Fermi level of p Type Semiconductor

A P-type semiconductor is an intrinsic semiconductor (like Si) in which an impurity acting as an acceptor (like e.g. boron B in Si) has been intentionally added. These impurities are called acceptors since once they are inserted in the crystalline lattice, they lack one or several electrons to realize a full bonding with the rest of the crystal.

Figure 5 : schematic representation of a Si crystal doped with boron (B)

From figure 5, we see that a p-type semiconductor has a lower electron density n and a higher hole density p than the same intrinsic semiconductor. Electrons are said to be the minority carriers whereas holes are the majority carriers.

For extrinsic semiconductors, the dopant density is always far higher than the intrinsic carrier density : NA>ni. In the case of a p-type material, the hole density is then close to the dopant density NA. Since the law of mass action is always true, we obtain the following expressions for the carrier densities

The Fermi level for a p-type semiconductor or chemical potential is then :

When the acceptor density is increased, the Fermi level moves closer to the edge of the valence band. If NA=Nv the Fermi level enters the valence band, the semiconductor is then said to be degenerate.