Impurities

For today’s technology pure materials are not the most valuable. Instead, a wide range of devices — from LEDs to computer chips — use almost pure materials into which a small quantity of a different element — an impurity has been introduced. Then materials with different impurities are joined.

Suppose we start with a pure material and add atoms of a different element. These different elements will have a different number of electrons than the atoms of the original material. We place the impurities into two groups:

• Donors have more electrons than the material’s pure elements. They donate electrons to the solid.
• Acceptors have fewer electrons than the material’s pure element. They accept electrons from the solid.

Both the donors and acceptors have zero electrical charge. They have more or less charge in the nucleus to balance the more or fewer electrons.

The LED chip consists of two solids – a material that has been supplied with donor atoms and the same material that has been supplied acceptor atoms. We will now use the LED Constructor computer program to understand how these two materials are combined to construct an LED.