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!

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

LED characteristic curves Image credit: http://www.electronics-tutorials.ws/diode/diode_8.html

Practical LED circuit. Rs: current limiting resistor Image credit: http://www.electronics-tutorials.ws/diode/diode_8.html

Driving LEDs Limited current only LED transistor driver (better for higher current) Driving LEDs Image credit: http://www.electronics-tutorials.ws/diode/diode_8.html

The Silicon Valley

Transistor Inventors

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

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

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

Energy Level Diagrams

Electron-Hole Pairs (EHPs)

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

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

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

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

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.

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

The PN junction http://www.youtube.com/watch?v=DbjR-2knrpo (scottish language, around 6 min is very useful animation) https://www.youtube.com/watch?v=JBtEckh3L9Q

VB I The Diode Equation

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

Let there be Light… http://www.youtube.com/watch?v=O3x7NdUuu0Q&feature=related (english language) http://www.youtube.com/watch?v=WzvXOqFocJQ (german language) http://www.youtube.com/watch?v=DbjR-2knrpo (scottish language, around 6 min is very useful animation)

A bright idea—2014 Nobel prize for the blue LED Isamu Akasaki Hiroshi Amano Shuji Nakamura https://www.youtube.com/watch?v=6e8hBJ5-fdc (good youtube video about manufacturing LEDs) Decent intro to pieces of LEDs too: http://www.lighting.philips.com/pwc_li/main/connect/Lighting_University/internet-courses/LEDs/led-lamps8.html

All the Colors of the Rainbow

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

EWH kit

NPN Transistors C B E

Phototransistor

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://electrons.wikidot.com/methods-for-the-determination-of-ground-state-wavefunction http://www.electronics-tutorials.ws/diode/diode_8.html http://www.nobelprize.org/nobel_prizes/physics/laureates/2014/press.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