Question

Identify the property which is not characteristic for a semi-conductor______
1. at a very low temperatures it behaves like an insulator.
2. at higher temperatures two types of charge carriers will cause conductivity.
3. The charge carriers are electrons and holes in the valance band at higher temperatures
4. the semiconductor is electrically neutral. 
5. None of the above

Answer 1

Correct Answer - Option 3 : The charge carriers are electrons and holes in the valance band at higher temperatures

CONCEPT:

• The material which is not a good conductor or a good insulator is called a semiconductor.
• For example: Silicon
• The charge carriers which are present in more quantity in a semiconductor compared to other particles are called the majority charge carrier.

There are two types of semiconductors:

P-type semiconductor	N-type semiconductor
The semiconductor having holes as majority charge carriers and electrons as a minority charge carrier is called as P-type semiconductor.	The semiconductor having electrons as majority charge carriers and holes as a minority charge carrier are called N-type semiconductor.
When a trivalent impurity is doped in an intrinsic semiconductor then we got a P-type semiconductor. For example: gallium, indium	When a pentavalent impurity is doped in an intrinsic semiconductor then we got an N-type semiconductor. For example: Arsenic

EXPLANATION:

• At a very low-temperature valence band is full of electrons and the conduction band is empty, hence there are no free electrons in the conduction band and holes in the valence band. Hence semiconductor behaves like an insulator. Therefore option 1 is correct.
• As temperature increases, more and more hole and electron pairs are generated, and thus the two types of charge carriers will cause conductivity. Therefore option 2 is correct.
• At a very low-temperature valence band is full of electrons and the conduction band is empty but as temperature increase, more and more electron starts moving from the valence band to the conduction band. Therefore option 3 is incorrect.
• In a semiconductor, the number of electrons and holes are equal. Therefore the semiconductor is electrically neutral. Therefore option 4 is correct.