Understanding Semiconductor Doping

Semiconductors are materials with electrical conductivity between conductors and insulators. Intrinsic semiconductors are pure materials like Silicon (Si) or Germanium (Ge). Doping is the process of intentionally adding impurities to these intrinsic semiconductors to modify their electrical properties.

Forming P-Type Semiconductors

Doping can create two types of semiconductors:

• N-type semiconductor: Created by doping with pentavalent impurities (elements with 5 valence electrons, e.g., Phosphorus (P), Arsenic (As)). These impurities donate extra electrons, which become the majority charge carriers.
• P-type semiconductor: Created by doping with trivalent impurities (elements with 3 valence electrons, e.g., Boron (B), Aluminum (Al)). These impurities create vacancies or 'holes' (absence of electrons) in the semiconductor crystal structure. These holes act as positive charge carriers and are the majority carriers in p-type semiconductors.

Analyzing the Dopant Options

Let's examine the options provided in the context of doping an intrinsic semiconductor:

• As (Arsenic): Arsenic is in Group V of the periodic table, having 5 valence electrons. Doping an intrinsic semiconductor with Arsenic introduces extra electrons, forming an N-type semiconductor.
• P (Phosphorus): Phosphorus is also in Group V, with 5 valence electrons. Similar to Arsenic, doping with Phosphorus creates an N-type semiconductor due to the excess electrons.
• B (Boron): Boron is in Group III, possessing 3 valence electrons. When Boron is used as a dopant, it lacks one electron to complete the covalent bonds with the surrounding semiconductor atoms (like Si or Ge). This creates a deficiency, or a 'hole', which can accept an electron. Therefore, doping with Boron results in a P-type semiconductor.
• Ge (Germanium): Germanium is an intrinsic semiconductor material itself (Group IV). Adding more Germanium does not introduce impurities to change the semiconductor type. It is typically the base material being doped.

Conclusion on P-Type Formation

To form a p-type semiconductor, we need to introduce impurities that create holes. Trivalent impurities achieve this. Among the given options, only Boron (B) is a trivalent impurity.