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Silicon has 4 electrons in outer layerIt wants 8                 Si
• Silicon atoms can share electrons with  other atoms to get 8 electrons in outer  layer.• Silicon atoms combining togethe...
all silicon atoms in a         crystal
Doping• Doping means adding other kinds of  atoms to the silicon crystal.• Phosphorus and Arsenic atoms have 5  outer elec...
As        As        AsAs        As     As                    As               As        AsAs
extra electronsin Arsenic atoms
Al        Al                        Al     holes (missing electrons)        in Aluminum atoms Al                AlAl      ...
• N type material = semiconductor with  extra negative charges (extra electrons)• P type material = semiconductor with ext...
PN Junction• What happens when P type material and  N type material are placed together?
• Electrons from Arsenic atoms in N type  material are attracted to holes (missing  electron positions) in Aluminum atoms ...
+   -+   -+   -
• Atoms have the same number of electrons  as protons.• When electrons leave Arsenic atoms, they  now have more protons th...
N Type           P Typeextra electrons   holes (missing electrons)
N Type           P Typeextra electrons   holes (missing electrons)
N Type            P Typeextra electrons   holes (missing electrons)           depletion zone
• Harder and harder to get the depletion  zone to be wider because  – electrons are repelled by negative aluminum    ions ...
N Type            P Typeextra electrons   holes (missing electrons)           depletion zone
N Type            P Typeextra electrons   holes (missing electrons)           depletion zone             stabilized
What happens when a voltage source    is applied to the 2 ends of thediode?
• Electrons are pushed from the negative  supply into the N side of the diode.• Holes are pushed (electrons are drained)  ...
What happens when a voltage source    is applied to the 2 ends of thediode?
As more and more charges build up,  easier for charges to move across the  depletion zoneCurrent flows as electrons flow f...
Forward Biased• To cross depletion zone, must apply  enough voltage (pressure or push) to get  electrons past negatively c...
What happens if the voltage  polarity is reversed?
What happens if the voltage  polarity is reversed?       depletion zone           widens
Reversed Bias• When diodes are reverse biased, depletion  zone widens• Harder for charges to cross depletion zone• High en...
Semiconductors, how they work
Semiconductors, how they work
Semiconductors, how they work
Semiconductors, how they work
Semiconductors, how they work
Semiconductors, how they work
Semiconductors, how they work
Semiconductors, how they work
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Semiconductors, how they work

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Semiconductors, how they work

  1. 1. Silicon has 4 electrons in outer layerIt wants 8 Si
  2. 2. • Silicon atoms can share electrons with other atoms to get 8 electrons in outer layer.• Silicon atoms combining together forms a crystal.• Pure silicon crystals are not good electrical conductors, they are insulators.
  3. 3. all silicon atoms in a crystal
  4. 4. Doping• Doping means adding other kinds of atoms to the silicon crystal.• Phosphorus and Arsenic atoms have 5 outer electrons.• Aluminum and Gallium have 3 outer electrons.• Doping makes the crystal into a semiconductor.
  5. 5. As As AsAs As As As As AsAs
  6. 6. extra electronsin Arsenic atoms
  7. 7. Al Al Al holes (missing electrons) in Aluminum atoms Al AlAl Al Al
  8. 8. • N type material = semiconductor with extra negative charges (extra electrons)• P type material = semiconductor with extra positive charged holes (fewer electrons or missing negative charges)
  9. 9. PN Junction• What happens when P type material and N type material are placed together?
  10. 10. • Electrons from Arsenic atoms in N type material are attracted to holes (missing electron positions) in Aluminum atoms in P type material.• Electrons from N type material move and fill in holes in P type.
  11. 11. + -+ -+ -
  12. 12. • Atoms have the same number of electrons as protons.• When electrons leave Arsenic atoms, they now have more protons than electrons.• Arsenic atoms become positive ions.• When aluminum atoms pick up extra electrons, they now have more electrons than protons.• Aluminum atoms become negative ions.
  13. 13. N Type P Typeextra electrons holes (missing electrons)
  14. 14. N Type P Typeextra electrons holes (missing electrons)
  15. 15. N Type P Typeextra electrons holes (missing electrons) depletion zone
  16. 16. • Harder and harder to get the depletion zone to be wider because – electrons are repelled by negative aluminum ions – holes are repelled by positive arsenic ions
  17. 17. N Type P Typeextra electrons holes (missing electrons) depletion zone
  18. 18. N Type P Typeextra electrons holes (missing electrons) depletion zone stabilized
  19. 19. What happens when a voltage source is applied to the 2 ends of thediode?
  20. 20. • Electrons are pushed from the negative supply into the N side of the diode.• Holes are pushed (electrons are drained) from the P side of the diode into the positive side of the supply.
  21. 21. What happens when a voltage source is applied to the 2 ends of thediode?
  22. 22. As more and more charges build up, easier for charges to move across the depletion zoneCurrent flows as electrons flow from N typethrough holes of P type out to positive source
  23. 23. Forward Biased• To cross depletion zone, must apply enough voltage (pressure or push) to get electrons past negatively charged region of depletion zone.• Forward bias voltage about 0.7 V for silicon diodes and 0.3 V for germanium diodes.
  24. 24. What happens if the voltage polarity is reversed?
  25. 25. What happens if the voltage polarity is reversed? depletion zone widens
  26. 26. Reversed Bias• When diodes are reverse biased, depletion zone widens• Harder for charges to cross depletion zone• High enough voltage will force charges across depletion zone – Heat from large reverse current destroys diode – Breakdown voltage = voltage level that causes diodes to conduct when reverse biased

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