Power semiconductor device
A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics. Such a device is called a power device or, when used in an integrated circuit, a power IC. A power semiconductor device is used in "commutation mode", therefore has a design optimized for such usage. Linear power circuits are widespread as voltage regulators, audio amplifiers, radio frequency amplifiers. Power semiconductors are found in systems delivering as little as a few tens of milliwatts for a headphone amplifier, up to around a gigawatt in a high voltage direct current transmission line; the first semiconductor device used in power circuits was the electrolytic rectifier - an early version was described by a French experimenter, A. Nodon, in 1904; these were popular with early radio experimenters as they could be improvised from aluminum sheets, household chemicals. They had low withstand limited efficiency; the first solid-state power semiconductor devices were copper oxide rectifiers, used in early battery chargers and power supplies for radio equipment, announced in 1927 by L.
O. Grundahl and P. H. Geiger; the first germanium power semiconductor device appeared in 1952 with the introduction of the power diode by R. N. Hall, it had a reverse voltage blocking capability of 200 V and a current rating of 35 A. Germanium bipolar transistors with substantial power handling capabilities were introduced around 1952. Power handling capability evolved and by 1954 germanium alloy junction transistors with 100 watt dissipation were available; these were all low-frequency devices, used up to around 100 kHz, up to 85 degrees Celsius junction temperature. Silicon power transistors were not made until 1957, but when available had better frequency response than germanium devices, could operate up to 150 C junction temperature; the thyristor appeared in 1957. It is able to withstand high reverse breakdown voltage and is capable of carrying high current. However, one disadvantage of the thyristor in switching circuits is that once it becomes'latched-on' in the conducting state. Thyristors which could be turned off, called gate turn-off thyristors, were introduced in 1960.
These overcome some limitations of the ordinary thyristor, because they can be turned on or off with an applied signal. Due to improvements in the MOSFET technology, the power MOSFET became available in the late 1970s. International Rectifier introduced a 25 A, 400 V power MOSFET in 1978; this device allows operation at higher frequencies than a bipolar transistor, but is limited to low voltage applications. The Insulated-gate bipolar transistor was developed in the 1980s, became available in the 1990s; this component has the power handling capability of the bipolar transistor and the advantages of the isolated gate drive of the power MOSFET. Some common power devices are the power diode, power MOSFET, IGBT; the power diode and power MOSFET operate on similar principles to their low-power counterparts, but are able to carry a larger amount of current and are able to withstand a larger reverse-bias voltage in the off-state. Structural changes are made in a power device in order to accommodate the higher current density, higher power dissipation, and/or higher reverse breakdown voltage.
The vast majority of the discrete power devices are built using a vertical structure, whereas small-signal devices employ a lateral structure. With the vertical structure, the current rating of the device is proportional to its area, the voltage blocking capability is achieved in the height of the die. With this structure, one of the connections of the device is located on the bottom of the semiconductor die. A power device may be classified as one of the following main categories: A two-terminal device, whose state is dependent on the external power circuit to which it is connected. A three-terminal device, whose state is dependent on not only its external power circuit, but the signal on its driving terminal. A four terminal device. SCS is a type of thyristor having four layers and four terminals called anode, anode gate, cathode gate and cathode; the terminals are connected to the first, second and fourth layer respectively. Another classification is less obvious, but has a strong influence on device performance: A majority carrier device.
A minority carrier device. A majority carrier device is faster, but the charge injection of minority carrier devices allows for better on-state performance. An ideal diode should have the following characteristics: When forward-biased, the voltage across the end terminals of the diode should be zero, no matter the current that flows through it; when reverse-biased, the leakage current should be zero, no matter the voltage. The transition between the on-state and the off-state should be instantaneous. In reality, the design of a diode is a trade-off between performance in on-st
The metal-oxide-semiconductor field-effect transistor is a type of field-effect transistor, most fabricated by the controlled oxidation of silicon. It has an insulated gate; this ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. A metal-insulator-semiconductor field-effect transistor or MISFET is a term synonymous with MOSFET. Another synonym is IGFET for insulated-gate field-effect transistor; the basic principle of the field-effect transistor was first patented by Julius Edgar Lilienfeld in 1925. The main advantage of a MOSFET is that it requires no input current to control the load current, when compared with bipolar transistors. In an enhancement mode MOSFET, voltage applied to the gate terminal increases the conductivity of the device. In depletion mode transistors, voltage applied at the gate reduces the conductivity; the "metal" in the name MOSFET is sometimes a misnomer, because the gate material can be a layer of polysilicon.
"oxide" in the name can be a misnomer, as different dielectric materials are used with the aim of obtaining strong channels with smaller applied voltages. The MOSFET is by far the most common transistor in digital circuits, as billions may be included in a memory chip or microprocessor. Since MOSFETs can be made with either p-type or n-type semiconductors, complementary pairs of MOS transistors can be used to make switching circuits with low power consumption, in the form of CMOS logic; the basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925. In 1959, Dawon Kahng and Martin M. Atalla at Bell Labs invented the metal-oxide-semiconductor field-effect transistor as an offshoot to the patented FET design. Operationally and structurally different from the bipolar junction transistor, the MOSFET was made by putting an insulating layer on the surface of the semiconductor and placing a metallic gate electrode on that, it used crystalline silicon for the semiconductor and a thermally oxidized layer of silicon dioxide for the insulator.
The silicon MOSFET did not generate localized electron traps at the interface between the silicon and its native oxide layer, thus was inherently free from the trapping and scattering of carriers that had impeded the performance of earlier field-effect transistors. The semiconductor of choice is silicon; some chip manufacturers, most notably IBM and Intel, have started using a chemical compound of silicon and germanium in MOSFET channels. Many semiconductors with better electrical properties than silicon, such as gallium arsenide, do not form good semiconductor-to-insulator interfaces, thus are not suitable for MOSFETs. Research continues on creating insulators with acceptable electrical characteristics on other semiconductor materials. To overcome the increase in power consumption due to gate current leakage, a high-κ dielectric is used instead of silicon dioxide for the gate insulator, while polysilicon is replaced by metal gates; the gate is separated from the channel by a thin insulating layer, traditionally of silicon dioxide and of silicon oxynitride.
Some companies have started to introduce a high-κ dielectric and metal gate combination in the 45 nanometer node. When a voltage is applied between the gate and body terminals, the electric field generated penetrates through the oxide and creates an inversion layer or channel at the semiconductor-insulator interface; the inversion layer provides a channel through which current can pass between source and drain terminals. Varying the voltage between the gate and body modulates the conductivity of this layer and thereby controls the current flow between drain and source; this is known as enhancement mode. The traditional metal-oxide-semiconductor structure is obtained by growing a layer of silicon dioxide on top of a silicon substrate and depositing a layer of metal or polycrystalline silicon; as the silicon dioxide is a dielectric material, its structure is equivalent to a planar capacitor, with one of the electrodes replaced by a semiconductor. When a voltage is applied across a MOS structure, it modifies the distribution of charges in the semiconductor.
If we consider a p-type semiconductor, a positive voltage, V GB, from gate to body creates a depletion layer by forcing the positively charged holes away from the gate-insulator/semiconductor interface, leaving exposed a carrier-free region of immobile, negatively charged acceptor ions. If V GB is high enough, a high concentration of negative charge carriers forms in an inversion layer located in a thin layer next to the interface between the semiconductor and the insulator. Conventionally, the gate voltage at which the volume density of electrons in the inversion layer is the same as the volume density of holes in the body is called the threshold voltage; when the voltage between transistor gate and source exceeds the threshold voltage, the difference is known as overdrive voltage. This structure with p-type body is the basis of the n-type MOSFET, which requires the addition of n-type source and drain regions; the MOS capacitor structure is the heart of the MOSFET. Let's consider a MOS capacitor.
If a positive voltage is applied at
A display device is an output device for presentation of information in visual or tactile form. When the input information, supplied has an electrical signal the display is called an electronic display. Common applications for electronic visual displays are televisions or computer monitors. In the history of display technology, a variety of display devices and technologies have been used. There are various designs for display devices. Several components are common to most display devices. Display, or screen, the portion of the device that displays changeable image Bezel, the area surrounding portion that displays changing information Housing, the enclosure of the display These are the technologies used to create the various displays in use today. Electroluminescent display Liquid crystal display with Light-emitting diode -backlit LCD display Light-emitting diode display OLED display AMOLED display Plasma display Quantum dot display Some displays can show only digits or alphanumeric characters.
They are called segment displays, because they are composed of several segments that switch on and off to give appearance of desired glyph. The segments are single LEDs or liquid crystals, they are used in digital watches and pocket calculators. There are several types: Seven-segment display Fourteen-segment display Sixteen-segment display HD44780 LCD controller a accepted protocol for LCDs. Incandescent filaments Vacuum fluorescent display Cold cathode gas discharge Light-emitting diode Liquid crystal display Physical vane with electromagnetic activation 2-dimensional displays that cover a full area are called video displays, since it is the main modality of presenting video. Full-area 2-dimensional displays are used in, for example: Television set Computer monitors Head-mounted display Broadcast reference monitor Medical monitors Underlying technologies for full-area 2-dimensional displays include: Cathode ray tube display Light-emitting diode display Electroluminescent display Electronic paper, E Ink Plasma display panel Liquid crystal display High-Performance Addressing display Thin-film transistor display Organic light-emitting diode display Digital Light Processing display Surface-conduction electron-emitter display Field emission display Laser TV Carbon nanotubes Quantum dot display Interferometric modulator display Digital microshutter display The multiplexed display technique is used to drive most display devices.
Swept-volume display Varifocal mirror display Emissive volume display Laser display Holographic display Light field displays Ticker tape Split-flap display Flip-disc display Rollsign Tactile electronic displays are intended for the blind. They use electro-mechanical parts to dynamically update a tactile image so that the image may be felt by the fingers. Optacon, using metal rods instead of light in order to convey images to blind people by tactile sensation. Society for Information Display - An international professional organization dedicated to the study of display technology University of Waterloo Stratford Campus - A university that offers students the opportunity to display their work on the school's 3-storey Christie MicroTile wall
An LED display is a flat panel display, which uses an array of light-emitting diodes as pixels for a video display. Their brightness allows them to be used outdoors where they are visible in the sun for store signs and billboards. In recent years, they have become used in destination signs on public transport vehicles, as well as variable-message signs on highways. LED displays are capable of providing general illumination in addition to visual display, as when used for stage lighting or other decorative purposes. LED diode came into existence in 1962 and were red in color for the first decade; the first practical LED was invented by Nick Holonyak, Jr. in 1962 while he was at General Electric company. Early models were monochromatic by design; the efficient Blue LED completing the color triad, did not commercially arrive until the late 1980s. In the late 1980s Aluminium Indium Gallium Phosphide LEDs arrived and these provided an efficient source of red and amber, were used to good effect in information displays.
But it was still impossible to achieve full colour. The available “green” was hardly green at all – yellow, an early blue needed a power station to run it, it was only when Shuji Nakumura at Nichia Chemical, announced the development of the blue LED based on Indium Gallium Nitride that the game was on for big LED video displays. However the whole idea of what could be done with LED was given an early shake up by Mark Fisher’sled history u2 popmart tour set electrosonic bob simpson design for U2’s “Popmart” tour of 1997, he realized that with long viewing distances wide pixel spacing could be used to achieve large images if viewed at night. The system had to be suitable for touring so an open mesh arrangement was used that could be rolled up for transport; the whole display was 52m 17m high. It had a total of 000 pixels. Amazingly the company that supplied the LED pixels and their driving system, SACO Technologies of Montreal, had never engineered a video system before, being more used to building mimic panels for powerstation control rooms.
Large displays use high-brightness diodes to generate a wide spectrum of colors. It took three decades and organic light-emitting diodes for Sony to introduce an OLED TV, the Sony XEL-1 OLED screen, marketed in 2009. At CES 2012, Sony presented Crystal LED, a TV with a true LED-display. Jumbotron Sony Crystal LED Samsung Onyx for Cinema Direct View LED Video Walls The 2011 UEFA Champions League Final match between Manchester United and Barcelona was broadcast live in 3D format in Gothenburg, on an EKTA screen, it had a refresh rate of 100 Hz, a diagonal of 7.11 m and a display area of 6.192×3.483 m, was listed in the Guinness Book of Records as the largest LED 3D TV. A claim, it was developed and documented by James P. Mitchell in 1977. Initial public recognition came from the Westinghouse Educational Foundation Science Talent Search group, a Science Service organization; the paper entry was named in the "Honors Group" publicized to universities on January 25, 1978. The paper was subsequently invited and presented at the Iowa Academy of Science at the University of Northern Iowa.
The operational prototype was displayed at the Eastern Iowa SEF on March 18 and obtained a top "Physical Sciences" award and IEEE recognition. The project was again displayed at the 29th International SEF at the Anaheim Ca. Convention Center on May 8–10; the ¼-inch thin miniature flat panel modular prototype, scientific paper, full screen schematic with video interface were displayed at this event. It received awards by General Motors Corporation; this project marked some of the earliest progress towards the replacement of the 70+ year old high-voltage analog CRT system with a digital x-y scanned LED matrix driven with a NTSC television RF video format. Mitchell's paper projected the future replacement of CRTs and included foreseen application to battery operated devices due the advantages of low-power. Displacement of the electromagnetic scan systems included the removal of inductive deflection, electron beam and color convergence circuits and has been a significant achievement; the unique properties of the light emitting diode as an emissive device simplifies matrix scanning complexity and has helped the modern television adapt to digital communications and shrink into its current thin form factor.
The 1977 model was monochromatic by design. AMOLED QLED Media related to LED displays at Wikimedia Commons
David Packard was an American electrical engineer and co-founder, with William Hewlett, of Hewlett-Packard, serving as president, CEO, Chairman of the Board of HP. He served as U. S. Deputy Secretary of Defense from 1969 to 1971 during the Nixon administration. Packard served as President of the Uniformed Services University of the Health Sciences from 1976 to 1981, he was chairman of the Board of Regents from 1973 to 1982. Packard was the recipient of the Presidential Medal of Freedom in 1988 and is noted for many technological innovations and philanthropic endeavors. David Packard was born in Pueblo and attended Centennial High School, where early on he showed an interest in science, engineering and leadership, his father was an attorney. He earned his B. A. from Stanford University in 1934, where he earned letters in football and basketball and attained membership in the Phi Beta Kappa Society and was a Brother of the Alpha Delta Phi Literary Fraternity. Stanford is where he met two people who were important to Lucile Salter and Bill Hewlett.
Packard attended the University of Colorado at Boulder before taking a position with the General Electric Company in Schenectady, New York. In 1938, he returned to Stanford, where he earned a master's degree in electrical engineering that year. In the same year, he married Lucile Salter, with whom he had four children: David, Nancy and Julie. Lucile Packard died in 1987. In 1939, Packard and Hewlett established Hewlett-Packard in Packard's garage with an initial capital investment of $538. Packard mentions in his book The HP Way that the name Hewlett-Packard was determined by the flip of a coin: HP, rather than PH, their first product was an audio frequency oscillator sold to Walt Disney Studios for use on the soundtrack of Fantasia. The company grew into the world's largest producer of electronic measurement devices, it became a major producer of calculators and laser and ink jet printers. HP incorporated in 1947, with Packard becoming its first president, serving in that role until 1964, he was elected Chief Executive Officer and Chairman of the Board, holding those positions through 1968.
Packard left HP in 1969 to serve in the Nixon administration until 1971, at which time he returned to HP and was re-elected Chairman of the Board, serving from 1972 to 1993. In 1991, Packard oversaw a major reorganization at HP, he retired from HP in 1993. At the time of his death in 1996, Packard's stake in the company was worth more than $1 billion. At Packard's instruction, the domain name "HP.com" was registered on March 3, 1986, as such was one of the earliest to be registered. Upon entering office in 1969, President Richard M. Nixon appointed Packard U. S. Deputy Secretary of Defense under Secretary of Defense Melvin Laird. Packard returned to Hewlett-Packard in 1972 as Chairman of the Board. While serving in the Department of Defense, he brought concepts of resource management used in business to the military, as well as establishing the Defense Systems Management College. In 1970, Packard issued a memorandum that contained a number of major reforms designed to address "the real mess we have on our hands."
A key reform was elimination of Robert MacNamara's Total Package Procurement except in rare situations. Near the end of his time at DoD, Packard wrote the "Packard Memo" or "Employment of Military Resources in the Event of Civil Disturbances". Enacted in February 1972, the act describes exceptions to the 1878 Posse Comitatus Act, which limited the powers of the federal government to use the U. S. military for law enforcement, except where expressly authorized by the Constitution or Act of Congress — noting that the Constitution provides an exception when needed "to prevent loss of life or wanton destruction of property and to restore governmental functioning and public order when sudden and unexpected civil disturbances, disasters, or calamities endanger life and property and disrupt normal governmental functions to such an extent that duly constituted local authorities are unable to control the situations" and "to protect Federal property and Federal governmental functions when the need for protection exists and duly constituted local authorities are unable or decline to provide adequate protection".
§ 214.5 states that "employment of DoD military resources for assistance to civil authorities in controlling civil disturbances will be predicated upon the issuance of a Presidential Executive order or Presidential directive authorizing", with exceptions "limited to: Cases of sudden and unexpected emergencies as described in §215.4, which require that immediate military action be taken. Providing military resources to civil authorities as prescribed in §215.9 of this part."According to Lindorff, these exceptions reinstate the possibility of martial law in the U. S. prohibited since 1878. In the 1970s and 1980s Packard was a prominent advisor to the White House on defense procurement and management, he served as chairman of The Business Council in 1973 and 1974. From 1985-86, he served as chairman of The Packard Commission. From the early 1980s until his death in 1996, Packard dedicated much of his time and money to philanthropic projects. Prompted by his daughters Nancy Packard Burnett and Julie Packard, in 1978 Dave and Lucile Packard created the Monterey Bay Aquarium Foundation.
The couple donated $55 million to build the new aquarium, which opened in 1984 with Julie Packard as executive director. In 1987, Packard gave $13 million to create the Monterey Bay Aquarium Research Institute. In 1964, the couple founded the David and Lucile Pa
Network analyzer (electrical)
A network analyzer is an instrument that measures the network parameters of electrical networks. Today, network analyzers measure s–parameters because reflection and transmission of electrical networks are easy to measure at high frequencies, but there are other network parameter sets such as y-parameters, z-parameters, h-parameters. Network analyzers are used to characterize two-port networks such as amplifiers and filters, but they can be used on networks with an arbitrary number of ports. Network analyzers are used at high frequencies. Special types of network analyzers can cover lower frequency ranges down to 1 Hz; these network analyzers can be used for example for the stability analysis of open loops or for the measurement of audio and ultrasonic components. The two basic types of network analyzers are scalar network analyzer —measures amplitude properties only vector network analyzer —measures both amplitude and phase propertiesA VNA is a form of RF network analyzer used for RF design applications.
A VNA may be called a gain-phase meter or an automatic network analyzer. An SNA is functionally identical to a spectrum analyzer in combination with a tracking generator; as of 2007, VNAs are the most common type of network analyzers, so references to an unqualified "network analyzer" most mean a VNA. Three prominent VNA manufacturers are Keysight and Rohde & Schwarz. Another category of network analyzer is the microwave transition analyzer or large signal network analyzer, which measure both amplitude and phase of the fundamental and harmonics; the MTA was commercialized before the LSNA, but was lacking some of the user-friendly calibration features now available with the LSNA. The basic architecture of a network analyzer involves a signal generator, a test set, one or more receivers and display. In some setups, these units are distinct instruments. Most VNAs have two test ports, permitting measurement of four S-parameters, but instruments with more than two ports are available commercially; the network analyzer needs a test signal, a signal generator or signal source will provide one.
Older network analyzers did not have their own signal generator, but had the ability to control a stand-alone signal generator using, for example, a GPIB connection. Nearly all modern network analyzers have a built-in signal generator. High-performance network analyzers have two built-in sources. Two built-in sources are useful for applications such as mixer test, where one source provides the RF signal, another the LO, or amplifier intermodulation testing, where two tones are required for the test; the test set takes the signal generator output and routes it to the device under test, it routes the signal to be measured to the receivers. It splits off a reference channel for the incident wave. In a SNA, the reference channel may go to a diode detector whose output is sent to the signal generator's automatic level control; the result is better control of better measurement accuracy. In a VNA, the reference channel goes to the receivers. Directional couplers or two resistor power dividers are used for signal separation.
Some microwave test sets include the front end mixers for the receivers. The receivers make the measurements. A network analyzer will have one or more receivers connected to its test ports; the reference test port is labeled R, the primary test ports are A, B, C.... Some analyzers will dedicate a separate receiver to each test port, but others share one or two receivers among the ports; the R receiver may be less sensitive than the receivers used on the test ports. For the SNA, the receiver only measures the magnitude of the signal. A receiver can be a detector diode; the simplest SNA will have a single test port, but more accurate measurements are made when a reference port is used. The reference port will compensate for amplitude variations in the test signal at the measurement plane, it is possible to share a single detector and use it for both the reference port and the test port by making two measurement passes. For the VNA, the receiver measures the phase of the signal, it needs a reference channel to determine the phase, so a VNA needs at least two receivers.
The usual method down converts the reference and test channels to make the measurements at a lower frequency. The phase may be measured with a quadrature detector. A VNA requires at least two receivers, but some will have three or four receivers to permit simultaneous measurement of different parameters. There are some VNA architectures that infer magnitude from just power measurements. With the processed RF signal available from the receiver / detector section it is necessary to display the signal in a format that can be interpreted. With the levels of processing that are available today, some sophisticated solutions are available in RF network analyzers. Here the reflection and transmission data is formatted to enable the information to be interpreted as as possible. Most RF network analyzers incorporate features including linear and logarithmic sweeps and log formats, polar plots, Smith charts, etc. Trace markers, limit lines and pass / fail criteria may be added in many instances. A VNA is a test system that enables the RF performance of radio frequency and microwave devices to be ch
A light-emitting diode is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons; this effect is called electroluminescence. The color of the light 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 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. Modern LEDs are available across the visible and infrared wavelengths, with high light output. Early LEDs were used as indicator lamps, replacing small incandescent bulbs, in seven-segment displays. Recent developments have produced white-light LEDs suitable for room lighting.
LEDs have led to new displays and sensors, while their high switching rates are useful in advanced communications technology. LEDs have many advantages over incandescent light sources, including lower energy consumption, longer lifetime, improved physical robustness, smaller size, faster switching. Light-emitting diodes are used in applications as diverse as aviation lighting, automotive headlamps, general lighting, traffic signals, camera flashes, lighted wallpaper and medical devices. Unlike a laser, the color of light emitted from an LED is neither coherent nor monochromatic, but the spectrum is narrow with respect to human vision, functionally monochromatic. Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector. Russian inventor Oleg Losev reported creation of the first LED in 1927, his research was distributed in Soviet and British scientific journals, but no practical use was made of the discovery for several decades.
In 1936, Georges Destriau observed that electroluminescence could be produced when zinc sulphide powder is suspended in an insulator and an alternating electrical field is applied to it. In his publications, Destriau referred to luminescence as Losev-Light. Destriau worked in the laboratories of Madame Marie Curie an early pioneer in the field of luminescence with research on radium. Hungarian Zoltán Bay together with György Szigeti pre-empted led lighting in Hungary in 1939 by patented a lighting device based on SiC, with an option on boron carbide, that emmitted white, yellowish white, or greenish white depending on impurities present. Kurt Lehovec, Carl Accardo, Edward Jamgochian explained these first light-emitting diodes in 1951 using an apparatus employing SiC crystals with a current source of battery or pulse generator and with a comparison to a variant, crystal in 1953. Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide and other semiconductor alloys in 1955.
Braunstein observed infrared emission generated by simple diode structures using gallium antimonide, GaAs, indium phosphide, silicon-germanium alloys at room temperature and at 77 kelvins. In 1957, Braunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance; as noted by Kroemer Braunstein "…had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away; this signal was played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup." This setup presaged the use of LEDs for optical communication applications. In September 1961, while working at Texas Instruments in Dallas, James R. Biard and Gary Pittman discovered near-infrared light emission from a tunnel diode they had constructed on a GaAs substrate. By October 1961, they had demonstrated efficient light emission and signal coupling between a GaAs p-n junction light emitter and an electrically isolated semiconductor photodetector.
On August 8, 1962, Biard and Pittman filed a patent titled "Semiconductor Radiant Diode" based on their findings, which described a zinc-diffused p–n junction LED with a spaced cathode contact to allow for efficient emission of infrared light under forward bias. After establishing the priority of their work based on engineering notebooks predating submissions from G. E. Labs, RCA Research Labs, IBM Research Labs, Bell Labs, Lincoln Lab at MIT, the U. S. patent office issued the two inventors the patent for the GaAs infrared light-emitting diode, the first practical LED. After filing the patent, Texas Instruments began a project to manufacture infrared diodes. In October 1962, TI announced the first commercial LED product, which employed a pure GaAs crystal to emit an 890 nm light output. In October 1963, TI announced the first commercial hemispherical LED, the SNX-110; the first visible-spectrum LED was developed in 1962 by Nick Holonyak, Jr. while working at General Electric. Holonyak first reported his LED in the journal Applied Physics Letters on December 1, 1962.
M. George Craford, a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T. P. Pearsall created the first high-brightness, high-efficiency LEDs for optical fiber telecommunicat