Question

The resistance of a semiconductor material (germanium or silicon) ______ with a rise in temperature.
A) Increases
B) Decreases
C) Remains the same
D) First increases then decreases

Answer 1

Hint : In this solution, we will use the properties of semiconductors to determine the change in resistance of semiconductor materials. The current in a semiconductor is carried through pairs of holes and electrons.

Complete step by step answer:
In a semiconductor, the current is carried by electron-hole pairs. When we increase the temperature of the semiconductor, the thermal energy will be transferred to the semiconductor material so more electron-hole pairs will be produced. For a solid crystal, the covalent bonds between the atoms and the electrons are broken through this thermal energy, and as a result, there are more electrons and holes in the system which can carry current. This implies that the resistance of the material is inversely proportional to the temperature of the system. If the temperature increases, the resistance increases, and vice versa.
Hence if the free electrons and hole pairs in the material increase, the resistance of the semiconductor material decreases. Germanium and silicon are both semiconductors of the same kind so for both, the resistance will decrease with increasing temperature.
Hence, the correct choice is option (B).

Note:
The decrease in temperature can also be thought of in terms of the temperature coefficient of resistance of semiconductors. For semiconductors, the coefficient is negative which implies that the resistance of the material will decrease with increasing temperature. For metals, the temperature coefficient is positive for most metals and negative for most non-metals. This implies that metals’ resistance will increase with an increase in temperature but for non-metals, the resistance will decrease with an increase in temperature.