Question

Consider the following statements.
1. In a semiconductor, the uppermost band is the valence band.
2. All semiconductors are electrically neutral.
3. With increase of temperature, the resistivity of a semiconductor decreases.
4. Addition of a small amount of impurity of a III or V group elements to a pure semiconductor increases its resistivity.
Choose the correct statements.

• A. 1 and 2
• B. 2 and 3
• C. 3 and 4
• D. 1 and 4

Answer 1

Answer: (B)

2 and 3

In a semiconductor, upper most band is a conduction band.
Addition of impurity in the pure semiconductor increases the majority charge carriers which increases its conductivity and thus decreases its resistivity. So statements 1 and 4 are incorrect.
With increase in temperature, more electrons jump into the conduction band which increases its conductivity and decreases its resistivity. So statement 3 and 2 are correct becasue all the semiconductors are electrically neutral.