20 question 

20. Explain why there is no net current across the p-n junction in equilibrium and how this equilibrium condition is achieved. What
is junction field? How can this junction field be increased? 

Dear Student,

At equilibrium( i.e zero bias condition) coulomb force from ions prevents further migration across the p-n junction. The electrons which had migrated across from the N to the P region in the forming of the depletion layer have now reached equilibrium. Other electrons from the N region cannot migrate because they are repelled by the negative ions in the P region which attracted by the positive ions in the N region. Thus as long as this depletion region exists, electrons cannot travel from one end to another, thus there is no net current.

Addition of a certain voltage i.e the junction is forward biased, destroys this depletion region and the pn diode starts conducting.

By junction field i hope you are not referring to JFET. In the context of P-N diode, junction field is the minimum voltage required after which the P-N diode starts conducting, i.e the field/voltage which is required to destroy the depletion region.

To increase the junction field value, i.e increasing the size of the depletion region can be achieved by increasing the doping concentration of the P-N region.



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