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Why is black phosphorus semiconductor with direct bandgap?

  1. Mar 9, 2015 #1
    Why is black phosphorus a semiconductor with a direct bandgap?

    The problem is mentioned by the two following references:
    "The three bonds take up all three valence electrons of phosphorus,so, unlike graphene, monolayer black phosphorus is a semiconductor with a predicted direct bandgap of 2 eV at the G point of the first Brillouin zone."
    (see http://www.nature.com/nnano/journal/v9/n5/full/nnano.2014.35.html)

    "Unlike carbon, phosphorus has only three valance electrons which leads to BP being semiconducting since each atom is bonded to three neighboring atoms."
    (see http://scitation.aip.org/content/aip/journal/apl/104/10/10.1063/1.4868132)

    In order to check the point,I input the keyword "valence" in wiki:

    I found that typical valencies are three and five for phosphorus,but only four for carbon.I somehow doubt the explaination in the references and some meticulous and clear details shoud be supplied.
    Last edited: Mar 9, 2015
  2. jcsd
  3. Mar 10, 2015 #2


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    Science Advisor

    p has a full s orbital and 3 additional electrons in the remaining three p orbitals. Hence these three orbitals can form 3 covalent bonds with neighbouring atoms. There are also 3 anti-bonding orbitals at higher energy. The bonding orbitals will form a full valence band and the anti-bonding orbitals an empty conduction band.
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