8B - 20_Solids_11.ppt - Solids Electrical Conduction...

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Solids Electrical Conduction
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Electrical Conduction in Solids Metals (Cu, Au, Al,. .) conduct electricity and heat relatively well, are shiny, flexible. Insulators (table salt, diamond,. .) opposite to metals. Semiconductors (germanium, silicon, gray (crystalline) tin,selenium, tellurium, Ga As) are between metals and insulators…and can be adjusted. Makes them useful in electronics.
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Band Structure of Solids Bringing atoms close together enough to have wavefunctions overlap causes the energy levels to broaden into bands . Like the separation between atomic energy levels, there are energy gaps between the bands. Lowest levels are filled first but limited by Pauli Exclusion.
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Insulators, Semiconductors and Metals The crucial difference is the size of the gaps, E g .
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Electronic Energy Bands Energy gap > 3 eV No energy gap for electrons.
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I = V/R Ohm’s Law Divide both sides by A and multiply RHS by d/d: " = 1 # = d RA $ -1 m % 1 d A i Defines conductivity, σ , a property of the material (and temperature). Ohm’s Law and conductivity Current density V E, where E = V/d and I/A = j = (V/d) (d/RA) = Results in an expression for the current density that is independent of geometry.
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v time v d Link between micro (number, n, and scattering time, τ , of
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8B - 20_Solids_11.ppt - Solids Electrical Conduction...

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