Photodetector

A photodetector converts incident light into an electrical signal. Its response may measure light intensity or encode spatial, spectral, or temporal information.

Photoelectric effect: The emission or redistribution of electrons caused by light interacting with matter. It explains how photons can free charge carriers that produce a measurable current.
Semiconductor: A material whose electrical conductivity lies between that of an insulator and a conductor and can be controlled by doping or fields. Many photodetectors use semiconductors because light can generate mobile charge carriers in them.
Photodiode: A semiconductor diode that converts absorbed light into current or voltage. It is a widely used photodetector for sensing light and receiving optical signals.
Phototransistor: A light-sensitive transistor in which illumination controls a larger electrical current. It offers internal current gain, unlike a basic photodiode, but often responds more slowly.
Photoconductivity: An increase in a material’s electrical conductivity caused by absorbed light. Photoconductive detectors register illumination through changes in resistance.
p–n junction: An interface between p-type and n-type semiconductor regions that creates an internal electric field. Its field separates light-generated electrons and holes in common photodiodes.
Charge-coupled device: An image sensor that transfers accumulated charge between capacitive regions to read out pixel signals. It detects light across an image and moves the resulting pixel charges for readout.
Avalanche photodiode: A photodiode operated at high reverse bias to amplify photocurrent through impact ionization. It is a high-gain photodetector alternative when ordinary photodiode signals are too small.
Photovoltaic effect: The generation of voltage or current in a material exposed to light, without an external bias being required. It enables photodetectors that generate electrical output from light directly.
Signal-to-noise ratio: The ratio of a measured signal’s strength to the background noise that accompanies it. It determines whether a photodetector can distinguish weak illumination from fluctuations.

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