Editing PIN diode (section)

=== Photodetector and photovoltaic cell ===
The PIN photodiode was invented by [[Jun-ichi Nishizawa]] and his colleagues in 1950.<ref>{{cite book|url=https://books.google.com/books?id=PbYgBQAAQBAJ&pg=PA137|title=Electronic Inventions and Discoveries: Electronics from Its Earliest Beginnings to the Present Day|first=G. W. A.|last=Dummer|date=22 October 2013|publisher=Elsevier|isbn=9781483145211|access-date=14 April 2018|via=Google Books}}</ref>

PIN photodiodes are used in fibre optic network cards and switches. As a photodetector, the PIN diode is reverse-biased. Under reverse bias, the diode ordinarily does not conduct (save a small dark current or I<sub>s</sub> leakage). When a [[photon]] of sufficient energy enters the [[depletion region]] of the diode, it creates an [[electron-hole pair]]. The reverse-bias field sweeps the carriers out of the region, creating current. Some detectors can use [[avalanche photodiode|avalanche multiplication]].

The same mechanism applies to the PIN structure, or '''p-i-n junction''', of a [[solar cell]]. In this case, the advantage of using a PIN structure over conventional semiconductor [[p–n junction]] is better long-wavelength response of the former. In case of long wavelength irradiation, photons penetrate deep into the cell. But only those electron-hole pairs generated in and near the depletion region contribute to current generation. The depletion region of a PIN structure extends across the intrinsic region, deep into the device. This wider depletion width enables electron-hole pair generation deep within the device, which increases the [[quantum efficiency]] of the cell.

Commercially available PIN photodiodes have quantum efficiencies above 80-90% in the telecom wavelength range (~1500&nbsp;nm), and are typically made of [[germanium]] or [[indium gallium arsenide|InGaAs]]. They feature fast response times (higher than their p-n counterparts), running into several tens of gigahertz,<ref>{{Cite web |url= https://www.discoverysemi.com/Product%20Pages/40G_Products/40G_Modules.php |title= Discovery semiconductor 40G InGaAs photodetector modules}}</ref> making them ideal for high speed optical telecommunication applications. Similarly, [[silicon]] p-i-n photodiodes<ref>{{cite web |title = Si photodiodes {{!}} Hamamatsu Photonics |url= https://www.hamamatsu.com/eu/en/product/optical-sensors/photodiodes/si-photodiodes/index.html |website= hamamatsu.com |access-date= 2021-03-26}}</ref> have even higher quantum efficiencies, but can only detect wavelengths below the bandgap of silicon, i.e. ~1100&nbsp;nm.

Typically, [[amorphous silicon]] [[thin-film solar cell|thin-film cells]] use PIN structures. On the other hand, [[CdTe]] cells use NIP structure, a variation of the PIN structure. In a NIP structure, an intrinsic CdTe layer is sandwiched by n-doped CdS and p-doped ZnTe; the photons are incident on the n-doped layer, unlike in a PIN diode.

A PIN photodiode can also detect [[ionizing radiation]] in case it is used as a [[semiconductor detector]].

In modern fiber-optical communications, the speed of optical transmitters and receivers is one of the most important parameters. Due to the small surface of the photodiode, its parasitic (unwanted) capacitance is reduced. The bandwidth of modern pin photodiodes is reaching the microwave and millimeter waves range.<ref>Attila Hilt, Gábor Járó, Attila Zólomy, Béatrice Cabon, Tibor Berceli, Tamás Marozsák: "Microwave Characterization of High-Speed pin Photodiodes", Proc. of the 9th Conference on Microwave Techniques COMITE’97, pp.21-24, Pardubice, Czech Republic, 16-17 Oct. 1997.</ref>