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This simple animation video clearly explains the topics PN junction semi conductor or diode, what is forward bias and reverse bias, what is diffusion current and drift current, what is avalanche breakdown etc

What is a P N junction semiconductor and how is it formed?

The PN junction semi conductor is a combination of P type semiconductor with N type semiconductor to achieve the practical utility of both. It's formed, when a P type semi conductor is joined to an N type semiconductor.

The P type semiconductor has free holes with positive charged and the N type semiconductor has free electrons with negatively charge.

What happens when a PN junction is made?

When P and N semiconductors are joined to make the PN junction semiconductor diode, the electrons near the PN junction jump from N to P and holes near the junction jump from P to N. This phenomenon creates a space charge region or a depletion layer as shown in the video. At this space charge region due to the movement we have electrons in P region and holes in N region. For some time the electrons move back from P to N in the space region or depletion layer and some holes move back from N to P in the space region. This continues to happen till equilibrium is reached. This movement of electrons and holes in the space region or diffusion layer gives rise to Diffusion current.

What is Forward bias and how does it occur?

Forward bias occurs when the positive terminal of battery is connected to the P region and the negative terminal of battery is connected to the N region. In this condition what happens is the positive terminal repels the holes towards the junction and the negative terminal repels the electrons towards the junction. Due to this repulsion, the depletion region or space region narrows down as shown in the video.

But at a particular condition, If the voltage in the forward bias is above a specified range, the electrons in the N region drifts through the junction and migrates to the P region and the holes in the P region drifts through the junction and migrates to the N region.

Now the current flows across the circuit and this current are called the Drift current.

What is Reverse bias and how does it occur?

Reverse bias occurs when the negative terminal of the battery is connected with the N region and positive terminal with the P region. In this condition holes (positively charged) from the P region get attracted to the negative terminal of the battery and electrons (negatively charged) get attracted to the positive terminal of the battery. This results in the depletion layer to widen up.

Now the PN junction acts as an insulator and will not allow any current to flow in the circuit. But at a condition, if the battery voltage is above a particular limit, which is called as the reverse bias breakdown voltage level. Electrons and the holes breakdown through the PN junction and cross over resulting in the current to flow through the circuit. This break down is called avalanche breakdown

In this process the current flowing through the PN junction is very high and ultimately the PN junction gets damaged due to overheating caused by the excess flow of current.
This is how a PN junction semiconductor works.



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Answer to all the below questions are available in this video:

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