Ge Doping and P-Type Semiconductor Formation

When a pure semiconductor material like Germanium (Ge) is intentionally mixed with a small amount of an impurity element, this process is known as doping. Doping is crucial for altering the electrical conductivity of semiconductors, making them suitable for various electronic applications. Depending on the type of impurity added, either an n-type or a p-type semiconductor can be formed.

P-Type Semiconductor Formation with Boron

A p-type semiconductor is formed when a tetravalent semiconductor element, such as Germanium (Ge) or Silicon (Si) (both belonging to Group 14 of the periodic table), is doped with a trivalent impurity. Trivalent impurities are elements that have three valence electrons and belong to Group 13 of the periodic table.

• Boron (B) is a Group 13 element, having 3 valence electrons. When boron is introduced into the Germanium crystal lattice, it replaces a Ge atom.
• Since boron has only three valence electrons, it cannot complete the four covalent bonds required by the surrounding Germanium atoms. This creates a deficiency of one electron, which is known as a hole.
• These holes act as positive charge carriers and can readily accept an electron from a neighboring atom, thus enabling electrical conduction. Because these impurities "accept" electrons, they are called acceptor impurities.
• Therefore, doping Ge with boron leads to the formation of a p-type semiconductor, where holes are the majority charge carriers.

Comparison with Other Doping Impurities

Let's consider the other options provided and their effect on Germanium doping:

• Phosphorous (P): Phosphorous is a Group 15 element (pentavalent) with 5 valence electrons. When doped into Ge, it donates an extra electron, creating an n-type semiconductor where electrons are the majority carriers. These are called donor impurities.
• Arsenic (As): Arsenic is also a Group 15 element (pentavalent) with 5 valence electrons. Similar to phosphorous, doping Ge with arsenic forms an n-type semiconductor.
• Antimony (Sb): Antimony is another Group 15 element (pentavalent) with 5 valence electrons. Doping Ge with antimony also results in an n-type semiconductor.

In summary, to form a p-type semiconductor from Germanium (Ge), it must be doped with a trivalent impurity from Group 13. Among the given options, boron is the correct choice as it is a Group 13 element.