P- and N- type semiconductors

The P in P-type and the N in N-type stand for positive and negative respectively.

P-Type semiconductor

The addition of trivalent impurities such as boron to the semiconductor creates holes. As can be seen, the acceptor impurity creates a hole as indicated by the arrowed circle.

N-Type Semiconductor

To illustrate how the N-type doping is like, we can look at the example below.

The addition of pentavalent impurities such as Antimony contributes free electrons, greatly increasing the conductivity of the semiconductor.

Similarly, the explanation of what an acceptor is -

The process of doping a semiconductor with an impurity which has fewer protons per atom (fewer electrons per atom) is done with the semiconductor accepting electrons from the impurity, thereby rendering the semiconductor an acceptor.

The atoms in a semiconductor will form bonds with neighbouring atoms in such a manner that each atom sees a “closed shell”. Since the acceptor atom introduces fewer electrons, the shell is not closed; all of the electrons are tightly bound. If an additional electron can be found, it will tend to fit the shell. The semiconductor atoms that have lost an electron are known as holes.

An acceptor-doped semiconductor is called a P-type semiconductor because it has positive charge carriers.

The purpose of P-type doping is to create an abundance of holes.

Bands for Doped Semiconductors

The application of band theory to N-type and P-type semiconductors shows that extra levels can be added by impurities. In N-type materials, there are electron energy levels near the top of the band gap so that they can easily move into the conduction band. In P-type materials, extra holes in the band gap allow electrons from the valence band, leaving mobile holes in the valence band.