How Diodes works

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A diode is the two-terminal semiconductor device which allows the current to flow only in one direction and blocks the current that flows in the opposite direction.

Symbol of the diode:








   A diode is made by connecting a part of N-type material to P-type Material,N-type material has excess of negative charged particles(electrons) whereas P-type material has excess of positive charged particles(holes).



As there are more holes in P-type and more electrons in N-type whenever both  are connected,holes will move from P-type to N-type and electrons will move from N-type to P-type and the holes and electrons combine and form depletion layer.In the depletion region , semiconductor will return back to the insulating state.



To remove the depletion region,you have to apply enough potential which will make the electrons will move from  N-type to P-type and holes will move P-type to N-type.To do this,connect the N-type to of the diode to the negative terminal of the battery and P-type of the diode to positive terminal of the battery.The electrons in the N-type will be repelled by the negative side of the battery electrode and move towards P-type and the holes will be repelled by the positive electrode and holes will move the other way.When the potential difference is more than the electrons in  the depletion region are boosted out of their holes and move freely again and depletion region disappears and charge flows.This connection of diode to the battery is also known as forward bias.



If you connect the diode to the battery in the other way. that is connecting the N-type is connected to the positive side of the battery and P-type is connected to the negative side of the battery. This connection is known as Reverse Bias. In this the holes present on the P-type are attracted towards the negative side and electrons in the N-type are attracted towards the positive side of the battery and hence no current flows in the other direction.





References:

1.http://electronics.howstuffworks.com/led1.htm
2.http://en.wikibooks.org/wiki/Semiconductor_Electronics/Diode/Construction_and_Operation

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