Compared with a conductor, a pure semiconductor at room temperature has
- A. far fewer free charge carriers, and a conductivity that rises with temperature
- B. more free carriers
- C. the same number of carriers
- D. no carriers at any temperature
Explanation
A pure semiconductor has a small energy gap, so only a few electrons have enough thermal energy to cross it at room temperature, but heating promotes many more and conductivity climbs sharply. In a metal the carrier number is fixed and heating only increases scattering, so resistance rises. Doping raises the carrier concentration enormously without needing heat.