What is the difference in mechanisms in which IB1 and IB2 are formed?

[anhnha]

Hi,
Can anyone help me? What is the difference in mechanisms in which IB1 and IB2 are formed in the picture below?

http://en.wikipedia.org/wiki/File:NPN_BJT_Basic_Operation_(Active).svg
Thanks.

 

[anhnha]

valence electrons or free electrons

Hi,
I am a bit confused about base current in BJT transistor. Please help.
Here is a picture from a lecture.

I want to ask about iB1 (hole injection from B to E).
Holes in base are injected into emitter and then they recombined with electrons in emitter.
Are electrons in emitter that recombine with holes from base valence electrons?
If, for example, all electrons in emitter that recombine with holes from base are free electrons then
hole injected from B to E iEp will not exist, right?

 

[anhnha]

Hi, can anyone help?

 

[anhnha]

iB1: holes in Base move from Base to Emitter
This is same as electrons from emitter, recombining with holes in Base to become valance electrons and they continue move to B.
iB2: electrons from emitters recombining with holes in Base and continue move to B
I don't see any difference. Please help.