Q. 20

To get a n-type semiconductor from silicon, it should be doped with a substance with valence__________.
A. 2

B. 1

C. 3

D. 5

Answer :

In order to build a n-type semiconductor from silicon, it has to be doped with electron-rich impurities (element having more valence electrons).


As group 14 element Si has 4 valence electrons, therefore to get an extra electron carrier for the semiconductor it has to be doped with elements of valency 5 i.e. group 15 elements such as P or As.


Four out of five electrons of group 15 element (P or As) will be forming four covalent bonds with the four silicon atoms which are adjacent.


The fifth valence electron of the group 15 element now becomes an extra and gets freed and delocalised. These delocalised electrons enhance the conductivity of doped silicon.



Hence, other 3 options (i) 2 (ii) 1(iii) 3 are incorrect, because their doping would not form any n type semiconductor.

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