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| ==History== | ==History== | ||
| Although the crystal semiconductor diode was popular before the ] diode, thermionic (]) diodes and ] |
Although the crystal semiconductor diode was popular before the ] diode, thermionic (]) diodes and ] | ||
| ===Vacuum tube diodes=== | |||
| {{see also | Vacuum tube#History and development}} | |||
| In 1873, ] discovered the basic principle of operation of thermionic diodes.<ref> Owen W. Richardson, "Thermionic phenomena and the laws which govern them," December 12, 1929</ref> Guthrie discovered that a positively charged ] could be discharged by bringing a ] piece of white-hot metal close to it (but not actually touching it). The same did not apply to a negatively charged electroscope, indicating that the current flow was only possible in one direction. | |||
| ] independently rediscovered the principle on February 13, 1880. At the time, Edison was investigating why the filaments of his carbon-filament light bulbs nearly always burned out at the positive-connected end. He had a special bulb made with a metal plate sealed into the glass envelope. Using this device, he confirmed that an invisible current flowed from the glowing filament through the ] to the metal plate, but only when the plate was connected to the positive supply. | |||
| Edison devised a circuit where his modified light bulb effectively replaced the resistor in a ] ]. Edison was awarded a patent for this invention in 1884.<ref>Thomas A. Edison "Electrical Meter" {{US patent|307030}} Issue date: Oct 21, 1884</ref> Since there was no apparent practical use for such a device at the time, the patent application was most likely simply a precaution in case someone else did find a use for the so-called ]. | |||
| About 20 years later, ] (scientific adviser to the ] | |||
| and former Edison employee) realized that the Edison effect could be used as a precision ]. Fleming patented the first true thermionic diode, the ], in Britain on November 16, 1904<ref>{{cite web|url=http://www.jmargolin.com/history/trans.htm |title=Road to the Transistor |publisher=Jmargolin.com |date= |accessdate=2008-09-22}}</ref> (followed by {{US patent|803684}} in November 1905). | |||
| ===Solid-state diodes=== | |||
| In 1874 German scientist ] discovered the "unilateral conduction" of crystals.<ref></ref> Braun patented the crystal rectifier in 1899.<ref>{{cite web|url=http://encyclobeamia.solarbotics.net/articles/diode.html |title=Diode |publisher=Encyclobeamia.solarbotics.net |date= |accessdate=2010-08-06}}</ref> ] and ]s were developed for power applications in the 1930s. | |||
| Indian scientist ] was the first to use a crystal for detecting radio waves in 1894.<ref>{{Cite journal | |||
| | last = Emerson | |||
| | first = D. T. | |||
| | authorlink = | |||
| | coauthors = | |||
| | title = The work of Jagadish Chandra Bose: 100 years of mm wave research | |||
| | journal = IEEE Transactions on Microwave Theory and Techniques | |||
| | volume = 45 | |||
| | issue = 12 | |||
| | pages = 2267–2273 | |||
| | publisher = | |||
| | date = Dec. 1997 | |||
| | url = http://books.google.com/books?id=09Zsv97IH1MC&pg=PA88 | |||
| | issn = | |||
| | doi =10.1109/22.643830 | |||
| | accessdate = 2010-01-19|bibcode = 1997ITMTT..45.2267E }}</ref><ref name="Sarkar">{{Cite book | |||
| | last = Sarkar | |||
| | first = Tapan K. | |||
| | authorlink = | |||
| | coauthors = | |||
| | title = History of wireless | |||
| | publisher = John Wiley and Sons | |||
| | year = 2006 | |||
| | location = USA | |||
| | page = 94, 291-308 | |||
| | url = http://books.google.com/books?id=NBLEAA6QKYkC&pg=PA291 | |||
| | doi = | |||
| | isbn = 0-471-71814-9,}}</ref> The ] was developed into a practical device for ] by ], who invented a ] crystal detector in 1903 and received a patent for it on November 20, 1906.<ref>{{US patent|836531}}</ref> Other experimenters tried a variety of other substances, of which the most widely used was the mineral ] (]). Other substances offered slightly better performance, but galena was most widely used because it had the advantage of being cheap and easy to obtain. The crystal detector in these early ] sets consisted of an adjustable wire point-contact (the so-called "cat's whisker"), which could be manually moved over the face of the crystal in order to obtain optimum signal. This troublesome device was superseded by thermionic diodes by the 1920s, but after high purity semiconductor materials became available, the crystal detector returned to dominant use with the advent of inexpensive fixed-] diodes in the 1950s. | |||
| ===Etymology=== | |||
| At the time of their invention, such devices were known as ]. In 1919, the year ]s were invented, ] coined the term '''''diode''''' from the ] ''di'' (from ''δί''), meaning "two", and ''ode'' (from ''ὁδός''), meaning "path". | |||
| ==Thermionic diodes== | |||
| ] | |||
| Thermionic diodes are ] devices (also known as ]s, tubes, or valves), which are arrangements of ]s surrounded by a vacuum within a glass envelope. Early examples were fairly similar in appearance to ]s. | |||
| In thermionic-valve diodes, a current through the heater ] indirectly heats the ], another internal electrode treated with a mixture of ] and ] ]s, which are ]s of ]s; these substances are chosen because they have a small ]. (Some valves use direct heating, in which a tungsten filament acts as both heater and cathode.) The heat causes ] of electrons into the vacuum. In forward operation, a surrounding metal electrode called the ] is positively charged so that it ] attracts the emitted electrons. | |||
| However, electrons are not easily released from the unheated anode surface when the ] polarity is reversed. Hence, any reverse flow is negligible. | |||
| In a ], an arc forms between a refractory conductive anode and a pool of liquid mercury acting as cathode. Such units were made with ratings up to hundreds of kilowatts, and were important in the development of ] power transmission. Some types of smaller thermionic rectifiers sometimes had mercury vapor fill to reduce their forward voltage drop and to increase current rating over thermionic hard-vacuum devices. | |||
| Until the development of semiconductor diodes, valve diodes were used in analog signal applications and as rectifiers in many power supplies. They rapidly ceased to be used for most purposes, an exception being some high-voltage high-current applications subject to large transient peaks, where their robustness to abuse made them the best choice. {{As of|2012}} some enthusiasts favoured vacuum tube amplifiers for ] applications, sometimes using valve rather than semiconductor rectifiers. | |||
| ==Semiconductor diodes==<!-- This section is linked from ] --> | |||
| ].]] | |||
| ===Point-contact diodes=== | |||
| A '''point-contact diode''' works the same as the junction diodes described below, but their construction is simpler. A block of n-type semiconductor is built, and a conducting sharp-point contact made with some group-3 metal is placed in contact with the semiconductor. Some metal migrates into the semiconductor to make a small region of p-type semiconductor near the contact. The long-popular 1N34 germanium version is still used in radio receivers as a detector and occasionally in specialized analog electronics. | |||
| ===Junction diodes=== | |||
| Most diodes today are silicon junction diodes. A junction is formed between the p and n regions which is also called a depletion region. | |||
| ====p–n junction diode==== | |||
| {{main|p–n diode}} | |||
| A p–n junction diode is made of a crystal of ]. Impurities are added to it to create a region on one side that contains negative ]s (electrons), called ], and a region on the other side that contains positive charge carriers (]), called ]. The diode's terminals are attached to each of these regions. The boundary between these two regions, called a ], is where the action of the diode takes place. The crystal allows electrons to flow from the N-type side (called the ]) to the P-type side (called the ]), but not in the opposite direction. | |||
| ====Schottky diode==== | |||
| {{main|Schottky diode}} | |||
| Another type of junction diode, the ], is formed from a ] rather than a p–n junction, which reduces capacitance and increases switching speed. | |||
| ===Current–voltage characteristic=== | |||
| A semiconductor diode’s behavior in a circuit is given by its ], or I–V graph (see graph below). The shape of the curve is determined by the transport of charge carriers through the so-called '']'' or '']'' that exists at the ] between differing semiconductors. When a p–n junction is first created, conduction-band (mobile) electrons from the N-] region diffuse into the P-] region where there is a large population of holes (vacant places for electrons) with which the electrons "recombine". When a mobile electron recombines with a hole, both hole and electron vanish, leaving behind an immobile positively charged donor (dopant) on the N side and negatively charged acceptor (dopant) on the P side. The region around the p–n junction becomes depleted of ]s and thus behaves as an ]. | |||
| However, the width of the depletion region (called the ]) cannot grow without limit. For each ] that recombines, a positively charged ] ion is left behind in the N-doped region, and a negatively charged dopant ion is left behind in the P-doped region. As recombination proceeds more ions are created, an increasing electric field develops through the depletion zone that acts to slow and then finally stop recombination. At this point, there is a "built-in" potential across the depletion zone. | |||
| If an external voltage is placed across the diode with the same polarity as the built-in potential, the depletion zone continues to act as an insulator, preventing any significant electric current flow (unless electron/hole pairs are actively being created in the junction by, for instance, light. see ]). This is the '']'' phenomenon. However, if the polarity of the external voltage opposes the built-in potential, recombination can once again proceed, resulting in substantial electric current through the p–n junction (i.e. substantial numbers of electrons and holes recombine at the junction). For silicon diodes, the built-in potential is approximately 0.7 V (0.3 V for Germanium and 0.2 V for Schottky). Thus, if an external current is passed through the diode, about 0.7 V will be developed across the diode such that the P-doped region is positive with respect to the N-doped region and the diode is said to be "turned on" as it has a '']''. | |||
| A diode’s '']'' can be approximated by four regions of operation. | |||
| ] | |||
| At very large reverse bias, beyond the ] or PIV, a process called reverse ] occurs that causes a large increase in current (i.e., a large number of electrons and holes are created at, and move away from the p–n junction) that usually damages the device permanently. The ] is deliberately designed for use in the avalanche region. In the ], the concept of PIV is not applicable. A Zener diode contains a heavily doped p–n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is "clamped" to a known value (called the ''Zener voltage''), and avalanche does not occur. Both devices, however, do have a limit to the maximum current and power in the clamped reverse-voltage region. Also, following the end of forward conduction in any diode, there is reverse current for a short time. The device does not attain its full blocking capability until the reverse current ceases. | |||
| The second region, at reverse biases more positive than the PIV, has only a very small reverse saturation current. In the reverse bias region for a normal P–N rectifier diode, the current through the device is very low (in the µA range). However, this is temperature dependent, and at sufficiently high temperatures, a substantial amount of reverse current can be observed (mA or more). | |||
| The third region is forward but small bias, where only a small forward current is conducted. | |||
| As the potential difference is increased above an arbitrarily defined "cut-in voltage" or "on-voltage" or "diode forward voltage drop (V<sub>d</sub>)", the diode current becomes appreciable (the level of current considered "appreciable" and the value of cut-in voltage depends on the application), and the diode presents a very low resistance. The current–voltage curve is ]. In a normal silicon diode at rated currents, the arbitrary cut-in voltage is defined as 0.6 to 0.7 ]s. The value is different for other diode types—]s can be rated as low as 0.2 V, Germanium diodes 0.25 to 0.3 V, and red or blue ]s (LEDs) can have values of 1.4 V and 4.0 V respectively. | |||
| At higher currents the forward voltage drop of the diode increases. A drop of 1 V to 1.5 V is typical at full rated current for power diodes. | |||
| ===Shockley diode equation=== | |||
| The ''Shockley ideal diode equation'' or the ''diode law'' (named after ] co-inventor ]) gives the I–V characteristic of an ideal diode in either forward or reverse bias (or no bias). The equation is: | |||
| :<math>I=I_\mathrm{S} \left( e^{V_\mathrm{D}/(n V_\mathrm{T})}-1 \right),\,</math> | |||
| where | |||
| :''I'' is the diode current, | |||
| :''I''<sub>S</sub> is the reverse bias ] (or scale current), | |||
| :''V''<sub>D</sub> is the voltage across the diode, | |||
| :''V''<sub>T</sub> is the ], and | |||
| :''n'' is the ''ideality factor'', also known as the ''quality factor'' or sometimes ''emission coefficient''. The ideality factor ''n'' varies from 1 to 2 depending on the fabrication process and semiconductor material and in many cases is assumed to be approximately equal to 1 (thus the notation ''n'' is omitted). | |||
| The ] ''V''<sub>T</sub> is approximately 25.85 mV at 300 K, a temperature close to "room temperature" commonly used in device simulation software. At any temperature it is a known constant defined by: | |||
| :<math>V_\mathrm{T} = \frac{k T}{q} \, ,</math> | |||
| where ''k'' is the ], ''T'' is the absolute temperature of the p–n junction, and ''q'' is the magnitude of charge on an ] (the ]). | |||
| The reverse saturation current, ''I''<sub>S</sub>, is not constant for a given device, but varies with temperature; usually more significantly than ''V''<sub>T</sub>, so that ''V''<sub>D</sub> typically decreases as ''T'' increases. | |||
| The ''Shockley ideal diode equation'' or the ''diode law'' is derived with the assumption that the only processes giving rise to the current in the diode are drift (due to electrical field), diffusion, and thermal ] (R–G). It also assumes that the R–G current in the depletion region is insignificant. This means that the Shockley equation doesn’t account for the processes involved in reverse breakdown and photon-assisted R–G. Additionally, it doesn’t describe the "leveling off" of the I–V curve at high forward bias due to internal resistance. | |||
| Under ''reverse bias'' voltages (see Figure 5) the exponential in the diode equation is negligible, and the current is a constant (negative) reverse current value of −''I<sub>S</sub>''. The reverse ''breakdown region'' is not modeled by the Shockley diode equation. | |||
| For even rather small ''forward bias'' voltages (see Figure 5) the exponential is very large because the thermal voltage is very small, so the subtracted ‘1’ in the diode equation is negligible and the forward diode current is often approximated as | |||
| :<math>I=I_\mathrm{S} e^{V_\mathrm{D}/(n V_\mathrm{T})}</math> | |||
| The use of the diode equation in circuit problems is illustrated in the article on ]. | |||
| ===Small-signal behavior=== | |||
| For circuit design, a small-signal model of the diode behavior often proves useful. A specific example of diode modeling is discussed in the article on ]. | |||
| ===Reverse-recovery effect=== | |||
| Following the end of forward conduction in a p–n type diode, a reverse current flows for a short time. The device does not attain its blocking capability until the mobile charge in the junction is depleted. | |||
| The effect can be significant when switching large currents very quickly.<ref></ref> A certain amount of "reverse recovery time" t<sub>r</sub> (on the order of tens of nanoseconds to a few microseconds) may be required to remove the reverse recovery charge Q<sub>r</sub> from the diode. During this recovery time, the diode can actually conduct in the reverse direction. <!-- That is to say, current will effectively flow from the cathode to the anode! --> In certain real-world cases it can be important to consider the losses incurred by this non-ideal diode effect.<ref></ref> However, when the ] of the current is not so severe (e.g. Line frequency) the effect can be safely ignored. | |||
| For most applications, the effect is also negligible for Schottky diodes. | |||
| The reverse current ceases abruptly when the stored charge is depleted; this abrupt stop is exploited in ]s for generation of extremely short pulses. | |||
| ==Types of semiconductor diode== | |||
| ] | |||
| There are several types of ]s, which either emphasize a different physical aspect of a diode often by geometric scaling, doping level, choosing the right electrodes, are just an application of a diode in a special circuit, or are really different devices like the Gunn and laser diode and the ]: | |||
| Normal (p–n) diodes, which operate as described above, are usually made of doped ] or, more rarely, ]. Before the development of silicon power rectifier diodes, ] and later ] was used; its low efficiency gave it a much higher forward voltage drop (typically 1.4 to 1.7 V per "cell", with multiple cells stacked to increase the peak inverse voltage rating in high voltage rectifiers), and required a large heat sink (often an extension of the diode’s metal ]), much larger than a silicon diode of the same current ratings would require. The vast majority of all diodes are the p–n diodes found in ] ], which include two diodes per pin and many other internal diodes. | |||
| ]s | |||
| :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 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 V) and the Zener is that the channel length of the former exceeds the mean free path of the electrons, so there are collisions between them on the way out. The only practical difference is that the two types have temperature coefficients of opposite polarities. | |||
| ] | |||
| :These are a type of point-contact diode. The cat’s whisker diode consists of a thin or sharpened metal wire pressed against a semiconducting crystal, typically ] or a piece of ]. The wire forms the anode and the crystal forms the cathode. Cat’s whisker diodes were also called crystal diodes and found application in ]s. Cat’s whisker diodes are generally obsolete, but may be available from a few manufacturers.{{Citation needed|date=June 2009}} | |||
| ]s | |||
| :These are actually a ]<ref></ref> with the gate shorted to the source, and function like a two-terminal current-limiter analog to the Zener diode, which is limiting voltage. 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''. | |||
| ] or ]s | |||
| :These have a region of operation showing ] caused by ],<ref>Jonscher, A. K. The physics of the tunnel diode. British Journal of Applied Physics 12 (Dec. 1961), 654–659.</ref> allowing amplification of signals and very simple bistable circuits. Due to 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>Dowdey, J. E., and Travis, C. M. An analysis of steady-state nuclear radiation damage of tunnel diodes. IRE Transactions on Nuclear Science 11, 5 (November 1964), 55–59.</ref> Because of these properties, they are often used in spacecraft. | |||
| ]s | |||
| :These are similar to tunnel diodes in that they are made of materials such as GaAs or InP that exhibit a region of ]. With appropriate biasing, dipole domains form and travel across the diode, allowing high frequency ] ] to be built. | |||
| ]s (LEDs) | |||
| :In a diode formed from a ] semiconductor, such as ], carriers that cross the junction emit ] when they recombine with the majority carrier on the other side. Depending on the material, ]s (or colors)<ref></ref> from the ] to the near ] 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 |accessdate=2010-08-06}}</ref> The forward potential of these diodes depends on the wavelength of the emitted photons: 2.1 V corresponds to red, 4.0 V to violet. The first LEDs were red and yellow, and higher-frequency diodes have been developed over time. All LEDs produce incoherent, narrow-spectrum light; "white" LEDs are actually combinations of three LEDs of a different color, or a blue LED with a yellow ] coating. 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 ]. | |||
| ]s | |||
| :When an LED-like structure is contained in a ] formed by polishing the parallel end faces, a ] can be formed. Laser diodes are commonly used in ] devices and for high speed ]. | |||
| ]s | |||
| :This term is used both for conventional p–n diodes used to monitor temperature due to their varying forward voltage with temperature, and for ] for ]. Peltier heat pumps may be made from semiconductor, though they do not have any rectifying junctions, they use the differing behaviour of charge carriers in N and P type semiconductor to move heat. | |||
| ]s | |||
| :All semiconductors are subject to optical ] generation. This is typically an undesired effect, so most semiconductors are packaged in light blocking material. Photodiodes are intended to sense light(]), so they are packaged in materials that allow light to pass, and are usually PIN (the kind of diode most sensitive to light).<ref></ref> A photodiode can be used in ]s, in ], or in ]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 ]s. | |||
| ]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 |accessdate=2010-08-06}}</ref> They are used as radio frequency switches and attenuators. They are also used as large volume ionizing radiation detectors and as ]s. PIN diodes are also used in ], as their central layer can withstand high voltages. Furthermore, the PIN structure can be found in many ]s, such as ]s, power ]s, and ]s. | |||
| ]s | |||
| :] diodes are constructed from a 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 mA is in the range 0.15 V to 0.45 V, which makes them useful in voltage ] and prevention of transistor saturation. They can also be used as low loss ], although their reverse leakage current is in general higher than that of other diodes. Schottky diodes are ] 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 ], ]s, and ]. | |||
| 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. | |||
| ]-doped diodes | |||
| :As a dopant, gold (or ]) acts as recombination centers, which helps a fast recombination of minority carriers. This allows the diode to operate at 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></ref><ref>S. M. Sze, ''Modern Semiconductor Device Physics'', Wiley Interscience, ISBN 0-471-15237-4</ref> A typical example is the 1N914. | |||
| Snap-off or ]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 ] 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. | |||
| ]s or ''Forward Reference Diodes'' | |||
| : The term ''stabistor'' refers to a special type of diodes featuring extremely stable ] 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. | |||
| ] (TVS) | |||
| :These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltage ].<ref></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. | |||
| ] or varactor diodes | |||
| : These are used as voltage-controlled ]. These are important in PLL (]) and FLL (]) circuits, allowing tuning circuits, such as those in television receivers, to lock quickly. They also enabled tunable oscillators in early discrete tuning of radios, where a cheap and stable, but fixed-frequency, crystal oscillator provided the reference frequency for a ]. | |||
| ]s | |||
| :Diodes that can be made to conduct backward. This effect, called ], occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference. In practical voltage reference circuits, Zener and switching diodes are connected in series and opposite directions to balance the temperature coefficient 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 ], a registered trademark). The Zener diode is named for Dr. ] of Carnegie Mellon University, inventor of the device. | |||
| Other uses for semiconductor diodes include sensing temperature, and computing analog ]s (see ]). | |||
| {{float_begin|side=right}} | |||
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| | Diode | |||
| | ] | |||
| | ] | |||
| | ] | |||
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| | ] | |||
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| {{float_end|caption=Figure 6: Some diode symbols.}} | |||
| ==Numbering and coding schemes== | |||
| There are a number of common, standard and manufacturer-driven numbering and coding schemes for diodes; the two most common being the ]/] standard and the European ] standard: | |||
| ===EIA/JEDEC=== | |||
| The standardized 1N-series numbering ''EIA370'' system was introduced in the US by EIA/JEDEC (Joint Electron Device Engineering Council) about 1960. Among the most popular in this series were: 1N34A/1N270 (Germanium signal), 1N914/1N4148 (Silicon signal), ]-1N4007 (Silicon 1A power rectifier) and 1N54xx (Silicon 3A power rectifier)<ref>{{cite web|url=http://www.jedec.org/Home/about_jedec.cfm |title=About JEDEC |publisher=Jedec.org |date= |accessdate=2008-09-22}}</ref><ref>{{cite web|url=http://news.elektroda.net/introduction-dates-of-common-transistors-and-diodes-t94332.html |title=EDAboard.com |publisher=News.elektroda.net |date=2010-06-10 |accessdate=2010-08-06}}</ref><ref>{{cite web|url=http://semiconductormuseum.com/Museum_Index.htm |title=Transistor Museum Construction Projects Point Contact Germanium Western Electric Vintage Historic Semiconductors Photos Alloy Junction Oral History |publisher=Semiconductormuseum.com |author=I.D.E.A |date= |accessdate=2008-09-22}}</ref> | |||
| ===JIS=== | |||
| The ] system has all semiconductor diode designations starting with "1S". | |||
| ===Pro Electron=== | |||
| The European ] coding system for ]s was introduced in 1966 and comprises two letters followed by the part code. The first letter represents the semiconductor material used for the component (A = Germanium and B = Silicon) and the second letter represents the general function of the part (for diodes: A = low-power/signal, B = Variable capacitance, X = Multiplier, Y = Rectifier and Z = Voltage reference), for example: | |||
| *AA-series germanium low-power/signal diodes (e.g.: AA119) | |||
| *BA-series silicon low-power/signal diodes (e.g.: BAT18 Silicon RF Switching Diode) | |||
| *BY-series silicon rectifier diodes (e.g.: BY127 1250V, 1A rectifier diode) | |||
| *BZ-series silicon Zener diodes (e.g.: BZY88C4V7 4.7V Zener diode) | |||
| Other common numbering / coding systems (generally manufacturer-driven) include: | |||
| *GD-series germanium diodes (e.g.: GD9){{spaced ndash}}this is a very old coding system | |||
| *OA-series germanium diodes (e.g.: OA47){{spaced ndash}}a ] developed by ], a UK company | |||
| As well as these common codes, many manufacturers or organisations have their own systems too{{spaced ndash}}for example: | |||
| *HP diode 1901-0044 = JEDEC 1N4148 | |||
| *UK military diode CV448 = Mullard type OA81 = ] type GEX23 | |||
| ==Related devices== | |||
| *] | |||
| *] | |||
| *] or silicon controlled rectifier (SCR) | |||
| *] | |||
| *] | |||
| *] | |||
| In optics, an equivalent device for the diode but with laser light would be the ], also known as an Optical Diode, that allows light to only pass in one direction. It uses a ] as the main component. | |||
| ==Applications== | |||
| ===Radio demodulation=== | |||
| The first use for the diode was the demodulation of ] (AM) radio broadcasts. The history of this discovery is treated in depth in the ] article. In summary, an AM signal consists of alternating positive and negative peaks of a radio carrier wave, whose ] or ] is proportional to the original audio signal. The diode (originally a crystal diode) ] the AM radio frequency signal, leaving only the positive peaks of the carrier wave. The audio is then extracted from the rectified carrier wave using a simple ] and fed into an audio amplifier or ], which generates sound waves. | |||
| ===Power conversion=== | |||
| ]s are constructed from diodes, where they are used to convert ] (AC) electricity into ] (DC). Automotive ]s are a common example, where the diode, which rectifies the AC into DC, provides better performance than the ] or earlier, ]. Similarly, diodes are also used in ''] ]s'' to convert AC into higher DC voltages. | |||
| ===Over-voltage protection=== | |||
| Diodes are frequently used to conduct damaging high voltages away from sensitive electronic devices. They are usually reverse-biased (non-conducting) under normal circumstances. When the voltage rises above the normal range, the diodes become forward-biased (conducting). For example, diodes are used in (] and ]) ] and ] circuits to de-energize coils rapidly without the damaging ]s that would otherwise occur. (Any diode used in such an application is called a ]). Many ] also incorporate diodes on the connection pins to prevent external voltages from damaging their sensitive ]. Specialized diodes are used to protect from over-voltages at higher power (see ] above). | |||
| ===Logic gates=== | |||
| Diodes can be combined with other components to construct ] and ] ]s. This is referred to as ]. | |||
| ===Ionizing radiation detectors=== | |||
| In addition to light, mentioned above, ] diodes are sensitive to more ] radiation. In ], ]s and other sources of ionizing radiation cause ] ]s and single and multiple bit errors. | |||
| This effect is sometimes exploited by ]s to detect radiation. A single particle of radiation, with thousands or millions of ]s of energy, generates many charge carrier pairs, as its energy is deposited in the semiconductor material. If the depletion layer is large enough to catch the whole shower or to stop a heavy particle, a fairly accurate measurement of the particle’s energy can be made, simply by measuring the charge conducted and without the complexity of a magnetic spectrometer, etc. | |||
| These semiconductor radiation detectors need efficient and uniform charge collection and low leakage current. They are often cooled by ]. For longer-range (about a centimetre) particles, they need a very large depletion depth and large area. For short-range particles, they need any contact or un-depleted semiconductor on at least one surface to be very thin. The back-bias voltages are near breakdown (around a thousand volts per centimetre). Germanium and silicon are common materials. Some of these detectors sense position as well as energy. | |||
| They have a finite life, especially when detecting heavy particles, because of radiation damage. Silicon and germanium are quite different in their ability to convert ]s to electron showers. | |||
| ]s for high-energy particles are used in large numbers. Because of energy loss fluctuations, accurate measurement of the energy deposited is of less use. | |||
| ===Temperature measurements=== | |||
| A diode can be used as a ] measuring device, since the forward voltage drop across the diode depends on temperature, as in a ]. From the Shockley ideal diode equation given above, it might ''appear'' that the voltage has a ''positive'' temperature coefficient (at a constant current), but usually the variation of the ] term is more significant than the variation in the thermal voltage term. Most diodes therefore have a ''negative'' temperature coefficient, typically −2 mV/˚C for silicon diodes at room temperature. This is approximately linear for temperatures above about 20 ]s. Some graphs are given for: series, and . | |||
| ===Current steering=== | |||
| Diodes will prevent currents in unintended directions. To supply power to an electrical circuit during a power failure, the circuit can draw current from a ]. An ] may use diodes in this way to ensure that current is only drawn from the battery when necessary. Likewise, small boats typically have two circuits each with their own battery/batteries: one used for engine starting; one used for domestics. Normally, both are charged from a single alternator, and a heavy-duty split-charge diode is used to prevent the higher-charge battery (typically the engine battery) from discharging through the lower-charge battery when the alternator is not running. | |||
| Diodes are also used in ]. To reduce the amount of wiring needed in electronic musical keyboards, these instruments often use ] circuits. The keyboard controller scans the rows and columns to determine which note the player has pressed. The problem with matrix circuits is that, when several notes are pressed at once, the current can flow backwards through the circuit and trigger "]" that cause "ghost" notes to play. To avoid triggering unwanted notes, most keyboard matrix circuits have diodes soldered with the switch under each key of the ]. The same principle is also used for the switch matrix in solid-state ]s. | |||
| ==Abbreviations== | |||
| Diodes are usually referred to as ''D'' for diode on ]. Sometimes the abbreviation ''CR'' for ''crystal rectifier'' is used.<ref>{{cite book|author=John Ambrose Fleming|year=1919|url=http://books.google.com/books?id=xHNBAAAAIAAJ&pg=PA550&dq=%22crystal+rectifier%22+CR&as_brr=1|title=The Principles of Electric Wave Telegraphy and Telephony|place=London|publisher=Longmans, Green|page=550}}</ref> | |||
| ==Two-terminal nonlinear devices== | |||
| Many other two-terminal nonlinear devices exist, for example a ] has two terminals in a glass envelope and has interesting and useful nonlinear properties. Lamps including arc-discharge lamps, ]s, ]s and ]s have two terminals and display nonlinear current–voltage characteristics. | |||
| ==See also== | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| ==References== | |||
| {{reflist|2}} | |||
| ==External links== | |||
| ===Interactive and animations=== | |||
| *, University of Cambridge | |||
| * | |||
| {{Electronic component}} | |||
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| {{Link FA|tt}} | |||
| {{Link FA|eo}} | |||
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Revision as of 08:30, 9 August 2012
In electronics, a diode is a two-terminal electronic component with asymmetric transfer characteristic, with low (ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p-n junction connected to two electrical terminals. A vacuum tube diode, now rarely used except in some high-power technologies and by enthusiasts, is a vacuum tube with two electrodes, a plate (anode) and cathode.
The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be viewed as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, including extraction of modulation from radio signals in radio receivers—these diodes are forms of rectifiers.
However, diodes can have more complicated behavior than this simple on–off action. Semiconductor diodes do not begin conducting electricity until a certain threshold voltage or cut-In voltage is present in the forward direction (a state in which the diode is said to be forward-biased). The voltage drop across a forward-biased diode varies only a little with the current, and is a function of temperature; this effect can be used as a temperature sensor or voltage reference.
Semiconductor diodes' nonlinear current–voltage characteristic can be tailored by varying the semiconductor materials and introducing impurities into (doping) the materials. These are exploited in special-purpose diodes that perform many different functions. For example, diodes are used to regulate voltage (Zener diodes), to protect circuits from high voltage surges (avalanche diodes), to electronically tune radio and TV receivers (varactor diodes), to generate radio frequency oscillations (tunnel diodes, Gunn diodes, IMPATT diodes), and to produce light (light emitting diodes). Tunnel diodes exhibit negative resistance, which makes them useful in some types of circuits.
Diodes were the first semiconductor electronic devices. The discovery of crystals' rectifying abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor diodes, called cat's whisker diodes, developed around 1906, were made of mineral crystals such as galena. Today most diodes are made of silicon, but other semiconductors such as germanium are sometimes used.
History
Although the crystal semiconductor diode was popular before the thermionic diode, thermionic (vacuum tube) diodes and [[solid state (electronics)|solid shis modified light bulb effectively replaced the resistor in a DC
- "Physical Explanation – General Semiconductors". 2010-05-25. Retrieved 2010-08-06.
- "The Constituents of Semiconductor Components". 2010-05-25. Retrieved 2010-08-06.