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 Aspendos Theatre, Turkey Conduction Band Band gap Valence Band

9. Energy Level Diagrams

10. Electron-Hole Pairs (EHPs)

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

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

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

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

15. 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.

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

17. The PN junction

18. Let there be Light…

19. The Diode Equation VBVB I

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

21. Rainbow of Fruit Flavors

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

23. Sources 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- 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://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