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I have three questions regarding the material Gallium Oxide. I was reading in several articles and they introduced its structure as it has monoclinic structure and it consists tetrahedral and octahedral structures in it. What I can't understand I can connect this structure to the chemical formula: Ga2O3... because in octahedral or tetrahedral the gallium is bonded to 4 or 6 oxygen atoms.

My second question is: how the plane 100 or 001 in the pictures below is crossing the unit cell I can't read this actually?

My last question is regarding the material, that it is a n-type semiconductor... Why it should be n-type if all the oxygen atoms are bonded with gallium atoms? why should be free electrons in the conduction band even there is no doping?!!

enter image description here

The first image (in left) is from the article: https://journals.aps.org/prb/pdf/10.1103/PhysRevB.96.081409

The second image (in right) is from the presentation: https://www.spiedigitallibrary.org/...ce-Presentation/10.1117/12.2292778.full?SSO=1

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  • $\begingroup$ The original article on crystal structure is doi.org/10.1063/1.1731237 and another good article is doi.org/10.1063/1.4983814 - note that there are 2 distinct Ga sites, one with 4 oxygen neighbors and one with 6, and 3 oxygen sites, two with 3 Ga neighbors and one with 4. They are balancing some being slightly unhappier than others to benefit overall crystal bonding. "Pure" Ga2O3 is thought to be unintentionally doped with silicon (a donor here), but oxygen vacancies are also donors. $\endgroup$
    – Jon Custer
    Commented Nov 9, 2021 at 14:48
  • $\begingroup$ Thank you so much for your comment especially the articles! I'm just confused how it comes that the gallium can bond to 6 or 4 while it has just 3 valence electrons.. $\endgroup$
    – stdscience
    Commented Nov 9, 2021 at 19:27
  • $\begingroup$ you are thinking molecules, not solids. In a crystal, electron wavefunctions extend throughout the crystal - they are not localized to specific atoms. $\endgroup$
    – Jon Custer
    Commented Nov 9, 2021 at 19:38
  • $\begingroup$ Oh yes yes I see yep thank you :)) $\endgroup$
    – stdscience
    Commented Nov 9, 2021 at 19:45

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