Q43
General SciencePhysics
Pure silicon at 0 K is
- a.semiconductor
- b.metal
- c.insulator
- d.superconductor
Answer: (C) insulator
In a pure (intrinsic) semiconductor at absolute zero ($0\,K$) the valence band is completely filled and the conduction band completely empty; with no thermal energy to lift electrons across the band gap (about $1.1\,eV$ for silicon) there are no free charge carriers, so it behaves as a perfect insulator. It starts conducting only as the temperature rises - the conductivity of a semiconductor increases with temperature, the opposite of a metal. A superconductor, by contrast, loses all resistance below a critical temperature (mercury at $4.2\,K$).