What is the difference between an n-channel and a p-channel MOS transistor?
Negative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors.
The primary difference between an n-channel and a p-channel metal-oxide-semiconductor field-effect transistor (MOSFET) lies in the type of semiconductor material used and the charge carriers that facilitate current flow.12
- NMOS (n-channel): These transistors consist of n-type source and drain regions established in a p-type semiconductor substrate. A positive gate voltage attracts electrons to form a conductive channel, allowing current to flow. Because electrons have higher mobility in silicon than holes, NMOS transistors can generally operate at higher frequencies.12
- PMOS (p-channel): These consist of p-type source and drain regions formed in an n-type semiconductor material. A negative gate voltage induces a layer of holes, which act as the charge carriers to permit current flow.1
These devices respond in a complementary fashion to gate voltages: a voltage that turns an n-channel transistor on will typically turn a p-channel transistor off. When paired together in complementary metal-oxide-semiconductor (CMOS) circuits, they consume minimal power during standby, making them essential for modern microchips.31