After the electrons enter the base region, they are first concentrated near the emitter junction, and gradually form a difference in electron concentration. Under the action of the concentration difference, the electron flow is promoted to diffuse to the collector junction in the base region, and is pulled into the collector by the electric field of the collector junction. region forms the collector current Ic. There is also a very small part of the electrons (because the base area is very thin) to recombine with the holes in the base area, and the ratio of the diffused electron flow to the recombination electron flow determines the amplification ability of the triode.