Q1(i). Temperature and conductivity

Answer in brief

Heating creates many more mobile carriers in a semiconductor; in metals carrier density changes little while scattering increases.

Key points

• In an intrinsic semiconductor, thermal excitation promotes electrons across the band gap, creating electron–hole pairs. Approximately nᵢ∝ e^(-E_g/(2kT)) times a temperature prefactor.
• Conductivity is σ=q(nμₑ+pμₕ). Although phonon scattering reduces mobility, the rapid increase in carrier concentration usually dominates the intrinsic regime.
• In a metal, many carriers already occupy available conduction states. Heating increases lattice vibrations and electron scattering, reducing mobility and conductance.