Hi. So my question is about npn bipolar transistors. As we know, the moment you apply high enough voltage to the base emitter junction swarms of electrons flow into the base where they recombine, they fill all the holes in there and those who are still free can't go back to the emitter because of the negative electric field from the acceptor ions and so they get sucked in the collector by its strong positive e field. No base voltage = no turning on.
And here comes the essential part of my question: if the collector is in possession of such a positive electric field, why can't it by itself free the electrons from the base-emitter junction? I remember reading this somewhere that the collector's electric field is not strong enough to reach that area and that's the reason why.

 

The collector-base junction is reversed bias, hence a depletion region is created. Electrons have difficulty crossing this region until the base-emitter current is increased.

 

Hi,

If you let the base float you might see some conduction because of the collector base leakage current which tends to power the base. That would be an unusual connection though.

 

No base voltage = no turning on.
And here comes the essential part of my question: if the collector is in possession of such a positive electric field, why can't it by itself free the electrons from the base-emitter junction?

It can. Look at the \( \small V_{CEO}\) parameter.

 

Thanks everyone!

 

And here comes the essential part of my question: if the collector is in possession of such a positive electric field, why can't it by itself free the electrons from the base-emitter junction?.

It can.
There is probably such a large electric voltage, where the transistor is open without being polarized in the base.

If you experience this, put a series of resistance to not burn it.

It should be the same as a reverse conduction in diode. Eg. zener diode,
https://ecee.colorado.edu/~bart/book/book/chapter4/ch4_5.htm
When the applied reverse voltage is large enough to create the electrical potential conditions, yes, the current can pass reverse.

Same at transistor.

NPN BJT - The electrons leave the emitter and reach the collector