The metal oxide semiconductor FET (MOSFETS)

The metal oxide semiconductor FET (MOSFETS): MOSFETS are another type of unipolar transistors which are similar, in many respects, to JFETS. MOSFETS also have drain, source and gate terminals similar to JFETS. Here also, the voltage across gate-source terminals contains the drain current. The only difference is that the gate terminal in a MOSFET is insulated from its channel region by using metal oxide. There are two types of MOSFETS.  They are:

        I.            Enhancement type or E-MOSFETS

      II.            Depletion type or D-MOSFETS

Enhancement type MOSFETS: These types of MOSFETS do not have channel formed during its construction. The voltage applied to the gate develops a channel of charge carriers. So, that a current flows when a voltage is applied across the drain source terminals. A channel is said to be enhanced by the application of suitable gate-source bias voltage. So, it is called enhancement MOSFET. There can be both n-channel & p-channel in E-MOSFETS.

Depletion type MOSFETS: These types of MOSFETS already have a channel present in it even when no gate voltage applied. The voltage applied to the gate determines whether the channel is increased or decreased. For an n-channel D-MOSFETS, if the channel is increased by applying positive gate voltage, then the channel is said to be enhanced or enhancement mode. If the channel is decreased by applying negative gate voltage, then the channel is said to be depleted or depletion mode. Hence, a D-MOSFET can be operated in both enhancement as well as depletion mode.