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I was reading about indium tin oxide (ITO) and that it is considered a n-type semiconductor. However, that doesn’t make sense to me. If just one In(III) is replaced by Sn(IV) then we would have an excess positive charge and an oxygen deficiency. However, from what I read, is that exactly because ITO has oxygen vacancies, it is considered an n-type semiconductor.

That doesn’t make sense to me, could someone explain?

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Conductivity in ITO comes from oxygen vacancies, which effectively mean the indium and tin are not both fully oxidized to In(III) and Sn(IV). The valence electrons that are not captured because of this deficiency in oxygen atoms are then the n-type carriers. We can promote these oxygen vacancies by depositing the ITO film in a reducing atmosphere. See Ren et al.[1].

Reference

  1. Yang Ren, Ping Liu, Rongxin Liu, Yunwei Wang, Yubin Wei, Lihua Jin, Gaoyang Zhao, "The key of ITO films with high transparency and conductivity: Grain size and surface chemical composition", Journal of Alloys and Compounds, Volume 893, 2022, 162304, ISSN 0925-8388, https://doi.org/10.1016/j.jallcom.2021.162304.
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  • $\begingroup$ I thought i might see an answer from you to Are there any 2D materials whose bonding can be best described as metallic rather than covalent? though the question may be overly semantically challenging (metallic behavior vs metallic bonding) $\endgroup$
    – uhoh
    Commented 2 days ago
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    $\begingroup$ I couldn't top Paul Koik. Also I was deterred by comments that metallic bonding is really a form of covalent bonding anyway. $\endgroup$ Commented 2 days ago
  • $\begingroup$ Yes I was confused by that. I'm beginning to think that there's a lot of subjectivity in the terms and that the covalent vs metallic descriptions are context-dependent, but if say a 2D material maintains a simple honeycomb structure doesn't collapse into a close-packed hexagonal structure, then those bonds "feel" more covalent than metallic. $\endgroup$
    – uhoh
    Commented 2 days ago

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