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.
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