The Energy Band Model

An insulator is a poor conductor since it requires a lot of energy, 5-8 eV, to excite the electrons enough to get to the conduction band. We can say that the width of the band gap is very large, since it requires that much energy to traverse the band gap, and draw the band diagram respectively.

A metal is an excellent conductor because, at room temperature, it has electrons in its conduction band constantly, with little or no energy being applied to it. This may be because of its narrow or nonexistent band gap, the conduction band may be overlapping the valence band so they share the electrons. The band diagram would be drawn with E_c and E_v very close together, if not overlapping.

The reason semiconductors are so popular is because they are a medium between a metal and an insulator. The band gap is wide enough to where current is not going through it at all times, but narrow enough to where it does not take a lot of energy to have electrons in the conduction band creating a current.

For a more detailed explanation, not to mention action, watch the movie. To run you will need the Shockwave plug-in for your browser. It will run properly in the Vectra lab, but not on the Sun workstations. Also, for better viewing, use the "full screen" on your browser. After viewing, to return to this page, you must use the "back" button on your browser.