This question might get down votes, I presume, because it has already been asked before but I will still go for it.
In terms of doped Silicon:
Donor atom releases its 5th electron (and gets excited to conduction band) after some thermal energy occurs. Acceptor atom accepts extra electron after some thermal energy occurs (so the valence bond is satisfied). Acceptor atom becomes negatively charged ion. Donor atom becomes positively charged ion.
1.) After electrons are excited in conduction band and valence bonds are bonded, what happens next? Electrons flow out of the semiconductor bar, and new ones come inside?
2.) What is the point of transporting extra electron in conduction band if those extra electrons get to be pushed away from the semiconductor bar after specific amount of voltage is applied?
3.) Is it important for me to understand this in details if I want to become well-educated electrical engineer?