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Draw the construction of PIN diode. Describe working principle.

Subject: Advance Communication System

Difficulty: Medium

Marks: 4 marks

1 Answer
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Operation:

Zero bias:

  • At zero bias the diffusion of the holes and electrons across the junction causes space charge region of thickness inversely proportional to the impurity concentration.
  • An ideal ā€˜iā€™ layer has no depletion region i.e. p layer has a fixed negative charge and n layer has a fixed positive charge.

Reverse bias:

  • As reverse bias is applied the space charge regions in the p and n layers will become thicker.
  • The reverse resistance will be very high and almost constant.

Forward bias:

  • With forward bias carrier will be injected into the I layer and p and n space charge regions will become thinner.
  • So the electrons and holes are injected into the i layer from p and n layers respectively. This increases the carrier concentration in the I layer above equilibrium. Thus resistivity decreases as increase in forward bias. Therefore low resistance is offered in the forward direction
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