Power MOSFET is a voltage controlled device and it requires only small input current.It has extremely high input impedance and is widely used in switching devices.The switching is high and the switching time is in the order of nanoseconds.They are used in low power high frequency converters.MOSFETs are of two types.

i) Depletion Type MOSFET ii) Enhancement type MOSFET

i) Depletion Type MOSFET

A depletion type n-channel MOSFET has a lightly doped p-type substrate into which two highly doped n-region(n+) are diffused.These two regions acts as drain and source.A thin insulating silicon dioxide layer is grown across the semiconductor surface.

The two holes cut into the oxide layer allow contact with the source and drain.A metal layer is then deposited on the oxide.This layer forms the gate.Due to the presence of silicon dioxide layer,the gate is insulated from the semiconductor.This layer results in very high input resistance.

A p-channel depletion type MOSFET consists of an n-type substrate into which two highly dopped p-regions and a p-channel are diffused.These two regions acts as drain and source.

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