Silicon can be doped using one of the following elements as dopant:

(A) Arsenic

(B) Indium
(C) Phosphorus
(D) Boron

To get n-type semiconductor, the dopants that can be used are ________.
Fill in the blank with the correct answer from the options given below.

The correct option is (A) and (C) only.

To understand why this is the correct answer, let us look at the principles of semiconductor doping:
Silicon (Si) is a tetravalent element belonging to Group 14 of the periodic table, meaning it has 4 valence electrons. To obtain an n-type (negative-type) semiconductor, silicon must be doped with a pentavalent impurity (an element belonging to Group 15 of the periodic table) which has 5 valence electrons.

When a pentavalent atom replaces a silicon atom in the crystal lattice, four of its valence electrons form covalent bonds with four neighboring silicon atoms. The fifth valence electron is loosely bound and becomes free to conduct electricity, thereby increasing the concentration of negative charge carriers (electrons).

Let us analyze the given elements:
1. Arsenic (A): Belongs to Group 15 (pentavalent, 5 valence electrons). Doping silicon with Arsenic produces an n-type semiconductor.
2. Indium (B): Belongs to Group 13 (trivalent, 3 valence electrons). Doping silicon with Indium produces a p-type semiconductor.
3. Phosphorus (C): Belongs to Group 15 (pentavalent, 5 valence electrons). Doping silicon with Phosphorus produces an n-type semiconductor.
4. Boron (D): Belongs to Group 13 (trivalent, 3 valence electrons). Doping silicon with Boron produces a p-type semiconductor.

Therefore, to get an n-type semiconductor, the dopants that can be used are Arsenic (A) and Phosphorus (C) only.