Editing Diode (section)

===Types of semiconductor diode===
[[File:Forward_and_Reverse_Characteristics_for_diodes-en.svg|thumb|upright=1.4|[[Current–voltage characteristic|Current–voltage curves]] of several types of diodes]]
Normal (p–n) diodes, which operate as described above, are usually made of doped [[silicon]] or [[germanium]]. Before the development of silicon power rectifier diodes, [[cuprous oxide]] and later [[selenium]] was used. Their low efficiency required a much higher forward voltage to be applied (typically 1.4 to 1.7&nbsp;V per "cell", with multiple cells stacked so as to increase the peak inverse voltage rating for application in high voltage rectifiers), and required a large heat sink (often an extension of the diode's metal [[Substrate (semiconductor)|substrate]]), much larger than the later silicon diode of the same current ratings would require. The vast majority of all diodes are the p–n diodes found in [[CMOS]] [[integrated circuits]],<ref>{{Cite journal|last=Roddick|first=R.G.|title=Tunnel Diode Circuit Analysis|date=1962-10-01|doi=10.2172/4715062|url=https://digital.library.unt.edu/ark:/67531/metadc1033487/}}</ref> which include two diodes per pin and many other internal diodes.

; [[Avalanche diode]]s
: These are diodes that conduct in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. These are electrically very similar to Zener diodes (and are often mistakenly called Zener diodes), but break down by a different mechanism: the ''avalanche effect''. This occurs when the reverse electric field applied across the p–n junction causes a wave of ionization, reminiscent of an avalanche, leading to a large current. Avalanche diodes are designed to break down at a well-defined reverse voltage without being destroyed. The difference between the avalanche diode (which has a reverse breakdown above about 6.2&nbsp;V) and the Zener is that the channel length of the former exceeds the mean free path of the electrons, resulting in many collisions between them on the way through the channel. The only practical difference between the two types is they have temperature coefficients of opposite polarities.
; [[Constant-current diode]]s
: These are actually [[JFET]]s<ref>[http://digikey.com/Web%20Export/Supplier%20Content/Vishay_8026/PDF/Vishay_CurrentRegulatorDiodes.pdf Current regulator diodes]. Digikey.com (2009-05-27). Retrieved 2013-12-19.</ref> with the gate shorted to the source, and function like a two-terminal current-limiting analog to the voltage-limiting Zener diode. They allow a current through them to rise to a certain value, and then level off at a specific value. Also called ''CLDs'', ''constant-current diodes'', ''diode-connected transistors'', or ''current-regulating diodes''.
; [[#Point-contact diodes|Crystal rectifiers or crystal diodes]]
: These are point-contact diodes.<ref name="HC" /> The 1N21 series and others are used in mixer and detector applications in radar and microwave receivers.<ref name="SG" /><ref name="AS"/><ref name="MB"/> The 1N34A is another example of a crystal diode.<ref>{{cite web| url = http://www.nteinc.com/specs/original/1N34A.pdf| title = NTE data sheet}}</ref>
; [[Gunn diode]]s
: These are similar to tunnel diodes in that they are made of materials such as GaAs or InP that exhibit a region of [[negative resistance|negative differential resistance]]. With appropriate biasing, dipole domains form and travel across the diode, allowing high frequency [[microwave]] [[electronic oscillator|oscillators]] to be built.
;[[Light-emitting diode]]s (LEDs)
:In a diode formed from a [[Direct bandgap|direct band-gap]] semiconductor, such as [[gallium arsenide]], charge carriers that cross the junction emit [[photon]]s when they recombine with the majority carrier on the other side. Depending on the material, [[wavelength]]s (or colors)<ref>[http://digikey.com/Web%20Export/Supplier%20Content/Vishay_8026/PDF/Vishay_ClassificationOfComponents.pdf Classification of components]. Digikey.com (2009-05-27). Retrieved 2013-12-19.</ref> from the [[infrared]] to the near [[ultraviolet]] may be produced.<ref>{{cite web |url=http://www.element-14.com/community/docs/DOC-22517/l/component-construction--vishay-optoelectronics |title=Component Construction |date=2010-05-25 |access-date=2010-08-06 |archive-url=http://arquivo.pt/wayback/20160516081713/http://www.element-14.com/community/docs/DOC-22517/l/component-construction--vishay-optoelectronics |archive-date=2016-05-16 |url-status=dead }}</ref> The first LEDs were red and yellow, and higher-frequency diodes have been developed over time. All LEDs produce incoherent, narrow-spectrum light; [[Light-emitting diode#White|"white" LEDs]] are actually a blue LED with a yellow [[scintillator]] coating, or combinations of three LEDs of a different color. LEDs can also be used as low-efficiency photodiodes in signal applications. An LED may be paired with a photodiode or phototransistor in the same package, to form an [[opto-isolator]].
; [[Laser diode]]s
: When an LED-like structure is contained in a [[optical cavity|resonant cavity]] formed by polishing the parallel end faces, a [[laser]] can be formed. Laser diodes are commonly used in [[optical storage]] devices and for high speed [[optical communication]].
; [[Thermal diode]]s
: This term is used both for conventional p–n diodes used to monitor temperature because of their varying forward voltage with temperature, and for [[Peltier–Seebeck effect|Peltier heat pumps]] for [[thermoelectric cooling|thermoelectric heating and cooling]]. Peltier heat pumps may be made from semiconductors, though they do not have any rectifying junctions, they use the differing behavior of charge carriers in N and P-type semiconductor to move heat.
; [[Photodiode]]s
: All semiconductors are subject to optical [[charge carrier]] generation. This is typically an undesired effect, so most semiconductors are packaged in light-blocking material. Photodiodes are intended to sense light ([[photodetector]]), so they are packaged in materials that allow light to pass, and are usually PIN (the kind of diode most sensitive to light).<ref>[http://digikey.com/Web%20Export/Supplier%20Content/Vishay_8026/PDF/Vishay_ComponentConstruction.pdf Component Construction]. Digikey.com (2009-05-27). Retrieved 2013-12-19.</ref> A photodiode can be used in [[solar cell]]s, in [[photometry (optics)|photometry]], or in [[optical communication]]s. Multiple photodiodes may be packaged in a single device, either as a linear array or as a two-dimensional array. These arrays should not be confused with [[charge-coupled device]]s.
; [[PIN diode]]s
: A PIN diode has a central un-doped, or ''intrinsic'', layer, forming a p-type/intrinsic/n-type structure.<ref>{{cite web |url=http://www.element-14.com/community/docs/DOC-22516/l/physics-and-technology--vishay-optoelectronics |title=Physics and Technology |date=2010-05-25 |access-date=2010-08-06 |archive-url=http://arquivo.pt/wayback/20160516081725/http://www.element-14.com/community/docs/DOC-22516/l/physics-and-technology--vishay-optoelectronics |archive-date=2016-05-16 |url-status=dead }}</ref> They are used as radio frequency switches and attenuators. They are also used as large-volume, ionizing-radiation detectors and as [[photodetector]]s. PIN diodes are also used in [[power electronics]], as their central layer can withstand high voltages. Furthermore, the PIN structure can be found in many [[power semiconductor device]]s, such as [[IGBT]]s, power [[MOSFET]]s, and [[thyristor]]s.
;[[Schottky diode]]s
:[[Walter H. Schottky|Schottky]] diodes are constructed from metal to semiconductor contact. They have a lower forward voltage drop than p–n junction diodes. Their forward voltage drop at forward currents of about 1&nbsp;mA is in the range 0.15&nbsp;V to 0.45&nbsp;V, which makes them useful in voltage [[Clamper (electronics)|clamping applications]] and prevention of transistor saturation. They can also be used as low loss [[rectifier]]s, although their reverse leakage current is in general higher than that of other diodes. Schottky diodes are [[majority carrier]] devices and so do not suffer from minority carrier storage problems that slow down many other diodes—so they have a faster reverse recovery than p–n junction diodes. They also tend to have much lower junction capacitance than p–n diodes, which provides for high switching speeds and their use in high-speed circuitry and RF devices such as [[switched-mode power supply]], [[Frequency mixer|mixers]], and [[Detector (radio)|detectors]].
; Super barrier diodes
: Super barrier diodes are rectifier diodes that incorporate the low forward voltage drop of the Schottky diode with the surge-handling capability and low reverse leakage current of a normal p–n junction diode.
;[[Gold]]-doped diodes
: As a dopant, gold (or [[platinum]]) acts as recombination centers, which helps the fast recombination of minority carriers. This allows the diode to operate at higher signal frequencies, at the expense of a higher forward voltage drop. Gold-doped diodes are faster than other p–n diodes (but not as fast as Schottky diodes). They also have less reverse-current leakage than Schottky diodes (but not as good as other p–n diodes).<ref>[http://www.ixyspower.com/images/technical_support/Application%20Notes%20By%20Topic/FREDs,%20Schottky%20and%20GaAS%20Diodes/IXAN0044.pdf Fast Recovery Epitaxial Diodes (FRED) Characteristics – Applications – Examples] {{Webarchive|url=https://web.archive.org/web/20090326113147/http://www.ixyspower.com/images/technical_support/Application%20Notes%20By%20Topic/FREDs,%20Schottky%20and%20GaAS%20Diodes/IXAN0044.pdf |date=2009-03-26 }}. (PDF). Retrieved 2013-12-19.</ref><ref>Sze, S. M. (1998) ''Modern Semiconductor Device Physics'', Wiley Interscience, {{ISBN|0-471-15237-4}}</ref> A typical example is the 1N914.
; Snap-off or [[step recovery diode]]s
: The term ''step recovery'' relates to the form of the reverse recovery characteristic of these devices. After a forward current has been passing in an [[Step recovery diode|SRD]] and the current is interrupted or reversed, the reverse conduction will cease very abruptly (as in a step waveform). SRDs can, therefore, provide very fast voltage transitions by the very sudden disappearance of the charge carriers.
; [[Stabistor]]s or ''forward reference diodes''
: The term ''stabistor'' refers to a special type of diodes featuring extremely stable [[p–n junction#Forward bias|forward voltage]] characteristics. These devices are specially designed for low-voltage stabilization applications requiring a guaranteed voltage over a wide current range and highly stable over temperature.
;[[Transient voltage suppression diode]] (TVS)
: These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltage [[Transient (oscillation)|transients]].<ref>[http://digikey.com/Web%20Export/Supplier%20Content/Vishay_8026/PDF/Vishay_ProtectingLowCurrentLoads.pdf Protecting Low Current Loads in Harsh Electrical Environments]. Digikey.com (2009-05-27). Retrieved 2013-12-19.</ref> Their p–n junctions have a much larger cross-sectional area than those of a normal diode, allowing them to conduct large currents to ground without sustaining damage.
; [[Tunnel diode]]s or [[Leo Esaki|Esaki diodes]]
: These have a region of operation showing [[negative resistance]] caused by [[quantum tunneling]],<ref>{{cite journal|author=Jonscher, A. K. |doi=10.1088/0508-3443/12/12/304|title=The physics of the tunnel diode|year=1961|journal=British Journal of Applied Physics|volume=12|issue=12|page=654|bibcode = 1961BJAP...12..654J }}</ref> allowing amplification of signals and very simple bistable circuits. Because of the high carrier concentration, tunnel diodes are very fast, may be used at low (mK) temperatures, high magnetic fields, and in high radiation environments.<ref>{{cite journal|author1=Dowdey, J. E. |author2=Travis, C. M. |doi= 10.1109/TNS2.1964.4315475|title=An Analysis of Steady-State Nuclear Radiation Damage of Tunnel Diodes|year=1964|journal=IEEE Transactions on Nuclear Science|volume=11|issue=5|page=55|bibcode = 1964ITNS...11...55D }}</ref> Because of these properties, they are often used in spacecraft.
; [[Varicap]] or varactor diodes
: These are used as voltage-controlled [[capacitors]]. These are important in PLL ([[phase-locked loop]]) and FLL ([[frequency-locked loop]]) circuits, allowing tuning circuits, such as those in television receivers, to lock quickly on to the frequency. They also enabled tunable oscillators in the early discrete tuning of radios, where a cheap and stable, but fixed-frequency, crystal oscillator provided the reference frequency for a [[voltage-controlled oscillator]].
; [[Zener diode]]s
: These can be made to conduct in reverse bias (backward), and are correctly termed reverse breakdown diodes. This effect called [[Zener breakdown]], occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference. The term Zener diodes is colloquially applied to several types of breakdown diodes, but strictly speaking, Zener diodes have a breakdown voltage of below 5 volts, whilst avalanche diodes are used for breakdown voltages above that value. In practical voltage reference circuits, Zener and switching diodes are connected in series and opposite directions to balance the temperature coefficient response of the diodes to near-zero. Some devices labeled as high-voltage Zener diodes are actually avalanche diodes (see above). Two (equivalent) Zeners in series and in reverse order, in the same package, constitute a transient absorber (or [[Transorb]], a registered trademark).