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, 9 (4), 044208
eCollection

Superconductivity in Transparent Zinc-Doped In 2 O 3 Films Having Low Carrier Density

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Superconductivity in Transparent Zinc-Doped In 2 O 3 Films Having Low Carrier Density

Kazumasa Makise et al. Sci Technol Adv Mater.

Abstract

Thin polycrystalline zinc-doped indium oxide (In2O3-ZnO) films were prepared by post-annealing amorphous films with various weight concentrations x of ZnO in the range 0⩽x ⩽0.06. We have studied the dependences of the resistivity ρ and Hall coefficient on temperature T and magnetic field H in the range 0.5⩽T ⩽300 K, H⩽6 Tfor 350 nm films annealed in air. Films with 0⩽x⩽0.03 show the superconducting resistive transition. The transition temperature Tc is below 3.3 K and the carrier density n is about 1025-1026 m-3. The annealed In2O3-ZnO films were examined by transmission electron microscopy and x-ray diffraction analysis revealing that the crystallinity of the films depends on the annealing time. We studied the upper critical magnetic field Hc2 (T) for the film with x = 0.01. From the slope of dHc2 /dT, we obtain the coherence length ξ (0) ≈ 10 nm at T = 0 K and a coefficient of electronic heat capacity that is small compared with those of other oxide materials.

Keywords: annealing effect; carrier density; electrical resistivity; superconductivity; transparent thin films.

Figures

Figure 1
Figure 1
(a) T dependence of ρ of polycrystalline In2O3–ZnO film with weight concentration of ZnO x = 0.005 in various magnetic fields perpendicular to the film surface: H = 0, 0.1, 0.3, 1.0, 2.0, 3.0, and 4.0 T. The film was prepared by annealing as-grown amorphous In2O3–ZnO at 300 °C for 2 h. The inset shows the detailed data near the onset of superconducting transition at H=0 (•) and H = 5 T (○). (b) Normalized magnetoresistivity defined as Δ ρ = [ρ (H) - ρ (0)]/ρ (0) at temperatures T = 1.5, 2, 2.5, 3 and 3.5 K from top to bottom.
Figure 2
Figure 2
(a) Cross-sectional HAADF-STEM image of grains and grain boundaries of In2O3–ZnO film with x = 0.05. (b) Intensity of HAADF–STEM and (c) EELS O-K edges. Line shows the profile taken on thick line crossing the grain boundary in HAADF–STEM image in (a). The point indicated by the arrow corresponds to the grain boundary.
Figure 3
Figure 3
(a) XRD pattern of films annealed at 200 °C for different annealing times ta. (b) ta dependence of crystallinity factor P defined as P(ta) =∑Pi (ta)/∑ Pi (ta = 20 h). The quantity Pi (ta) corresponds to the peak height of diffractions (211), (222), (400), (440) and (622) for a film annealed for duration ta. (c) TEM images for films annealed at 200 °C for 0.5, 4.0 and 20 h.
Figure 4
Figure 4
(a) ρ (T) dependence for films with x = 0.01 annealed at 200 °C for 0 (amorphous), 0.5, 1.0, 2.0, 4.0, 20 and 48 h from bottom to top. (b) Normalized resistance R(T)/R(T = 4.2 K) for five films annealed for 0.5, 1.0, 2.0, 4.0 and 20 h from left to right.
Figure 5
Figure 5
(a) Dependences of Tc (•) and n (▪) on annealing time ta for films with x = 0.01. The value of Tc was defined as the temperature at which half of the normal-state resistance was restored. (b) Dependence of Tc on crystallinity factor P.
Figure 6
Figure 6
Dependence of Tc on carrier concentration n for films with x = 0.005 (•), x = 0.01 (▪) and x = 0.02 (▴) annealed at 200 °C. The symbols on the horizontal axis are data of as-grown amorphous films.
Figure 7
Figure 7
(a) Tdependence of ρ of In2O3–ZnO with x = 0.01 annealed at 200 °C for 2 h at magnetic fields H = 0, 0.1, 0.3, 0.8, 1.0, 2.0, 3.0, 4.0 and 6.0 T. (b) T dependence of the upper critical magnetic field Hc2.

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