Generally, VBM lies at a high symmetry point on the Fermi level. Please explain the situation mentioned in the question. If possible please provide the references. Thanks in advance.
Hi Dr M.A. Hadi,
The valence band ''maximum'' (in fact it is the VB minimum because hole positive energies are reversed with respect to electron positive energies by convention in order not to have meaningless negative effective masses for holes) can occur anywhere in the Brillouin Zone depending on symmetry properties of the given material and on structural properties including lattice deformations.
In most materials and more particularly cubic symmetry materials (Diamond-like or Zinc-Blende-like) the valence band maximum occurs always at the Brillouin Zone center at k=(0,0,0).
However there are some cases of Würtzite or Rocksalt materials where strong p-d orbitals interactions can lead to the appearance of VB max at off-zone center points of the Brillouin Zone
See for instance the following paper:
https://materialsmodeling.org/assets/publications/ErhKleEgd07.pdf
I hope it'll help you
Best regards,
Professor A. Kadri.
Thank you dear Prof. Abderrahmane Kadri for the nice discussions and providing an useful paper.
Best regards,
M.A. Hadi
Dear Dr M. A. Hadi,
You are welcome,
It is my pleasure,
Best regards,
Prof. A. Kadri
Prof. M. A. Hadi
Very interesting question and answer. The valence band is by definition the outermost electron orbital of an atom that electrons occupy in a solid-state crystal.
This relates to the idea of having valence electrons. Being this linked to the Gamma point shows how important is symmetry in determining all physical properties of solids.
In semiconductors, there is a bandgap and 2 electrons per cell, so symmetries are really important to properly understand electrical and optical properties.
Best Regards.
Thank you for the very explicative answer, Prof. Abderrahmane Kadri.
Best Regards.
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