Q. Explain the working of depletion MOSFET ?

The gate voltage can control the resistance of the n-channel but as the gate is insulated from the channel, we can apply either a positive or a negative gate voltage.

When a negative voltage is applied to VGS, it will tend to pressure electrons toward the p-type substrate and attract holes from the p-type substrate. Depending on the magnitude of the negative bias established by VGS, recombination between electrons and holes will occur that will reduce the number of free electrons in the n-channel available for conduction. The more the negative bias, the higher the rate of recombination. The resulting level of drain current is therefore reduced with increasing negative bias for VGS. The device is said to be operating in the ‘depletion mode'.

When a positive voltage is applied to VGS, the positive gate will draw additional electrons from the p-type substrate due to the reverse leakage current and establish new carriers through the collisions resulting between accelerating particles. As the gate-to- source voltage continues to increase in the positive direction, the drain current will increase at a rapid rate. The device is said to be operating in the' enhancement mode'.