What is the difference between intrinsic and extrinsic semiconductors, and how does temperature affect their conductivity?

• A. Intrinsic semiconductors are doped; extrinsic are pure; intrinsic conductivity decreases with temperature; extrinsic increases with temperature.
• B. Intrinsic semiconductors are pure; extrinsic are doped; intrinsic conductivity increases with temperature; extrinsic conductivity increases with carrier concentration introduced by dopants but can saturate with temperature.
• C. Intrinsic semiconductors are liquids; extrinsic are solids.
• D. Intrinsic conductivity is independent of temperature; extrinsic never increases.

Answer: (B)

Intrinsic semiconductors are pure materials, so their conductivity comes from thermally generated electron–hole pairs. As temperature rises, more pairs form, and conductivity increases. Extrinsic semiconductors are doped with impurities that introduce energy levels near the band edges, providing extra carriers regardless of the pure material’s intrinsic excitation. Those dopants set the carrier concentration, so conductivity rises with the amount of dopant, but as temperature increases the dopants become fully ionized and further temperature rise mainly affects how easily carriers move, causing the conductivity to level off or increase more slowly.