p17-semiconductor photon detectors
TRANSCRIPT
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17. Semiconductor Photon Detectors
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The Internal Photoeffect: Photoconductivity
Æ Excited carriers remain within the material, serve to increase electr ical conductivi ty.
.
Transport: An applied electric field induces these carriers to move,which results in a circuit current.
Amplification: large electric fields enhance the responsivity of the detector.
Photoconductors
Quantum efficiency Photon noisePhotoelectron noise
Avalanche photodiodes (APD) Response time.Gain noise
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Quantum efficiency of photodetectors
Internal Quantum Efficiency
α η −
⎣ ⎦= = −int
1
Number of Photons *Entering* detector de
( ) α ζ ν
η −⎡ ⎤⎣ ⎦= = − − =ext
/Number of Collected electrons
Number of Photons *Incident* on detector 1 1
/F
ph
o
di q
PR e
h
Fresnel loss Fraction absorbed
in detection region
ur ace recom na on e ec
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Photoconductors
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Photoconductors
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Photodiodes
n
P +- i p
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Two operation modes of PN photodiodes
-
operation of PDs
or -c rcu p o ocon uc ve
operation of PDs
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Open-circuit (photovotaic) operation of PDs
Photovoltage Vp
with increasing photon flux.
This mode of operation is used,
for example, in solar cells
Short-circuit operation of PDs
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Heterojunction Photodiodes
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Comparison CCD/CMOS sensorsCMOS: low cost CCD : medium to high-end
Source: B. Diericks: CMOS image sensor concepts. Photonics West 2000 Short course (Web)
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Charge-coupled devices (CCD)
charge transfer to next pixel cell
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• Vertical charge transfer
•
• Output capacitor reset
CCD
Outputcapacitor
Amp
or zon a eg s er
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■
Very tolerant to high-energy radiation sources (long life time).■ On- chip system integration
(low power, low weight and compact designs).
■ g spee ow no se opera on
(inherently a parallel- random access readout device).
Deficiencies
■
Currently lacks performance in most areas compared to the CCDc arge genera on co ec on rans er an measuremen .
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Avalanche Photodiodes (APD)
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APD with only one type of carrier (e or h) is desirable.
: ionization coefficients of e and h
Ionization ratio :
Æ Æ Æe Æ h Æ e Æ …..
-
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APD gain