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Explain the working of a pn-junction diode in forward- and reverse-biased modes. |
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Answer» Solution :Forward-biased mode: A PN junction diode is said to be forward-biased when the positive terminal of a battery is connected to the p side of the junction and the negative terminal to the n side In this case, the DEPLETION the potential barrier is lowered. Then the diode has a very low resistance.  The electrons travel from then side to the p side and go to the positiverminal of the battery. The holes that travel fron the p side to the n side combine with the electrons injected into the n-region from the negative terminal of the battery. This way, the diode conductswhen forward biased and acts as a closed switch. The total current across the junction is CALLED the forward current and is due to motion of both electrons and holes. Reverse-biased mode : A pn-junction diode is said to be reverse biased when the positive terminal of the battery is connected to the n side of the junction, and the negative terminal to the p side.  In this case, the depletion region widens and the potential barrier is increased so that the diode has a high resistance. The holes in the pregion combinewith the electrons injected into the pregion from the negative terminal of the battery.The way, the majority charge carrier concentration in each region decreases from the equilibrium concentration and the diffusion current across the jinction becomes zero. thus, the diode doesnot conduct when reverse biased and is said to be in a non-conducting state i.e., it acts as an open switch (ALMOST). However , there is a very small current due to the motion ofminority charge carries. The potential barrier sids the flow of minority CHANGE carriers, electrons in the p-region and holes in the n-region, to cross junction in opposite directions. This current is called the reverse current. |
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