Question

Assertion – Silicon is preferred over germanium for making semiconductor devices.
Reason – The energy gap for germanium is more than the energy gap of silicon.
A) Both assertion and reason are correct and reason is the correct explanation for assertion.
B) Both assertion and reason are correct but reason is not the correct explanation of the assertion.
C) Assertion is correct but reason is wrong.
D) Both reason and assertion are wrong.

Answer 1

Hint: We need to understand the materials used in making the semiconductors, the characteristics of these materials and the special properties possessed by these to differentiate between the materials used in serving as semiconductor devices

Complete step-by-step answer:
Semiconductor devices are those devices which exploit the special properties of the semi-metals or metalloids that can conduct electric current by the transfer of positive and negative charges.
The semiconductors have valence electrons which can ionise with very less energy. The electrons which are freed from the atoms creates a hole (a positive charge) in the system. The free electrons and the holes contribute to the current in these.
From the explanation we can understand that a semiconductor is more effective when it can easily ionise the electrons from the atom.
The ionization energy of the atom of an element is the energy gap of that element. It is the minimum energy required to ionise the electrons and make possible the conduction in the semiconductors.
We are given two semiconductors – silicon and germanium. The energy gap of silicon is 1.1eV whereas that of the germanium is 0.7eV.
But Silicon is widely used for making semiconductor devices, this is because silicon can control the creation of excess electron-hole pairs due to thermal energy involved. We need a controlled flow of current which can be guaranteed by a slightly larger energy gap.
Therefore, the given assertion is correct, but the reason is wrong.

So, the correct answer is “Option C”.

Note: If we use germanium instead of silicon in the semiconductor devices, the current through the circuit will become so high and uncontrollable, which is not favourable. Also, the germanium is costlier than the silicon and is therefore the most apt.