P-type Semiconductor Doping

An extrinsic semiconductor is created by adding impurities to an intrinsic semiconductor like Silicon (Si) or Germanium (Ge). Intrinsic semiconductors have 4 valence electrons per atom and form perfect covalent bonds.

There are two main types of extrinsic semiconductors:

• N-type semiconductor: Doped with impurities that donate excess electrons.
• P-type semiconductor: Doped with impurities that accept electrons, creating "holes".

Impurity Valence Electrons in P-type

To create a P-type extrinsic semiconductor, the intrinsic semiconductor (like Si or Ge, which have 4 valence electrons) is doped with an impurity element that has fewer valence electrons than the semiconductor atoms. Specifically, an impurity element with 3 valence electrons is used. These impurities are often from Group 13 of the periodic table, such as Boron (B), Aluminum (Al), or Gallium (Ga).

When an atom with 3 valence electrons replaces a semiconductor atom (with 4 valence electrons) in the crystal lattice, it forms covalent bonds with three of its neighboring semiconductor atoms. However, it cannot form a complete bond with the fourth neighbor because it only has 3 valence electrons. This results in a missing electron, which is known as a hole.

This hole acts as a positive charge carrier and can accept an electron from a neighboring atom, causing the hole to move through the crystal. In P-type semiconductors, holes are the majority charge carriers.

Therefore, a P-type extrinsic semiconductor is doped with an impurity having 3 valence electrons.