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1 year ago in Electrical , Physics By Sylvia

Why does the conductivity of metals increase with decreasing temperature, semiconductors increase with increasing temperature, and alloys remain the same?

As I’m reviewing my solid-state physics notes for a PhD qualifying exam, I keep stumbling over this classic textbook question. In metals, conductivity rises as it gets colder; in semiconductors, it’s the opposite. And alloys seem unaffected. I understand the basic mechanisms electron scattering, band gaps, impurities but I'd really appreciate a clear, practical explanation that ties it all together in a way that sticks.

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By Adi Answered 3 months ago

From my work in the lab, I've observed this is all about what limits electron flow. In pure metals, cooling reduces lattice vibrations, so electrons scatter less conductivity goes up. With semiconductors, heating gives more electrons the energy to jump into the conduction band, so conductivity increases. For alloys, I've found the scattering from intentionally added impurity atoms is so dominant that temperature changes have a negligible effect. I'd recommend visualizing it as a competition between phonon scattering and charge carrier density.

   

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