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Photoconductive Switches

Definition: electric switches controlled by light via photo-induced conductivity

German: photoleitende Schalter

Categories: photonic devices, optoelectronics

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A photoconductive switch is an electrical switch which is based on the photoconductivity of a material, i.e. an increase in its electrical conductance as a consequence of irradiation with light. In nearly all cases, one uses a semiconductor material, where the absorbed light (with a photon energy above the band gap energy) generates free carriers, which then contribute to the conductivity. Frequently used materials are chromium-doped gallium arsenide (Cr-GaAs), low-temperature grown gallium arsenide (LT-GaAs), indium phosphide (InP), amorphous silicon, and silicon on sapphire (SoS). In order to reduce the recovery time of the switch (determined by the lifetime of photoexcited carriers), one typically uses low-temperature growth (often followed by rapid thermal annealing), some doping (e.g. chromium in GaAs), or ion bombardment for producing crystal defects. Apart from the recovery time, important criteria are the bandgap energy, dark resistivity, and electrical breakdown resistance.

There are different designs of photoconductive switches:

All such devices are of the metal–semiconductor–metal (MSM) type.

Photoconductive switches are used for various purposes:

Bibliography

[1]F. W. Smith et al., “Picosecond GaAs-based photoconductive optoelectronic detectors”, Appl. Phys. Lett. 54 (10), 890 (1989)
[2]D. Krokel et al., “Subpicosecond electrical pulse generation using photoconductive switches with long carrier lifetimes”, Appl. Phys. Lett. 54, 1046 (1989)
[3]C. H. Lee, “Picosecond optics and microwave technology”, IEEE Trans. Microwave Theory Technol. 38 (5), 596 (1990)

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See also: photoconductive sampling, electro-optic sampling
and other articles in the categories photonic devices, optoelectronics

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