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Current Crowding
Current crowding (also current crowding effect, or CCE) is a nonuniform distribution of current density through a conductor or semiconductor, especially in the vicinity of electrical contacts and over PN junctions. Current crowding is one of the factors limiting the efficiency of light-emitting diodes. Materials with low electron mobility, mobility of charge carriers (e.g., aluminium gallium indium phosphide (AlGaInP)) are especially prone to current crowding phenomena. It is the dominant loss mechanism in some LEDs, where the current densities, especially around the P-side contacts, reach an area of the emission characteristics with lower brightness/current efficiency. Current crowding can lead to localized overheating and formation of thermal hotspots, in catastrophic cases leading to thermal runaway. Nonhomogenous distribution of current also aggravates electromigration effects and the formation of voids (see, e.g., the Kirkendall effect). Formation of voids causes localized nonh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Current Density
In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point. In SI base units, the electric current density is measured in amperes per square metre. Definition Assume that ''A'' (SI unit: m2) is a small surface centred at a given point ''M'' and orthogonal to the motion of the charges at ''M''. If ''I'' (SI unit: A) is the electric current flowing through ''A'', then electric current density ''j'' at ''M'' is given by the limit: :j = \lim_ \frac = \left.\frac \_, with surface ''A'' remaining centered at ''M'' and orthogonal to the motion of the charges during the limit process. The current density vector j is the vector whose magnitude is the electric current density, and whose dire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Contact
An electrical contact is an electrical circuit component found in electrical switches, relays, connectors and circuit breakers. Each contact is a piece of electrically conductive material, typically metal. When a pair of contacts touch, they can pass an electrical current with a certain contact resistance, dependent on surface structure, surface chemistry and contact time; when the pair is separated by an insulating gap, then the pair does not pass a current. When the contacts touch, the switch is ''closed''; when the contacts are separated, the switch is ''open''. The gap must be an insulating medium, such as air, vacuum, oil, SF6. Contacts may be operated by humans in push-buttons and switches, by mechanical pressure in sensors or machine cams, and electromechanically in relays. The surfaces where contacts touch are usually composed of metals such as silver or gold alloysMatsushita Electronics, "Relay Techninal Information: Definition of Relay Terminology", § Contact, http ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PN Junction
PN may refer to: Arts and entertainment * ''Purple Noon'', a 1960 film * Patriotic Nigras, a griefing group in the game ''Second Life'' Business and economics * Pacific National, a rail freight company in Australia * Participatory notes, issued to unregistered overseas investors in Indian stock markets * Pennsylvania Northeastern Railroad (reporting mark PN) * Promissory note, a contract where one party makes an unconditional promise in writing to pay a sum of money to another * West Air (China) (IATA airline code PN) Organizations Navies * Pakistan Navy * Peruvian Navy * Philippine Navy * Portuguese Navy Political parties * National Renaissance Front The National Renaissance Front ( ro, Frontul Renașterii Naționale, FRN; also translated as ''Front of National Regeneration'', ''Front of National Rebirth'', ''Front of National Resurrection'', or ''Front of National Renaissance'') was a Romani ..., Partidul Naţiunii, a political party in Romania * Partit Nazzjonali ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light-emitting Diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresponding to the energy of the photons) is determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device. Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared (IR) light. Infrared LEDs are used in remote-control circuits, such as those used with a wide variety of consumer electronics. The first visible-light LEDs were of low intensity and limited to red. Early LEDs were often used as indicator lamps, replacing small incandescent bulbs, and in seven-segment displays. Later developments produced LEDs available in visible, ultraviolet (UV) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Mobility
In solid-state physics, the electron mobility characterises how quickly an electron can move through a metal or semiconductor when pulled by an electric field. There is an analogous quantity for holes, called hole mobility. The term carrier mobility refers in general to both electron and hole mobility. Electron and hole mobility are special cases of electrical mobility of charged particles in a fluid under an applied electric field. When an electric field ''E'' is applied across a piece of material, the electrons respond by moving with an average velocity called the drift velocity, v_d. Then the electron mobility ''μ'' is defined as v_d = \mu E. Electron mobility is almost always specified in units of cm2/( V⋅ s). This is different from the SI unit of mobility, m2/( V⋅ s). They are related by 1 m2/(V⋅s) = 104 cm2/(V⋅s). Conductivity is proportional to the product of mobility and carrier concentration. For example, the same conductivity could come from a small numbe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charge Carrier
In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used most commonly in solid state physics. In a conducting medium, an electric field can exert force on these free particles, causing a net motion of the particles through the medium; this is what constitutes an electric current. In conducting media, particles serve to carry charge: *In many metals, the charge carriers are electrons. One or two of the valence electrons from each atom are able to move about freely within the crystal structure of the metal. The free electrons are referred to as conduction electrons, and the cloud of free electrons is called a Fermi gas. Many metals have electron and hole bands. In some, the majority carriers are holes. *In electrolytes, such as salt water, the charge carriers are ions, which are atoms or molecul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aluminium Gallium Indium Phosphide
Aluminium gallium indium phosphide (, also AlInGaP, InGaAlP, GaInP, etc.) is a semiconductor material that provides a platform for the development of novel multi-junction photovoltaics and optoelectronic devices, as it spans a direct bandgap from deep ultraviolet to infrared. AlGaInP is used in manufacture of light-emitting diodes of high-brightness red, orange, green, and yellow color, to form the heterostructure emitting light. It is also used to make diode lasers. Formation AlGaInP layer is often grown by heteroepitaxy on gallium arsenide or gallium phosphide in order to form a quantum well structure. Heteroepitaxy is a kind of epitaxy performed with materials that are different from each other. In heteroepitaxy, a crystalline film grows on a crystalline substrate or film of a different material. This technology is often used to grow crystalline films of materials for which single crystals cannot 1D view. Another example of heteroepitaxy is gallium nitride (GaN) on sapphire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IMEC
Interuniversity Microelectronics Centre (IMEC) is an international research & development organization, active in the fields of nanoelectronics and digital technologies, with headquarters in Belgium. Luc Van den hove has served as President and CEO since 2009. In September 2016, imec merged with the Flemish digital research center, iMinds. Overview Imec employs around 4,000 researchers from more than 90 countries; it has numerous facilities dedicated to research and development around the world, including 12,000 square meters of cleanroom capacity for semiconductor processing. The imec headquarters are located in Leuven. History In 1982, the Flemish Government set up a program to strengthen the microelectronics industry in Flanders. This program included setting up a laboratory for advanced research in microelectronics (imec), a semiconductor foundry (former Alcatel Microelectronics, now STMicroelectronics and AMI Semiconductor,) and a training program for VLSI design enginee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Runaway
Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. It is a kind of uncontrolled positive feedback. In chemistry (and chemical engineering), thermal runaway is associated with strongly exothermic reactions that are accelerated by temperature rise. In electrical engineering, thermal runaway is typically associated with increased current flow and power dissipation. Thermal runaway can occur in civil engineering, notably when the heat released by large amounts of curing concrete is not controlled. In astrophysics, runaway nuclear fusion reactions in stars can lead to nova and several types of supernova explosions, and also occur as a less dramatic event in the normal evolution of solar-mass stars, the " he ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromigration
Electromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect is important in applications where high direct current densities are used, such as in microelectronics and related structures. As the structure size in electronics such as integrated circuits (ICs) decreases, the practical significance of this effect increases. History The phenomenon of electromigration has been known for over 100 years, having been discovered by the French scientist Gerardin. The topic first became of practical interest during the late 1960s when packaged ICs first appeared. The earliest commercially available ICs failed in a mere three weeks of use from runaway electromigration, which led to a major industry effort to correct this problem. The first observation of electromigration in thin films was made by I. Blech.I. Blech: ''Electromigration in Thin Aluminum Fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kirkendall Effect
The Kirkendall effect is the motion of the interface between two metals that occurs as a consequence of the difference in diffusion rates of the metal atoms. The effect can be observed for example by placing insoluble markers at the interface between a pure metal and an alloy containing that metal, and heating to a temperature where atomic diffusion is reasonable for the given timescale; the boundary will move relative to the markers. This process was named after Ernest Kirkendall (1914–2005), assistant professor of chemical engineering at Wayne State University from 1941 to 1946. The paper describing the discovery of the effect was published in 1947. The Kirkendall effect has important practical consequences. One of these is the prevention or suppression of voids formed at the boundary interface in various kinds of alloy to metal bonding. These are referred to as Kirkendall voids. History The Kirkendall effect was discovered by Ernest Kirkendall and Alice Smigelskas in 1947 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bipolar Junction Transistor
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between the terminals, making the device capable of amplification or switching. BJTs use two p–n junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material. The junctions can be made in several different ways, such as changing the doping of the semiconductor material as it is grown, by depositing metal pellets to form alloy junctions, or by such methods as diffusion of n-type and p-type doping substances into the crystal. The superior predictability and performance of junction transistors quickly displaced the original point-contact transistor. Diffused transistors, along wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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