Avalanche photodiodes (APDs) are photodetectors that can be regarded as the semiconductor analog to photomultipliers. By applying a high reverse bias voltage (typically 100-200 V in silicon), APDs show an internal current gain effect (around 100) due to impact ionization (avalanche effect). The higher the reverse voltage the higher the gain. This multplication factor (M) is given by the formula Photosensors or photodetectors appear in several varieties: Photoresistors or Light Dependant Resistors (LDR) which change resistance when illuminated Photovoltaic cells or solar cells which produce a voltage and supply an electric current when illuminated Photodiodes which can operate in photovoltaic mode or photoconductive mode Phototubes containing a photocathode which emits... Photomultipliers, or photomultiplier tubes (PMT) are extremely sensitive detectors of light in the ultraviolet, visible and near infrared. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... Impact ionization is the process in a material by which one energetic charge carrier can lose energy by the creation of other charge carriers. ... Avalanche Breakdown is a phenomena that can occur in both insulating and semiconducting materials, it is a form of current multiplication which can allow very large currents to flow in situations where that would normally not be possible. ...

Where V is the applied voltage, V_BR is the breakdown voltage and n is an empirically derived value between 2 and 6. APD gain varies strongly with applied reverse voltage and temperature (again in silicon) so it is necessary to control the reverse voltage in order to keep a stable gain. Avalanche photodiodes therefore are more sensitive compared to other semiconductor photodiodes. A photodiode A photodiode is an electronic component and a type of photodetector. ...

If very high gain is needed (10⁵ to 10⁶), a reverse voltage above the APD's breakdown voltage can be applied if the current is limited to below the APD's latching current (Geiger mode). This is particularly useful for single photon detection. Breakdown Voltage (Insulator) = The voltage minimum that makes a insulator react as a conductor. ...

A typical application for APDs is laser range finders and long range fiber optic telecommunication. New applications include positron emission tomography and particle physics [1]. APD arrays are becomming commercially available. A laser range-finder, or LIDAR (LIght Detection And Ranging), is a device which uses a laser beam in order to determine the distance to an opaque object. ... Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ... BlackBerry 7100t Telecommunication refers to communication over long distances. ... Image of a typical positron emission tomography (PET) facility Positron emission tomography (PET) is a nuclear medicine medical imaging technique which produces a three dimensional image or map of functional processes in the body. ... Particles erupt from the collision point of two relativistic (100GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...

Sensitivity depends on these factors: quantum efficiency (how much light is absorbed), leakage current in the dark at the operating voltage and noise. Noise components are thermal noise, Shot noise (random counting noise) and excess noise which is due to the multiplicaton process. A graph showing variation of quantum efficiency with wavelength of the CCD chips in the Hubble Space Telescopes Wide Field and Planetary Camera 2. ... Johnson-Nyquist noise (sometimes thermal noise, Johnson noise or Nyquist noise) is the noise generated by the equilibrium fluctuations of the electric current inside an electrical conductor, which happens without any applied voltage, due to the random thermal motion of the charge carriers (the electrons). ... Shot noise consists of random fluctuations of the electric current in an electrical conductor, which are caused by the fact that the current is carried by discrete charges (electrons). ...

Materials

In principle any semiconductor material can be used as a multiplication region:

• Silicon will detect in the visible and near infrared, with low multiplication noise (excess noise).
• Germanium (Ge) will detect infrared out to a wavelength of 1.7µm, but has high multiplication noise.
• InGaAs will detect out to longer than 1.6µm, and has less multiplication noise than Ge. It is normally used as the multiplication region of a heterostructure diode. This detector material is compatible with high-speed telecommunications using optical fibers. Commercial devices are available to speeds of at least 10Gbit/s.
• Gallium nitride based diodes have been used for operation with ultraviolet light.
• HgCdTe based diodes operate in the infrared, typically out to a maximum wavelength of about 14µm, but require cooling to reduce dark currents. Very low excess noise can be achieved in this material system.

General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Atomic mass 72. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of microwave radiation. ... Indium gallium arsenide (InGaAs) is a semiconductor composed of indium, gallium and arsenic. ... An area location represented by a point, or a line segment that is bound or unbound, or a plane surface bound or unbound, or a structure that can be represented by multi-plane surfaces that bounds the contained area. ... Optical fibers An optical fiber (or fibre) is a transparent thin fiber, usually made of glass or plastic, for transmitting light. ... Gallium nitride (GaN) is a wide bandgap semiconductor material used in optoelectronic, high-power and high-frequency devices. ... Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ... HgCdTe or Mercury cadmium telluride (also Cadmium Mercury Telluride or CMT) is an alloy of CdTe and HgTe and is sometimes claimed to be the third semiconductor of technological importance after Si and GaAs. ...

Excess Noise

The noise is due to the multiplication process at a multiplication, M is denoted by by F(M) and is given by kM + (1 − k)(2 − 1 / M). k is the ratio of the impact ionization rates of the two signs of charge carriers. For an electron multiplication device it is given by the hole impact ionization rate divided by the electron impact ionization rate. It is desirable to have a large asymmetry between these rates, in order to minimize F(M).

See also

• avalanche diode
• Avalanche breakdown

An avalanche diode is a silicon diode that is designed to break down and conduct at a specified reverse bias voltage. ... Avalanche Breakdown is a phenomena that can occur in both insulating and semiconducting materials, it is a form of current multiplication which can allow very large currents to flow in situations where that would normally not be possible. ...

References

• Fully ion-implanted p + -n germanium avalanche photodiodes, S. Kagawa, T. Kaneda, T. Mikawa, Y. Banba, Y. Toyama, and O. Mikami, Applied Physics Letters vol. 38, Iss. 6, pp. 429-431 (1981) DOI:10.1063/1.92385
• Breakdown characteristics in InP/InGaAs avalanche photodiode with p-i-n multiplication layer structure, Hyun, Kyung-Sook; Park, Chan-Yong; Journal of Applied Physics, vol. 81, Iss. 2, pp.974-984 (1997) DOI:10.1063/1.364225

A digital object identifier (or DOI) is a permanent identifier (permalink) given to a World Wide Web file or other Internet document so that if its Internet address changes, users will be redirected to its new address. ... A digital object identifier (or DOI) is a permanent identifier (permalink) given to a World Wide Web file or other Internet document so that if its Internet address changes, users will be redirected to its new address. ...

External links

• Characteristics and use of Si APD (Avalanche Photodiode) Hamamatsu Photonics
• Recent Progress of Photosensor Hamamatsu Photonics
• Page on Zener and avalanche diodes
• User's Guide Perkin-Elmer Corporation
• Judson Germanium APD