What are the Characteristics of pn junction diode?

The variation of diode current with the applied voltage to the junction diode is known as the characteristics of PN junction diode.

Basically there are 2 types of characteristics of pn junction diode i.e. Forward bias characteristics and Reverse bias characteristics.

Characteristics of pn junction diode

• Forward bias characteristics.
• Reverse bias characteristics.

Forward bias characteristics of pn junction diode

When the battery voltage is zero, diode does not conduct and the diode current is zero. As the battery voltage (V) is increased, the barrier potential starts decreasing and a small current begins to flow.

This is the circuit diagram to study forward bias characteristics.

The forward current increases slowly at first but as soon as the battery voltage becomes greater than the barrier potential (Vb), the forward current increases rapidly. The battery voltage at which the forward current starts increasing rapidly is known as knee voltage (Vk).

After knee voltage, the junction diode behaves almost like a conductor. And the variation of current with voltage applied across the junction diode is almost linear.

However, there is a limit of current that can pass through the diode without damaging it. This maximum current is known as maximum forward current. A high current through the diode produces a large amount of heat which may burn the diode.

Reverse bias characteristics of pn junction diode

When the p-n junction is Reverse biased, the majority carriers in the p and n region are repelled away from the junction. There is a small current due to the minority carriers.

This current attains its maximum or saturation value immediately and is independent of the applied reverse voltage. it depends on the temperature of the junction diode. 

This is the circuit diagram to study reverse bias characteristics.

As the reverse voltage is increased to a certain value, called breakdown voltage, large amounts of covalent bonds are broken. As a result of this, the last electron-hole pair is produced which diffuses through the junction, and hence there is a sudden rise in the reverse current.

Once breakdown voltage is reached, the high reverse current may damage the junction diode.The maximum reverse voltage that can applied to PN junction without damaging the junction is called peak inverse voltage (PIV).

The forward and reverse bias characteristics of junction diode is also known as voltage ampere characteristics. 

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