Semiconductor Materials

Step 1: Understanding the Concept:
This question tests the definitions of p-type semiconductors, including the type of dopant atom used and the nature of the majority and minority charge carriers.

Step 2: Detailed Explanation:
A p-type semiconductor is created by doping an intrinsic semiconductor (like silicon or germanium, which are Group 14 elements) with trivalent impurity atoms (Group 13, e.g., Boron, Aluminium, Gallium).
- A trivalent atom has three valence electrons. When it replaces a silicon atom (which has four), it forms covalent bonds with three neighboring silicon atoms, leaving one bond incomplete. This creates a vacancy for an electron, which is known as a hole.
- This process introduces a large number of holes into the crystal lattice. These holes act as positive charge carriers.
- Therefore, in a p-type semiconductor, holes are the majority charge carriers. - Thermally generated electrons still exist, but they are far fewer in number than the holes. Thus, electrons are the minority charge carriers.
Let's evaluate the statements:
(A) Holes are minority carriers (Incorrect) and pentavalent atoms are the dopants (Incorrect).
(B) Electrons are majority carriers (Incorrect) and trivalent atoms are the dopants (Correct). The first part is wrong.
(C) Holes are majority carriers (Correct) and trivalent atoms are the dopants (Correct). This statement is entirely true.
(D) Electrons are minority carriers (Correct) and pentavalent atoms are the dopants (Incorrect). Pentavalent dopants create n-type semiconductors.

Step 3: Final Answer:
The options are: 1. (B) only, 2. (C) only, 3. (C) and (D) only, 4. (A) and (C) only. The best fit is option 2. Let's re-examine statement (D) one more time in case it is intended to be paired with something else. Pentavalent dopants are for n-type semiconductors, where electrons are majority carriers and holes are minority. Statement D mixes these up. It is definitively incorrect. So only (C) is correct.