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)

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 SolidsQuantum Mechanics: Energy levels occupied by

electrons are discrete. Amphitheatre analogy

Aspendos Theatre, Turkey

Conduction Band

Band gap

Valence Band

Energy Level Diagrams

Electron-Hole Pairs (EHPs)

Wait—what’s a hole?

Vacancy in the valence bandActs like mobile positive chargeAn 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 (?)

III (extra hole)

IV

V (extra e-)

Group Number

That’s dope: N and P type

N-type: Extra electrons P-type: Extra holes

Dopant electrons and holes are mobileNuclei 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

The Diode Equation

VB

I

Silicon Diodes as Rectifiers

“Electronic Valve” action

Current can essentially flow in one direction only

Reverse bias Forward bias

0.7 V

Let there be Light…

Rainbow of Fruit Flavors

Idealized LED turn-on voltages

VF (volts)

I (mA)

1.8V 3.5V 3.6V

A bright idea—2014 Nobel prize for the blue LED

Isamu Akasaki Hiroshi Amano Shuji Nakamura

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.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 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