- N Type Semiconductor Definition: An n-type semiconductor is defined as a type of semiconductor that has been doped with pentavalent impurities to increase its conductivity by adding free electrons.
- Doping Process: Doping involves adding impurities like antimony, arsenic, or phosphorus to a pure semiconductor, which increases the number of free electrons.
- Majority Carriers: In n-type semiconductors, free electrons are the majority carriers, meaning they primarily carry the electrical charge.
- Minority Carriers: Holes, created when covalent bonds break, are the minority carriers in n-type semiconductors.
- Electrical Neutrality: N-type semiconductors, despite having many free electrons, remain electrically neutral because the total number of protons equals the total number of electrons.
An n-type semiconductor is a crystal doped with pentavalent atoms so extra free electrons carry most of the current. Those extra electrons come from the dopant, not from a net charge on the lattice. Host atoms still tend toward eight valence electrons.
Electrons in the outer shell are valence electrons. If that shell has fewer than eight, the missing places are vacancies that can accept electrons.
Silicon and germanium are the usual hosts. Silicon has 14 electrons as 2, 8, 4. Germanium has 32 electrons as 2, 8, 18, 4. Both semiconductors have four valence electrons and four vacancies.
Each of those four valence electrons bonds to a neighbour, so the vacancies fill. In an ideal undoped crystal every valence electron is in a bond and none is free.
At 0o K that picture holds. Raise the crystal to room temperature and some bonded electrons leave, so a few free electrons appear. Those thermal electrons give the conductivity of the semiconductor above absolute zero.
Doping raises that conductivity further. An intrinsic semiconductor is given pentavalent atoms such as antimony, arsenic or phosphorus. Each donor sits on a host site. Four of its five valence electrons bond to four neighbours.
The fifth valence electron is not in a bond and is only loosely held. Room-temperature heat frees it.
Due to this phenomenon, there will be a considerable number of free electrons, but still, there are breakdowns of covalent bonds in the crystal due to thermal excitation at room temperature. The free electrons in addition to free electrons created due to the breakdown of a semiconductor to semiconductor and semiconductor to impurities covalent bonds cause the total of free electrons in the crystal.
Although whenever a free electron gets created during the breakdown of a semiconductor to semiconductor covalent bond, there is a vacancy created in the broken bond. These vacancies are referred to as holes. Each of these holes is considered as a positive equivalent of a negative electron as it gets created due to lack of one electron. Here electrons are main mobile charge carriers. In an n-type semiconductor there will be both free electrons and holes.
But the number of holes is quite smaller than that of electrons because holes are created only due to the breakdown of the semiconductor to semiconductor covalent bond whereas free electrons are created both due to loosely bounded non-bonded fifth valence electron of impurity atoms and breakdown of the semiconductor to semiconductor covalent bonds.
Hence free electrons >> holes.
Electrons are the majority carriers and holes the minority carriers in an n-type semiconductor. The name is negative-type because electrons carry most of the current. The crystal is still electrically neutral: every extra free electron is balanced by a proton on the donor ion.
