Lecture12

In a box or in a solid there are a large number of

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Unformatted text preview: al of the atom  Energy depends on k in each band. 4 The Fermi Energy  Since electrons are Fermions (spin ½ ), they must all go into different states.  At low temperature, the lowest energy levels will be filled up.  In a box, or in a solid, there are a large number of states for electrons and we may fill them up to some level, called the Fermi level.  The biggest filled (or the lowest empty) energy level gives us the Fermi Energy EF 5 Band Structure   RepresentaLve density of states diagrams of metals, insulators, intrinsic and n ­doped semiconductors. Shaded areas represent energy levels filled at absolute zero, below the Fermi energy.   We can use (and manipulate) these energy bands in semiconductors to make all kinds of devices. 6 Metals In metals, there is no band gap between the filled valence band and the empty conducLon band.   An E field can easily move electrons to flow in one direcLon as those states get a lower energy in the field.   In a metal, electrons conduct electricity and heat well.   ConducLon band electron states are spread out over the whole metal.   !! ! ! ik !r ! ( r ) = e un ( r ) Na 7 Insulators  Insulators...
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This note was uploaded on 02/24/2014 for the course PHYS 2D taught by Professor Hirsch during the Winter '08 term at UCSD.

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