The document provides a comprehensive overview of semiconductors, including definitions of key terms such as energy bands, valence electrons, and Fermi levels. It discusses intrinsic and extrinsic semiconductors, as well as the properties and applications of pn junctions, which are fundamental components in various electronic devices. Additionally, it covers the effects of biasing on pn junctions and their applications in light sources and photodetectors.

1. 1
Semiconductors
MEC

2. 2
Contents
• Definitions.
• Energy Band Diagrams.
• Intrinsic Semiconductors.
• Extrinsic Semiconductors.
• Comparison.
• PN Junction.
• PN Junction Applications.

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
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
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
Energy Band Concept
6 eV
1.1 eV/0.72 eV

7. 7
Fermi Level in Solids
Top of the collection of electron energy levels at absolute zero temperature.

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
Semiconductor Types

10. 10
Comparison

11. 11
Doping

12. 12
Doped Semiconductors

13. 13
Intrinsic Semiconductors

14. 14
Intrinsic Semiconductors

15. 15
Fermi Level

16. 16

17. 17

18. 18
Compound Semiconductor
- Gallium Arsenide
Face Centered Cubic Structure
(FCC)

19. 19
Compound Semiconductors
Gallium Arsenide Crystal Structure

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
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
Biased PN Junctions

23. 23

24. 24
Comparison

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
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
Transistor
Two PN Junctions

28. 28
Silicon Controlled Rectifier
Three PN Junctions

29. 29
Light Emitting Diode

30. 30
Photodiodes
PN Junction Photodiode PIN Photodiode

31. 31
Schottky Junction
Metal – Semiconductor Junction

32. 32
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