Excitons

[timmyeatchips]

With regards to semiconductors - am I correct in thinking the term 'exciton' refers to an electron/hole pair?
Also what does it mean when I am told that the Bohr radius of a silicon exciton is 5nm - how can such an entity have a set radius?

[humanino]

Yes, this is correct. See this (http://www.wordiq.com/definition/Exciton) for instance.
The radius correspond to the mean distance between the electron and the hole I guess.

example of research thema (www.iapp.de/~mi-hoffm/spex/ExModels/exmodels.html)
The Travels of An Exciton (http://focus.aps.org/story/v12/st15) about
Near-field Optical Mapping of Exciton Wave Functions in a GaAs Quantum dot
K. Matsuda, T. Saiki, S. Nomura, M. Mihara, Y. Aoyagi, S. Nair, and T. Takagahara
Phys. Rev. Lett. 91, 177401

[ZapperZ]

This should have been posted in Atom, Molecules, and Solids, since it's a condensed matter problem.

An exciton is indeed an electron-hole pair. The reason why there is a "Bohr radius" for it is because this is simply a hydrogenic "atom", i.e. you have an negative charge (the electron) being bound by a central positive charge (the hole). So the Rydberg-type model applies to such exciton as far as the energy-orbital states are concerned.

Zz.

[toozie]

Excitons are indeed an electron-hole pair, and the important feature here is that they are correlated. I.e., there is a significant Coulomb interaction energy, and they are bound such that to separate them, one must supply an energy equivalent to the "exciton binding energy".