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How does a transistor work

This video explains how n-type and p-type semiconductors can be used to create a transistor.

The explanation

n-type semiconductors are made from silicon that has been doped with phosphorous.  The additional electron from the P can be used to form a current. P-type semiconductors are made by doping silicon with boron. Boron has a deficiency of electrons (positive holes). This also allows current to flow in the semiconductor. It refers to positive holes moving, yet does explain that it is the electrons moving into the vacancies that creates the current.

The construction of a npn transistor is shown.  Electrons from the n-types diffuse into the p-type to fill the holes.  This creates a depletion layer in the n-type.  The resultant negative charge in the p-type prevents other electrons moving across.  This is like a switch being off.  However, by applying a small positive voltage to the gate on the p-type the depletion layer is shrunk and electrons are then free to move through the transistor, i.e., placing a voltage switches the transistor on.

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