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P-type electrical conduction in transparent thin films of CuAlO2

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Abstract

Optically transparent oxides tend to be electrical insulators, by virtue of their large electronic bandgap (⩾3.1 eV). The most notable exceptions are doped versions of the oxides In2O3, SnO2 and ZnO—all n-type (electron) conductors—which are widely used as the transparent electrodes in flat-panel displays1,2. On the other hand, no transparent oxide exhibiting high p-type (hole) conductivity is known to exist, whereas such materials could open the way to a range of novel applications. For example, a combination of the two types of transparent conductor in the form of a pn junction could lead to a ‘functional’ window that transmits visible light yet generates electricity in response to the absorption of ultraviolet photons. Here we describe a strategy for identifying oxide materials that should combine p-type conductivity with good optical transparency. We illustrate the potential of this approach by reporting the properties of thin films of CuAlO2, a transparent oxide having room-temperature p-type conductivity up to 1 S cm−1. Although the conductivity of our candidate material is significantly lower than that observed for the best n-type conducting oxides, it is sufficient for some applications, and demonstrates that the development of transparent p-type conductors is not an insurmountable goal.

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Figure 1: Crystal structure of CuAlO2 delafossite consisting of stacked layers of –O–Al–O–Cu–O–.
Figure 2: X-ray powder diffraction patterns of CuAlO2 delafossites.
Figure 3: Transmittance spectra of CuAlO2 thin film.
Figure 4: Temperature dependence of electrical conductivity for the CuAlO2 thin film.

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Author notes

  1. Masahiro Yasukawa

    Present address: National Industrial Research Institute of Nagoya, 1-1 Hirate-cho, Kita-ku, Nagoya, 462, Japan

Authors and Affiliations

  1. Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku, 226, Yokohama, Japan

    Hiroshi Kawazoe, Hiroyuki Hyodo, Masaaki Kurita, Hiroshi Yanagi & Hideo Hosono

Authors
  1. Hiroshi Kawazoe
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  2. Masahiro Yasukawa
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  3. Hiroyuki Hyodo
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  4. Masaaki Kurita
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  5. Hiroshi Yanagi
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  6. Hideo Hosono
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Correspondence to Hiroshi Kawazoe.

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Kawazoe, H., Yasukawa, M., Hyodo, H. et al. P-type electrical conduction in transparent thin films of CuAlO2. Nature 389, 939–942 (1997). https://doi.org/10.1038/40087

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