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EST 130, Semiconductors

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EST 130, Semiconductors

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The attached narrated power point presentation mentions the different materials used for the construction of semiconductors. It offers structural and energy level explanation on the properties exhibited by the semiconductor materials. It also throws light on the structure and behaviour of a PN junction and use of PN junctions in active electronic components. The material will be useful for KTU first year students who prepare for the subject EST 130, Part B, Basic Electronics Engineering.

The attached narrated power point presentation mentions the different materials used for the construction of semiconductors. It offers structural and energy level explanation on the properties exhibited by the semiconductor materials. It also throws light on the structure and behaviour of a PN junction and use of PN junctions in active electronic components. The material will be useful for KTU first year students who prepare for the subject EST 130, Part B, Basic Electronics Engineering.

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EST 130, Semiconductors

  1. 1. 1 Semiconductors MEC
  2. 2. 2 Contents • Definitions. • Energy Band Diagrams. • Intrinsic Semiconductors. • Extrinsic Semiconductors. • Comparison. • PN Junction. • PN Junction Applications.
  3. 3. 3 Definitions • Energy Band : The range of energies possessed by an electron in a solid. • Valence Electron : Electrons in the outermost orbit of an atom. • Valence Band : Range of energies possessed by valence band electrons. • Conduction Band : Range of energies possessed by free electrons.
  4. 4. 4 Definitions • Fermi Level : - highest energy level that an electron can occupy at the absolute zero temperature. - lies between valence and conduction bands at absolute zero temperature. - tends to change as solids are warmed. - value of Fermi level at absolute zero temperature known as Fermi energy.
  5. 5. 5 Definitions • Forbidden Energy Gap : - gap between valence band and conduction band. - electron can be moved from valence band to conduction band by applying energy more than forbidden energy gap. • Hole : absence of an electron, +ve charge.
  6. 6. 6 Energy Band Concept 6 eV 1.1 eV/0.72 eV
  7. 7. 7 Fermi Level in Solids Top of the collection of electron energy levels at absolute zero temperature.
  8. 8. 8 Semiconductors • Resistivity: 10-5 to 106 Ωm. • Conductivity: 105 to 10-6 mho/m. • Temperature coefficient of resistance: Negative. • Current Flow: Due to electrons and holes. • Materials: Silicon, Germanium, Gallium Arsenide.
  9. 9. 9 Semiconductor Types
  10. 10. 10 Comparison
  11. 11. 11 Doping
  12. 12. 12 Doped Semiconductors
  13. 13. 13 Intrinsic Semiconductors
  14. 14. 14 Intrinsic Semiconductors
  15. 15. 15 Fermi Level
  16. 16. 16
  17. 17. 17
  18. 18. 18 Compound Semiconductor - Gallium Arsenide Face Centered Cubic Structure (FCC)
  19. 19. 19 Compound Semiconductors Gallium Arsenide Crystal Structure
  20. 20. 20 PN Junction Concentration gradient causes carriers to move to the other side of the junction. Potential Barrier opposes carrier movement. Junction Depletion Region Forward bias reduces the width, reverse bias increases the width. Immobile ions VB = 0.7 V for Si. = 0.3 V for Ge. Holes Electrons
  21. 21. 21 Biasing a PN Junction • Forward Bias – Positive terminal of the battery connected to the P - type material, negative terminal of the battery connected to N - type material. • Current flow during forward bias. • Reverse Bias – Positive terminal of the battery connected to the N - type material, negative terminal of the battery connected to P - type material. • No current flow during reverse bias.
  22. 22. 22 Biased PN Junctions
  23. 23. 23
  24. 24. 24 Comparison
  25. 25. 25 Applications of PN Junction • Elementary building blocks of active (semiconductor) electronic components or devices. • Semiconductor Diode – One PN Junction. • Bipolar Junction Transistor – Two PN Junctions. • Thyristors – Multiple PN Junctions. • Schottky Junction – metal –semiconductor junction, metal replaces an extrinsic semiconductor material.
  26. 26. 26 Applications of PN Junction • Light Sources – Light Emitting Diodes (LEDs) and Laser Diodes. • Photodetectors – PN Junction Photodiode, PIN Photodiode, Avalanche Photodiode etc. LED Photodiodes
  27. 27. 27 Transistor Two PN Junctions
  28. 28. 28 Silicon Controlled Rectifier Three PN Junctions
  29. 29. 29 Light Emitting Diode
  30. 30. 30 Photodiodes PN Junction Photodiode PIN Photodiode
  31. 31. 31 Schottky Junction Metal – Semiconductor Junction
  32. 32. 32 Thank You

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