lecture12 - 18 Lecture 12, February 11, 2008 B....

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18 Lecture 12, February 11, 2008 B. Conductivity 1. Conductors are materials that have integrated valence and conduction bands. Thermal energy (i.e., energy available at room temperature from heat) is generally sufficient to initiate conduction, although conductivity decreases slightly with increasing T due to increased atomic vibration within the lattice structure of the solid. 2. Semiconductors have a small energy gap between the valence and conduction bands ("bandgap"). Usually, there is not enough thermal energy to begin conduction, but the addition of energy from an external source can allow conduction to begin. Conductivity increases with T since more and more electrons can cross the bandgap. 3. Insulators have a wide bandgap and essentially do not conduct under most conditions. 4. Superconductors act like insulators but due to special atomic arrangements, below a certain temperature their resistance to electronic conduction goes to zero, so their conductivity becomes infinite. C. Doped Semiconductors
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lecture12 - 18 Lecture 12, February 11, 2008 B....

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