Why does the width of the depletion region of a p-n junction diode increase when it's reverse biased by connecting it to an external voltage source?

  • $\begingroup$ Well, consider what happens if it does not - you have unbalanced forces on the charge carriers. $\endgroup$ – Jon Custer Jul 12 '16 at 14:56
  • $\begingroup$ In an open circuit p-n junction diode the field set up by the ionised donors and acceptors prevents the further diffusion of carriers. Reverse biasing increases the field strength across the depletion region. But why does the width of the depletion region increase? $\endgroup$ – Debasis buxy Jul 12 '16 at 15:22

In a somewhat simplistic explanation, since the N side is connected to the positive side of the external voltage source, electrons are attracted to that positive terminal. The same goes for the holes in the P side being attracted to the negative terminal. With an excess of electrons and holes at the end of the PN junction there is a buildup of positive and negative ions at the depletion region making it wider. @Debasis buxy is also correct about the E field strengthening.

This is a great site to explain both forward and reversed bias with some excellent diagrams: http://conceptselectronics.com/diodes/diode-biasing/

Hope this helps!

Check these out also or search for "energy bands in PN junction" or "potential energy barrier in PN junction" http://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun2.html http://ecee.colorado.edu/~bart/book/book/chapter4/ch4_2.htm

  • $\begingroup$ Ok I've understood why the width of the depletion region increases.... But can u explain when does the width stop increasing? $\endgroup$ – Debasis buxy Jul 12 '16 at 18:11
  • $\begingroup$ So, the depletion region can be thought of as an energy potential barrier and this energy barrier is increased by the added reverse bias (made lessen if forward biased). The stronger the reverse bias, the more it attracts the majority carriers to their respective terminals and the more wide the region becomes. $\endgroup$ – Garrettfromhp Jul 12 '16 at 18:33

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