File:Bjt forward active bands.svg

Summary
Energy band diagram of a simple NPN bipolar junction transistor in forward-active mode showing electron energy versus position. The depletion regions of the emitter-base and base-collector junctions are marked. $$E_c$$ is the conduction band, $$E_f$$ indicates the quasi-fermi energy levels, $$E_i$$ is the intrinsic Fermi level of the undoped semiconductor, and $$E_v$$ is the valence band. This band alignment is due to the biasing conditions that correspond with forward-active mode; forward bias on the emitter-base junction and reverse bias on the base-collector junction.