Question

The impurity element used for p-type semiconductor is

• A. Boron
• B. Bismuth
• C. Arsenic
• D. Phosphorus

Hint:

A helpful mnemonic to remember dopants is: \textbf{B-Al-Ga-In-Tl} (Elements of Group 13) are trivalent impurities that create \textbf{p-type} semiconductors (they are acceptor atoms). \textbf{P-As-Sb-Bi} (Elements of Group 15) are pentavalent impurities that create \textbf{n-type} semiconductors (they are donor atoms).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Semiconductors like Silicon (Si) and Germanium (Ge) belong to Group 14 of the periodic table and are tetravalent (have 4 valence electrons). Their electrical conductivity can be significantly increased by adding a small amount of a suitable impurity, a process called doping. This creates extrinsic semiconductors.
Step 2: Detailed Explanation:
p-type semiconductor: This type is formed when a tetravalent semiconductor (like Si) is doped with a trivalent impurity (an element with 3 valence electrons, from Group 13). The trivalent impurity atom replaces a silicon atom in the crystal lattice. It forms covalent bonds with three neighboring Si atoms, but there is a deficiency of one electron to bond with the fourth Si atom. This deficiency is called a "hole," which acts as a positive charge carrier.
n-type semiconductor: This type is formed by doping with a pentavalent impurity (an element with 5 valence electrons, from Group 15). The fifth electron is loosely bound and can easily become a free electron, acting as a negative charge carrier.
Step 3: Analyzing the Options:
(A) Boron (B): Belongs to Group 13, it is trivalent. Doping with Boron creates holes, resulting in a p-type semiconductor.
(B) Bismuth (Bi): Belongs to Group 15, it is pentavalent. Used for n-type doping.
(C) Arsenic (As): Belongs to Group 15, it is pentavalent. Used for n-type doping.
(D) Phosphorus (P): Belongs to Group 15, it is pentavalent. Used for n-type doping.
Step 4: Final Answer:
To create a p-type semiconductor, a trivalent impurity is required. Among the given options, only Boron is a trivalent element. Therefore, option (A) is correct.