Question

Why conductivity of conductor decreases while of semiconductor increases with increasing temperature?

Answer 1

Conductivity of a material depends on two factors
Factor 1: no,ofelectron in conduction band
Factor 2: Collision of conduction electron with core atom. Factor 1 increases conductivity and Factor 2 decreases.

Increase in temperature causes both factor to increases. For conductor factor 2 dominates over factor 1 because conduction and valence band overlap so all the electrons of valence band are already in conduction band hence there is no increase in conduction electron with temperature but collision rate of conduction electron with core atom increases resistance. For semiconductor factor 1 dominates over factor 2. As temperature increases electrons from valance band jump to conduction band. Hence, no. of electron in conduction band increases and conductivity increases.