p2f10_lec13_energybands - Physics 1200 Lecture 13 F2010...

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Unformatted text preview: Physics 1200 Lecture 13 F2010 Energy bands in solids Electron occupation (Pauli Exclusion) Metals and semiconductos Fermi Level Resistivity of metals Resistivity of intrinsic semiconductors Doping Atoms and Potential Energy Wells The potential energy wells of finite depth that we studied can be thought of as simple models of atoms. In both, electrons are trapped in discrete energy levels in a region of low potential energy. When two or more are brought close together they can bond. Atoms and Potential Energy Wells The next few slides show what happens to the energy levels in a pair of potential energy wells as they are brought close together. When the wells are far apart, it does not matter if one of the wave functions is multiplied by 1. That changes as they get closer. Two wells Far apart Approximate energy levels as two separate wells. Two wells Closer Two wells Closer yet Two wells Touching Approximate energy levels as one big well. Energy Levels What has happened to the energies? Case (a) looks like an n = 1 level. Case (b) looks like an n = 2 level. The next slide shows how the energy levels change as the separation changes. Bonding More energy levels If each well had one electron in its ground state, they would both be in the lower state of the combined system, and the energy of the system would reduce as the wells came closer. They would bond. Also, where there was one energy level, now there are two. The level split into two. Extrapolate that result If three wells (atoms) are brought together, each energy level would split into three levels. 10 23 atoms would result in each level splitting into 10 23 . They form bands. Energy levels in a solid An example of a set of energy bands....
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p2f10_lec13_energybands - Physics 1200 Lecture 13 F2010...

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