Zener breakdown: When reverse bias is increased the electric field at the junction also increases. At some stage the electric field becomes so high that it breaks the covalent bonds building electron, hole pairs. Thus a big number of carriers are created. This causes a large current to flow. This mechanism is called as Zener breakdown.
Avalanche breakdown: At high reverse voltage, because high electric field, the minorities charge carriers, while crossing the junction acquires very high velocities. A chain reaction is prepared, giving rise to high current. This mechanism is known as avalanche breakdown.
Special purpose diodes:
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Zener diode
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Light emitting diode (LED)
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Photo diode
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Solar cells
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It is a highly doped p-n junction which is not damaged by high reverse current. The breakdown voltage is made very sharp. In the forward bias, the zener diode acts as ordinary diode. It can be used as voltage regulator
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Specially designed diodes, which give out light radiations when forward biases. LED'S are made of GaAsp, Gap etc.
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In these diodes electron and hole pairs are created by junction photoelectric effect. That is the covalent bonds are broken by the EM radiations absorbed by the electron in the V.B. These are used for detecting light signals.
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It is based on the photovoltaic effect. One of the semiconductor regions is made so thin that the light incident on it reaches the p-n junction and gets absorbed. It converts solar energy into electrical energy.
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P-N junction diode as a Rectifier
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Half wave rectifier
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Full wave rectifier
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During positive half cycle
Diode → forward biased
Output signal → obtained
During negative half cycle
Diode → reverse biased
Output signal → not obtained
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During positive half cycle
Diode : D1 → forward biased
D2 → reverse biased
Output signal → obtained due to D1 only
During negative half cycle
Diode : D1 → reverse biased
D2 → forward biased
Output signal → obtained due to D2 only
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