Determine the N-type drain and gate

When gate is made positive with respect to source and substrate, negative (i.e. minority) charge carriers within the substrate are attracted to positive gate and accumulate close to the surface of substrate.  As gate voltage is increased, more and  more  electrons  accumulate  under  the  gate.   As these  electrons  can't flow across the insulated layer of silicon dioxide to the gate, so they accumulate at the surface of substrate just below the gate. These accumulated minority charge carriers make N-type channel stretching from drain to source. When this takes place, a channel is induced by forming what is termed an inversion layer (n-type). N-type drain and gate are now connected by the n-type channel and current can flow from drain to source.