View source for Photocurrent

{{Short description|An electric current through a photosensitive device}}
{{refimprove|date=February 2018}}
'''Photocurrent''' is the [[electric current]] through a [[photosensitive]] device, such as a [[photodiode]], as the result of exposure to [[radiant power]].  The photocurrent may occur as a result of the [[photoelectric]], photoemissive, or [[photovoltaic effect]].  The photocurrent may be enhanced by internal [[Gain (electronics)|gain]] caused by interaction among ions and photons under the influence of applied fields, such as occurs in an [[avalanche photodiode]] (APD).

When a suitable radiation is used, the photoelectric current is directly proportional to intensity of radiation and increases with the increase in [[Potential|accelerating potential]] till the stage is reached when photo-current becomes maximum and does not increase with further increase in accelerating potential. The highest (maximum) value of the photo-current is called [[saturation current]]. The value of retarding potential at which photo-current becomes zero is called [[Cutoff voltage|cut-off voltage]] or stopping potential for the given frequency of the incident ray.

==Photovoltaics==
{{main|Theory of solar cells}}
The generation of a photocurrent forms the basis of the [[photovoltaic cell]].

==Photocurrent spectroscopy==
A characterization technique called '''photocurrent spectroscopy''' ('''PCS'''), also known as '''photoconductivity spectroscopy''', is widely used for studying optoelectronic properties of semiconductors and other light absorbing materials.<ref name="RSC-def">
{{cite web |url=https://www.rsc.org/publishing/journals/prospect/ontology.asp?id=CMO:0002602&MSID=C2JM15027A |title=RSC Definition - Photocurrent spectroscopy |website=RSC |access-date=2020-07-19 }}
</ref>  The setup of the technique involves having a semiconductor contacted with electrodes allowing for application of an electric bias, while at the same time a tunable light source incident with a given specific wavelength (energy) and power, usually pulsed by a mechanical chopper.<ref name="QW-PCS">
{{cite book|last1=Lu|first1=Wei|last2=Fu|first2=Ying |title=Spectroscopy of Semiconductors|chapter=Photocurrent Spectroscopy  |series=Springer Series in Optical Sciences|volume=215 |year=2018 |pages=185–205 |issn=0342-4111 |doi=10.1007/978-3-319-94953-6_6|isbn=978-3-319-94952-9}}
</ref><ref name="15.3">
{{cite book |last1=Lamberti |first1=Carlo |last2=Agostini |first2=Giovanni |date=2013 |title=Characterization of Semiconductor Heterostructures and Nanostructures |chapter=15.3 - Photocurrent spectroscopy |edition=2 |location=Italy |publisher=Elsevier |page=652-655 |isbn=978-0-444-59551-5 |doi=10.1016/B978-0-444-59551-5.00001-7 }}
</ref>  

The quantity measured is the electrical response of the circuit, coupled with the spectrograph obtained by varying the incident light energy by a [[monochromator]].  The circuit and optics are coupled by use of a [[lock-in amplifier]]. The measurements give information related to the band gap of the semiconductor, allowing for identification of various charge transitions like [[exciton]] and [[Trion (physics)|trion]] energies. This is highly relevant for studying semiconductor nanostructures like quantum wells,<ref>
{{cite journal
|author1=O. D. D. Couto |author2=J. Puebla |author3=E.A. Chekhovich |author4=I. J. Luxmoore |author5=C. J. Elliott |author6=N. Babazadeh |author7=M.S. Skolnick |author8=A.I. Tartakovskii |author9=A. B. Krysa |title = Charge control in InP/(Ga,In)P single quantum dots embedded in Schottky diodes
|journal = [[Phys. Rev. B]]
|volume = 84 |pages = 7
|year = 2011
|doi = 10.1103/PhysRevB.84.125301
|bibcode =  2011PhRvB..84d5306P|issue = 12 |arxiv=1107.2522 |s2cid=119215237 }}
</ref> and other nanomaterials like [[transition metal dichalcogenide monolayers]].<ref>
{{cite journal|last1=Mak|first1=Kin Fai|last2=Lee|first2=Changgu|last3=Hone|first3=James|last4=Shan|first4=Jie|last5=Heinz|first5=Tony F.|title=Atomically ThinMoS2: A New Direct-Gap Semiconductor|journal=Physical Review Letters|volume=105|issue=13|year=2010|page=136805|issn=0031-9007|doi=10.1103/PhysRevLett.105.136805|pmid=21230799|arxiv=1004.0546|bibcode=2010PhRvL.105m6805M|s2cid=40589037}}
</ref>

Furthermore, by using a piezo stage to vary the lateral position of the semiconductor with micron precision, one can generate a micrograph false color image of the spectra for different positions.  This is called '''scanning photocurrent microscopy''' ('''SPCM''').<ref>
{{cite journal|last1=Graham|first1=Rion|last2=Yu|first2=Dong|title=Scanning photocurrent microscopy in semiconductor nanostructures|journal=Modern Physics Letters B|volume=27|issue=25|year=2013|pages=1330018|issn=0217-9849|doi=10.1142/S0217984913300184|bibcode=2013MPLB...2730018G}}
</ref>

==See also==
* [[Photoconductivity]]
* [[Transient photocurrent]] (TPC)

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

[[Category:Electromagnetism]]


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