Photodet

Photodet, short for photodetector, is a broad class of devices that convert light into an electrical signal. Photodetectors are used across imaging, communications, spectroscopy, and sensing, and include technologies ranging from simple photodiodes to advanced single-photon detectors. The common operating principle is that photon absorption generates charge carriers, which are then collected as a current or as a voltage. Detectors may operate in photovoltaic mode (zero bias), photoconductive mode (reverse bias), or photon-counting mode, depending on the architecture and application.

Major families include silicon and compound-semiconductor photodiodes for fast imaging and communications; phototransistors that provide current gain; photomultiplier tubes for high-sensitivity light detection in low-light environments; avalanche photodiodes and single-photon avalanche diodes for high gain and timing; and superconducting nanowire single-photon detectors for extreme sensitivity at cryogenic temperatures. Emerging materials such as perovskites and graphene are being explored for specialized photodetectors, as are hybrid organic-inorganic devices.

Key performance metrics for Photodets are responsivity (A/W), quantum efficiency, dark current, noise, rise and fall times, bandwidth, dynamic range, and spectral response. The choice of detector depends on factors such as required sensitivity, speed, wavelength range, and operating conditions.

Applications of Photodets include optical communication systems, imaging and photography, environmental sensing, LIDAR, spectroscopy, and biomedical instrumentation. Developments continue in areas like low-noise, high-speed detectors and room-temperature single-photon devices.