Question

Which of the following is/are true about semiconductors?

• A. Resistivity decreases with rise in temperature.
• B. Resistivity is influenced by the presence of small amount of impurities.
• C. Number of free charge carriers per unit volume decrease with rise in temperature.
• D. Number of free charge carriers per unit volume, is independent of the temperature.

Answer 1

Answer: (A), (B)

The correct options are
A Resistivity decreases with rise in temperature.
B Resistivity is influenced by the presence of small amount of impurities.

As the temperature increases, more number of bounded electrons acquire sufficient energy and become free or unbounded. Now they can also participate in the conduction process. Thus number of free charge carriers per unit volume also increases thereby decreasing the resistivity. Furthermore with addition of impurities similar influence comes into picture and again resistivity is brought down.