The Fermi energy is the energy of highest occupied state at zero temperature by definition, therefore, it is in semiconductors always the top of the valence band.
Everything else will be an arbitrary choice ! (Or are there any occupied states inside of the gap ? ;-) Do not confuse the Fermi energy with the chemical potential that enters the Fermi-Dirac distribution. I guess the thing you call "Fermi-level" is never clearly in the middle of the band gap (or only by chance), because its position depends not only on the temperature and the doping of the semi conductor but also on the shape of the density of states in the valence and conduction bands. Too bad that sometimes even textbooks use "laboratory slang" rather then clear well defined expressions. Ciao Gerhard DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy: "I think the problem, to be quite honest with you, is that you have never actually known what the question is." ==================================== Dr. Gerhard H. Fecher Institut of Inorganic and Analytical Chemistry Johannes Gutenberg - University 55099 Mainz and Max Planck Institute for Chemical Physics of Solids 01187 Dresden ________________________________________ Von: Wien [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von tarek.ben-n...@laposte.net [tarek.ben-n...@laposte.net] Gesendet: Donnerstag, 20. Oktober 2016 10:33 An: firstname.lastname@example.org Betreff: [Wien] Fermi level Dear Wien users, I have searched in the archives to understand why the fermi level is at the maximum of the valence band in band structure plot of a semiconductor, I found that it was an arbitrary choice but untill now i can't explain this from a physical point of view since for me the fermi level must be in the middle of the gap. Thank you for your help _______________________________________________ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://email@example.com/index.html