photodiodessemiconductor

Photodiodes are semiconductor devices that convert incident light into an electric current through the photovoltaic effect or photoconductive effect. They consist of p‑type, n‑type, or alloyed semiconductor regions forming a depletion zone where charge carriers are generated by photons. When light of sufficient energy strikes the junction, electron–hole pairs are created and separated by the internal electric field, resulting in a measurable photocurrent proportional to the incident optical power.

The most common photodiode structures are p‑n, PIN, and Schottky. A PIN photodiode incorporates a wide‑bandgap intrinsic layer between the p and n regions, which extends the depletion width and improves quantum efficiency across a broad wavelength range. Schottky photodiodes use a metal–semiconductor junction, providing exceptionally fast response times but typically lower responsivity than junction photodiodes. Crystalline materials such as silicon, gallium arsenide, indium gallium phosphide, and single‑crystal silicon carbide are frequently employed, each offering distinct spectral sensitivities: silicon is efficient in the visible to near‑infrared, gallium arsenide extends into the ultraviolet, and indium gallium phosphide covers the deep‑red to near‑infrared.

Photodiodes operate in either photovoltaic mode, generating a current under zero bias, or photoconductive mode, where an external bias enhances carrier extraction and speed. Key performance metrics include quantum efficiency, responsivity, dark current, bandwidth, and noise figure. Low dark current and high fill factor are essential for high‑dynamic‑range imaging and sensing applications, whereas large bandwidth is required for high‑speed optical communication and LIDAR.

Applications of semiconductor photodiodes span imaging sensors, optical communication receivers, environmental monitoring, medical diagnostics, and laser ranging. Advances in materials, nanostructuring, and integration with readout electronics continue to expand their functionality, enabling compact, low‑power, and high‑performance photonic systems.