Question

Which one of the following elements, when present as an impurity in silicon makes it a $p$-type semiconductor?

• A. $As$
• B. $P$
• C. $In$
• D. $Sb$

Answer 1

The correct option is C $In$

Here, in figure, in place of $B$ we can use In to form the p-type semiconductor as both $B$ and $In$ are 3-valent dopants.
Indium has 3 valency, and when it is used in doping in silicon crystal then there is hole formation. and p-type semiconductor is formed.
The 3-valent dopants can catch an additional outer electron, thus leaving a hole in the valence band of silicon atoms. Therefore the electrons in the valence band become mobile. The holes move in the opposite direction to the movement of the electrons. The necessary energy to lift an electron into the energy level of indium as a dopant, is only 1 % of the energy which is needed to raise a valence electron of silicon into the conduction band.