why does depletion region decreases in case of forward bias please explain ? also explain why it increases in case of reverse bias

Asked by Sounak das | 11th Nov, 2014, 04:55: PM

Expert Answer:

Depletion Region:
The thin layer region on both sides of a p-n junction which has immobile ions and is devoid of any charge carrier is called depletion region or depletion layer.
Forward Bias:
A p-n junction is said to be forward biased if the positive terminal of the external battery is connected to p-side and the negative terminal to the n-side of p-n junction.In forward biasing the voltage drop across p-side and n-side of the p-n junction is negligibly small. 
During forward biasing, the applied d.c voltage opposes the fictitious battery developed across the p-n junction. Due to this the potential drop across the junction decreases and as a result the diffusion of holes and electrons across the junction increases.It makes the depletion layer thin and as such the junction diode offers low resistance during forward bias.
 
Reverse Bias:
A p-n juction is said to be reverse biased if the positive terminal of the battery is connected to n-side and the negative terminal to the p-side of the p-n junction.
In reverse biasing the applied voltage of battery mostly drops across the depletion region of the p-n junction and its direction of voltage is same as that of the potential barrier.Due to it, the reverse bias voltage supports the potential barrier. 
i..e during reverse biasing the applied dc voltage aids the fictitious battery developed across the junction. Due to this the potential drop across the junction increases and as a result the diffusion of holes and electrons across the junction decreases. It makes the depletion layer thick and the juction diode offers high resistance during reverse bias. 
 

Answered by Jyothi Nair | 12th Nov, 2014, 09:20: AM

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