Figure 1: Closeup of the image below, showing the square shaped semiconductor crystal

Figure 2: Various semiconductor diodes. Bottom: A bridge rectifier

Figure 3: Structure of a vacuum tube diode

In electronics, a diode is a two-terminal device (except that thermionic diodes may also have one or two ancillary terminals for a heater). A diode bridge or bridge rectifier is an arrangement of four diodes in a bridge configuration that provides the same polarity of output Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy A heater is any object that emits Heat or causes another body to achieve a higher Temperature. Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional current property. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e The varicap diode is used as an electrically adjustable capacitor. In Electronics, a varicap diode, varactor diode, variable capacitance diode or tuning diode is a type of Diode which has a variable

The directionality of current flow most diodes exhibit is sometimes generically called the rectifying property. A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. The most common function of a diode is to allow an electric current to pass in one direction (called the forward biased condition) and to block it in the opposite direction (the reverse biased condition). Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Thus, the diode can be thought of as an electronic version of a check valve. A check valve, clack valve, non-return valve or one-way valve is a Mechanical device, a Valve, which normally allows Fluid Real diodes do not display such a perfect on-off directionality but have a more complex non-linear electrical characteristic, which depends on the particular type of diode technology. This article describes the use of the term nonlinearity in mathematics Diodes also have many other functions in which they are not designed to operate in this on-off manner.

Early diodes included “cat’s whisker” crystals and vacuum tube devices (also called thermionic valves). Cat’s whisker refers to a thin Wire that lightly touches a semiconducting crystal to make an imperfect contact-junction detector in a Crystal radio This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. Today the most common diodes are made from semiconductor materials such as silicon or germanium. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Germanium (dʒɚˈmeɪniəm is a Chemical element with the symbol Ge and Atomic number 32

History

Although the crystal diode was popularized before the thermionic diode, thermionic and solid state diodes were developed in parallel. The principle of operation of thermionic diodes was discovered by Frederick Guthrie in 1873. Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy Frederick Guthrie (1833 - 1886 was a British scientific writer and professor ^[1] The principle of operation of crystal diodes was discovered in 1874 by the German scientist, Karl Ferdinand Braun. Karl Ferdinand Braun ( 6 June 1850 in Fulda, Germany &ndash 20 April 1918 in New York City, U ^[2]

Thermionic diode principles were rediscovered by Thomas Edison on February 13, 1880 and he was awarded a patent in 1883 (U.S. Patent 307,031 ), but developed the idea no further. Events 1258 - Baghdad falls to the Mongols, and the Abbasid Caliphate is destroyed Year 1880 ( MDCCCLXXX) was a Leap year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a Leap year Braun patented the crystal rectifier in 1899 [1]. Braun's discovery was further developed by Jagdish Chandra Bose into a useful device for radio detection. Sir Jagadish Chandra Bose, CSI, CIE, FRS (জগদীশ চন্দ্র বসু Jôgodish Chôndro Boshu) ( November 30

The first radio receiver using a crystal diode was built around 1900 by Greenleaf Whittier Pickard. Greenleaf Whittier Pickard ( February 14, 1877, Portland Maine - January 8, 1956, Newton Massachusetts) was a The first thermionic diode was patented in Britain by John Ambrose Fleming (scientific adviser to the Marconi Company and former Edison employee[2]) on November 16, 1904 (U.S. Patent 803,684  in November 1905). Sir John Ambrose Fleming ( November 29, 1849 - April 18, 1945) was an English Electrical engineer and Physicist The Marconi Company Ltd was founded by Guglielmo Marconi in 1897 as The Wireless Telegraph & Signal Company (sometimes presented as Wireless Events 534 - A second and final revision of the Codex Justinianus is published Year 1904 ( MCMIV) was a Leap year starting on Friday (link will display calendar of the Gregorian calendar (or a Leap year starting on Pickard received a patent for a silicon crystal detector on November 20, 1906 [3] (U.S. Patent 836,531 ). Events 284 - Diocletian was chosen as Roman Emperor. 762 - Bögü Khan of the Uyghurs, Year 1906 ( MCMVI) was a Common year starting on Monday (link will display full calendar of the Gregorian calendar (or a Common year starting

At the time of their invention, such devices were known as rectifiers. A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. In 1919, William Henry Eccles coined the term diode from Greek roots; di means "two", and ode (from odos) means "path". William Henry Eccles ( August 23 1875 - April 29 1966) was a British Physicist and a pioneer in the development of radio The following is an alphabetical list of Greek and Latin roots commonly used in English

Thermionic and gaseous state diodes

Figure 4: The symbol for an indirect heated vacuum tube diode. From top to bottom, the components are the anode, the cathode, and the heater filament.

Thermionic diodes are thermionic valve devices (also known as vacuum tubes), which are arrangements of electrodes surrounded by a vacuum within a glass envelope. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e Early examples were fairly similar in appearance to incandescent light bulbs. The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general

In thermionic valve diodes, a current is passed through the heater filament. An electrical filament is a thread of Metal, usually Tungsten, which is used to convert Electricity into light in Incandescent light bulbs (as developed This indirectly heats the cathode, another filament treated with a mixture of barium and strontium oxides, which are oxides of alkaline earth metals; these substances are chosen because they have a small work function. A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device Barium (ˈbɛəriəm is a Chemical element. It has the symbol Ba, and Atomic number 56 Strontium (ˈstrɒntiəm /ˈstrɒnʃiəm/) is a Chemical element with the symbol Sr and the Atomic number 38 An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element Biological occurrences Beryllium's low aqueous solubility means it is rarely available to biological systems it has no known role in living organisms and when encountered In Solid state physics, the work function is the minimum Energy (usually measured in Electron volts needed to remove an Electron from a solid (Some valves use direct heating, in which a tungsten filament acts as both cathode and emitter. ) The heat causes thermionic emission of electrons into the vacuum. Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy In forward operation, a surrounding metal electrode, called the anode, is positively charged, so that it electrostatically attracts the emitted electrons. An anode is an Electrode through which Electric current flows into a polarized electrical device Electrostatics is the branch of Science that deals with the Phenomena arising from what seems to be stationary Electric charges Since Classical However, electrons are not easily released from the unheated anode surface when the voltage polarity is reversed and hence any reverse flow is a very tiny current.

For much of the 20th century, thermionic valve diodes were used in analog signal applications, and as rectifiers in many power supplies. Today, valve diodes are only used in niche applications, such as rectifiers in guitar and hi-fi valve amplifiers, and specialized high-voltage equipment.

Semiconductor diodes

Most modern diodes are based on semiconductor p-n junctions. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact In a p-n diode, conventional current can flow from the p-type side (the anode) to the n-type side (the cathode), but cannot flow in the opposite direction. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. An anode is an Electrode through which Electric current flows into a polarized electrical device A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device Another type of semiconductor diode, the Schottky diode, is formed from the contact between a metal and a semiconductor rather than by a p-n junction. The Schottky diode (named after German physicist Walter H Schottky; also known as hot carrier diode) is a Semiconductor Diode with

Current–voltage characteristic

A semiconductor diode's current–voltage characteristic, or I–V curve, is related to the transport of carriers through the so-called depletion layer or depletion region that exists at the p-n junction between differing semiconductors. A current–voltage characteristic is a relationship typically represented as a Chart or graph between an Electric current and a corresponding Voltage In Semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region In Semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact When a p-n junction is first created, conduction band (mobile) electrons from the N-doped region diffuse into the P-doped region where there is a large population of holes (places for electrons in which no electron is present) 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 on the N-side and negatively charged acceptor on the P-side. The region around the p-n junction becomes depleted of charge carriers and thus behaves as an insulator. In Physics, a charge carrier denotes a free (mobile unbound particle carrying an Electric charge. Nonconductors or electrical insulators are materials which lack movable electric charges and which therefore lack a low-resistance path for charge flow

However, the depletion width cannot grow without limit. In Semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region For each electron-hole pair that recombines, a positively-charged dopant 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 and more ions are created, an increasing electric field develops through the depletion zone which 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. This is the reverse bias phenomenon. A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact 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. For silicon diodes, the built-in potential is approximately 0. 6 V. Thus, if an external current is passed through the diode, about 0. 6 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 forward bias. A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact

Figure 5: I–V characteristics of a P-N junction diode (not to scale).

A diode’s I–V characteristic can be approximated by four regions of operation (see the figure at right).

At very large reverse bias, beyond the peak inverse voltage or PIV, a process called reverse breakdown occurs which causes a large increase in current that usually damages the device permanently. The peak inverse voltage is the specified maximum voltage that a Diode rectifier will block Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials The avalanche diode is deliberately designed for use in the avalanche region. An avalanche diode is a Diode (usually made from Silicon, but can be made from another Semiconductor) that is designed to go through Avalanche breakdown In the zener diode, the concept of PIV is not applicable. A Zener diode is a type of Diode that permits current in the forward direction like a normal diode but also in the reverse direction if the voltage is larger 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.

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).

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", 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 exponential. In a normal silicon diode at rated currents, the arbitrary "cut-in" voltage is defined as 0. 6 to 0. 7 volts. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The value is different for other diode types — Schottky diodes can be as low as 0. The Schottky diode (named after German physicist Walter H Schottky; also known as hot carrier diode) is a Semiconductor Diode with 2 V and red light-emitting diodes (LEDs) can be 1. 4 V or more and blue LEDs can be up to 4. 0 V.

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 transistor co-inventor William Bradford Shockley, not to be confused with tetrode inventor Walter H. Schottky) is the I–V characteristic of an ideal diode in either forward or reverse bias (or no bias). In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals William Bradford Shockley ( February 13, 1910 &ndash August 12, 1989) was a British -born American Physicist A tetrode is an electronic device having four active Electrodes The term most commonly applies to a two-grid Vacuum tube. Walter Hermann Schottky ( 23 July 1886, Zürich, Switzerland – 4 March 1976, Pretzfeld, West Germany The equation is:

where

I is the diode current,

I_S is a scale factor called the saturation current,

V_D is the voltage across the diode,

V_T is the thermal voltage,

and n is the emission coefficient, also known as the ideality factor. Saturation current is a term used to describe a limit to the amount of current that can flow in an Electronic circuit or device Bridge from macroscopic to microscopic physics Boltzmann's constant k is a bridge between Macroscopic and microscopic physics Emission coefficient is a Coefficient in the power output per unit time of an Electromagnetic source a calculated value in Physics. The emission coefficient n varies from about 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 thermal voltage V_T is approximately 25. Bridge from macroscopic to microscopic physics Boltzmann's constant k is a bridge between Macroscopic and microscopic physics 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:

where

q is the magnitude of charge on an electron (the elementary charge),

k is Boltzmann’s constant,

T is the absolute temperature of the p-n junction in kelvins

The Shockley ideal diode equation or the diode law is derived with the assumption that the only processes giving rise to current in the diode are drift (due to electrical field), diffusion, and thermal recombination-generation. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The elementary charge, usually denoted e, is the Electric charge carried by a single Proton, or equivalently the negative of the electric charge carried Bridge from macroscopic to microscopic physics Boltzmann's constant k is a bridge between Macroscopic and microscopic physics The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic It also assumes that the recombination-generation (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_S. 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

The use of the diode equation in circuit problems is illustrated in the article on diode modeling. In Electronics, diode modeling refers to the mathematical models used to approximate the actual behavior of real diodes to enable calculations and circuit analysis

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 small-signal circuits. Small-signal modeling is a common analysis method used in Electrical engineering to describe Nonlinear devices in terms of Linear equations.

Types of semiconductor diode

Diode	Zener diode	Schottky diode	Tunnel diode
Light-emitting diode	Photodiode	Varicap	Silicon controlled rectifier

Figure 7: Some diode symbols

There are several types of junction diodes, 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 MOSFET:

Normal (p-n) diodes which operate as described above. A Zener diode is a type of Diode that permits current in the forward direction like a normal diode but also in the reverse direction if the voltage is larger The Schottky diode (named after German physicist Walter H Schottky; also known as hot carrier diode) is a Semiconductor Diode with A tunnel Diode or Esaki diode is a type of Semiconductor diode which is capable of very fast operation well into the Microwave frequency A photodiode is a type of Photodetector capable of converting Light into either current or Voltage, depending upon the mode of operation In Electronics, a varicap diode, varactor diode, variable capacitance diode or tuning diode is a type of Diode which has a variable A silicon-controlled rectifier (or semiconductor-controlled rectifier) is a four-layer solid state device that controls current. Usually made of doped silicon or, more rarely, germanium. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Germanium (dʒɚˈmeɪniəm is a Chemical element with the symbol Ge and Atomic number 32 Before the development of modern silicon power rectifier diodes, cuprous oxide and later selenium was used; its low efficiency gave it a much higher forward voltage drop (typically 1. Copper(I oxide or cuprous oxide (Cu2O is an Oxide of Copper. It is Insoluble in water and organic Solvents. Selenium (səˈliniəm is a Chemical element with the Atomic number 34 represented by the chemical symbol Se, an atomic mass of 78 4–1. 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 substrate), 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 CMOS integrated circuits, which include two diodes per pin and many other internal diodes. Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside

Avalanche diodes

Diodes that conduct in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. An avalanche diode is a Diode (usually made from Silicon, but can be made from another Semiconductor) that is designed to go through Avalanche breakdown 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.

Cat’s whisker or crystal diodes

These are a type of point contact diode. Cat’s whisker refers to a thin Wire that lightly touches a semiconducting crystal to make an imperfect contact-junction detector in a Crystal radio The cat’s whisker diode consists of a thin or sharpened metal wire pressed against a semiconducting crystal, typically galena or a piece of coal. Galena is the natural mineral form of Lead sulfide. It is the most important Lead Ore mineral [4] The wire forms the anode and the crystal forms the cathode. Cat’s whisker diodes were also called crystal diodes and found application in crystal radio receivers. Cat’s whisker diodes are obsolete.

Constant current diodes

These are actually a JFET with the gate shorted to the source, and function like a two-terminal current-limiting analog to the Zener diode; they allow a current through them to rise to a certain value, and then level off at a specific value. The junction gate field-effect transistor ( JFET or JUGFET) is the simplest type of Field effect transistor. Also called CLDs, constant-current diodes, diode-connected transistors, or current-regulating diodes. [5], [6]

Esaki or tunnel diodes

these have a region of operation showing negative resistance caused by quantum tunneling, thus allowing amplification of signals and very simple bistable circuits. Leona Esaki also known as Leo Esaki (江崎 玲於奈 Esaki Reona, born March 12, 1925) is a Japanese physicist who shared the A tunnel Diode or Esaki diode is a type of Semiconductor diode which is capable of very fast operation well into the Microwave frequency Negative resistance (or negative differential resistance (NDR or differential negative resistance (DNR is a property of Electrical circuit elements composed In Quantum mechanics, quantum tunnelling is a nanoscopic phenomenon in which a particle violates the principles of Classical mechanics by penetrating a These diodes are also the type most resistant to nuclear radiation.

Gunn diodes

These are similar to tunnel diodes in that they are made of materials such as GaAs or InP that exhibit a region of negative differential resistance. A Gunn diode, also known as a transferred electron device ( TED) is a form of Diode used in high-frequency Electronics. Negative resistance (or negative differential resistance (NDR or differential negative resistance (DNR is a property of Electrical circuit elements composed With appropriate biasing, dipole domains form and travel across the diode, allowing high frequency microwave oscillators to be built. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 An electronic oscillator is an Electronic circuit that produces a repetitive electronic signal often a Sine wave or a Square wave.

Light-emitting diodes (LEDs)

In a diode formed from a direct band-gap semiconductor, such as gallium arsenide, carriers that cross the junction emit photons when they recombine with the majority carrier on the other side. In Semiconductor Physics, a direct Bandgap means that the minimum energy of the Conduction band lies directly above the maximum energy of the Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Depending on the material, wavelengths (or colors) from the infrared to the near ultraviolet may be produced. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The forward potential of these diodes depends on the wavelength of the emitted photons: 1. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. 2 V corresponds to red, 2. 4 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 scintillator coating. A scintillator is a substance that absorbs high-energy (ie Ionizing) electromagnetic or charged Particle radiation then in response fluoresces 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. In Electronics, an opto-isolator (or optical isolator, optocoupler, photocoupler, or photoMOS)

Laser diodes

When an LED-like structure is contained in a resonant cavity formed by polishing the parallel end faces, a laser can be formed. A laser diode is a Laser where the active medium is a Semiconductor similar to that found in a Light-emitting diode. An optical cavity or optical resonator is an arrangement of Mirrors that forms a Standing wave Cavity resonator for Light waves Optical A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. Laser diodes are commonly used in optical storage devices and for high speed optical communication. Optical storage is a term from Engineering referring to the storage of data on an optically readable medium Optical communication is any form of Telecommunication that uses Light as the transmission medium

Peltier diodes

are used as sensors, heat engines for thermoelectric cooling. The thermoelectric effect is the direct conversion of temperature differences to electric Voltage and vice versa A heat engine is a physical or theoretical device that converts Thermal energy to mechanical output Thermoelectric cooling uses the Peltier effect to create a Heat flux between the junction of two different types of materials Charge carriers absorb and emit their band gap energies as heat.

Photodiodes

All semiconductors are subject to optical charge carrier generation. A photodiode is a type of Photodetector capable of converting Light into either current or Voltage, depending upon the mode of operation In Physics, a charge carrier denotes a free (mobile unbound particle carrying an Electric charge. 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). Photosensors or photodetectors are Sensors of Light or other Electromagnetic energy A photodiode can be used in solar cells, in photometry, or in optical communications. A solar cell or photovoltaic cell is a device that converts Solar energy into Electricity by the photovoltaic effect. This article deals with the usage of this term in Optics and Lighting. Optical communication is any form of Telecommunication that uses Light as the transmission medium 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 devices. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors

Point-contact diodes

These work the same as the junction semiconductor diodes described above, 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.

PIN diodes

A PIN diode has a central un-doped, or intrinsic, layer, forming a p-type/intrinsic/n-type structure. A PiN diode is a Diode with a wide lightly doped 'near' Intrinsic semiconductor region between a P-type semiconductor and an N-type semiconductor They are used as radio frequency switches and attenuators. They are also used as large volume ionizing radiation detectors and as photodetectors. Photosensors or photodetectors are Sensors of Light or other Electromagnetic energy PIN diodes are also used in power electronics, as their central layer can withstand high voltages. This article refers to the technology of power electronics For the musical genre see power electronics Power electronics is the applications Furthermore, the PIN structure can be found in many power semiconductor devices, such as IGBTs, power MOSFETs, and thyristors. Power semiconductor devices are semiconductor devices used as switches or rectifiers in power electronic circuits ( switch mode power supplies The insulated-gate bipolar transistor or IGBT is a three-terminal Power semiconductor device, noted for high efficiency and fast switching The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals The thyristor is a solid-state Semiconductor device with four layers of alternating N and P-type material

Switching diodes

Switching diodes, sometimes also called small signal diodes, are a single p-n diode in a discrete package. A switching diode provides essentially the same function as a switch. Below the specified applied voltage it has high resistance similar to an open switch, while above that voltage it suddenly changes to the low resistance of a closed switch. They are used in devices such as ring modulation. Ring modulation is a signal-processing effect in electronics related to Amplitude modulation or frequency mixing, performed by multiplying two signals where one

Schottky diodes

Schottky diodes are constructed from a metal to semiconductor contact. The Schottky diode (named after German physicist Walter H Schottky; also known as hot carrier diode) is a Semiconductor Diode with Walter Hermann Schottky ( 23 July 1886, Zürich, Switzerland – 4 March 1976, Pretzfeld, West Germany 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 clamping applications and prevention of transistor saturation. A clamper is an Electric circuit that prevents a signal from exceeding a certain defined magnitude They can also be used as low loss rectifiers although their reverse leakage current is generally higher than that of other diodes. A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. 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. In Physics, a charge carrier denotes a free (mobile unbound particle carrying an Electric charge. 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, mixers and detectors. A switched-mode power supply, switching-mode power supply or SMPS, is an electronic Power supply unit (PSU that incorporates a switching regulator In Telecommunication, a mixer is a Nonlinear or time-varying circuit or device that accepts as its Input two different frequencies and presents A detector is a device that recovers Information of interest contained in a Modulated wave

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 help a fast recombination of minority carriers. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 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). [7]. ^[3] A typical example is the 1N914.

Snap-off or Step recovery diodes

The term ‘step recovery’ relates to the form of the reverse recovery characteristic of these devices. In Electronics, a Step recovery diode ( SRD) is a semiconductor junction diode having the ability to generate extremely short pulses In Electronics, a Step recovery diode ( SRD) is a semiconductor junction diode having the ability to generate extremely short pulses After a forward current has been passing in an SRD and the current is interrupted or reversed, the reverse conduction will cease very abruptly (as in a step waveform). In Electronics, a Step recovery diode ( SRD) is a semiconductor junction diode having the ability to generate extremely short pulses SRDs can therefore provide very fast voltage transitions by the very sudden disappearance of the charge carriers.

Transient voltage suppression diode (TVS)

These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltage transients. A transient voltage suppression (TVS diode is an Electronic component used to protect sensitive Electronics from Voltage spikes induced on connected wires 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.

Varicap or varactor diodes

These are used as voltage-controlled capacitors. In Electronics, a varicap diode, varactor diode, variable capacitance diode or tuning diode is a type of Diode which has a variable In Electronics, a varicap diode, varactor diode, variable capacitance diode or tuning diode is a type of Diode which has a variable A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors 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, replacing older designs that took a long time to warm up and lock. A phase-locked loop or phase lock loop (PLL is a Control system that generates a signal that has a fixed relation to the phase of a "reference" A frequency-lock or frequency-locked loop (FLL is an electronic Control system that generates a signal that is locked to the frequency of an input or "reference" A PLL is faster than an FLL, but prone to integer harmonic locking (if one attempts to lock to a broadband signal). 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 voltage-controlled oscillator. A voltage-controlled oscillator or VCO is an Electronic oscillator designed to be controlled in Oscillation Frequency by a Voltage

Zener diodes

Diodes that can be made to conduct backwards. A Zener diode is a type of Diode that permits current in the forward direction like a normal diode but also in the reverse direction if the voltage is larger This effect, called Zener breakdown, 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 below). Two (equivalent) Zeners in series and in reverse order, in the same package, constitute a transient absorber (or Transorb, a registered trademark). A transient voltage suppression (TVS diode is an Electronic component used to protect sensitive Electronics from Voltage spikes induced on connected wires The Zener diode is named for Dr. Clarence Melvin Zener of Southern Illinois University, inventor of the device. Clarence Melvin Zener ( December 1, 1905 – July 15, 1993) was the American Physicist who first described the electrical

Other uses for semiconductor diodes include sensing temperature, and computing analog logarithms (see Operational amplifier applications#Logarithmic). In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce This article illustrates some typical applications of solid-state integrated circuit Operational amplifiers A simplified schematic notation is used and the reader is reminded that many

Numbering

A standardized 1N-series numbering system was introduced in the US by EIA/JEDEC (Joint Electron Device Engineering Council) about 1960. JEDEC Solid State Technology Association, formerly known as J oint E lectron D evice E ngineering C ouncil ( JEDEC) or Joint Among the most popular in this series were: 1N34A/1N270 (Germanium signal), IN914/1N4148 (Silicon signal) and 1N4001-1N4007 (Silicon 1A power rectifier). [8] [9] [10]

Related devices

• Transistor
• Thyristor or silicon controlled rectifier (SCR)
• TRIAC
• Diac
• Varistor

In optics, an equivalent device for the diode but with laser light would be the Optical isolator, also known as an Optical Diode, that allows light to only pass in 1 direction. In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals The thyristor is a solid-state Semiconductor device with four layers of alternating N and P-type material A TRIAC, or TRIode for Alternating Current is an electronic component approximately equivalent to two Silicon-controlled rectifiers ( SCRs The DIAC, or diode for alternating current, is a bidirectional trigger Diode that conducts current only after its Breakdown voltage has been A varistor is an electronic component with a significant non- ohmic current - Voltage characteristic An optical isolator, or optical diode, is an optical component which allows the transmission of light in only one direction It uses a Faraday rotator as the main component. A Faraday rotator is an optical device that rotates the Polarization of Light due to the Faraday effect, which in turn is based on a Magneto-optic

Applications

Figure 8: Several types of diodes. The scale is centimeters.

Radio demodulation

The first use for the diode was the demodulation of amplitude modulated (AM) radio broadcasts. Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave The history of this discovery is treated in depth in the radio article. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. In summary, an AM signal consists of alternating positive and negative peaks of voltage, whose amplitude or “envelope” is proportional to the original audio signal, but whose average value is zero. Amplitude is the magnitude of change in the oscillating variable with each Oscillation, within an oscillating system The diode (originally a crystal diode) rectifies the AM signal, leaving a signal whose average amplitude is the desired audio signal. A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. The average value is extracted using a simple filter and fed into an audio transducer, which generates sound. Electronic filters are Electronic circuits which perform Signal processing functions specifically intended to remove unwanted signal components and/or enhance wanted A transducer is a device usually electrical, electronic, Electro-mechanical, Electromagnetic, Photonic, or Photovoltaic

Power conversion

Rectifiers are constructed from diodes, where they are used to convert alternating current (AC) electricity into direct current (DC). A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant Direct current ( DC) is the unidirectional flow of Electric charge. Automotive alternators are a common example, where the diode provides better performance than the commutator of earlier dynamo. alternator is an electromechanical device that converts mechanical energy to Alternating current electrical energy In Mathematics, the commutator gives an indication of the extent to which a certain Binary operation fails to be Commutative. In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic Similarly, diodes are also used in Cockcroft–Walton voltage multipliers to convert AC into higher DC voltages. The Cockcroft-Walton (CW generator, or multiplier, was named after the two men who in 1932 used this circuit design to power their Particle accelerator, performing

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 ( stepper motor and H-bridge ) motor controller and relay circuits to de-energize coils rapidly without the damaging voltage spikes that would otherwise occur. A stepper motor (or step motor) is a brushless, synchronous Electric An H-bridge is an Electronic circuit which enables DC Electric motors to be run forwards or backwards A motor controller is a device or group of devices that serves to govern in some predetermined manner the performance of an Electric motor. A relay is an electrical Switch that opens and closes under the control of another Electrical circuit. (Any diode used in such an application is called a flyback diode). A flyback diode (sometimes called a Snubber diode freewheeling diode, suppressor diode, or catch diode) is a Diode used to eliminate Many integrated circuits also incorporate diodes on the connection pins to prevent external voltages from damaging their sensitive transistors. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals Specialized diodes are used to protect from over-voltages at higher power (see Diode types above).

Logic gates

Diodes can be combined with other components to construct AND and OR logic gates. In Logic and/or Mathematics, logical conjunction or and is a two-place Logical operation that results in a value of true if both of A logic gate performs a logical operation on one or more logic inputs and produces a single logic output This is referred to as diode logic. Diode logic or Diode-resistor logic, is a circuit style that uses Diodes to construct Boolean Logic gates for circuits.

Ionising radiation detectors

In addition to light, mentioned above, semiconductor diodes are sensitive to more energetic radiation. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In electronics, cosmic rays and other sources of ionising radiation cause noise pulses and single and multiple bit errors. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on is a one volume manga created by Tsutomu Nihei as a prequel to his ten-volume work Blame!. In Medicine, a person's pulse is the throbbing of their arteries. This effect is sometimes exploited by particle detectors to detect radiation. In experimental and applied Particle physics and Nuclear engineering, a particle detector, also known as a radiation detector, is a device used to A single particle of radiation, with thousands or millions of electron volts 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 or etc. These semiconductor radiation detectors need efficient and uniform charge collection and low leakage current. They are often cooled by liquid nitrogen. Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of 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 gamma rays to electron showers. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions

Semiconductor detectors for high energy particles are used in large numbers. A semiconductor detector is a device that uses a semiconductor (usually Silicon or Germanium) to detect Because of energy loss fluctuations, accurate measurement of the energy deposited is of less use.

Temperature measuring

A diode can be used as a temperature measuring device, since the forward voltage drop across the diode depends on temperature, as in a Silicon bandgap temperature sensor. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The silicon bandgap temperature sensor is an extremely common form of temperature sensor ( Thermometer) used in electronic equipment From the Shockley ideal diode equation given above, it appears the voltage has a positive temperature coefficient (at a constant current) but depends on doping concentration and operating temperature (Sze 2007). The temperature coefficient can be negative as in typical thermistors or positive for temperature sense diodes down to about 20 kelvins.

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 battery. In electronics a battery is a combination of two or more Electrochemical cells which store chemical Energy which can be converted into electrical energy An Uninterruptible power supply may use diodes in this way to ensure that current is only drawn from the battery when necessary. An uninterruptible power supply ( UPS) also known as a continuous power supply ( CPS) or a battery backup is a device which maintains a continuous Similarly, 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 charged battery when the alternator is not running [[11]].

Diodes are also used in electronic musical keyboards. An electronic keyboard or digital keyboard is a type of Keyboard instrument. To reduce the amount of wiring needed in electronic musical keyboards, these instruments often use keyboard matrix circuits. Most electronic keyboards used in Synthesizers Electronic organs and Digital pianos use a keyboard matrix circuit to connect the switches for each 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 "ghost" notes. To avoid triggering unwanted notes, most keyboard matrix circuits have diodes soldered with the switch under each key of the musical keyboard. A musical keyboard is the set of adjacent depressible levers or keys on a Musical instrument, particularly the piano

Abbreviations

Diodes are usually referred to as D for diode on PCBs. A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces Sometimes the abbreviation CR for crystal rectifier is seen. ^[4]

See also

• Diode modelling
• P-N junction
• Small-signal model

Notes

1. ^ 1928 Nobel Lecture: Owen W. In Electronics, diode modeling refers to the mathematical models used to approximate the actual behavior of real diodes to enable calculations and circuit analysis A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact Small-signal modeling is a common analysis method used in Electrical engineering to describe Nonlinear devices in terms of Linear equations. Richardson, "Thermionic phenomena and the laws which govern them," December 12, 1929
2. ^ Historical lecture on Karl Braun
3. ^ S. M. Sze, Modern Semiconductor Device Physics, Wiley Interscience, ISBN 0-471-15237-4
4. ^ John Ambrose Fleming. Sir John Ambrose Fleming ( November 29, 1849 - April 18, 1945) was an English Electrical engineer and Physicist (1919). The Principles of Electric Wave Telegraphy and Telephony. London: Longmans, Green. 550.

External links

• The Unusual Diode FAQ
• Interactive Explanation of Semiconductor Diode
• “Device Cross Section” for pn diode, Schottky diode, and silicon controlled rectifier.