|
|
| (One intermediate revision by one other user not shown) |
| Line 1: |
Line 1: |
| [[File:Avalanche photodiode.JPG|thumb|Avalanche photodiode.]]
| | Valery precisely what people call her however it's not the most feminine name out a lot of. My family lives in Kansas. I am currently a people manager and I'll be promoted within the. What her family and her love is baseball and she'll be starting something else along together with. Check out my website here: http://penae5.soup.io/post/430082517/Sobre-La-Versatilidad-De-La-Resina-Epoxi<br><br>Here is my site :: [http://penae5.soup.io/post/430082517/Sobre-La-Versatilidad-De-La-Resina-Epoxi epoxi resina] |
| An '''avalanche photodiode (APD)''' is a highly sensitive semiconductor electronic device that exploits the [[photoelectric effect]] to convert light to electricity. APDs can be thought of as [[photodetector]]s that provide a built-in first stage of gain through [[Avalanche_breakdown#The_avalanche_process|avalanche multiplication]]. From a functional standpoint, they can be regarded as the semiconductor analog to [[photomultiplier]]s. 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 breakdown|avalanche effect]]). However, some silicon APDs employ alternative doping and beveling techniques compared to traditional APDs that allow greater voltage to be applied (> 1500 V) before breakdown is reached and hence a greater operating gain (> 1000). In general, the higher the reverse voltage the higher the gain. Among the various expressions for the APD multiplication factor (''M''), an instructive expression is given by the formula
| |
| | |
| :<math>M = \frac{1}{1 - \int_0^L\alpha(x)\, dx}</math>
| |
| | |
| where ''L'' is the space charge boundary for electrons and <math>\alpha</math> is the multiplication coefficient for electrons (and holes). This coefficient has a strong dependence on the applied electric field strength, temperature, and doping profile. Since APD gain varies strongly with the applied reverse bias and temperature, it is necessary to control the reverse voltage to keep a stable gain. Avalanche photodiodes therefore are more sensitive compared to other semiconductor [[photodiode]]s.
| |
| | |
| If very high gain is needed (10<sup>5</sup> to 10<sup>6</sup>), certain APDs ([[single-photon avalanche diode]]s) can be operated with a reverse voltage above the APD's [[breakdown voltage]]. In this case, the APD needs to have its signal current limited and quickly diminished. Active and passive current quenching techniques have been used for this purpose. APDs that operate in this high-gain regime are in Geiger mode. This mode is particularly useful for single photon detection provided that the dark count event rate is sufficiently low.
| |
| | |
| A typical application for APDs is [[laser rangefinder]]s and long range [[fiber optic]] [[telecommunication]]. New applications include [[positron emission tomography]] and [[particle physics]]. APD arrays are becoming commercially available.
| |
| | |
| APD applicability and usefulness depends on many parameters. Two of the larger factors are: [[quantum efficiency]], which indicates how well incident optical photons are absorbed and then used to generate primary charge carriers; and total leakage current, which is the sum of the dark current and photocurrent and noise. Electronic dark noise components are series and parallel noise. Series noise, which is the effect of [[shot noise]], is basically proportional to the APD capacitance while the parallel noise is associated with the fluctuations of the APD bulk and surface dark currents. Another noise source is the excess noise factor, ENF. It describes the statistical noise that is inherent with the stochastic APD multiplication process. This is not to be confused with the [[fano noise]] (F), which describes the fluctuation of the total electric charge collected in the APD.
| |
| | |
| ==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 1.7 µm, but has high multiplication noise.
| |
| *[[InGaAs]] will detect out to longer than 1.6 µm, and has less multiplication noise than Ge. It is normally used as the absorption region of a [[heterostructure]] diode, most typically involving [[Indium phosphide|InP]] as a substrate and as a multiplication layer.<ref name=tsang>{{cite book|title=Semiconductors and Semimetals|volume=Vol. 22, Part D "Photodetectors"|editor=Tsang, W.T.|publisher=Academic Press|year=1985}}</ref> This material system is compatible with an absorption window of roughly 0.9-1.7 µm. [[Indium gallium arsenide|InGaAs]] exhibits a high [[absorption coefficient]] at the wavelengths appropriate to high-speed telecommunications using [[optical fiber]]s, so only a few micrometres of [[InGaAs]] are required for nearly 100% light absorption.<ref name=tsang/> The excess noise factor is low enough to permit a gain-bandwidth product in excess of 100 GHz for a simple InP/InGaAs system,<ref>{{cite journal|author=Tarof, L.E.|title=Planar InP/GaAs Avalanche Photodetector with Gain-Bandwidth Product in Excess of 100 GHz|journal=Electronics Letters|volume= 27|pages=34–36|year=1991|doi=10.1049/el:19910023}}</ref> and up to 400 GHz for InGaAs on silicon.<ref>{{cite journal|author=Wu, W.; Hawkins, A.R.; Bowers, J.E.|title=Design of InGaAs/Si avalanche photodetectors for 400-GHz gain-bandwidth product|journal=Proceedings of SPIE|volume=3006|pages=36–47|year=1997|doi=10.1117/12.264251}}</ref> Therefore high speed operation is possible: commercial devices are available to speeds of at least 10 Gbit/s.<ref>{{cite journal|author=Campbell, J. C.|title=Recent advances in Telecommunications Avalanche Photodiodes|journal=IEEE Journal of Lightwave Technology|volume=25|pages=109–121|doi=10.1109/JLT.2006.888481|year=2007}}</ref>
| |
| *[[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 14 µm, but require cooling to reduce dark currents. Very low excess noise can be achieved in this material system.
| |
| | |
| ==Excess noise==
| |
| As mentioned above, this is the noise due to the multiplication process at a gain, ''M'' and is denoted by ENF(''M'') and can often be expressed as:
| |
| :<math>\text{ENF} = \kappa M + \left(2 - \frac{1}{M}\right)\left(1 - \kappa\right)</math>
| |
| | |
| where <math>\kappa\,</math> is the ratio of the hole impact ionization rate to that of electrons. 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 to minimize ENF(''M''), since ENF(''M'') is one of the main factors that limit, among other things, the best possible energy resolution obtainable.
| |
| | |
| ==Performance limits==
| |
| In addition to excess noise, there are limits to device performance associated with the capacitance, transit times and avalanche multiplication time.<ref name=tsang/> The capacitance increases with increasing device area and decreasing thickness. The transit times (both electrons and holes) increase with increasing thickness, implying a tradeoff between capacitance and transit time for performance. The avalanche multiplication time times the gain is given to first order by the gain-bandwidth product, which is a function of the device structure and most especially <math>\kappa\,</math>.
| |
| | |
| ==See also==
| |
| *[[Avalanche diode]]
| |
| *[[Avalanche breakdown]]
| |
| *[[Single-Photon Avalanche Diode]]
| |
| | |
| ==References==
| |
| {{reflist|2}}
| |
| | |
| ==Further reading==
| |
| * Avalanche photodiode - A User Guide[http://www.excelitas.com/downloads/app_apd_a_user_guide.pdf]
| |
| * Avalanche Photodiode - Low noise APD receivers[http://www.excelitas.com/downloads/app_lownoiseopticalreceiverusingsiapd.pdf]
| |
| *{{cite journal|doi=10.1063/1.92385|title=Fully ion-implanted p+-n germanium avalanche photodiodes|year=1981|last1=Kagawa|first1=S.|journal=Applied Physics Letters|volume=38|pages=429|issue=6}}
| |
| *{{cite journal|doi=10.1063/1.364225|title=Breakdown characteristics in InP/InGaAs avalanche photodiode with p-i-n multiplication layer structure|year=1997|last1=Hyun|first1=Kyung-Sook|last2=Park|journal=Journal of Applied Physics|volume=81|pages=974|first2=Chan-Yong|issue=2}}
| |
| *[http://www.lasercomponents.com/de/fileadmin/user_upload/home/Datasheets/lc/applikationsreport/avalanche-photodiodes.pdf Selecting the right APD]
| |
| *[http://www.lasercomponents.com/de/fileadmin/user_upload/home/Datasheets/lc/veroeffentlichung/progress-through-photonics.pdf Pulsed Laserdiodes and Avalanche Photodiodes for Industrial Applications]
| |
| * Excelitas Technologies Photonic Detectors [http://www.excelitas.com/Pages/Product/Photonic-Detectors.aspx]
| |
| | |
| [[Category:Optical diodes]]
| |
Valery precisely what people call her however it's not the most feminine name out a lot of. My family lives in Kansas. I am currently a people manager and I'll be promoted within the. What her family and her love is baseball and she'll be starting something else along together with. Check out my website here: http://penae5.soup.io/post/430082517/Sobre-La-Versatilidad-De-La-Resina-Epoxi
Here is my site :: epoxi resina