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.[2] 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 :

• the conductive polymer polyvinylcarbazole,[3] used extensively in photocopying (xerography);
• lead sulfide, used in infrared detection applications, such as the U.S. Sidewinder and Soviet (now Russian) Atoll heat-seeking missiles;
• selenium, employed in early television and xerography.

Applications

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, infrared detectors, nanophotonic systems and low-dimensional photo-sensors devices.[4]

Negative photoconductivity

Some materials exhibit deterioration in photoconductivity upon exposure to illumination.[5] One prominent example is hydrogenated amorphous silicon (a-Si:H) in which a metastable reduction in photoconductivity is observable[6] (see Staebler–Wronski effect). Other materials that were reported to exhibit negative photoconductivity include molybdenum disulfide,[7] graphene,[8] indium arsenide nanowires,[9] and metal nanoparticles.[10]

Magnetic photoconductivity

In 2016 it was demonstrated that in some photoconductive material a magnetic order can exist.[11] One prominent example is CH₃NH₃(Mn:Pb)I₃. In this material a light induced magnetization melting was also demonstrated[11] thus could be used in magneto optical devices and data storage.

Photoconductivity spectroscopy

The characterization technique called photoconductivity spectroscopy (also known as photocurrent spectroscopy) is widely used in studying optoelectronic properties of semiconductors.[12][13]

See also

• Photodiode
• Photoresistor (LDR)
• Photocurrent
• Photo conductive polymers
• Infrared detector
  • Lead selenide (PbSe)
  • Indium antimonide (InSb)

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. Saghaei, Jaber; Fallahzadeh, Ali; Saghaei, Tayebeh (June 2016). "Vapor treatment as a new method for photocurrent enhancement of UV photodetectors based on ZnO nanorods". Sensors and Actuators A: Physical. 247: 150–155. doi:10.1016/j.sna.2016.05.050.
3. Law, Kock Yee (1993). "Organic photoconductive materials: recent trends and developments". Chemical Reviews. 93: 449–486. doi:10.1021/cr00017a020.
4. Hernández-Acosta, M A; Trejo-Valdez, M; Castro-Chacón, J H; Torres-San Miguel, C R; Martínez-Gutiérrez, H; Torres-Torres, C (23 February 2018). "Chaotic signatures of photoconductive Cu ZnSnS nanostructures explored by Lorenz attractors". New Journal of Physics. 20 (2): 023048. Bibcode:2018NJPh...20b3048H. doi:10.1088/1367-2630/aaad41.
5. N V Joshi (25 May 1990). Photoconductivity: Art: Science & Technology. CRC Press. ISBN 978-0-8247-8321-1.
6. Staebler, D. L.; Wronski, C. R. (1977). "Reversible conductivity changes in discharge-produced amorphous Si". Applied Physics Letters. 31 (4): 292. Bibcode:1977ApPhL..31..292S. doi:10.1063/1.89674. ISSN 0003-6951.
7. Serpi, A. (1992). "Negative Photoconductivity in MoS2". Physica Status Solidi A. 133 (2): K73–K77. Bibcode:1992PSSAR.133...73S. doi:10.1002/pssa.2211330248. ISSN 0031-8965.
8. 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. arXiv:1410.7495. Bibcode:2015JAP...117a5101H. doi:10.1063/1.4905192. ISSN 0021-8979.
9. Alexander-Webber, Jack A.; Groschner, Catherine K.; Sagade, Abhay A.; Tainter, Gregory; Gonzalez-Zalba, M. Fernando; Di Pietro, Riccardo; Wong-Leung, Jennifer; Tan, H. Hoe; Jagadish, Chennupati (2017-12-11). "Engineering the Photoresponse of InAs Nanowires". ACS Applied Materials & Interfaces. 9 (50): 43993–44000. doi:10.1021/acsami.7b14415. ISSN 1944-8244. PMID 29171260.
10. 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. Bibcode:2009Natur.460..371N. doi:10.1038/nature08131. ISSN 0028-0836. PMID 19606145.
11. Náfrádi, Bálint (24 November 2016). "Optically switched magnetism in photovoltaic perovskite CH3NH3(Mn:Pb)I3". Nature Communications. 7 (13406): 13406. arXiv:1611.08205. Bibcode:2016NatCo...713406N. doi:10.1038/ncomms13406. PMC 5123013. PMID 27882917.
12. "RSC Definition - Photocurrent spectroscopy". RSC. Retrieved 2020-07-19.
13. Lamberti, Carlo; Agostini, Giovanni (2013). "15.3 - Photocurrent spectroscopy". Characterization of Semiconductor Heterostructures and Nanostructures (2 ed.). Italy: Elsevier. p. 652-655. doi:10.1016/B978-0-444-59551-5.00001-7. ISBN 978-0-444-59551-5.