P17-Semiconductor Photon Detectors

7/27/2019 P17-Semiconductor Photon Detectors

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17. Semiconductor Photon Detectors









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



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





Photoconductors



Photoconductors



Photodiodes

n

P +- i p



Two operation modes of PN photodiodes

-

operation of PDs

or -c rcu p o ocon uc ve

operation of PDs



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







Heterojunction Photodiodes







Comparison CCD/CMOS sensorsCMOS: low cost CCD : medium to high-end

Source: B. Diericks: CMOS image sensor concepts. Photonics West 2000 Short course (Web)



Charge-coupled devices (CCD)

charge transfer to next pixel cell



• Vertical charge transfer

•

• Output capacitor reset

CCD

Outputcapacitor

Amp

or zon a eg s er









■

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 .



Avalanche Photodiodes (APD)





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 …..

-



APD gain

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P17-Semiconductor Photon Detectors