Question

The n-type semiconductor is
A) Neutral
B) Positively charged
C) Negatively charged
D) Negatively or positively charged depending on the amount of impurity added

Answer 1

Hint The n-type semiconductor is the class of semiconductors in which semiconductors are doped with impurities that have one more valence electron than the number of valence electrons in the semiconductor. The net charge of the semiconductor depends on the amount of positive and negative charges in it.

Complete step by step answer
An n-type semiconductor is an intrinsic semiconductor that is doped with elements from group V like phosphorus (P), arsenic (As), or antimony (Sb) as an impurity. The main element in such semiconductors is Silicon of Group IV that has four valence electrons.
Elements of Group V have five valence electrons so when an element of group V substitutes an atom from group IV, there is an extra electron in the semiconductor. So, the majority charge carrier is the electron. However, the net charge of the semiconductor will still be zero which means the semiconductor is neutral.
For e.g. If a small amount of phosphorus which has five valence electrons is added to a pure silicon crystal which has four valence electrons, one of the valence electrons of phosphorus becomes free to move around as an extra electron. When this free electron is attracted to the positive electrode and moves in the crystal, the current flows. In this case the semiconductor the extra electron charge is compensated by the extra ionic charge that phosphorus has compared to silicon which balances out the charge of the extra electron and hence the semiconductor is neutral which is choice (A).

Note
It is a common mistake to think of the semiconductor as negatively charged since electrons are the majority charge carriers in n-type semiconductor however we must remember that the net charge of the semiconductor will still be zero (hence neutral) since the impurity ion’s positive charge will balance the charge of the extra electron.