Construction of Uni Junction Transistor (UJT)

This transistor is similar to the BJT except it has only one junction. The schematic view of the UJT is given below –

As shown in above figure, the UJT is made up of an n-channel with a p-layer inserted into the channel nearer to base-2 than base-1.

Thus it has one PN junction with two internal resistances R_b1 and R_b2 such that R_b1 is the internal resistance between base-1 and emitter. And R_b2 is the internal resistance between base-2 and emitter. So it is clear that R_b1 >> R_b2 because emitter layer is nearer to base-2 than base-1.

The important parameter of the UJT is known as intrinsic standoff ratio as follows –

η = R_b1 / ( R_b1 + R_b2 )