An atom which is likely to give off one or more electrons when placed in a crystal. In semiconductors a donor material, such as phosphorus, is intentionally added to a pure semiconductor material in order to increase the population of free electrons in that semiconductor, resulting in a net negative charge.
A semiconductor that has had donor material added to it is called "n-type."
The free electrons are easily exited into the conduction band where they increase the electrical conductivity over that of an undoped semiconductor.
The level that donates conduction electrons to the system.