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I would like to know why does the depletion region gets shrinked when a potential is given to a diode(Forward Bias).Is it because we have given a higher voltage than the voltage of the depletion region?But still how does that voltage turn out to break the depletion region?Could anyone help me.

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Without any voltage between the diode terminals there is an internal voltage across the pn junction caused by diffusion (diffusion voltage). This voltage leads to a stop of the diffusion process and causes a state of equilibrium - and results in a zone of depletion. Now - when we connect a voltage between the outer terminals in a direction opposite to the diffusion voltage the depletion zone is shrinked because the outer voltage acts against the internal diffusion voltage (two voltages in series with different polarities). The polarity of this voltage is called "forward bias".

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  • \$\begingroup\$ :Thanks for your answer.But could you explain what do you meant by:"outer voltage acts against the internal diffusion voltage" and the "two voltages in series".I'm just learning about diodes. \$\endgroup\$
    – justin
    Nov 26 '14 at 9:39
  • \$\begingroup\$ The internally developped diffusion voltage Vd is directed from the n region to the p region (from "+" to "-") because the n region has lost electrons due to diffusion. If the external voltage is directed from the p region to the n region it has an opposite direction to the diffusion voltage and reduces the state of equilibrium and, thus, the depletion zone. \$\endgroup\$
    – LvW
    Nov 26 '14 at 10:46
  • \$\begingroup\$ :But isn't external voltage connected as negative to n region and positive to p region or whether it's opposite as you said? \$\endgroup\$
    – justin
    Nov 26 '14 at 10:49
  • \$\begingroup\$ In the n-region we have a POSITIVE space charge because electrons (majorities) were moving into the p-region. And we connect the external voltage with its NEGATIVE side to the n-region. Thus, electrons are injected into this region and form/allow the current in "forward" direction. \$\endgroup\$
    – LvW
    Nov 26 '14 at 13:13
  • \$\begingroup\$ :Could you say which region you stated while saying about "electrons are injected into this region". \$\endgroup\$
    – justin
    Nov 26 '14 at 13:16

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