Conductors vs semiconductors

Why metals conduct freely, insulators barely conduct, and semiconductors sit in between.

What you’ll learn

How free electrons differ across material types
The role of temperature
Why the difference comes down to energy bands

Why it matters

The conductor/insulator/semiconductor distinction is the foundation for everything that follows.

Explanation

In a conductor, huge numbers of electrons are free to move, so current flows with little resistance. In an insulator, electrons are tightly bound and almost none are free. A semiconductor has few free carriers at room temperature but that number rises sharply with temperature or doping.

Counter-intuitively, heating a metal *reduces* its conductivity (more atomic vibration scatters electrons), while heating a pure semiconductor *increases* it (more electrons gain enough energy to move).

Visual explanation

Three bars comparing free-carrier density: metal (very high), semiconductor (low, temperature-dependent), insulator (near zero).

Key terminology

Free carrier: An electron (or hole) available to carry current.
Resistivity: A material's intrinsic opposition to current flow.

Example

Copper conducts about 10^20 times better than glass; silicon lands many orders of magnitude in between and moves within that range as you dope it.

Common mistakes

Watch out for:

Assuming all materials conduct better when hot — pure semiconductors do, metals do not.

Real-world application

Temperature sensitivity is exploited in thermistors and must be managed in every chip's thermal design.

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