Phonons in polar and non-polar semiconductors

[Apolo]

I don't understand the concept for polar and non-polar semiconductors, generally speaking about propagation of existence of phonons (acustic or optics).

Thanks.
I don't find any thread about this concepts.

 

[DrDu]

I don't know too much about this. The classical semiconductors like Si or Ge crystallize in a diamond structure, with two symmetry equivalent atoms per primitive unit cell. In semiconductors like GaAs or ZnS, there are two different atoms with different electronegativity in that unit cell hence the material can easily be polarized and especially the dispersion relation for phonons may be considerably different from that in non-polar materials due to the interaction of the atomic vibrations with electromagnetic radiation. The combined electronic and vibrational excitation is called a polariton.
See e.g. fig. 9.9 in
http://books.google.de/books?id=ZJz...ge&q=phonon dispersion polar crystals&f=false