Basic Construction of Junction FET (JFET)

BASIC CONSTRUCTION OF JUNCTION FET (JFET)

The JFET consists of a P-type (or) N-type silicon bar containing two PN junction at the sides as shown in fig.3.59.

If the silicon bar is N-type then it is called N-channel JFET and if the bar is P-type then it is called P-channel JFET.

For the fabrication of N-channel, a narrow bar of N type semiconductor material is taken on the opposite sides of its middle part, two heavily doped p-type regions are formed by diffusion.

This forms PN junction called as Gate (G). The gap between the gate is called a channel. The two P-regions are internally connected and single lead is taken out which is called gate junction. The two ends of N-type semiconductor bar one end is called Source (S) and the other as Drain (D).

When a potential difference between source and drain, a current flow from one end the other end in N-type material which forms a sort of channel and current flow due to majority carriers (electrons). Similarly a P-channel JFET fabricated by P-type semiconductor bar and diffusing N type junctions, in this case current flow due to majority carriers (holes) only.

The JFET three terminal functions:

Source: The source S is a terminal through which the majority carriers enter the bar.

 Drain: The drain D is a terminal through which the majority carriers leave the bar.