Why do the electron loose energy when it moves from base to collector region? In a npn transistor first emitter base junction is forward biased so electrons move to the base region . The electrons are minority carriers for base .now when base collector region is revered biased ,as the electrons injected in the base move towards the CB junction it gets easily transmitted to the collector region since the reverse bias produces a strong field which helps the electrons to move.so my question is the electron after reaching the CB junction feels a field i.e a force which further helps it to move to the collector region.so the electrons should be gaining energy and also reverse bias depletion region will not act as as a resistor.


1 Answer 1


The electric field between the CB junction and the Collector contact pulls the electrons to the Collector contact because it has a positive voltage compared to the Base and CB junction. The electrons loose potential energy as they travel from CB junction to the Collector contact.

Perhaps you are thinking about the speed of the electrons but that is irrelevant. You should think about the potential energy instead. Pulling an electron back to the CB junction would work against that electric field so would cost energy. So an electron traveliing to the collector contact looses potential energy.

  • \$\begingroup\$ Energy will be lost when resistance is provided but here the depletion region helps or instantly attracts electrons and doesn't provide resistance instead it gives a extra pull which should increase the energy \$\endgroup\$
    – user133636
    Dec 26, 2016 at 22:52
  • \$\begingroup\$ You go on about resistance, show me where in the literature about the subject anyone talks about electrons encountering resistance in this context. The movement of electrons is determined by diffusion and electric fields. I think you should loose this thought about electrons encountering resistance in a PN junction because (electrical) resistance is not something which is considered at the atomic level, which is what detemines the behavior in this case. Resistance describes how a certain material is able to allow current to flow depeding on the applied voltage. \$\endgroup\$ Dec 27, 2016 at 11:23
  • \$\begingroup\$ In case anyone is still reading this. Can we use the Fermi band diagram to explain this? clearly electrons are way lower in energy once in the C region. \$\endgroup\$
    – eliu
    Jun 24, 2020 at 23:03

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