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PN Junction Diode

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Published in: Physics
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Information about PN Junction Diode

Paridhi G / Indore

4 years of teaching experience

Qualification: M.Sc. Physics, B.Ed. , CTET

Teaches: Mathematics, Science, Physics

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  1. P-N JUNCTION DIODE
  2. P-NJUNCTION p-njunction is a boundary or interface between two types of semiconductor material/ p- type and n-type, inside a single crystal of semiconductor. It is created by doping.
  3. o Electronic Symbol .....the triangle shows indicated the direction of current P type N type Depletion layer forms an insulator between the 2 sides
  4. Formation of depletion layer the excess electrons in the N region cross the junction and combine with the excess holes in the P region. N region loses its electrons ......becomes + VIY charged P region accepts the electrons ......becomes -vly charged At one point , the migratory action is stopped.
  5. An additional electrons from the N region are repelled by the net negative charge of the p region. Similarly, o An additional holes from the P region are repelled by the net positive charge of the n region. o Net result a creation of a thin layer of each side of the junction which is depleted (emptied) of mobile charge carriers.... This is known as DEPLETION LAYER ..Thickness is of the order of 10-6meter.
  6. o The depletion layer contains no free and mobile charge carriers but only fixed and immobile ions. e Its width depends upon the doping level.. thin depletion layer e Heavy doped o lightly doped thick depletion layer
  7. POTENTIAL BARRIER The electrons in the N region have to climb the potential hill in order to reach the P region Electrons trying to cross from the N region to P region experience a retarding field of the battery and therefore repelled. Similarly for holes from P region. o Potential thus produced are called ..potential barrier Ge..O.3V Si ..o.7V
  8. PN junction can basically work in two modes, (A battery is connected to the diode ) Oforward bias mode ( positive terminal connected to p-region and negative terminal connected to n region) areverse bias mode ( negative terminal connected to p-region and positive terminal connected to n region) .
  9. Forward biased PN junction o. It forces the majority charge carriers to move across the junction ... .decreasing the width of the depletion layer.
  10. Once the junction is crossed, a number of electrons and the holes will recombine . o For each hole in the P section that combines with an electron from the N section, a covalent bond breaks and an electron is liberatyed which enters the positive terminal Thus creating an electron hole pair. Current in the N region is carried by ....electrons Current in the P region is carried by . . Holes.
  11. Reverse biased junction If the + of the battery is connected to the n-type and the - terminal to the p-type, the free electrons and free holes are attracted back towards the battery, hence back from the depletion layer, hence the depletion layer grows. Thus a reverse biased pn junction does not conduct current.
  12. o Thus the P N junction diode allows the electrons flow only when P is positive , o This property is used for the conversion of AC into DC , Which is called rectification.
  13. 40 30 20 10 40 Forward Bias Region 140 V (volts) 120 80 0.4 2 6 0.8 12 V (volts) Reverse Bias Region Figure 5.1: Diode Characteristics
  14. ADVANTAGES: o No filament is necessary Occupies lesser space o Long life,
  15. APPLICATIONS- as rectifiers to convert AC into DC. o As an switch in computer circuits. o As detectors in radios to detect audio signals o As LED to emit different colours.
  16. Thank you

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