Difference between Depletion MOSFET and Enhancement MOSFET

In Enhancement MOSFET, the channel does not exist initially and is induced i.e the channel is developed by applying a voltage greater than threshold voltage, at the gate terminals.

On the other hand, in depletion MOSFET, the channel is permanently fabricated (by doping) at the time of construction of MOSFET itself.

That's it ! it is the only difference .

Lets analyse how this , small and the only , difference brings difference in their characteristics.

Depletion MOSFET

Depletion MOSFET is simply called D-MOSFET. Lets apply a voltage V_DS between D and S.

When,

V_GS=0 , current between drain and source flows due to implated channel.

V_GS = +ve , The gate behaving as capacitor, is charged by +ve V_GS .Therefore, the channel further grows as shown.

V_GS = -ve , The gate behaving as capacitor is charged by the gate-source voltage V_GS , but in opposite direction. Therefore, some of the channel charges are neutralised and the channel reduces.

The variation of I_D with V_DS is called drain characteristics given below.

Similarly, transfer characteristics are given by

Enhancement MOSFET

Enhancement MOSFET is simply called E-MOSFET. Lets apply a voltage V_DSbetween D and S.

V_GS = 0 , There will be no current flow between drain and source as there is no channel between them.

V_GS = +ve , Positive gate voltage with respect to source will charge the capacitor (gate acts as capacitor). Therefore, a channel is induced and current flows betwween D and S. As V_GSincreases, channel width increases and therefore, I_D increases.