When an impurity like arsenic is added to germanium it will change the germanium crystal lattice in such a way as to leave one electron relatively free in the crystal structure. Because this type of material conducts by electron movement, it is called a negative carrier (N-type) semiconductor.
Pure germanium may be converted into an N-type semiconductor by doping it with a donor impurity consisting of any element containing five electrons in its outer shell. The amount of the impurity added is very small.
An impurity element can also be added to pure germanium to dope the material so as to leave one electron lacking in the crystal lattice, thereby creating a hole in the lattice. Because this semiconductor material conducts by the movement of holes which are positive charges, it is called a positive carrier (P-type) semiconductor.
When an electron fills a hole, the hole appears to move to the spot previously occupied by the electron. As stated previously, both holes and electrons are involved in conduction.
In N-type material the electrons are the majority carriers and holes are the minority carriers. In P-type material the holes are the majority carriers and the electrons are the minority carriers.
Conduction in this type of semiconductor is similar to conduction in a copper conductor. That is, an application of voltage across the material will cause the loosely bound electron to be released from the impurity atom and move toward the positive potential point.
In current flow through a P-type material, conduction in this material is by positive carrier (holes) from the positive to the negative terminal. Electrons from the negative terminal cancel holes in the vicinity of the terminal, while, at the positive terminal, electrons are being removed from the crystal lattice, thus creating new holes.
The new holes then move toward the negative terminal (the electrons shifting to the positive terminal) and are canceled by more electrons emitted into the material from the negative terminal. This process continues as a steady stream of holes (hole current) move toward the negative terminal.