- Free electrons in emitter are in conduction band.
- Free holes in base are in valence band.
- Since base is thin, most electrons pass the base while staying in the conduction band and enter the collector.
Since the life time of free electron in base region is quite large due to thin doping, is it possible for some free electrons in base region to reach the base terminal staying in the conduction band? That is can some base current happen entirely in conduction band avoiding the recombination?
In other words: Why must every electron that enters the base terminal be from the valence band? Why can't the base terminal attract few conduction band electrons like the collector?
EDIT: Intuitively it feels like the electrons that entered the base from emitter have 3 options:
- Go directly into the collector
- Recombine - fall into valence band and go out the base lead to the base supply
- Go directly out the base lead to the base supply