Question #917c9

2 Answers

Please, specify better the phrase "in states /ev f.u". :)

I can say you that more than values, in case of density of states in solids, is important the distribution of the permitted energy states values of the solid, in relation with energy of his external electron.

Distribution of the permitted states in a metal it is like that the maximum of energy of external-electrons is centered in a range of permitted states of conduction, and then the electrons has always the right energy to conduct electric current.

In an insulator, the maximum electron energy (Fermi level Ef), it is very far and lower from firsts permitted states of conduction. Then never there are electrons disposable to conduct current because the conduction band of conduction states is empty and too high in energy to be filled by the too low external electron energy.

In a semiconductor (intrinsic), the Fermi level Ef it is not centered in range of permitted state. However the necessary energy to promote electrons in the firsts conduction states (conduction band) is small enough or very small (Eg, energy gap), and then it is sufficient a small extra energy furnished by heat, by light, etc to send electrons in conduction bands and then transform an intrinsic semiconductor in a conductor, similar to a second rate metal.