1.08 P type semiconductor.

Pure silicon is doped with a group 3 element, such as boron, aluminium or indium. These materials have atoms with three valence electrons (trivalent atoms). The three electrons will form covalent bonds with neighbouring silicon atoms. However there are not enough electrons to form the fourth covalent bond. This leaves a hole in the covalent bond structure and therefore a hole in the valence band of the energy level diagram. Every impurity atom will contribute a hole to the valence band. These holes will drift to produce an electrical current if a voltage is applied to the material and the P type semiconductor is more conductive than the intrinsic pure silicon material.

P type semiconductor

Again, it is important to point out that the material is called P type semiconductor because the mobile charge carriers produced by the doping process are positively charged holes. The P type material itself is of course not positively charged. (The positive charge of the virtual holes is actually representing the deficit in electrons in the covalent bonds around the donor atoms, which is balanced by the fact that the donor atoms also have one less positively charged proton than the silicon atoms).

Energy band diagram.

The diagram below shows an energy band diagram for P type semiconductor. The valence band contains holes due to the incomplete covalent bond around each donor atom. The conduction band is empty as there are no free electrons.

Energy band diagram for P type semiconductor