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Semiconductors

In conductors there are a large number of free electrons which wander randomly in the conductor and are responsible for electrical conductivity. In insulators the electrons are tightly bound to the nuclei. There are some substances such as germanium and silicon which are neither good conductors nor insulators. Their conductivity lies in between that of conductors and insulators. Such substances are called semiconductors.
 
Diodes
 
When a donor impurity is added to one side and an acceptor impurity is added to the other side of a pure semiconductor, the first becomes n-type and the other side becomes p-type. This type of p–n junction that is formed is called a junction diode or a semiconductor diode.
 
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Biasing the Diodes
 
When the p–n junction is connected to an external source of emf, it is said to be biased.
 
Forward Biased When the positive terminal of a cell is connected to the p-side and the negative terminal to the n-side of a p–n junction, it is said to be forward biased.
 
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Reverse Biased When the positive terminal of a cell is connected to the n-side and the negative terminal to the p-side of a p–n junction, it is said to be reverse biased.
 
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The p–n junction allows current to pass through only in one direction. This action is called ‘rectifying action’ and the device is called a rectifier.
 
Applications of Diodes
  1. Diodes are used to convert AC into DC.
  2. Diodes are used as voltage regulators.





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