View source for Photodiode

{{short description|Converts light into current}}
{{Infobox electronic component
|name              = Photodiode 
|image             = Image:Fotodio.jpg
|image_size        =
|caption           = One Ge (top) and three Si (bottom) photodiodes
|type              = [[passivity (engineering)|Passive]], [[diode]]
|working_principle = Converts [[light]] into [[electric current|current]]
|invented          = 
|first_produced    =
|symbol            = [[File:Photodiode symbol.svg|150px]]
|pins              = [[anode]] and [[cathode]]
}}

A '''photodiode''' is a semiconductor [[diode]] sensitive to [[photon]] radiation, such as visible light, infrared or ultraviolet radiation, [[X-rays]] and [[gamma rays]].<ref name="pears1">{{cite book|last1=Pearsall|first1=Thomas|title=Photonics Essentials, 2nd edition|publisher=McGraw-Hill|date=2010|url=https://www.mheducation.com/highered/product/photonics-essentials-second-edition-pearsall/9780071629355.html|isbn=978-0-07-162935-5|access-date=2021-02-25|archive-date=2021-08-17|archive-url=https://web.archive.org/web/20210817005021/https://www.mheducation.com/highered/product/photonics-essentials-second-edition-pearsall/9780071629355.html}}</ref> It produces an electrical current when it absorbs photons. This can be used for detection and measurement applications, or for the generation of electrical power in [[solar cells]]. Photodiodes are used in a wide range of applications throughout the electromagnetic spectrum from visible light photocells to gamma ray spectrometers.

==Principle of operation==

A photodiode is a [[PIN diode|PIN structure]] or [[p–n junction]]. When a [[photon]] of sufficient energy strikes the diode, it creates an [[electron]]–[[electron hole|hole]] pair. This mechanism is also known as the inner [[photoelectric effect]]. If the absorption occurs in the junction's [[depletion region]], or one diffusion length away from it, these carriers are swept from the junction by the built-in electric field of the depletion region. Thus holes move toward the [[anode]], and electrons toward the [[cathode]], and a [[photocurrent]] is produced. The total current through the photodiode is the sum of the dark current (current that is passed in the absence of light) and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device.<ref>Tavernier, Filip  and Steyaert, Michiel (2011) ''High-Speed Optical Receivers with Integrated Photodiode in Nanoscale CMOS''. Springer. {{ISBN|1-4419-9924-8}}. Chapter 3 ''From Light to Electric Current – The Photodiode''</ref> Therefore, photodiodes operate most ideally in [[reverse bias]].

To first order, for a given spectral distribution, the photocurrent is linearly proportional to the [[irradiance]].<ref name=haberlin>{{cite book |last1=Häberlin |first1=Heinrich |title=Photovoltaics: System Design and Practice |date=2012 |publisher=John Wiley & Sons |isbn=978-1-119-97838-1 |pages=SA3–PA11–14 |url=https://books.google.com/books?id=w8k3aXBnDP4C&q=photocurrent+proportional-to-irradiance&pg=SA3-PA11 |access-date=19 April 2019}}</ref>

===Photovoltaic mode===

[[File:Photodiode operation-en.svg|thumb|350px|I-V characteristic of a photodiode. The linear [[Load line (electronics)|load lines]] represent the response of the external circuit: I=(Applied bias voltage-Diode voltage)/Total resistance. The points of intersection with the curves represent the actual current and voltage for a given bias, resistance and illumination.]]

In photovoltaic mode (zero [[bias (electrical engineering)|bias]]), photocurrent flows into the anode through a short circuit to the cathode.  If the circuit is opened or has a load impedance, restricting the photocurrent out of the device, a voltage builds up in the direction that forward biases the diode, that is, anode positive with respect to cathode.  If the circuit is shorted or the impedance is low, a forward current will consume all or some of the photocurrent. This mode exploits the [[photovoltaic effect]], which is the basis for [[solar cell]]s – a traditional solar cell is just a large area photodiode.  For optimum power output, the photovoltaic cell will be operated at a voltage that causes only a small forward current compared to the photocurrent.<ref name=haberlin/>

===Photoconductive mode===

In photoconductive mode the diode is [[p–n junction#Reverse bias|reverse biased]], that is, with the cathode driven positive with respect to the anode.  This reduces the response time because the additional reverse bias increases the width of the depletion layer, which decreases the junction's [[capacitance]] and increases the region with an electric field that will cause electrons to be quickly collected. The reverse bias also creates [[Dark current (physics)|dark current]] without much change in the photocurrent.

Although this mode is faster, the photoconductive mode can exhibit more electronic noise due to dark current or avalanche effects.<ref>{{cite web | url =http://www.pacer.co.uk/Assets/Pacer/User/Photodiodes.pdf | title =Photodiode Application Notes – Excelitas – see note 4 | access-date =2014-11-13 | archive-url =https://web.archive.org/web/20141113175955/http://www.pacer.co.uk/Assets/Pacer/User/Photodiodes.pdf | archive-date =2014-11-13 }}</ref> The leakage current of a good PIN diode is so low (&lt;1 nA) that the [[Johnson–Nyquist noise]] of the load resistance in a typical circuit often dominates.

==Related devices==
'''[[Avalanche photodiode]]s''' are photodiodes with structure optimized for operating with high reverse bias, approaching the reverse breakdown voltage. This allows each ''photo-generated'' carrier to be multiplied by [[avalanche breakdown]], resulting in internal gain within the photodiode, which increases the effective ''responsivity'' of the device.<ref name="pears2">{{cite book|last1=Pearsall|first1=Thomas|last2=Pollack|first2=Martin|title=Compound Semiconductor Photodiodes, Semiconductors and Semimetals, Vol 22D|publisher=Elsevier|date=1985|pages=173–245|url=https://www.sciencedirect.com/bookseries/semiconductors-and-semimetals/vol/22/part/PD|doi=10.1016/S0080-8784(08)62953-1}}</ref>[[File:IEEE 315-1975 (1993) 8.6.16.svg|100px|thumb|Electronic symbol for a phototransistor]]
[[File:PhotoTransistor.jpg|thumb|S604B PhotoTransistor]]
A '''phototransistor''' is a light-sensitive transistor. A common type of phototransistor, the ''bipolar phototransistor'', is in essence a [[bipolar transistor]] encased in a transparent case so that [[light]] can reach the ''base–collector [[p–n junction|junction]]''. It was invented by [[John N. Shive]] at Bell Labs in 1948<ref name="crystal-fire">{{cite book |year=1998
 | title = Crystal Fire: The Invention of the Transistor and the Birth of the Information Age
 | isbn = 978-0-393-31851-7
 |author1=Riordan, Michael |author1-link=Michael Riordan (physicist) |author2=Hoddeson, Lillian | publisher = W. W. Norton & Company
 |author2-link=Lillian Hoddeson
}}</ref>{{rp|205}} but it was not announced until 1950.<ref>{{cite journal
 | url = http://www.smecc.org/phototransistor.htm
 | title = The phototransistor
 | date = May 1950
 | journal = Bell Laboratories Record
 | access-date = 2012-04-09
 | archive-date = 2015-07-04
 | archive-url = https://web.archive.org/web/20150704010847/http://www.smecc.org/phototransistor.htm
 }}</ref> The electrons that are generated by photons in the base–collector junction are injected into the base, and this photodiode current is amplified by the transistor's current gain β (or h<sub>fe</sub>). If the base and collector leads are used and the emitter is left unconnected, the phototransistor becomes a photodiode. While phototransistors have a higher [[responsivity]] for light they are not able to detect low levels of light any better than photodiodes.{{Citation needed|date=May 2011}} Phototransistors also have significantly longer response times. Another type of phototransistor, the ''field-effect phototransistor'' (also known as photoFET), is a light-sensitive field-effect transistor. Unlike photobipolar transistors, photoFETs control drain-source current by creating a gate voltage.

A '''[[solaristor]]''' is a two-terminal gate-less phototransistor. A compact class of such solaristors was demonstrated in 2018 by [[Catalan Institute of Nanoscience and Nanotechnology (ICN2)|ICN2]] researchers. The novel concept is a two-in-one power source plus transistor device that runs on solar energy by exploiting a memresistive effect in the flow of photogenerated carriers.<ref>{{Cite journal|last1=Pérez-Tomás|first1=Amador|last2=Lima|first2=Anderson|last3=Billon|first3=Quentin|last4=Shirley|first4=Ian|last5=Catalan|first5=Gustau|last6=Lira-Cantú|first6=Mónica|title=A Solar Transistor and Photoferroelectric Memory|journal=Advanced Functional Materials|volume=28|issue=17|article-number=1707099|language=en|doi=10.1002/adfm.201707099|issn=1616-3028|year=2018|url=http://ddd.uab.cat/record/215011|hdl=10261/199048|s2cid=102819292 |hdl-access=free}}</ref>

==Materials==
The material used to make a photodiode is critical to defining its properties, because only [[photon]]s with sufficient energy to excite [[electron]]s across the material's [[bandgap]] will produce significant photocurrents.

Materials commonly used to produce photodiodes are listed in the table below.<ref>Held. G, Introduction to Light Emitting Diode Technology and Applications, CRC Press, (Worldwide, 2008). Ch. 5 p. 116. {{ISBN|1-4200-7662-0}}</ref>

{| class="wikitable"
! Material
! [[Electromagnetic spectrum]]<br />[[wavelength]] range (nm)
|-
| [[Silicon]] || 190–1100
|-
| [[Germanium]] || 400–1700
|-
| [[Indium gallium arsenide]] || 800–2600
|-
| [[Lead(II) sulfide]] || <1000–3500
|-
| [[Mercury cadmium telluride]] || 400–14000
|}

Because of their greater bandgap, silicon-based photodiodes generate less noise than germanium-based photodiodes.

Binary materials, such as MoS<sub>2</sub>, and graphene emerged as new materials for the production of photodiodes.<ref>{{cite journal |last1=Yin |first1=Zongyou |last2=Li |first2=Hai |last3=Li |first3=Hong |last4=Jiang |first4=Lin |last5=Shi |first5=Yumeng |last6=Sun |first6=Yinghui |last7=Lu |first7=Gang |last8=Zhang |first8=Qing |last9=Chen |first9=Xiaodong |last10=Zhang |first10=Hua |title=Single-Layer MoS Phototransistors |journal=ACS Nano |date=21 December 2011 |volume=6 |issue=1 |pages=74–80 |doi=10.1021/nn2024557|pmid=22165908 |arxiv=1310.8066 |s2cid=27038582 }}</ref>

=={{anchor|LEAD}}Unwanted and wanted photodiode effects==
Any p–n junction, if illuminated, is potentially a photodiode. Semiconductor devices such as diodes, transistors and ICs contain p–n junctions, and will not function correctly if they are illuminated by unwanted light.<ref>Shanfield, Z. et al (1988) [http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA210165 Investigation of radiation effects on semiconductor devices and integrated circuits]{{dead link|date=June 2022|bot=medic}}{{cbignore|bot=medic}}, DNA-TR-88-221</ref><ref>Iniewski, Krzysztof (ed.) (2010), ''Radiation Effects in Semiconductors'', CRC Press, {{ISBN|978-1-4398-2694-2}}</ref> This is avoided by encapsulating devices in opaque housings. If these housings are not completely opaque to high-energy radiation (ultraviolet, X-rays, gamma rays), diodes, transistors and ICs can malfunction<ref>{{cite journal | last1 = Zeller | first1 = H.R. | year = 1995 | title = Cosmic ray induced failures in high power semiconductor devices | journal = Solid-State Electronics| volume =  38| issue = 12| pages = 2041–2046| doi=10.1016/0038-1101(95)00082-5| bibcode = 1995SSEle..38.2041Z }}</ref> due to induced photo-currents. Background radiation from the packaging is also significant.<ref>{{cite journal|title=Alpha-particle-induced soft errors in dynamic memories|journal=IEEE Transactions on Electron Devices|volume=26|issue=1|pages=2–9|doi=10.1109/T-ED.1979.19370|year=1979|last1=May|first1=T.C.|last2=Woods|first2=M.H.|bibcode=1979ITED...26....2M|s2cid=43748644}} Cited in {{cite journal|author=Baumann, R. C. |title=Soft errors in commercial integrated circuits|journal=[[International Journal of High Speed Electronics and Systems]]|volume=14|issue=2|pages=299–309|doi=10.1142/S0129156404002363|quote=alpha particles emitted from the natural radioactive decay of uranium, thorium, and daughter isotopes present as impurities in packaging materials were found to be the dominant cause of [soft error rate] in [dynamic random-access memories].|year=2004}}</ref> [[Radiation hardening]] mitigates these effects.

In some cases, the effect is actually wanted, for example to use [[LED]]s as light-sensitive devices (see [[LED circuit#LED as a light sensor|LED as light sensor]]) or even for [[energy harvesting]], then sometimes called ''light-emitting and light-absorbing diodes'' (LEADs).<ref>{{cite journal |title=Halbleitertechnik Der LED fehlt der Doppelpfeil |author-first=Arno |author-last=Erzberger |journal=Elektronik |language=de |date=2016-06-21 |url=http://www.elektroniknet.de/elektronik/power/der-led-fehlt-der-doppelpfeil-131470.html |access-date=2017-02-14 |url-status=live |archive-url=https://web.archive.org/web/20170214181713/http://www.elektroniknet.de/elektronik/power/der-led-fehlt-der-doppelpfeil-131470.html |archive-date=2017-02-14}}</ref>

==Features==
[[File:Response silicon photodiode.svg|thumb|upright=1.2|Response of a silicon photo diode vs wavelength of the incident light]]
Critical performance parameters of a photodiode include spectral responsivity, dark current, response time and noise-equivalent power.

; [[Responsivity|Spectral responsivity]]: The spectral responsivity is a ratio of the generated photocurrent to incident light power, expressed in [[Ampere|A]]/[[Watt|W]] when used in photoconductive mode. The wavelength-dependence may also be expressed as a ''[[quantum efficiency]]'' or the ratio of the number of photogenerated carriers to incident photons which is a unitless quantity.
; [[Dark current (physics)|Dark current]]: The dark current is the current through the photodiode in the absence of light, when it is operated in photoconductive mode. The dark current includes photocurrent generated by background radiation and the saturation current of the semiconductor junction. Dark current must be accounted for by [[calibration]] if a photodiode is used to make an accurate optical power measurement, and it is also a source of [[Electronic noise|noise]] when a photodiode is used in an optical communication system.
; [[Response time (technology)|Response time]]: The response time is the time required for the detector to respond to an optical input. A photon absorbed by the semiconducting material will generate an electron–hole pair which will in turn start moving in the material under the effect of the electric field and thus generate a [[Electric current|current]]. The finite duration of this current is known as the transit-time spread and can be evaluated by using [[Shockley–Ramo theorem|Ramo's theorem]]. One can also show with this theorem that the total charge generated in the external circuit is [[Elementary charge|e]] and not 2e as one might expect by the presence of the two carriers. Indeed, the [[integral]] of the current due to both electron and hole over time must be equal to e. The resistance and capacitance of the photodiode and the external circuitry give rise to another response time known as [[RC time constant]] (<math>\tau=RC</math>). This combination of R and C integrates the photoresponse over time and thus lengthens the [[impulse response]] of the photodiode. When used in an optical communication system, the response time determines the bandwidth available for signal modulation and thus data transmission.
; [[Noise-equivalent power]]: Noise-equivalent power (NEP) is the minimum input optical power to generate photocurrent, equal to the rms noise current in a 1&nbsp;[[hertz]] bandwidth.  NEP is essentially the minimum detectable power. The related ''characteristic detectivity'' (<math>D</math>) is the inverse of NEP (1/NEP) and the ''[[specific detectivity]]'' (<math>D^\star</math>) is the detectivity multiplied by the square root of the area (<math>A</math>) of the photodetector (<math>D^\star=D\sqrt{A}</math>) for a 1&nbsp;Hz bandwidth.  The specific detectivity allows different systems to be compared independent of sensor area and system bandwidth; a higher detectivity value indicates a low-noise device or system.<ref>Brooker, Graham (2009) ''Introduction to Sensors for Ranging and Imaging'', ScitTech Publishing. p. 87. {{ISBN|9781891121746}}</ref> Although it is traditional to give (<math>D^\star</math>) in many catalogues as a measure of the diode's quality, in practice, it is hardly ever the key parameter.

When a photodiode is used in an optical communication system, all these parameters contribute to the ''[[sensitivity (electronics)|sensitivity]]'' of the optical receiver which is the minimum input power required for the receiver to achieve a specified ''[[bit error rate]]''.

==Applications==
P–n photodiodes are used in similar applications to other [[photodetector]]s, such as [[photoconductor]]s, [[charge-coupled device]]s (CCD), and [[photomultiplier]] tubes. They may be used to generate an output which is dependent upon the illumination (analog for measurement), or to change the state of circuitry (digital, either for control and switching or for digital signal processing).

Photodiodes are used in [[consumer electronics]] devices such as [[compact disc]] players, [[smoke detector]]s, medical devices<ref name=Aguilar>E. Aguilar Pelaez et al., "LED power reduction trade-offs for ambulatory pulse oximetry," 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Lyon, 2007, pp. 2296–2299. doi: 10.1109/IEMBS.2007.4352784, URL: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4352784&isnumber=4352185</ref> and the receivers for infrared [[Remote control|remote control devices]] used to control equipment from [[Television set|televisions]] to air conditioners. For many applications either photodiodes or photoconductors may be used. Either type of photosensor may be used for light measurement, as in [[camera]] light meters, or to respond to light levels, as in switching on street lighting after dark.

Photosensors of all types may be used to respond to incident light or to a source of light which is part of the same circuit or system. A photodiode is often combined into a single component with an emitter of light, usually a [[light-emitting diode]] (LED), either to detect the presence of a mechanical obstruction to the beam ([[slotted optical switch]]) or to [[Coupling (electronics)|couple]] two digital or analog circuits while maintaining extremely high electrical [[Galvanic isolation|isolation]] between them, often for safety ([[optocoupler]]). The combination of LED and photodiode is also used in many [[sensor]] systems to characterize different types of products based on their [[absorbance|optical absorbance]].

Photodiodes are often used for accurate measurement of light intensity in science and industry. They generally have a more linear response than photoconductors.

They are also widely used in various medical applications, such as detectors for [[computed tomography]] (coupled with [[scintillator]]s), instruments to analyze samples ([[immunoassay]]), and [[pulse oximeter]]s.

[[PIN diode]]s are much faster and more sensitive than p–n junction diodes, and hence are often used for [[optical communication]]s and in lighting regulation.

P–n photodiodes are not used to measure extremely low light intensities. Instead, if high sensitivity is needed, [[avalanche photodiode]]s, [[intensified charge-coupled device]]s or [[photomultiplier]] tubes are used for applications such as [[astronomy]], [[spectroscopy]], [[night vision equipment]] and [[laser rangefinder|laser rangefinding]].

===Comparison with photomultipliers===

Advantages compared to [[photomultiplier]]s:<ref>[http://sales.hamamatsu.com/assets/html/ssd/si-photodiode/index.htm Photodiode Technical Guide] {{Webarchive|url=https://web.archive.org/web/20070104122603/http://sales.hamamatsu.com/assets/html/ssd/si-photodiode/index.htm |date=2007-01-04 }} on Hamamatsu website</ref>

# Excellent linearity of output current as a function of incident light
# Spectral response from 190&nbsp;nm to 1100&nbsp;nm ([[silicon]]), longer [[wavelength]]s with other [[semiconductor materials]]
# Low noise
# Ruggedized to mechanical stress
# Low cost
# Compact and light weight
# Long lifetime
# High [[quantum efficiency]], typically 60–80%<ref>Knoll, F.G. (2010). ''Radiation detection and measurement'', 4th ed. Wiley, Hoboken, NJ. p. 298. {{ISBN|978-0-470-13148-0}}</ref>
# No high voltage required

Disadvantages compared to [[photomultiplier]]s:

# Small area
# No internal gain (except [[avalanche photodiode]]s, but their gain is typically 10<sup>2</sup>–10<sup>3</sup> compared to 10<sup>5</sup>-10<sup>8</sup> for the photomultiplier)
# Much lower overall sensitivity
# Photon counting only possible with specially designed, usually cooled photodiodes, with special electronic circuits
# Response time for many designs is slower
# Latent effect

===Pinned photodiode===
{{distinguish|PIN photodiode}}
The pinned photodiode (PPD) has a shallow implant (P+ or N+) in N-type or P-type diffusion layer, respectively, over a P-type or N-type (respectively) substrate layer, such that the intermediate diffusion layer can be fully depleted of majority carriers, like the base region of a [[bipolar junction transistor]].  The PPD (usually PNP) is used in [[CMOS]] [[active-pixel sensor]]s; a precursor NPNP triple junction variant with the MOS buffer capacitor and the back-light illumination scheme with complete charge transfer and no image lag was invented by Sony in 1975. This scheme was widely used in many applications of charge transfer devices.

Early charge-coupled device [[image sensor]]s suffered from [[shutter lag]]. This was largely explained  with the re-invention of the pinned photodiode.<ref name="Fossum2014"/> It was developed by [[Nobukazu Teranishi]], Hiromitsu Shiraki and Yasuo Ishihara at [[NEC]] in 1980.<ref name="Fossum2014"/><ref>{{US patent|4484210|U.S. Patent 4,484,210, which was a floating-surface type buried photodioe with the similar structure of the 1975 Philips invention. Solid-state imaging device having a reduced image lag}}</ref> Sony in 1975 recognized that lag can be eliminated if the signal carriers could be transferred from the photodiode to the CCD. This led to their invention of the pinned photodiode, a photodetector structure with low lag, low [[noise (electronics)|noise]], high [[quantum efficiency]] and low [[dark current (physics)|dark current]].<ref name="Fossum2014"/> It was first publicly reported by Teranishi and Ishihara with A. Kohono, E. Oda and K. Arai in 1982, with the addition of an anti-blooming structure.<ref name="Fossum2014"/><ref>{{cite book |last1=Teranishi |first1=Nobuzaku |author1-link=Nobukazu Teranishi |last2=Kohono |first2=A. |last3=Ishihara |first3=Yasuo |last4=Oda |first4=E. |last5=Arai |first5=K. |title=1982 International Electron Devices Meeting |chapter=No image lag photodiode structure in the interline CCD image sensor |date=December 1982 |pages=324–327 |doi=10.1109/IEDM.1982.190285|s2cid=44669969 }}</ref> The new photodetector structure invented by Sony in 1975, developed by NEC in 1982 by Kodak in 1984 was given the name "pinned photodiode" (PPD) by B.C. Burkey at Kodak in 1984. In 1987, the PPD began to be incorporated into most CCD sensors, becoming a fixture in [[consumer electronic]] [[video cameras]] and then [[digital still camera]]s.<ref name="Fossum2014"/>

A CMOS image sensor with a low-voltage-PPD technology was first fabricated in 1995 by a joint JPL and [[Kodak]] team. The CMOS sensor with PPD technology was further advanced and refined by R.M. Guidash in 1997, K. Yonemoto and H. Sumi in 2000, and I. Inoue in 2003. This led to CMOS sensors achieve imaging performance on par with CCD sensors, and later exceeding CCD sensors.

==Photodiode array==
[[File:Photodiode array chip.jpg|thumb|150px|right|A one-dimensional photodiode array chip with more than 200 diodes in the line across the center]]
[[File:Optical mouse chip detail.png|thumb|150px|right|A two-dimensional photodiode array of only 4 × 4 pixels occupies the left side of the first [[optical mouse]] sensor chip, c. 1982.]]

A one-dimensional array of hundreds or thousands of photodiodes can be used as a position [[sensor]], for example as part of an angle sensor.<ref>
{{cite book
 | title = Precision Nanometrology: Sensors and Measuring Systems for Nanomanufacturing
 | author = Gao, Wei 
 | publisher = Springer
 | year = 2010
 | isbn = 978-1-84996-253-7
 | pages = 15–16
 | url = https://books.google.com/books?id=N0ys_sSxD60C&pg=PA15
}}</ref>  A two-dimensional array is used in image sensors and [[optical mouse|optical mice]].

In some applications, photodiode arrays allow for high-speed parallel readout, as opposed to integrating scanning electronics as in a [[charge-coupled device]] (CCD) or [[CMOS sensor]].  The optical mouse chip shown in the photo has parallel (not multiplexed) access to all 16 photodiodes in its 4 × 4 array.

===Passive-pixel image sensor===
The [[passive-pixel sensor]] (PPS) is a type of photodiode array. It was the precursor to the [[active-pixel sensor]] (APS).<ref name="Fossum2014">{{cite journal |last1=Fossum |first1=Eric R. |author1-link=Eric Fossum |last2=Hondongwa |first2=D. B. |title=A Review of the Pinned Photodiode for CCD and CMOS Image Sensors |journal=IEEE Journal of the Electron Devices Society |date=2014 |volume=2 |issue=3 |pages=33–43 |doi=10.1109/JEDS.2014.2306412 |bibcode=2014IJEDS...2...33F |doi-access=free }}</ref> A passive-pixel sensor consists of passive pixels which are read out without [[amplifier|amplification]], with each pixel consisting of a photodiode and a [[MOSFET]] switch.<ref name="Kozlowski">{{cite journal |last1=Kozlowski |first1=L. J. |last2=Luo |first2=J. |last3=Kleinhans |first3=W. E. |last4=Liu |first4=T. |editor-first1=Bedabrata |editor-first2=Terrence S. |editor-last1=Pain |editor-last2=Lomheim |title=Comparison of passive and active pixel schemes for CMOS visible imagers |journal=Infrared Readout Electronics IV |date=14 September 1998 |volume=3360 |pages=101–110 |doi=10.1117/12.584474 |url=https://www.researchgate.net/publication/268189518 |publisher=International Society for Optics and Photonics|bibcode=1998SPIE.3360..101K |s2cid=123351913 }}</ref> In a photodiode array, pixels contain a [[p–n junction]], integrated [[capacitor]], and MOSFETs as selection [[transistors]]. A photodiode array was proposed by G. Weckler in 1968, predating the CCD.<ref name=fossum93>{{cite book |last1=Fossum |first1=Eric R. |chapter=Active pixel sensors: Are CCDS dinosaurs? |author1-link=Eric Fossum |title=Charge-Coupled Devices and Solid State Optical Sensors III |journal=SPIE Proceedings Vol. 1900: Charge-Coupled Devices and Solid State Optical Sensors III |volume=1900 |date=12 July 1993 |doi=10.1117/12.148585 |publisher=International Society for Optics and Photonics |pages=2–14 |editor1-last=Blouke |editor1-first=Morley M.|citeseerx=10.1.1.408.6558 |bibcode=1993SPIE.1900....2F |s2cid=10556755 }}</ref> This was the basis for the PPS.<ref name="Fossum2014"/>

The [[noise (electronics)|noise]] of photodiode arrays is sometimes a limitation to performance. It was not possible to [[semiconductor device fabrication|fabricate]] active pixel sensors with a practical pixel size in the 1970s, due to limited [[microlithography]] technology at the time.<ref name=fossum93/>

==See also==
{{div col|colwidth=22em}}
* [[Electronics]]
* [[Band gap]]
* [[Infrared]]
* [[Optoelectronics]]
* [[Optical interconnect]]
* [[Light Peak]]
* [[Interconnect bottleneck]]
* [[Optical fiber cable]]
* [[Optical communication]]
* [[Parallel optical interface]]
* [[Opto-isolator]]
* [[Semiconductor device]]
* [[Solar cell]]
* [[Avalanche photodiode]]
* [[Transducer]]
* [[LEDs as photodiode light sensors]]
* [[Light meter]]
* [[Image sensor]]
* [[Transimpedance amplifier]]
* [[Photoelectric sensor]]
{{div col end}}

==References==
{{FS1037C}}
{{Reflist}}

==External links==
{{Commons category|Photodiodes}}
* [https://naadal.com/photodiode/ Photodiode I–V characteristics] {{Webarchive|url=https://web.archive.org/web/20220226105607/https://naadal.com/photodiode/ |date=2022-02-26 }}
* [http://www.emant.com/324003.page Using the Photodiode to convert the PC to a Light Intensity Logger]
* [https://web.archive.org/web/20050205151917/http://www.fairchildsemi.com/an/AN/AN-3005.pdf Design Fundamentals for Phototransistor Circuits] (archived on February 5, 2005)
* [http://ece-www.colorado.edu/~bart/book/book/chapter4/ch4_7.htm Working principles of photodiodes] {{Webarchive|url=https://web.archive.org/web/20090212171128/http://ece-www.colorado.edu/~bart/book/book/chapter4/ch4_7.htm |date=2009-02-12 }}
* [https://web.archive.org/web/20160304182654/http://www.pacer.co.uk/assets/pacer/user/photodiodes.pdf Excelitas Application Notes on Pacer Website] (archived on March 4, 2016)

{{Electronic components}}

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[[Category:Optical diodes]]
[[Category:Photodetectors]]
[[Category:Silicon photonics devices]]