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Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsSemiconductor Electronic: Material, Devices And Simple Circuits1 Mark
MCQ
When a P - N junction is unbiased, the junction current at equilibrium is:
  • A
    Zero as no charges cross the junctions.
  • B
    Zero as equal number of charge carriers cross the barrier in opposite directions.
  • C
    Mainly due to diffusion of majority charge carriers.
  • D
    Mainly due to diffusion of minority charge carriers.
✓

Answer

  1. Zero as no charges cross the junctions.

Explanation:

When a diode is connected in a Zero Bias condition, no external potential energy is applied to the PN junction. However if the diodes terminals are shorted together, a few holes (majority carriers) in the P-type material with enough energy to overcome the potential barrier will move across the junction against this barrier potential. This is known as the Forward Current.

Likewise, holes generated in the N-type material (minority carriers), find this situation favourable and move across the junction in the opposite direction. This is known as the Reverse Current and is referenced as IR. This transfer of electrons and holes back and forth across the PN junction is known as diffusion.

Then an Equilibrium or balance will be established when the majority carriers are equal and both moving in opposite directions so that the net result is zero current flowing in the circuit. When this occurs the junction is said to be in a state of Dynamic Equilibrium.

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