Avalanche photodiode

An avalanche photodiode is a semiconductor light detector that uses a strong electric field to multiply photo-generated charge carriers, producing internal gain.

Impact ionization: A process in which a high-energy charge carrier creates additional electron–hole pairs by colliding with the crystal lattice. Accelerated carriers trigger the multiplication that gives an avalanche photodiode internal gain.
P–N junction: A semiconductor interface between p-type and n-type regions that forms a depletion region and rectifying electrical behavior. Most avalanche photodiodes build their electric-field region around a p–n junction.
Optical communication: The transmission of information using light, commonly through optical fiber or free-space optical links. Avalanche photodiodes detect weak, rapidly changing signals at optical receivers.
PIN photodiode: A photodiode with an intrinsic semiconductor layer between p-type and n-type regions, typically operated without avalanche gain. It avoids avalanche multiplication, usually offering lower noise and simpler biasing.
Avalanche breakdown: A rapid increase in semiconductor current caused by carrier multiplication under a strong electric field. The photodiode operates near this breakdown process to amplify its signal.
Depletion region: A region near a semiconductor junction depleted of mobile charge carriers and containing an internal electric field. Photocarriers generated here can be swept into the multiplication field.
Time-of-flight camera: A camera that estimates distance by measuring the travel time or phase delay of emitted light. Avalanche photodiodes can detect reflected pulses with high sensitivity and timing precision.
Photomultiplier tube: A vacuum photodetector that amplifies photoelectrons through a sequence of dynodes. It offers strong gain but requires a vacuum tube rather than a semiconductor junction.
Photoconductive effect: An increase in a material’s electrical conductivity caused by absorbed light creating mobile charge carriers. It is the broader light-to-current effect that avalanche multiplication amplifies.
Quantum efficiency: The fraction of incident photons that produce collected charge carriers in a detector. It describes photon conversion before avalanche gain is counted.

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