Title: photodiode
Long Title: IUPAC Gold Book - photodiode
DOI: 10.1351/goldbook.P04598
Status: current

Definition
A two-electrode, radiation-sensitive junction formed in a semiconductive material. A junction is formed by two successive regions of a semiconductive material having, respectively, an excess of electrons (n-type) or holes (p-type). A bias potential applied to the detector creates a region at the interface that is depleted of majority carriers. Each incident photon produces electron-hole pairs in the depletion region resulting in a measurable signal current. The photodiode can be operated either with zero bias in the photovoltaic mode where the photodiode is actually generating the electric potential supplied to the load. In a biased mode, the photoconductive mode, the reverse current is proportional to the irradiation. A Schottky-barrier photodiode is constructed by deposition of a metal film on a semiconductor surface in such a way that no interface layer is present. The barrier thickness depends on the impurity dopant concentration in the semiconductor layer. The incident radiation generates electon-hole pairs within the depletion region of the barrier where they are collected efficiently and rapidly by the built-in field. A PIN (p-intrinsic-n) diode is a planar diffused diode consisting of a single crystal having an intrinsic (undoped or compensated) region sandwiched between p- and n-type regions. A bias potential applied across the detector depletes the intrinsic region of charge carriers, constituting the radiation-sensitive detector volume. The number of electron-hole pairs produced is dependent on the energy of the incident photons. An avalanche photodiode is a photodiode in which the photogenerated electron-hole pairs are accelerated by a bias potential near to breakdown potential so that further electron-hole pairs are formed leading to saturation of the photocurrent. This operational mode for photon counting is the so-called Geiger mode, similar to that of the gas filled Geiger counter. Avalanche photodiodes can also be operated in the proportional mode.

Related Terms
- Geiger counter: https://goldbook.iupac.org/terms/view/G02598
- bias: https://goldbook.iupac.org/terms/view/M03796
- detector: https://goldbook.iupac.org/terms/view/R05054
- dopant: https://goldbook.iupac.org/terms/view/DT07203
- electric potential: https://goldbook.iupac.org/terms/view/E01935
- film: https://goldbook.iupac.org/terms/view/F02366
- interface: https://goldbook.iupac.org/terms/view/I03082
- irradiation: https://goldbook.iupac.org/terms/view/I03255
- mode: https://goldbook.iupac.org/terms/view/M03958
- photon counting: https://goldbook.iupac.org/terms/view/P04629
- saturation: https://goldbook.iupac.org/terms/view/S05472
- semiconductor: https://goldbook.iupac.org/terms/view/S05591

Source
- PAC, 1995, 67, 1745. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection of radiation (IUPAC Recommendations 1995)' on page 1755 (https://doi.org/10.1351/pac199567101745)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/P04598/html
- json: https://goldbook.iupac.org/terms/view/P04598/json
- xml: https://goldbook.iupac.org/terms/view/P04598/xml

Citation: Citation: 'photodiode' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.P04598
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Accessed: 2026-06-28T03:38:23+00:00