From: "JACK L. URETSKY (C)1998; HEP DIVISION, ARGONNE NATIONAL LAB ARGONNE, IL 60439" <JLU@hep.anl.gov>
Date: Sun, 4 Oct 1998 13:10:47 -0500
Hi all-
To add to Bob Sciamanda's
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Hi James!
Your point is well taken. It seems that the added electrons must, at
least locally, alter the band structure. Texts seem to indicate that, at
least in the case of the doping of semi-conductors, the added electrons
enter states somewhere within the forbidden gap. In an insulator this
must still be well out of reach of the conduction band.
I think that much of this surface physics is still a black art (I am
certainly a laymen here) and has only been vigorously explored in the
course of developing applications to semi-conductor device manufacturing.
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Conduction is an essentially quantum-mechanical phenomenon. In
order to get a conduction band, one needs a long array of atoms, say of
length L in every direction. There are then (approximate) plane wave
states with momenta separated by h-bar/L. These are the states in the
conduction band. These states reflect the symmetry of the geometry
under translations along any axis of the array (for sufficiently long
L).
Introduction of localized charges breaks the translation
symmetry and, thus, the spectrum of states in the conduction band.
The localized charges are then "defects" that affect the conductivity
of the material. The atomic properties then determine how the defects
behave in the material.
As in most such matters, a good place to start for an educated
overview is the Feynman Lectures. See Vol III, chapter 13.
Regards,
Jack
"I scored the next great triumph for science myself,
to wit, how the milk gets into the cow. Both of us
had marveled over that mystery a long time. We had
followed the cows around for years - that is, in the
daytime - but had never caught them drinking fluid of
that color."
Mark Twain, Extract from Eve's
Autobiography