Gentle Intro to Semiconductors

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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 Solids


Quantum
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
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 (?)

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
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

Let there be Light…

The Diode Equation

V
B

I

Silicon Diodes
as
Rectifiers


“Electronic Valve”
action


Current can essentially
flow in one direction
only

Reverse bias

Forward bias

0.7 V

Rainbow of Fruit
F
lavors




Idealized LED turn
-
on voltages


V
F
(volts)

I

(mA)

1.8V

3.5V

3.6V

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


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