Diode in Reverse Bias and Breakdown | Electronics Device and Circuits | EC

by / Monday, 18 September 2017 / Published in Technical Corner

Real Life Applications:
We all are using voltage reference circuits (Voltage regulators) in real life. This is because of breakdown in diodes and some time it will exceed maximum power handling capacity of the device then it will burn out. So it is important to see exactly what is happening inside the device.

Explanation:
Diode in Reverse biased condition:
As we will provide higher potential to N- side with respect to P- side then this entire voltage will exist across the depletion region, due to which depletion region width will keep on increasing. If depletion region is increasing then capacitance offered by diode in reverse bias will keep on decreasing. Applied electric field will be in direction of built in electric field. So total electric field will support the flow of minority carrier (thermally generated) of depletion region. Electric field direction will be from N to P. So total current will flow from N to P. But minority generation at any temperature will be constant so this current will also be constant. This current is known as Reverse saturation current of diode.

Breakdown in diode:

1. Avalanche Breakdown: (In low doped diode)

Principle: Avalanche Multiplication

As we will increase reverse bias voltage across the diode then in the depletion region energy of minority carriers will also increase. If this energy of electron and holes are sufficient enough that it will be able to rupture the bond of silicon atom after collision then they will generate new electron hole pair. These newly generated EHP again collide with other atom also and this process will keep on increasing. Due to this very large current will flow from N to P. This chain reaction process of EHP generation is known as Avalanche Multiplication and this large flow of current in reverse bias is known as Avalanche breakdown.

   2. Zener breakdown:(In high doped diode)

Principle: Quantum mechanical tunneling

If doping is high of both the side and junction is abrupt then depletion region will be very narrow. So very high electric field will exist across depletion region. Now as we will increase the reverse bias voltage across diode then electron will penetrate this narrow depletion with by quantum tunneling mechanism without achieving barrier energy. This process is known as Quantum Mechanical Tunneling. When particles will move due to this mechanism then high voltage is not required and this will be controlled mechanism. This type of getting large current from N to P is because of Zener breakdown.

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