TY - JOUR
T1 - Direct growth of transparent conducting Nb-doped anatase TiO2 polycrystalline films on glass
AU - Yamada, Naoomi
AU - Hitosugi, Taro
AU - Kasai, Junpei
AU - Hoang, Ngoc Lam Huong
AU - Nakao, Shoichiro
AU - Hirose, Yasushi
AU - Shimada, Toshihiro
AU - Hasegawa, Tetsuya
N1 - Funding Information:
The authors are grateful to S. Konuma of Kanagawa Academy of Science and Technology (KAST) for TEM observations. We also thank H. Odaka and I. Hayashi of Asahi Glass for supplying the sputtering target. This work was supported by MEXT Elements Science and Technology Project, Grant-in-Aid for Young Scientist (B) 19760475, 2007 and NEDO. FIG. 1. Typical XRD patterns of TNO films grown on LAO at T s = 400 ° C for 0.1 % ⩽ f ( O 2 ) ⩽ 1.0 % with (a) χ = 90 ° and (b) χ = 45 ° . χ is defined as the angle between the film surface and the diffractometer plane. FIG. 2. Room temperature (a) resistibility ρ , (b) carrier density n e , and (c) Hall mobility μ H of TNO films grown on La Al O 3 (100) (closed marks) and seed-layer covered glass (open marks) as functions of f ( O 2 ) . The films were grown at T s = 400 ° C . Dashed lines are typical values of PLD-grown T 0.94 Nb 0.06 O 2 epitaxial films on LAO ( ρ = 3.5 × 10 − 4 Ω cm , n e = 1.3 × 10 21 cm − 3 and μ H = 14 cm 2 V − 1 s − 1 ). FIG. 3. XRD patterns of TNO polycrystalline films grown on Si O 2 ∕ Si at (a) T s = 400 ° C and f ( O 2 ) = 0.35 % , (b) T s = 400 ° C and f ( O 2 ) = 1.0 % , and (c) T s = 250 ° C and f ( O 2 ) = 1.0 % . A ( h k l ) and R ( h k l ) denote the diffraction peak from the ( h k l ) plane of the anatase and rutile phase, respectively. The peak labeled Si(400) is from the Si O 2 ∕ Si substrate. FIG. 4. Growth parameter-based [ f ( O 2 ) and T s ] phase diagram of Ti 0.94 Nb 0.06 O 2 film on (a) LAO(100) and (b) Si O 2 ∕ Si substrates. Circle, cross, and triangle symbols denote pure anatase phase, pure rutile phase, and mixture of anatase and rutile phases, respectively. The films were grown under a total pressure P tot of 1.0 Pa . FIG. 5. XRD patterns of TNO polycrystalline films grown on seed-layer/ Si O 2 ∕ Si substrates under (a) f ( O 2 ) = 0.05 % and T s = 400 ° C , (b) f ( O 2 ) = 0.35 % and T s = 400 ° C . Line (c) represents the XRD pattern of a TNO film grown directly on bare Si O 2 ∕ Si [same as the line(c) in Fig. 3 ] for comparison. The seed-layer is an anatase TNO layer grown at T s = 250 ° C and f ( O 2 ) = 1.0 % . The bottom panel schematically illustrates the structure of the TNO film from which the diffraction pattern (a) was measured. FIG. 6. Surface morphology of TNO polycrystalline films grown by the seed-layer method (top panel) and the thermal annealing method (bottom panel) observed by POM (left) and AFM (right). The film shown in the bottom panel was fabricated under the same conditions described in Ref. 13 . FIG. 7. Cross sectional TEM images of TNO polycrystalline films grown by the seed-layer method (top panel) and the thermal annealing method (bottom panel). (b) and (d) are closeup images of (a) and (c), respectively. The film shown in the bottom panel was fabricated under the same conditions described in Ref. 13 . FIG. 8. Optical (a) transmittance T , (b) reflectance R , and (c) absorption A spectra of TNO polycrystalline films grown on bare glass and seed-layer/glass in the wavelength range 400 – 2300 nm . The films were deposited at T s = 400 ° C and f ( O 2 ) = 0.05 % .
PY - 2009
Y1 - 2009
N2 - This paper proposes a novel sputter-based method for the direct growth of transparent conducting Ti1-xNbxO2 (TNO) polycrystalline films on glass, without the need for any postdeposition treatments, by the use of an initial seed-layer. Anatase TNO epitaxial films grown on LaAlO3 (100) substrates under a reducing atmosphere exhibited a low resistivity (ρ) of (3-6) × 10-4 cm. On glass, however, highly resistive rutile phase polycrystalline films (ρ ∼100 Ωcm) formed preferentially under the same conditions. These results suggest that epitaxial stabilization of the oxygen-deficient anatase phase occurs on lattice-matched substrates. To produce a similar effect on a glass surface, we deposited a seed-layer of anatase TNO with excellent crystallinity under an increased oxygen atmosphere. As a result, anatase phase TNO polycrystalline films could be grown even under heavily reducing atmospheres. An optimized film exhibited ρ =1.1× 10-3 Ω cm and optical absorption lower than 10% in the visible region. This ρ value is more than one order of magnitude lower than values reported for directly deposited TNO polycrystalline films. This indicates that the seed-layer method has considerable potential for producing transparent conducting TNO polycrystalline films on glass.
AB - This paper proposes a novel sputter-based method for the direct growth of transparent conducting Ti1-xNbxO2 (TNO) polycrystalline films on glass, without the need for any postdeposition treatments, by the use of an initial seed-layer. Anatase TNO epitaxial films grown on LaAlO3 (100) substrates under a reducing atmosphere exhibited a low resistivity (ρ) of (3-6) × 10-4 cm. On glass, however, highly resistive rutile phase polycrystalline films (ρ ∼100 Ωcm) formed preferentially under the same conditions. These results suggest that epitaxial stabilization of the oxygen-deficient anatase phase occurs on lattice-matched substrates. To produce a similar effect on a glass surface, we deposited a seed-layer of anatase TNO with excellent crystallinity under an increased oxygen atmosphere. As a result, anatase phase TNO polycrystalline films could be grown even under heavily reducing atmospheres. An optimized film exhibited ρ =1.1× 10-3 Ω cm and optical absorption lower than 10% in the visible region. This ρ value is more than one order of magnitude lower than values reported for directly deposited TNO polycrystalline films. This indicates that the seed-layer method has considerable potential for producing transparent conducting TNO polycrystalline films on glass.
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U2 - 10.1063/1.3148267
DO - 10.1063/1.3148267
M3 - Article
AN - SCOPUS:67650227390
VL - 105
JO - Journal of Applied Physics
JF - Journal of Applied Physics
SN - 0021-8979
IS - 12
M1 - 123702
ER -