Low Electrically Resistive Transparent Indium-Tin-Oxide Epitaxial Film on (001) Surface of YSZ by Pulsed Laser Depositio
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Mat. Res. Soc. Symp. Proc. Vol. 623 © 2000 Materials Research Society
techniques have been tried. However, ITO films having resistivity below 10492cm have not been obtained so far. Use of new deposition techniques alone does not seem to lead to any dramatic improvement. The second one is to improve the crystal quality of ITO films. This may lead to an increase in the electron mobility due to the reduction of the scattering centers such as crystal imperfections and neutral donor centers. Use of a single crystal substrate', hopefully one lattice-matched with ITO, and a high temperature deposition process seem to be essentially important to accomplish it. The third approach is to design such a quantum structure that the donor-doped-layer is spatially separated from the carrier drifting one, which is analogous to a HEMT device. The mobility may be improved in this film structure because of the reduction of interaction between carriers and scattering centers. We have employed a combination of the first and the second approaches. That is, an ITO film was grown on an extremely flat yittria-stabilized-zirconia (YSZ)1 3 single crystal substrate at a temperature of 600'C by a pulsed laser deposition technique. Twice the cubic lattice constant of YSZ (1.02nm) is very close to that of ITO (1.01nm), which could make epitaxial growth of ITO possible. The PLD method is suited for oxide film preparation. Additionally, film composition is easily controlled by changing the target composition. We have obtained epitaxially grown ITO films using this approach and the resistivity was reproducibly reduced down to 7.8 x 10 5Qcm. EXPERIMENTAL Oxygen gas was introduced into the chamber with a pressure of 1.2 x 10-3Pa. YSZ (001) was used as the substrate. Surface polished Si0 2 glass was also used as a substrate for comparison.
The substrate temperature was maintained at 600 'C during film deposition. An ITO ceramic target (Sn0 2 concentration: 0"- 15wt.%) was set at the center of the PLD chamber, and the substrate was positioned facing the target. An ITO film was deposited on a rotating substrate by focusing a KrF (X=248nm) excimer laser onto the rotating target. The distance between the substrate and the target was 30mm. The pulsed laser with a repetition rate of 10Hz was focused onto the target with an energy density of about 6J/cm2 . The film thickness was determined by means of a conventional stylus profilometer (Taylor-Hobson, Tallystep). An atomic force microscope (AFM, S.I.I., SPI-3700) was used to investigate surface morphology of the films. The Sn0 2 concentration was analyzed by XRF measurement (RIX2100, Rigaku). Crystalline quality and orientation were analyzed by X-ray diffraction (ATX-G, Rigaku Co.), in which the woaxis was rotated in the horizontal plane and the 4 axis was rotated azimuthally. The detector was manipulated with both the 20 axis in the horizontal plane and the 20X axis in the vertical plane. Out-of-plane crystal orientation was measured by synchronous scan of the 20 with the woaxis. Tilting was analyzed from
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