The GATE Grind

GATE 2021 PH – Question 19

Solid State Physics · Metals, semiconductors and insulators · 1 mark · Multiple choice

Choose the correct statement.

  1. Silicon is a direct band gap semiconductor.
  2. Conductivity of metals decreases with increase in temperature.
  3. Conductivity of semiconductors decreases with increase in temperature.
  4. Gallium arsenide is an indirect band gap semiconductor.

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Show answer and explanation

Correct answer: (B) Conductivity of metals decreases with increase in temperature.

Explanation

In an ordinary metal, heating increases lattice scattering and reduces carrier mobility; carrier density changes relatively little. Its conductivity therefore decreases with temperature. Intrinsic semiconductor conductivity normally increases because thermally generated carriers increase strongly. Silicon has an indirect gap, whereas GaAs has a direct gap. Thus only B is correct.

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