1. When the width of depletion layer is different in P and N regions, why the ch
ID: 2248347 • Letter: 1
Question
1. When the width of depletion layer is different in P and N regions, why the charge stored on each side is same?
2. Why diffusion current or saturation current (Is) depends upon the temperature and not on the junction voltage (Vo)?
3. The the junction voltage (Vo) is about 0.7V in silicon diodes? Can we measure this voltage by voltmeter at the terminal of the diodes? If not why?
4. In forward bias diode the major component of current is diffusion current. This diffusion current consists of two parts. What are those two parts and are they majority carrier or minority carrier?
Explanation / Answer
1) The width of the depletion region in PN diode depends on the doping ,
width is inversely proportional to the doping in P and N region.If the doping is not done in equal ratio, the width will be different in P and N region.
As the P and N side is bonded, the majority charge carriers in N side (i.e electrons) diffuses inside P side and recombines with holes which is majority charge carrier in P side. This recombination generates positive ions in N side and negative ions in P side. The charge stored in either side due to ions will be same as these are created by majority charge carriers in each side , hence width can be different but charge stored is same.
2) The reverse saturation current is due to minority charge carriers which flows as the PN diode is reverse biased (i.e P side -ve potential and N side + potential).
In reverse biased condition the depletion region widens and no majority carrier is allowed to flow, only minority chare carrier flows, which is very less (in nanoamperes). Increasing the reverse voltage does not increases the saturation current.
But increasing the temperature increases the minority charge carriers hence increasing the saturation current.
3)As you will connect the voltmeter the charge carrier will start flowing through the voltmeter and you will not get correct potential in the diode.For measuring the voltage the voltage should be constant, current may vary
4).In forward bias , the depletion region reduces and becomes zero when volatge provided in more than 0.7 V .
In this situation diffusion current flows inside diode.
Electrons, which is majority charge carrier in N side diffuses to P side and holes which are majority charge carrier in P side diffuses to N side
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