When this occurs, a channel is induced by forming what is termed an inversion /ayer(N-type). Since these electrons can not flow across the insulated layer of silicon dioxide to the gate, so they accumulate at the surface of the substrate just below the gate. As the gate voltage is increased, more and more electrons accumulate under the gate. minority) charge carriers within the substrate are attracted to the positive gate and accumulate close to the-surface of the substrate.
This is the reason that it is called normally-off source voltage VGS MOSFET When the gate is made positive with respect to the source and the substrate, negative (i.e. The E MOSFET does not conduct when the gate- O. When drain is applied with positive voltage with respect to source and no potential is applied to the gate, a very small drain current that is, reverse leakage current flows. It operates with large positive gate voltage only. N CHANNEL ENHANCEMENT MOSFET OPERATION This MOSFET operates only in the enhancement mode and has no depletion mode.
The more positive the gate is made, more number of electrons from p substrate due to reverse leakage current and collisions between accelerating particles the more drain current flows. Here too much negative gate voltage can pinch-off the channel. In this mode of operation the device is referred to as a depletion-mode MOSFET.
The more negative the gate, the less the drain current. This creates a depletion region in the channel and, therefore, reduces the number of free electrons in the n channel, increases the channel resistance and reduces the drain current. This initiates recombination of holes and electrons. negative with respect to the substrate, the gate repels some of the When - negative charge carriers out of the N-channel ,and attracts holes from the p type substrate. In this mode of operation gate attracts the charge carriers from the P-substrate to the N- channel and thus reduces the channel resistance which increases the drain- current. OPERATION OF N CHANNEL DEPLETION MOSFET A D-MOSFET may be biased to operate in two modes: the Depletion mode or the Enhancement mode When /GS and drain is made positive with respect to source current(in the form of free electrons) can flow between source and drain, even with zero gate potential and the MOSFET is said to be operating in Enhancement mode.
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