Carriers are the objects of interest when dealing with semiconductors.
If there is a lack of carriers, there is little or no current flow. If
carriers are present, either an electron in the conduction band or a hole
in the valence band, a negative or positive current, respectively, will
result. A semiconductor is doped to increase the concentration of one or
both carriers to create a larger current flow. If donors are added making
the electron the majority carrier, the semiconductor is said to be n-type.
For a p-type semiconductor, acceptors are added to make holes the majority
carrier.