Spring 2007EE130 Lecture 21, Slide 1 Lecture #21 ANNOUNCEMENTS No coffee hour today Quiz #3 on...
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Transcript of Spring 2007EE130 Lecture 21, Slide 1 Lecture #21 ANNOUNCEMENTS No coffee hour today Quiz #3 on...
![Page 1: Spring 2007EE130 Lecture 21, Slide 1 Lecture #21 ANNOUNCEMENTS No coffee hour today Quiz #3 on Friday (March 9) –Material of HW #5 & #6 (Lectures 13-17)](https://reader036.fdocuments.us/reader036/viewer/2022081519/56649d6c5503460f94a4b2b3/html5/thumbnails/1.jpg)
EE130 Lecture 21, Slide 1
Spring 2007
Lecture #21
ANNOUNCEMENTS
• No coffee hour today • Quiz #3 on Friday (March 9)
– Material of HW #5 & #6 (Lectures 13-17)– Closed book, no calculators; 3 pages of notes allowed
OUTLINE
• pn Junctions:– transient response: turn-on
• Summary of important pn-diode concepts
• pn diode applications
Reading: Chapters 8 & 9
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EE130 Lecture 21, Slide 2
Spring 2007
x
Turn-On TransientAgain, consider a p+n diode (Qp >> Qn):
t
i(t)
t
vA(t)
0 pxx
n
qAD
i
dx
dp
n
For t > 0:
pn(x)
xn
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EE130 Lecture 21, Slide 3
Spring 2007
• By separation of variables and integration, we have
• If we assume that the build-up of stored charge occurs quasi-statically so that
then
0for ττ
tQ
IQ
idt
dQ
p
pF
p
pp
ptpFp eItQ τ/1τ)(
pkTqv
pdiffusionpAeIItQ τ1τ)( /
0
ptF
A eI
I
q
kTtv τ/
0
11ln)(
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EE130 Lecture 21, Slide 4
Spring 2007
• If p is large, then the time required to turn on the diode is approximately Q/IF
jp QQQ where
![Page 5: Spring 2007EE130 Lecture 21, Slide 1 Lecture #21 ANNOUNCEMENTS No coffee hour today Quiz #3 on Friday (March 9) –Material of HW #5 & #6 (Lectures 13-17)](https://reader036.fdocuments.us/reader036/viewer/2022081519/56649d6c5503460f94a4b2b3/html5/thumbnails/5.jpg)
EE130 Lecture 21, Slide 5
Spring 2007
Summary of Important Concepts
• Under forward bias, minority carriers are injected into the quasi-neutral regions of the diode
• Current flowing across junction is comprised of hole and electron components
• In order for one of these components to be dominant, the junction must be asymmetrically doped
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EE130 Lecture 21, Slide 6
Spring 2007
Summary of Important Concepts (cont.)
• The ideal diode equation stipulates the relationship between JN(-xp) and JP(xn)
If holes are forced to flow across a forward-biased junction, then electrons must also be injected across the junction
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EE130 Lecture 21, Slide 7
Spring 2007
Summary of Important Concepts (cont.)• Under reverse bias, minority carriers are collected
into the quasi-neutral regions of the diode• Minority carriers within a diffusion length of the
depletion region will diffuse into the depletion region and then be swept across the junction by the electric field.
Current flowing in a reverse-biased diode depends on the rate at which minority carriers are supplied in the quasi-neutral regions
![Page 8: Spring 2007EE130 Lecture 21, Slide 1 Lecture #21 ANNOUNCEMENTS No coffee hour today Quiz #3 on Friday (March 9) –Material of HW #5 & #6 (Lectures 13-17)](https://reader036.fdocuments.us/reader036/viewer/2022081519/56649d6c5503460f94a4b2b3/html5/thumbnails/8.jpg)
EE130 Lecture 21, Slide 8
Spring 2007
Varactor Diodes
• Voltage-controlled capacitor– Used in oscillators and detectors
(e.g. FM demodulation circuits in your radios)
– Response changes by tailoring doping profile:
21mn
biVV
for
VC
r
nrj
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EE130 Lecture 21, Slide 9
Spring 2007
Tunnel Diodes
• Degenerately doped such that EFp < Ev and EFn > Ec
• Can achieve negative differential resistance– useful in high-speed
circuits and perhaps static memories
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EE130 Lecture 21, Slide 10
Spring 2007
Tunnel Diodes (cont.)
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EE130 Lecture 21, Slide 11
Spring 2007
)(~)(
)1( A0
NPopNPopop
opkTVq
LLqAgLWLqAgI
IeII
Optoelectronic Diodes
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EE130 Lecture 21, Slide 12
Spring 2007
1ln
0A opnLp
L
LL
qkT
Ioc gVVp
n
nn
p
p
np
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EE130 Lecture 21, Slide 13
Spring 2007
p-i-n Photodiodes
• W Wi-region, so most carriers are generated in
the depletion region faster response time (~10 GHz operation)
• Operate near avalanche to amplify signal
![Page 14: Spring 2007EE130 Lecture 21, Slide 1 Lecture #21 ANNOUNCEMENTS No coffee hour today Quiz #3 on Friday (March 9) –Material of HW #5 & #6 (Lectures 13-17)](https://reader036.fdocuments.us/reader036/viewer/2022081519/56649d6c5503460f94a4b2b3/html5/thumbnails/14.jpg)
EE130 Lecture 21, Slide 14
Spring 2007
Light Emitting Diodes (LEDs)
•LEDs are typically made of compound semiconductors
(direct bandgap)
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EE130 Lecture 21, Slide 15
Spring 2007
Organic LEDs
• Some organic materials exhibit semiconducting properties– OLEDs are attractive for
low-cost, high-quality flat-panel displays