Photoconductivity

Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation.[1]

When light is absorbed by a material such as a semiconductor, the number of free electrons and electron holes increases and raises its electrical conductivity. To cause excitation, the light that strikes the semiconductor must have enough energy to raise electrons across the band gap, or to excite the impurities within the band gap. When a bias voltage and a load resistor are used in series with the semiconductor, a voltage drop across the load resistors can be measured when the change in electrical conductivity of the material varies the current through the circuit.

Classic examples of photoconductive materials include :

Applications

Further information: Photoresistor

When a photoconductive material is connected as part of a circuit, it functions as a resistor whose resistance depends on the light intensity. In this context, the material is called a photoresistor (also called light-dependent resistor or photoconductor). The most common application of photoresistors is as photodetectors, i.e. devices that measure light intensity. Photoresistors are not the only type of photodetector—other types include charge-coupled devices (CCDs), photodiodes and phototransistors—but they are among the most common. Some photodetector applications in which photoresistors are often used include camera light meters, street lights, clock radios, and infrared detectors.

Negative photoconductivity

Some materials exhibit deterioration in photoconductivity upon exposure to illumination.[3] One prominent example is hydrogenated amorphous silicon (a-Si:H) in which a metastable reduction in photoconductivity is observable[4] (see Staebler–Wronski effect). Other materials that were reported to exhibit negative photoconductivity include molybdenum disulfide,[5] graphene,[6] and metal nanoparticles.[7]

See also

References

  1. ↑ DeWerd, L. A.; P. R. Moran (1978). "Solid-state electrophotography with Al2O3". Medical Physics 5 (1): 23–26. Bibcode:1978MedPh...5...23D. doi:10.1118/1.594505. PMID 634229.
  2. ↑ Law, Kock Yee (1993). "Organic photoconductive materials: recent trends and developments". Chemical Reviews, American Chemical Society 93: 449–486. doi:10.1021/cr00017a020.
  3. ↑ N V Joshi (25 May 1990). Photoconductivity: Art: Science & Technology. CRC Press. ISBN 978-0-8247-8321-1.
  4. ↑ Staebler, D. L.; Wronski, C. R. (1977). "Reversible conductivity changes in discharge-produced amorphous Si". Applied Physics Letters 31 (4): 292. doi:10.1063/1.89674. ISSN 0003-6951.
  5. ↑ Serpi, A. (1992). "Negative Photoconductivity in MoS2,". Physica Status Solidi (a) 133 (2): K73–K77. doi:10.1002/pssa.2211330248. ISSN 0031-8965.
  6. ↑ Heyman, J. N.; Stein, J. D.; Kaminski, Z. S.; Banman, A. R.; Massari, A. M.; Robinson, J. T. (2015). "Carrier heating and negative photoconductivity in graphene". Journal of Applied Physics 117 (1): 015101. doi:10.1063/1.4905192. ISSN 0021-8979.
  7. ↑ Nakanishi, Hideyuki; Bishop, Kyle J. M.; Kowalczyk, Bartlomiej; Nitzan, Abraham; Weiss, Emily A.; Tretiakov, Konstantin V.; Apodaca, Mario M.; Klajn, Rafal; Stoddart, J. Fraser; Grzybowski, Bartosz A. (2009). "Photoconductance and inverse photoconductance in films of functionalized metal nanoparticles". Nature 460 (7253): 371–375. doi:10.1038/nature08131. ISSN 0028-0836.


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