N-channel JFET with gate open & V DD applied between drain and source Varying the value of V ds holding V gs constant
By varying the value of V gs we can vary the width of the channel.Ģ. As the reverse bias voltage increases the thickness of the depletion region also increases. Since there are no mobile carriers in the junction. So when no V ds is applied the depletion region is symmetrical and the conductivity becomes zero. But in N-channel FET P region is heavily doped than N-type thus depletion region extends more in N region than P region. If both P and N regions are heavily doped then the depletion region extends symmetrically on both sides. When a PN junction is reverse biased the electrons and holes diffuse across junction by leaving immobile ions on the N and P sides, the region containing these immobile ions is known as depletion region. 
The reverse bias is applied by a battery voltage Vgs connected between the gate and the source terminal i.e positive terminal of the battery is connected to the source and negative terminal to gate.
By Varying the value of V ds holding V gs constant. There are two ways to control the channel width 
When the negative gate bias voltage is further increased, the depletion regions meet at the center and Id is cut off completely. Its resistance is increased, and I d is reduced. The result is that the channel is narrowed. of charge carriers so it behaves as an insulator. 
Since depletion region is a region with less no.The channel is more lightly doped than the P-type gate blocks, so the depletion regions penetrate deeply into the channel. When the gate is biased negative with respect to the source, the PN junctions are reverse biased and depletion regions are formed.With the gate terminal not connected and the potential applied positive at the drain and negative at the source, a drain current I d flows.And the two pieces of P-type material are connected together and their terminal is called the gate.
The channel’s ends are designated the drain and the source. A piece of N-type material referred to as the channel, has two smaller pieces of P-type material attached to its sites, forming PN-Junctions. The overall operation of the JFET is based on varying the width of the channel to control the drain current. Since this channel is in the N-type bar, the FET is known as N-channel JFET.
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