Question

Explain p-n junction diode in forward and reverse biased.​

Answer 1

p - n junction:

One side of a single crystal of germanium or silicon is doped with acceptor (p - type) impurity atoms and other side is doped with donor (n - type) impurity atoms.) The junction formed where p - type and n - type regions meet.

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• Extra

Depletion region:

1. When p - n junction is formed, electrons in n - region diffuse across the junction and combine with the holes in p - region.
2. This makes n - region to loose free electrons forming positive layer of holes near the junction, electrons gone in p - region combines with the holes in p - region and create negative layer of electrons near the junction.
3. Positive ion due is formed in n region and negative ion is formed in p region due near the junction.
4. Positive or negative ions can't move on freely. This results in depletion layer, which blocks the flow of electrons from n region to p region.

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Forward bias:

Positive terminal of the battery is connected to the p - region and negative terminal is connected to n - region.

The negative terminal of the battery repels the free electrons in the n - region towards the junction.

The electrons cross the junction and fall into holes.

Due to this free electrons become valence electrons.

Valence electrons leave the crystal and flow into the positive terminal of the battery.

Due to forward biasing the potential depletion region reduces. In forward biased condition, the resistance of a diode acts as a closed switch.

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Reverse bias:

• The positive terminal of a battery is connected to n - region and negative terminal to the p - region.

1. Free electrons in n - region are attracted due to positive terminal of battery. Holes in p - region are attracted due to negative terminal of the battery.
2. Due to this the width of depletion layer increases. The depletion layer stops increasing when it's differce of potential equals the source voltage.
3. The negative terminal of the external bias voltage pushes minority carriers in p - region, which passes easily in n - region and current is developed.