Photodiodes

Ingle and Crouch, Ingle and Crouch, Spectrochemical AnalysisSpectrochemical Analysis

Photons incident on the Photons incident on the depletion layer induce a depletion layer induce a current.current.

In most cases, best In most cases, best response in the NIR.response in the NIR.

Response is linear over 6 – Response is linear over 6 – 7 orders of incident radiant 7 orders of incident radiant powerpower

Spectral Response of Photodiodes

Shinya Inoue and Kenneth Spring, Shinya Inoue and Kenneth Spring, Video MicroscopyVideo Microscopy, Plenum Press, New York, 1997., Plenum Press, New York, 1997.

Avalanche Photodiode

http://micro.magnet.fsu.edu/primer/java/digitalimaging/avalanche/index.htmlhttp://micro.magnet.fsu.edu/primer/java/digitalimaging/avalanche/index.html

Hamamatsu CatalogHamamatsu Catalog

Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.Saunders College Publishing, Fort Worth, 1992.

Simultaneous Simultaneous detection in detection in a spectrophotometer.a spectrophotometer.

Photodiode Arrays (PDA or DAD)

Charge Coupled Device (CCD)Charge Coupled Device (CCD)

Ingle and Crouch, Ingle and Crouch, Spectrochemical AnalysisSpectrochemical Analysiswww.piacton.comwww.piacton.com

CCD Architecture

http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/ccdanatomy.html and http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/ccdanatomy.html and Bryce Marquis (Haynes Lab)Bryce Marquis (Haynes Lab)

Image Area

serial registeramplifier

SiO2 backing

Pixel Arrayinsulating oxide

Top ViewTop View

CCD Architecture

Bryce Marquis (Haynes Lab)Bryce Marquis (Haynes Lab)

One pixel

“Channel Stops” form horizontal pixel boundaries

3 electrodesform verticalpixel boundaries

Top View

Cross section

Insulating oxiden-type silicon

p-type silicon

Electrode

Charge Generation/Collection

N-type

P-type

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Incident photons excite electron-hole pairs,electrons gather in potential wells in each pixel

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N-type silica is doped with pentavalent species = excess electrons

P-type is doped with trivalent species = excess holes

CCD Rain Bucket AnalogyCCD Rain Bucket Analogy

Shinya Inoue and Kenneth Spring, Shinya Inoue and Kenneth Spring, Video MicroscopyVideo Microscopy, Plenum Press, New York, 1997., Plenum Press, New York, 1997.

1. Generation 2. Collection3. Transfer4. Measurement

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Time-slice shown in diagram

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Charge Transfer

Every third electrode is coupled, charge packetsare walked towards serial registry

to serial registry

http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.htmlhttp://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

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Charge Transportation

• Pixels at end of the array dump charge into serial register• Serial register walks charge packets to amplifier, where it is

measured.

amplifier

Quantum Efficiency

www.piacton.comwww.piacton.com

Noise Sources in CCD

• Shot Noise– Statistical variation of signal over time

• Increases with the square of the intensity

• Dark Signal Noise– Caused by thermal liberation of electrons

• Strongly coupled to temperature

• Readout Noise– Summation of noise associated with amplification of

signal, and conversion from analogue to digital• Increases with the processing speed

222 )()()( readdarkshottotal NNNN

Other Issues: Bad Pixels

• Hot Pixels– Increased charge accumulation due to variations in chip

surface.• Dead Pixels

– Defective pixels that do not respond.

Increasing hot pixels

Other Issues: Blooming

Other Issues: Cosmic Rays

* indicates cosmic rays

Other Issues: Etaloning

Etaloning

www.piacton.comwww.piacton.com

Other Features: Binning

• On Chip Pixel Binning– Increases S/N

• Shot noise decrease

– Increased speed– Less storage space

needed

– Decreases resolution

http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/binning.htmlhttp://micro.magnet.fsu.edu/primer/digitalimaging/concepts/binning.html

Are you getting the concept?

List the advantages and disadvantages of using each of the discussed detectors to achieve single molecule detection.