At the potential barrier, all that atoms are "satisfied"; they each have the appropriate number of electrons in their valence shell since the free electrons on the n-type side fill the holes on the p-type side. According the videos I have watched, when the gate is on, the electrons in the junction flow up into the gate to produce the emitter current. But these electrons are "satisfied" so why does this happen? Is it because the gate potential difference is high enough? or something else?