When a small amount of pentavalent impurity is added to a pure semiconductor ,it provides a large number of free electrons in the crystal forming n-type semiconductor . Also some of the covalent bonds break at room temperature releasing small number of electron-hole pairs. So, n-type semiconductor contains a large number of free electrons and very small number of holes. So current conduction in n-type semiconductor is mostly due to free electrons. Thus majority is of free electrons and holes are in minority.
Similarly, When a small amount of trivalent impurity is added to a pure semiconductor ,it provides a large number of holes in the crystal forming p-type semiconductor . Also some of the covalent bonds break at room temperature releasing small number of electron-hole pairs. So, p-type semiconductor contains a large number of holes and very small number of free electrons. So current conduction in p-type semiconductor is mostly due to holes. Thus, there is majority of holes and electrons are in minority.
Thus we concluded that,
A) In n-type semiconductors , the electrons are the majority charge carriers, whereas, the holes are the minority carriers.
B) In p-type semiconductor the holes are the majority carriers, whereas the electrons are the minority carriers.
What are the charges on n-type or p-type semiconductor?
It is to note that a semiconductor is whether intrinsic or extrinsic , it remains electrically neutral.
Talking about n-type semiconductor , electron-hole pair are generated by thermal energy. The negative charge of free electrons thus generated is exactly balanced by the positive charge of the holes. And there are additional free electrons created because of the addition of donor atoms. Negative charge of these electrons is again balanced by the positive charge on immobile ions.
So the total number of holes and immobile ions is exactly same as the total number of free electrons created. Similarly in n-type semiconductor ,total number of electrons and immobile ions is exactly same as the total number of holes created.
Note that :
1)Immobile ions : Immobile ions are not able to move or fixed of ions i.e. positive or negative ions.
2)Ions : An ion is an atom or molecule that has a net electric charge. Since in an atom the charge of the electron is equal and opposite to that of the proton, the net charge of an ion is non-zero due to its total number of electrons being unequal to its total number of protons. A cation is a positively charged ion, with less number of electrons than protons, while an anion is negatively charged, with more electrons than protons.
3)In a pure semiconductor there are not enough free electrons and holes to be of much use. Their number can be greatly increased however by adding an impurity, called a donor/acceptor. If impurity atom gives up some extra free electrons we get an n-type semiconductor (n for negative).
If the impurity soaks up some of the free electrons we get a p-type semiconductor (p for positive). In both cases the impurity donates extra current carriers to the semiconductor.In n-type semiconductors there are more electrons than holes and they are the main current carriers. In p-type semiconductors there are more holes than electrons and they are the main current carriers. The impurity atoms become either positive ions (n-type) or negative ions (p-type)(shown in fig. ) .
N-type semiconductor shown in fig above.(picture showing immobile ions,holes and free electrons). In an n-type semiconductor, there are a large number of free electrons, a few holes and a sufficiently large number of immobile positive ions . Black circle represent an electron, white circle represents a hole and an immobile positive Donor ion by an encircled plus sign. Note that no Silicon and Germanium atoms are shown in figure, they should be assumed as a continuous structure over the whole background. The fixed ions are regularly distributed in the crystal structure. But the holes and electrons being free to move are randomly distributed at moment.