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pn
- junction diode or semiconductor diode
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INTRODUCTION
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| A pn - junction diode is an electronic device formed from a p-type and an n-type substance semiconductor. A semiconductor diode has the property of one way conduction i.e. it allows electric current to flow in only one direction. | ||||
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FABRICATION
OF pn-JUNCTION
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A
pn-junction is fabricated by placing a small amount of indium on a plate
or wafer of n -type germanium. Indium on heating at 550oC melts
and diffuses through a small part of the n-type germanium. Indium being
a p-type impurity, converts the part of the n-type germanium to p-type material.
Thus a junction is formed between p-type section and an n-type section of
germanium. A brass-base is used to fix the pn-junction to which leads are attached as shown: |
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| The whole apparatus is sealed in a glass tube or a metallic tube. | ||||
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WORKING
OF pn-JUNCTION DIODE
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| As
we know that a p-type substance has excess of mobile positive charge or
holes and n-type substance has an excess of negative charge or electrons,
the electrons from n-type and holes from p-type sections flow across the
junction and combine. In this way a layer of positive charges is formed
on the n-type and a layer of negative charges on p-type material. Due to induction of these layers a potential barrier is now developed across the junction and further flow of charges is prevented from one side to the other. |
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