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Gentle Intro to Semiconductors

Gentle Intro to Semiconductors. ENGN/PHYS 207. The ubiquitous LED. Collection of diodes. Diode = electronic valve. Forward bias : Current flows!. Reverse bias : No current flow!. The Silicon Valley. Warm-up question(s ).

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Gentle Intro to Semiconductors

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  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. The Silicon Valley

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

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

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

  9. Energy Level Diagrams

  10. Electron-Hole Pairs (EHPs)

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

  12. Thermal energy to move and shake around a lattice at (T = 300K) kT =1/40 eV = 0.025 eV Important Fact

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

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

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

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

  17. The PN junction

  18. Let there be Light…

  19. I VB The Diode Equation

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

  21. Rainbow of Fruit Flavors

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

  23. Images: • http://49chevy.blogs.com/fusor/2008/10/fun-with-electr.html • http://www-inst.eecs.berkeley.edu/~ee143/sp06/lectures/Semiconductor_tutorial.pdf • http://www.allaboutcircuits.com/vol_3/chpt_2/3.html • http://free-zg.t-com.hr/Julijan-Sribar/preview/vol1.html • http://www.launc.tased.edu.au/online/sciences/Physics/photonics/bias.htm • http://www.mtmscientific.com/diodes.html • http://www.mpoweruk.com/semiconductors.htm • http://free-zg.t-com.hr/Julijan-Sribar/preview/vol1.html • http://electrons.wikidot.com/methods-for-the-determination-of-ground-state-wavefunction • http://www.electronics-tutorials.ws/diode/diode_8.html Animations: • http://pvcdrom.pveducation.org/SEMICON/PN.HTM • http://www.acsu.buffalo.edu/~wie/applet/students/jiawang/pn.html • http://www.youtube.com/watch?v=O3x7NdUuu0Q&feature=related • http://www.youtube.com/watch?v=DbjR-2knrpo Sources

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