1. Gentle Intro to Semiconductors
ENGN/PHYS 207

2. The ubiquitous LED

3. Collection of diodes

4. Diode = electronic valve
Forward bias: Current flows!
Reverse bias: No current flow!

5. Silicon Diode Characteristic Curve
ID (mA)
VD (Volts)
Silicon Diode Characteristic Curve

6. LED characteristic curves
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7. Practical LED circuit. Rs: current limiting resistor
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8. Driving LEDs Limited current only LED transistor driver
(better for higher current)
Driving LEDs
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9. The Silicon Valley

10. Transistor Inventors

11. Warm-up question(s)
What does it mean for a material to be able to “conduct” electricity?

12. Pure silicon lattice (intrinsic semiconductor)
2D lattice model showing covalent bonds in Si crystal

13. Band Theory of Solids
Quantum Mechanics: Energy levels occupied by electrons are discrete.
Amphitheatre analogy
Conduction Band
Band gap
Valence Band
Aspendos Theatre, Turkey

14. Energy Level Diagrams

15. Electron-Hole Pairs (EHPs)

16. Wait—what’s a hole? Vacancy in the valence band
Acts like mobile positive charge
An electron can fall into a hole (Recombination)

17. Important Fact
Thermal energy to move and shake around a lattice at (T = 300K)
kT = 1/40 eV
= eV

18. Why pure silicon isn’t so hot
Large energy barrier!

19. Let’s dope up (?)
Group Number
III (extra hole) IV
V (extra e-)

20. That’s dope: N and P type
N-type: Extra electrons
P-type: Extra holes
Dopant electrons and holes are mobile
Nuclei locked in the lattice, they are NOT mobile.

21. Why doping is actually good for us
N-type: easily donates electrons into conduction band
P-type: easily accepts electrons into valence band

22. The PN junction
(scottish language, around 6 min is very useful animation)

23. VB I
The Diode Equation

24. Silicon Diodes as Rectifiers
“Electronic Valve” action
Current can essentially flow in one direction only
0.7 V
Reverse bias
Forward bias

25. Let there be Light…
(english language)
(german language)
(scottish language, around 6 min is very useful animation)

26. A bright idea—2014 Nobel prize for the blue LED
Isamu Akasaki Hiroshi Amano Shuji Nakamura
(good youtube video about manufacturing LEDs)
Decent intro to pieces of LEDs too:

27. All the Colors of the Rainbow

28. Idealized LED turn-on voltages
VF (volts)
I (mA)
1.8V
3.5V
3.6V

29. EWH kit

30. NPN Transistors C B E

31. Phototransistor

32. Images:
Animations:
Sources