how N-type and P-type semiconductors are electrically neutral

N-type and P-type semiconductors are indeed electrically neutral in their bulk forms, and this neutrality is a fundamental characteristic of semiconductors. Here is why they are neutral despite containing charged carriers!

N-type Semiconductors

• In an N-type semiconductor, such as silicon doped with phosphorus, extra electrons are introduced as dopants.
• These extra electrons are negatively charged.
• However, these extra negative charges are precisely balanced by the positive charges associated with the phosphorus atoms themselves.
• The silicon lattice structure remains electrically neutral because the number of positive charges from the phosphorus atoms equals the number of negative charges from the extra electrons.
• In other words, the negative charge carriers (electrons) are counterbalanced by the positive charge carriers (phosphorus ions) in the bulk of the N-type semiconductor, resulting in an overall neutral charge.

P-type Semiconductors

• In a P-type semiconductor, such as silicon doped with boron, holes (vacancies for electrons) are introduced as dopants.
• Holes are considered as positive charge carriers.
• Just like in the N-type case, the presence of these holes does not disturb the overall electrical neutrality of the silicon lattice.
• The positive charge associated with the holes is offset by the negative charge of the electrons that surround them and maintain charge neutrality.
• When an electron from a host atom (e.g. Silicon) fills this level, the host atom is positively charged and the dopant atom (Boron) is negatively charged but the semiconductor as a whole is electrically neutral!

The key point to understand is that the introduction of dopants in semiconductors does result in the creation of charged carriers (either extra electrons in N-type or holes in P-type), but these charges are localized around the dopant atoms and are balanced by the opposite charge of the dopant ions. As a result, the bulk of the semiconductor material remains electrically neutral. This neutrality is crucial for the overall behavior and proper functioning of semiconductor devices in electronic circuits.