Part 5: N-type and P-type

N-type and P-type semiconductor are created in a fabrication plant by adding elements to pure semiconductor under carefully controlled conditions. Both are better conductors than pure semiconductor, but it is the interaction between adjacent layers which creates electronic devices.

N-type Semiconductor

When elements with five valence electrons (such as arsenic, phosphorus and antimony) are added to pure silicon, the fifth electron is free to move through the crystal, much like the single valence electron in copper. These elements are referred to as donor elements. The resulting compound is known as N-type semiconductor. (This does not mean that it has a negative charge, merely that it has free electrons.) When a voltage is applied, the free electrons will move through the crystal.

P-type Semiconductor

P-type semiconductor is formed when elements with three valence electrons (such as boron, aluminium, gallium, or indium) are added to a pure semiconductor."Holes" are formed where the fourth electron would be, which can be filled by an available electron, so these elements are called acceptor elements. P-type semiconductor is electrically neutral, but when a voltage is applied, electrons can move through it by moving from one hole to another.