PN Junction forward,Reverse biased

Explain how a PN junction operates when it is forward biased and reverse biased.

Forward Biased PN Junction

• An ext. Battery applied with +ve on p-side, −ve on n- side.

• The holes on p-side repelled from the +ve bias, the electrons on n- side repelled from the −ve bias.

• The majority charge carriers driven towards the junction.

• This results in a reduction of depletion layer width and barrier potential.

• As the applied bias steadily increased from zero onwards the majority charge carriers attempt to cross junction.

• An ext. Battery applied with +ve on p-side, −ve on n- side.

• The holes on p-side repelled from the +ve bias, the electrons on n- side repelled from the −ve bias.

• The majority charge carriers driven towards the junction.

• This results in a reduction of depletion layer width and barrier potential.

• As the applied bias steadily increased from zero onwards the majority charge carriers attempt to cross junction.

Reverse Biased PN Junction

• The external bias voltage applied with +ve on n-side, −ve on p- side.

• This Reverse bias aids the internal field.

• The majority carriers i.e. holes on p-side, the electrons on n- side attracted by the

negative and positive terminal of the supply respectively.

• This widens the depletion layer width and strengthens the barrier potential.

• Few hole-electron pairs are created due to thermal agitation (minority carriers).

• As a result, small current flows across the junction called reverse saturation current I0 (uA for Germanium, nA for Silicon).

• Behaves as a high impedance element.