Question

Statement I : By doping silicon semiconductor with pentavalent material, the electrons density increases.
Statement II : The n-type semiconductor has net negative charge.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both Statement I and Statement II are true.
• B. Both Statement I and Statement II are false.
• C. Statement I is true but Statement II is false.
• D. Statement I is false but Statement II is true.

Hint:

Always remember: N-type or P-type semiconductors are electrically neutral. "N" stands for Negative carriers (electrons) being majority, not for a net negative charge.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Intrinsic semiconductors are doped with impurities to change their conductivity. Doping modifies the carrier concentration but must respect overall charge neutrality.
Step 2: Detailed Explanation:
1. Statement I: Silicon is tetravalent (4 valence electrons). Pentavalent dopants (like Phosphorus) have 5 valence electrons. Four electrons bond with Silicon, leaving one free electron. Thus, electron density increases. This statement is True.
2. Statement II: Although n-type semiconductors have more free electrons, they are formed by adding neutral dopant atoms to neutral Silicon atoms. For every free electron released, there remains a positive ion (the dopant nucleus) in the lattice. Therefore, the material as a whole remains electrically neutral. This statement is False.
Step 3: Final Answer:
Statement I is true but Statement II is false.