Source: MDPI

Understanding Photoconductive Switches

What are Photoconductive Switches?

A photoconductive switch is an electrical switch that operates based on the photoconductivity of a material. This means that the material’s electrical conductance increases when exposed to light. Typically, semiconductor materials are used for these switches. When light above the material’s band gap energy is absorbed, free carriers are generated, enhancing conductivity. Common materials include chromium-doped gallium arsenide (Cr-GaAs), low-temperature grown gallium arsenide (LT-GaAs), indium phosphide (InP), amorphous silicon, and silicon on sapphire (SoS).

Designs of Photoconductive Switches

There are various designs of photoconductive switches:

• Bulk devices: These are several millimeters or centimeters long with electrical contacts on the end faces, suitable for switching very high voltages.
• Microstrip devices: These have a small gap in a microstrip, either straight or interdigitated, with widths ranging from a few microns to tens of microns, used for low-power applications with high speed.
• Sliding contact devices: These offer the highest speed, where a point between two parallel strips of a coplanar stripline is illuminated.

Applications of Photoconductive Switches

Photoconductive switches find applications in various fields:

• Photoconductive sampling for testing high-speed integrated electronic circuits.
• Generation of terahertz pulses.
• Generation of microwaves and millimeter waves via direct DC to RF conversion.
• High-speed photodetectors in optical fiber communications.
• Very fast analog-to-digital converters.

Conclusion

Photoconductive switches play a crucial role in high-speed electronics and communication systems. Their ability to rapidly switch electrical signals based on light exposure makes them invaluable for various applications.

Source: LLNL-IPO – Lawrence Livermore National Laboratory
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