[Physics] Thickness of depletion layer in p-n junction

semiconductor-physics

Why does the thickness of depletion layer decrease in forward biased and why is resistance almost 0 in it?I am presently in class 12 so kindly answer in as simple way as possible

Best Answer

Background knowledge: Before answering to the question, it is important to know how depletion region is formed?

When n-type semiconductor (having electrons as a majority charge carriers) is attached with p-type semiconductor ( having holes as charge carriers). As a result there is the formation of junction between the two semiconductors called p-n junction. Electrons are continuously vibrating and the electrons of n-type material near the p-type material will be attracted towards that, they will move to fill up the holes (present near the junction) of p-type semiconductor. As a result some holes will be produced in n-type side near the p-n junction. this is diffusion current because of concentration difference. Now after that there comes a situation when no more electrons will move from n-type to p-type, in other words now the electrons are not further attracted by p-type (positive) region but are repelled by already existing electrons (travelled electrons). (This creates a region called depletion region. NO MORE ENTRY REGION!!!)

Now the situation is like one side ( of n-type material )will have layer of positive charge carriers (we call it p-side of n-type semiconductor) and p-type semiconductor will have layer of negative charge carriers(we call it n-side of p-type semiconductor). This all happens when there is NO connection with any power supply.

Forward biasing: When the p-type semiconductor is connected with the positive terminal of the battery (higher potential terminal) and n-type semiconductor is connected with negative terminal, the electrons travel from lower potential to higher potential and gain energy to reduce the depletion/barrier region. The positive terminal of the battery repel the holes of p-type and attracts the electrons of its 'n' side and negative terminal will push the electrons of n-type semiconductor region and attract the holes of its 'p' side. Causing flow of electrons in the circuit. Its the electrons that gain energy from battery to cross that barrier, as a result we say that depletion region is reduced in forward biasing.

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