why nmos is preferred over pmos?
Answers
Explanation: Nmos is preferred over pmos because n-channel mosfets have a lower Rdson*cost metric. This means you can get the same Rdson for a lower cost with an n-channel device, and everyone wants lower cost.
Manufacturing costs for a pmos wafer are pretty much the same as an nmos wafer. But, pmos needs a much larger die for the same Rdson compared to nmos due to lower mobility of P-type silicon as others here have stated. Because the needed die is bigger, die per wafer will be lower and the die cost (wafer cost/die per wafer) for a pmos device of the same Rdson will be higher.
There are applications where a p-channel device makes economical sense. Using an n-channel device as a high-side switch requires extra circuitry to drive the gate voltage higher than the supply voltage (usually via a charge pump). If the switching frequency is low or switching losses are of little concern, a p-channel device becomes the lower cost solution as the extra cost of the extra circuitry is not needed.