According to the book I'm referring to ("S.M. Sze Semiconductor Devices"), gallium has an oxidation state of +1 and arsenic has that of -1. This should not be possible as each of these elements forms a covalent bond with four atoms of the other element (structure of GaAs semiconductor). For that to be possible, shouldn't both of them have one electron in $\ce{3s}$ subshell and three electrons in $\ce{3p}$ subshell?
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$\begingroup$ Which book? And how meaningful are these oxidation states anyway? $\endgroup$– Oscar LanziJun 30, 2018 at 11:24
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$\begingroup$ Oxidation states are meaningful because they tell about the electronic configuration that might have existed during bonding $\endgroup$– GoyalJun 30, 2018 at 14:38
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$\begingroup$ @OscarLanzi The book I'm referring to is S.M. Sze Semiconductor Devices $\endgroup$– GoyalJul 1, 2018 at 3:39
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In general, gallium can have +1 and +3 oxidation states, though +1 is a very rare condition. In its turn arsenic possible oxidation states are -3, +3 and +5. As it is stated in Wikipedia, gallium oxidation state in gallium arsenide is +3. Once again, arsenic has -3 oxidation state in arsenides or intermetallic compounds. Therefore, gallium arsenide oxidation states are +3 for Ga and -3 for As. This is logical because the electronegativity of As is higher then Ga. As for Simon Sze, he is an electrical engineer and physicist and not a chemist. From the mathematical point of view (-3)(+3) is the same thing as (-1)(+1).
