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how semiconductors work

Not everything falls so neatly into the two categories of conductor or insulator. Put a big enough voltage across any material and it will become a conductor, whether it’s normally an insulator or not. That’s how lightning works. When a cloud moves through the air picking up electric charge, it creates a massive voltage between itself and the ground. Eventually, the voltage is so big that the air between the cloud and the ground (which is normally an insulator) suddenly “breaks down” and becomes a conductor—and you get a massive zap of lightning as electricity flows through it.

Certain elements found in the middle of the periodic table (the orderly grouping of chemical elements) are normally insulators, but we can turn them into conductors with a chemical process called doping. We call these materials semiconductors and silicon and germanium are two of the best known examples. Silicon is normally an insulator, but if you add a few atoms of the element antimony, you effectively sprinkle in some extra electrons and give it the power to conduct electricity. Silicon altered in this way is called n-type (negative-type) because extra electrons (shown here as black blobs) can carry negative electric charge through it.

In the same way, if you add atoms of boron, you effectively take away electrons from the silicon and leave behind “holes” where electrons should be. This type of silicon is called p-type (positive type) because the holes (shown here as white blobs) can move around and carry positive electric charge.