UNBIASED TRANSISTOR

• An unbiased transistor means a transistor with no external voltage (biasing) is   applied.   Obviously,  there   will   be  no   current  flowing  from  any   of  the transistor leads.

• Since transistor is like two pn junction diodes connected back to back, there     are  depletion  regions  at  both  the  junctions,  emitter  junction  and  collector junction, as shown in the Fig

• During  diffusion  process,  depletion  region  penetrates  more  deeply  into  the lightly  doped  side  in  order  to include  an  equal  number  of  impurity  atoms  in the each side of the junction.

• As shown in the Fig. depletion region at emitter junction penetrates less i the heavily doped emitter and extends more in the base region.

• Similarly, depletion region at collector junction penetrates less in the heavily doped collector and extends more in the base region.

• As collector is slightly less doped than the emitter, the depletion layer Width  at the collector junction is more than the depletion layer width at the emitter junction.