Q7Electrical Materials
Question
Q.7. Discuss the effect of temperature on the conductivity of materials.
Answer
For metals, conductivity decreases with rising temperature (more lattice scattering); for semiconductors and insulators, conductivity increases with temperature as more carriers are thermally excited across the band gap.
Temperature affects conductivity oppositely in different material classes. In metals, the free-electron density is essentially fixed, but rising temperature increases lattice (phonon) vibrations, which scatter electrons more frequently, reducing mobility — hence metallic conductivity decreases (resistivity rises roughly linearly) with temperature. In semiconductors, rising temperature exponentially increases the number of carriers thermally excited across the band gap, and this carrier-generation effect overwhelms the mobility reduction — hence semiconductor conductivity increases strongly (resistivity falls) with temperature. Insulators behave like wide-gap semiconductors: normally negligible conduction, but conductivity rises measurably at very high temperatures as carriers gain enough energy to cross the large gap.