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Photodiode Basics: Selection & Operation


A photodiode is a semiconductor device with a P-N junction that converts photons (or light) into electrical current. The P layer has an abundance of holes (positive) and the N layer has an abundance of electrons (negative). Photodiodes can be manufactured from a variety of materials including, but not limited to, Silicon, Germanium, and Indium Gallium Arsenide. Each material uses different properties for cost benefits, increased sensitivity, wavelength range, low noise levels, or even response speed.

There are a number of parameters used in choosing the right photodiode and whether or not to reverse bias the photodiode. These include material, size of the photodiode and active area, and cost. Careful consideration is needed when browsing for photodiodes for your research or application. Photodiodes made from different materials have varying levels of sensitivity as well as differing speeds and dark current. The material of the photodiode is critical when finding the right photodiode to incorporate into your laser diode system.

When deciding whether or not to reverse bias your photodiode, it all comes down to balancing speed and noise and deciding what is most important. The type of photodiode may also affect your decision of bias. Certain types of photodiodes can only be reverse biased and others may have amplification of the response internal to the system.

The information in datasheets for photodiodes include the type of photodiode, peak sensitivity wavelengths, and most importantly, size and cost. This application note presents the basics of photodiode selection and operation including types of photodiodes and performance specs as well as integration with laser diodes.

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