units appears in the Raman scattering spectra, confirming well-ordered crystalline domains. In contrast, HAp crystals grown on A -plane sapphire substrates are always oriented toward random orientations. Exhibiting all vibrational modes (ν 1, ν 3, and ν 4) of PO43− units in the Raman scattering spectra reflects random orientation, violating the Raman selection rule. If we assume that Raman intensities of PO43− units represent the crystallinity of HAp films, crystallization terminating the surface with the C-plane is hindered by the presence of excess H2O and OH species in the film, whereas crystallization at random orientations on the A-plane sapphire is rather promoted by these species. Such contrasting behaviors between C-plane and A-plane substrates will reflect surface-plane dependent creation of crystalline seeds and eventually determine the orientation of resulting HAp films.
    Journal of Crystal Growth 10/2014; 404:241–245. · 1.69 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: Li2O-Nb2O5 ternary compound thin films were deposited by dual sputtering from LiNbO3 and Li2O targets to cover a wide range of Li/Nb molar ratios. When all parts of the films were crystallized during sputtering at elevated temperatures, pyrochlore phase crystallites of Li3NbO4, LiNbO3, and LiNb3O8 were preferentially oriented toward their respective (222), (006), and (− 602) directions. These closely packed crystallographic planes having the lowest surface free energies were initially created under exposure to the plasma and the crystallization that followed proceeded exclusively on these seed planes. The volume fraction of each crystalline component as a function of the Li/Nb molar ratio obeyed the established phase diagram. In contrast, solid-phase crystallization of pre-deposited amorphous films through post annealing exhibited a non-equilibrium nature, and the volume fraction of each crystalline component depended on the crystallization rate rather than the Li/Nb molar ratio. Solid-phase crystallization decelerated when excess Li2O was contained in the film. Specifically, LiNbO3 crystallites with near-stoichiometric compositions were randomly oriented without the operating mechanism of preferential orientation toward c-planes. In certain situations, crystalline domains were spatially of inhomogeneous composition, resulting in the simultaneous coexistence of Li3NbO4, LiNbO3, and LiNb3O8.
    Thin Solid Films 04/2014; · 1.87 Impact Factor
  • Housei Akazawa, Yuko Ueno
    [Show abstract] [Hide abstract]
    ABSTRACT: Hydroxyapatite (HAp) films were deposited by electron cyclotron resonance plasma sputtering under a simultaneous flow of H2O vapor gas. Crystallization during sputter-deposition at elevated temperatures and solid-phase crystallization of amorphous films were compared in terms of film properties. When HAp films were deposited with Ar sputtering gas at temperatures above 460 °C, CaO byproducts precipitated with HAp crystallites. Using Xe instead of Ar resolved the compositional problem, yielding a single HAp phase. Preferentially c-axis-oriented HAp films were obtained at substrate temperatures between 460 and 500 °C and H2O pressures higher than 1×10−2 Pa. The absorption signal of the asymmetric stretching mode of the PO43− unit (ν3) in the Fourier-transform infrared absorption (FT-IR) spectra was the narrowest for films as-crystallized during deposition with Xe, but widest for solid-phase crystallized films. While the symmetric stretching mode of PO43− (ν1) is theoretically IR-inactive, this signal emerged in the FT-IR spectra of solid-phase crystallized films, but was absent for as-crystallized films, indicating superior crystallinity for the latter. The Raman scattering signal corresponding to ν1 PO43− sensitively reflected this crystallinity. The surface hardness of as-crystallized films evaluated by a pencil hardness test was higher than that of solid-phase crystallized films.
    Journal of Physics and Chemistry of Solids 01/2014; 75(1):94–99. · 1.59 Impact Factor
  • Housei Akazawa, Hiroyuki Shinojima
    [Show abstract] [Hide abstract]
    ABSTRACT: We found that ZnO:Eu films sputter-deposited with H2O vapor gas produce intense photoluminescence from Eu3+ ions through excitation of ZnO host crystals with a 325-nm laser light, whereas those deposited with O2 gas do not. At optimum annealing temperatures of 300--500 °C, the primary luminescence from Eu3+ ions appeared at 612 nm, which was much stronger than the near-band edge and defect emissions from ZnO. After annealing at higher temperatures, the 612-nm peak attenuated, and two emission lines at 612 and 620 nm, corresponding to two distinct chemical sites, had comparable intensities. These observations suggest that incorporating H+ and/or OH- species in ZnO crystals are prerequisite for emissions from Eu3+ ions to occur. Characterization with infrared absorption spectroscopy and X-ray diffraction suggested that Eu3+ ions substitute Zn2+ sites when OH- (H+) species are contained in ZnO crystals. The role of H+ and/or OH- species may be either charge compensation when substituting Zn2+ sites with Eu3+ ions or creation of trapping centers of excited energies that mediate efficient energy transfer from ZnO to Eu3+ ions.
    Japanese Journal of Applied Physics 07/2013; 52(7):2601-. · 1.06 Impact Factor
  • Housei Akazawa, Yuko Ueno
    [Show abstract] [Hide abstract]
    ABSTRACT: We deposited hydroxyapatite (HAp) thin films on Si(1 0 0) substrates by means of electron cyclotron resonance (ECR) plasma sputtering from a HAp target and characterized their structural properties by X-ray diffraction (XRD) and Fourier transform infrared absorption spectroscopy. Deposition in the presence of an H2O vapor at room temperature incorporated H2O and OH species in the deposited films. Post-annealing in an O2 ambient self-organized OH− and PO43− functional groups in HAp crystals. The XRD patterns revealed randomly orientation when the annealing temperature ranged between 700 and 900 °C. In contrast, preferentially c-axis-oriented HAp crystals nucleated after prolonged annealing at 550–600 °C. The possible scenario for the preferred orientation is that C-plane terminated HAp crystallites were initially created in the near-surface region, and the following crystallization proceeded exclusively on the seed surface. After post annealing in a vacuum or in an Ar gas ambient at 900 °C, films were reduced into tricalcium phosphate, increasing photoabsorption in the infrared range.
    Applied Surface Science 03/2013; 276:217. · 2.54 Impact Factor
  • Housei Akazawa, Hiroyuki Shinojima
    [Show abstract] [Hide abstract]
    ABSTRACT: We identified the conditions necessary for photoluminescence from Eu3+ ions doped in ZnO thin films to occur via indirect excitation of ZnO host crystal with a 325-nm laser light. The ZnO:Eu films were sputter-deposited on Si(100) substrates at room temperature with H2O vapor flowing as the oxygen source gas. A very narrow emission peak at 612 nm, assigned to 5D0-7F2 transition of Eu3+ ions, appeared after annealing at 200–300 °C in a vacuum or at 500 °C in an O2 ambient. At temperatures higher than these, the 612-nm emission peak attenuated and emission spectra exhibited weaker double peaks at 612 and 620 nm. This observation suggested that most Eu3+ ions withdrew from the most emission-active sites, and occupied two distinct chemical sites. With further increasing temperature, the double peaks merged to become broader, indicating that Eu3+ ions occupied sites more randomly. Emission intensity was the highest at an Eu content of 0.9 at. % and concentration quenching was observed as Eu content was increased. Substitution of Zn2+ cation sites with Eu3+ ions was confirmed from the primary X-ray diffraction peaks of ZnO(002); the ZnO lattice expanded as larger numbers of Eu3+ ions were incorporated. After the films were post-annealed at high temperatures, the diffraction angles approached those of undoped ZnO crystals, which reflected shifting Eu3+ ions into grain boundaries. The photoabsorption of OH species within a wavelength range of 2700–3000 nm and the Eu3+ emission intensity revealed correlated behavior. These results confirmed that the presence of OH and/or H species in the film is necessary for emissions from Eu3+ ions to appear. When OH and/or H species were diminished after high-temperature annealing, Eu3+ - ons existing at substitutional sites became unstable and their emissions were consequently deactivated. The origin of emission-active Eu3+ ions can be explained in terms of either the defect mediated energy transfer model or the substitutional model.
    Journal of Applied Physics 01/2013; 114(15):153502-153502-11. · 2.19 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the transparent conductive properties of hetero-double layers: Ga-doped ZnO (GZO) overlaid on undoped ZnO. We prepared five samples for given unit thicknesses h: ZnO and GZO films with a thickness of h to characterize the hybrid structure, ZnO and GZO films with a thickness of 2h, and a GZO/ZnO double layer with a thickness of h for each layer (h = 50, 100, 150, and 200 nm). If we assumed that the upper and bottom half of the 2h-thick GZO films as well as those of GZO/ZnO were connected in parallel in terms of the equivalent electric circuit, the calculated sheet resistance of the upper GZO layer scarcely depended on whether the bottom layer was GZO or ZnO. Hence, the bottom layer played the role of providing a crystalline template for the upper layer that actually governed electrical transport. Also, the infrared transmittance of the upper GZO layer was immune to what the bottom layer consisted of. While GZO/ZnO had 1.1–1.5 times higher sheet resistance than 2h-thick GZO, the optical transmittance of GZO/ZnO in the near-infrared region was 20–40% higher, demonstrating that the GZO/ZnO double layer structure is suitable for transparent electrodes in solar cells.
    Thin Solid Films 12/2012; 526:195–200. · 1.87 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: Adding N2 gas during reactive sputtering of a Ti target prevented the target surface from being severely poisoned by oxygen atoms and sustained a high deposition rate for titanium oxynitride films under metal-mode-like sputtering conditions. With progress in the degree of oxidization, films deposited onto a glass substrate varied from TiO1−xNx having a face-centered cubic (fcc) structure to TiO2−xNx having an anatase structure. Titanium oxynitride films deposited on an Al2O3(0 0 0 1) substrate were epitaxial with major orientations toward the (1 1 1) and (2 0 0) directions for fcc-TiO1−xNx and (1 1 2) for anatase-TiO2−xNx. Intermediately oxidized films between TiO1−xNx and TiO2−xNx were amorphous on the glass substrate but crystallized into a Magneli phase, TinO(N)2n−1, on the Al2O3(0 0 0 1) substrate. Partially substituting oxygen in TiO2 with nitrogen as well as continuously irradiating the growing film surface with a Xe plasma stream preferentially formed anatase rather than rutile. However, the occupation of anion sites with enough oxygen rather than nitrogen was the required condition for anatase crystals to form. The transparent conductive properties of epitaxial TiO2−xNx films on Al2O3(0 0 0 1) were superior to those of microcrystalline films on the glass substrate. Since resistivity and optical transmittance of TiOxNy films vary continuously with changing N2 flow rate, their transparent conductive properties can be controlled more easily than TiOx. Nb5+ ions could be doped as donors in TiO2−xNx anatase crystals.
    Applied Surface Science 12/2012; 263:307–313. · 2.54 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the thermal stability of the transparent conductive properties of undoped ZnO and Ga-doped ZnO (GZO) films when they were annealed in a high vacuum with stepwise increasing temperature. The ZnO samples included VO-rich and Zn-rich ZnO films; the primary donors were respectively oxygen vacancies (VO) or Zn atoms highly unsaturated with oxygen atoms. VO-rich ZnO was the most unstable against annealing; resistivity initially within the 10−3Ωcm range diverged higher than 10Ωcm when a critical temperature was exceeded. The critical temperature between 350 and 450°C depended on the film thickness, which indicated that VO's were diminished through recombination with migrating interstitial oxygen atoms. In contrast, Zn-rich ZnO films remained highly conductive up to 550°C. They became more and more transparent and their crystallinity improved at higher annealing temperatures, which was the consequence of metallic-like Zn atoms being removed through desorption from the surface or being accommodated into the crystalline lattice. Comparatively, GZO films were more robust against annealing with their resistivities remaining unchanged up to 350°C.
    Thin Solid Films 01/2012; · 1.87 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the structural and transparent conductive properties of oxygen-deficient TiOx films that were deposited by metal-mode reactive electron cyclotron resonance plasma sputtering from a Ti target at 400 °C. Crystallites in a strongly reduced state (x≈ 1) had face centered cubic (fcc) structures with the resistivities ranging from 10-4 to 10-3 Ω cm, and the optical transmittance in the visible wavelength was between 25 and 55%. In a sufficiently oxidized state (x≈ 2), rutiles nucleated with resistivites higher than 10-2 Ω cm, and the optical transmittance was between 60 and 80%. The intermediate composition (1< x < 2) corresponded to fcc structures although the crystallinity approached an amorphous state with increasing x. Crystallization into magneli phases (TinO2n-1) was observed only for thick films at deposition temperatures higher than 500 °C. Carriers were n-type for rutile, but p-type for the fcc and magneli phases. Nb-doped TiOx films were produced by metal-mode sputtering of TiOx with co-sputtering Nb and O from an Nb2O5 target. The donor role of Nb5+ could be identified only in the oxidized rutile state, but the resistivity increased at higher Nb2O5 sputtering powers due to oxidation of Nb atoms that substituted Ti sites.
    Japanese Journal of Applied Physics 01/2012; 51(1):5803-. · 1.06 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: Electron cyclotron resonance plasma sputtering of Pt with an O2/Ar gas mixture produced (111) oriented films with a surface roughness of ˜1 nm and resistivities between 20 and 27 muOmega cm. Continuous reduction of deposited film by Ar plasma is responsible for the formation of metallic Pt crystallites even under the presence of O2. The Pt(111) film was more adhesive to the substrate than that of Pt(200) film that was produced by post annealing magnetron-sputtered PtOx films. The Pt(111) films composed of columnar texture domains could be reversibly reduced or oxidized through annealing in a vacuum or in an O2 ambient, and the corresponding adhesive strength changed for one order of magnitude. The enhanced adhesion in the oxidized state was due to Pt films being softened by partial oxidation at the grain boundaries and the interface being immersed with oxygen species, which prevented chipping and cracking that are preludes to delamination.
    Japanese Journal of Applied Physics 06/2011; 50. · 1.06 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: By irradiating undoped ZnO and Ga-doped ZnO (GZO) films with electron cyclotron resonance Ar plasma, their electrical and optical properties have been modified. Both the carrier concentration and the Hall mobility increased with continuous irradiation in conductive ZnO films with a defect-rich crystalline lattice. Improved crystallinity was verified by intensifying the ZnO(002) x-ray diffraction peak and increasing the optical transmission level in the visible wavelength. This observation suggests network rearrangement through Zn atoms at interstitials or grain boundaries being oxidized or accommodated into the crystalline network. For insulating ZnO films that contain a sufficient number of oxygen atoms, the changes were better scaled with sheet resistance rather than resistivity. The interference fringes redshifted without lowering the transmittance level. Here, Ar ion impact will create oxygen vacancy donors in the near-surface region or desorb interstitial oxygen atoms that act as donor killers. In contrast, GZO films with resistivities in the 10-4 Ω cm range revealed little changes because there were very few imperfections in the crystalline lattice. The reduced amount of resistivity corresponded to the creation of oxygen vacancies in more resistive GZO films in the 10-3 Ω cm range.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 01/2011; 29(3):031304-031304-8. · 2.14 Impact Factor
  • Housei Akazawa, Hiroshi Ando
    [Show abstract] [Hide abstract]
    ABSTRACT: High-resolution x-ray photoelectron spectroscopy of strontium bismuth tantalate films revealed distinct chemical states of constituent atoms in fluorite and perovskite crystals. Reflecting the number of nearest-neighbor oxygen atoms coordinated with Bi3+ ions, the Bi 4f peak could be deconvoluted into Bi2O3 (sixfold coordination), Bi2O2 (fourfold coordination), and (Bi2O2)2+ (intermediate between sixfold and fourfold coordination) components. We found that amorphous and fluorite phases could be expressed as a mixture of Bi2O3 and Bi2O2, whereas the (Bi2O2)2+ component representing the bismuth oxide layer, being adjacent to the (SrTa2O7)2− block, predominated in the perovskite phase. Similarly, the Sr 3d peak could be deconvoluted into the components of Sr oxide (SrO) and Sr in (SrTa2O7)2−. The volume fraction of the (SrTa2O7)2− component increased at higher annealing temperatures. The Ta 4d peaks, in contrast, located at the same binding energy for all samples, indicated that an energetically stable TaO6 octahedron unit is preferentially created. The binding energies of the O 1s state corresponding to O–Bi, O–Ta, and O–Sr bonds were identified at 531, 530, and 528.9 eV, respectively.
    Journal of Applied Physics 10/2010; 108(8):083704-083704-7. · 2.19 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose the feasibility of using TiOxNy films as transparent conductors. The TiOxNy films deposited by electron cyclotron resonance plasma sputtering from a Ti target in the metal mode had a face-centered cubic crystal structure. As deposited films incorporated larger numbers of O and N atoms, their crystallinity approached an amorphous state and optical transparency improved, reflecting the decrease in carrier concentration. Our TiOxNy films extended the controllable range of resistivity and optical transmittance more than that with TiOx and TiNx films and outperformed those produced by conventional magnetron sputtering.
    Japanese Journal of Applied Physics 08/2010; 49(8). · 1.06 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: The simultaneous sputtering of ZnO and Ga <sub>2</sub> O <sub>3</sub> by electron cyclotron resonance and rf magnetron plasma sources produced Ga-doped ZnO (GZO) films with continuously varying Ga concentration over the substrate surface. Combinatorial evaluation of electrical and optical properties of GZO film grown on silica glass substrate without heater annealing enabled identification of minimum resistivity (0.5 m Ω  cm ) at a Ga <sub>2</sub> O <sub>3</sub> content of 5.5 wt % with an optical transmittance of 90% in the visible wavelength. The monotonically decreasing mobility that was associated with increasing carrier concentration as Ga <sub>2</sub> O <sub>3</sub> content was increased indicated that conduction was governed by ionized impurity scattering. Above the critical Ga <sub>2</sub> O <sub>3</sub> content (6 wt %), carrier concentration decreased since excess Ga atoms that were incorporated beyond the solubility limit at Zn sites hindered large crystalline domains from forming. The ZnO (002) x-ray diffraction peak was suppressed and peaks assigned to Ga <sub>2</sub> O <sub>3</sub> were observed at high Ga <sub>2</sub> O <sub>3</sub> content. The optimum Ga <sub>2</sub> O <sub>3</sub> content shifted to 3.5 wt % at a deposition temperature of 200 ° C and 2.5 wt % at 300 ° C , and the minimum resistivity was further decreased to 0.28 m Ω  cm at 200 °<roman- - >C . However, the resistivities at these elevated temperatures were incredibly high both at the lower and higher side of the optimum Ga <sub>2</sub> O <sub>3</sub> content.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 04/2010; · 2.14 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: Pt films directly deposited on SiO2 by electron-cyclotron-resonance (ECR) plasma sputtering and DC-magnetron sputtering have been compared in terms of their performance as electrodes. The DC-magnetron sputtered Pt film consisted of sharply (111) oriented crystallites, which was reflected in hexagonal crystallites observed in atomic force microscopy images. While ECR-sputtered Pt film was also (111) oriented, the X-ray diffraction rocking curve of the (111) peak was broader than that of the DC-magnetron sputtered film. The surface image revealed fine grains, thus having a flatter surface. A scratch test revealed that ECR-sputtered films had an adhesive strength about twice that of DC-magnetron-sputtered films, which was consistent with our tape-test results. Possible reasons for the different adhesion characteristics are discussed.
    Surface and Coatings Technology 02/2010; 204(11):1836-1841. · 2.20 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: Real-time spectroscopic ellipsometry was applied to the in situ monitoring of soft x-ray excited chemical vapor deposition of boron films on a Si(001) substrate. While B2H6 molecules cannot reactively stick to a Si clean surface below 400 °C, the decomposition of the precursor molecule through electronic excitation enables boron atoms to secure themselves on the surface. After the incubation period had ended, boron islands began to grow at isolated nucleation centers, exhibiting the Volmer–Weber-type growth. The activation energy for creating the nucleation centers was 2.9 kcal/mol, which presumably corresponded to the clustering of deposited boron atoms. The following growth stage was scaled with an activation energy of 10.3 kcal/mol. The thermally activated process corresponded to the networking of surface-terminating hydrides while releasing H2. As further growth continued, boron islands coalesced, which eventually became two-dimensional boron film. The amorphous boron films could be transformed into a crystallite phase through postannealing at 1000 °C and they were characterized in terms of their optical properties.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 01/2010; 28(3). · 2.14 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: Nanometer-scale Ge islands and pits are self-organized during GeH <sub>4</sub> vacuum-ultraviolet-excited chemical vapor deposition on a Ge(001) substrate. We carried out simulation and fitting on real-time ellipsometric Ψ-Δ trajectories that reflect undergoing changes in the surface morphology. The islanded Ge epitaxial layer was optically represented by multiple stacked slabs with linearly varying graded indices from the bottom to the top of the islands. The dielectric function of each slab was calculated by mixing the dielectric functions of Ge with that of voids under Bruggeman effective medium approximation. The only model that could reproduce the roughening Ψ-Δ trajectory was preferential nucleation of Ge on the top surface of truncated pyramidal islands after almost 100% of the initial surface had been wet. The smoothing section was consistent with the model assuming nucleation on the sidewalls of islands as well as on the top surface, which led to simultaneous deepening and narrowing of the valleys or pits between the islands. This smoothing model was supported by atomic force microscopy images.
    Journal of Applied Physics 12/2009; · 2.19 Impact Factor
  • Housei Akazawa
    [Show abstract] [Hide abstract]
    ABSTRACT: The electrical and optical properties of undoped ZnO films deposited by electron cyclotron resonance (ECR) plasma sputtering at room temperature were characterized. The lowest resistivity we achieved was 2.6×10−3 Ωcm with optical transmittance at visible wavelengths higher than 85%. The X-ray diffraction (002) peak was weak and the rocking curve was asymmetrical, indicating that oxygen vacancies prevented large crystalline domains from forming. At low argon-sputtering-gas pressure, carrier concentration and Hall mobility increased with increasing argon pressure. When the optimum pressure (40 mPa) was exceeded, however, Hall mobility and optical transmittance were severely reduced, which indicated that excess Zn atoms were populated at the interstitials of the network. Admitting only 0.67 mPa of O2 gas during deposition deteriorated resistivity over 1 MΩcm due to high excitation efficiency in the ECR plasma. Deposition under a higher magnetic field produced lower resistivities.
    Thin Solid Films 11/2009; 518(1):22-26. · 1.87 Impact Factor