Question

what changes does happen in a semiconductor (in the molecular level) such that the electrical resistivity drops suddenly to zero when they are cooled at sufficiently low temp.?

Answer 1

The conductivity of a semiconductor increases with increasing temperature, behavior opposite to that of a metal. From wiki

Answer 2

As per your theory , resistance would be less at high temp. but that's wrong .

Answer 3

and i wanted the the reason at molecular level. what happens at molecular level that it shows such behavior.

Answer 4

nsulator conductivity increases with temperature because heat provides energy to promote electrons across the band gap to the higher electron conduction energy levels (called the conduction band). Semiconductors, on the other hand, have an intermediate level of electric conductivity when compared to metals and insulators. Their band gap is small enough that small increase in temperature promotes sufficient number of electrons (to result in measurable currents) from the lowest energy levels (in the valence band) to the conduction band. This creates electron holes, or unoccupied levels, in the valence band, and very loosely held electrons in the conduction band.
I don't know how to explain it in human tongue rather then copy paste it from wikia. English isn't my main language.

Answer 5

And I believe I was right about resistivity.
As metal is heaten it losses it's conductivity and also increases it's resistivity if that's the right word.
Semiconductors, on the other hand, behave in opposite way. Electric current in semiconductors are created by both "holes" and "free-roaming electrons" while in metals it's just electrons.

Answer 6

Resistence in heaten metal increases because particles that were "thightly connected" starts vibrating and therefore disrupts the flow of electrons.
Semiconductors in case of heating "polarizes". Heating "gives so needed energy" for those electrons to jump out of their regular stance and therefore they "enchance" the possible current. THough you must remember that there is limited ammount of electrons in material so there is boundary when conductivity stops increasing because of heat.
I'm not sure if this is absolutely correct, it's just how I understand it.

Answer 7

Can I explain in terms of superconductor?

Answer 8

ya y not ???