Question

1. Explain Accumulation, Depletion and Inversion Regions of a NMOSFET.

2. Why MOSFET is a voltage controlled current source? Why it is a FET?

Answer 1

1.In NMOS P- substrate contains holes that acts as majority carriers on applying negative voltage to gate leads to accumulation of holes at the interface this process is known as Accumulation.

Negative voltage is applied at gate to source -Vgs that will reduce the current in Nmosfet since it deplete the conduction channel. It operates as normally open switch. Thus due to reduction of conduction layer by negative voltage is known as Depletion Region.

Applying voltage between gate and body produces electric field that penetrates through oxide and creates a inversion layer. That provides the channel which passes current from source to drain.This region is known as Inversion region.

2. In Nmosfet when input voltage is applied to gate ir controlls the current from source to drain. Since the current through mosfet is controlled by voltage at gate thus mosfet is known as Voltage controlled device.

Mosfet is insulated from main current carrying channel. This thin layer of silicon dioxide seperates the gate electrode and acts as capacitor. Other than that mosfet structure and working is simillar to FET. Thus it belongs to FET. Since FET is also a voltage controlled device.