A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal passive semiconductor electronic component, with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 1962 by physicist J. B. Gunn. Its largest use is in electronic oscillators to generate microwaves, in applications such as radar speed guns, microwave relay data link transmitters, and automatic door openers.
A diode is a two-terminal electronic component that conducts current primarily in one direction ; it has low resistance in one direction, and high resistance in the other. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other materials such as gallium arsenide and germanium are used.
Passivity is a property of engineering systems, used in a variety of engineering disciplines, but most commonly found in analog electronics and control systems. A passive component, depending on field, may be either a component that consumes but does not produce energy or a component that is incapable of power gain.
A semiconductor material has an electrical conductivity value falling between that of a metal, like copper, gold, etc. and an insulator, such as glass. Their resistance decreases as their temperature increases, which is behaviour opposite to that of a metal. Their conducting properties may be altered in useful ways by the deliberate, controlled introduction of impurities ("doping") into the crystal structure. Where two differently-doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers which include electrons, ions and electron holes at these junctions is the basis of diodes, transistors and all modern electronics. Some examples of semiconductors are silicon, germanium, and gallium arsenide. After silicon, gallium arsenide is the second most common semiconductor used in laser diodes, solar cells, microwave frequency integrated circuits, and others. Silicon is a critical element for fabricating most electronic circuits.
Its internal construction is unlike other diodes in that it consists only of N-doped semiconductor material, whereas most diodes consist of both P and N-doped regions. It therefore does not conduct in only one direction and cannot rectify alternating current like other diodes, which is why some sources do not use the term diode but prefer TED. In the Gunn diode, three regions exist: two of those are heavily N-doped on each terminal, with a thin layer of lightly n-doped material between. When a voltage is applied to the device, the electrical gradient will be largest across the thin middle layer. If the voltage is increased, the current through the layer will first increase, but eventually, at higher field values, the conductive properties of the middle layer are altered, increasing its resistivity, and causing the current to fall. This means a Gunn diode has a region of negative differential resistance in its current-voltage characteristic curve, in which an increase of applied voltage, causes a decrease in current. This property allows it to amplify, functioning as a radio frequency amplifier, or to become unstable and oscillate when it is biased with a DC voltage.
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction.
In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it.
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal. It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a power gain greater than one.
The negative differential resistance, combined with the timing properties of the intermediate layer, is responsible for the diode's largest use: in electronic oscillators at microwave frequencies and above. A microwave oscillator can be created simply by applying a DC voltage to bias the device into its negative resistance region. In effect, the negative differential resistance of the diode cancels the positive resistance of the load circuit, thus creating a circuit with zero differential resistance, which will produce spontaneous oscillations. The oscillation frequency is determined partly by the properties of the middle diode layer, but can be tuned by external factors. In practical oscillators an electronic resonator is usually added to control frequency, in the form of a waveguide, microwave cavity or YIG sphere. The diode is usually mounted inside the cavity. The diode cancels the loss resistance of the resonator, so it produces oscillations at its resonant frequency. The frequency can be tuned mechanically, by adjusting the size of the cavity, or in case of YIG spheres by changing the magnetic field. Gunn diodes are used to build oscillators in the 10 GHz to high (THz) frequency range.
An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave. Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal. They are widely used in many electronic devices. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games.
Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter; with frequencies between 300 MHz (1 m) and 300 GHz (1 mm). Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF bands. A more common definition in radio engineering is the range between 1 and 100 GHz. In all cases, microwaves include the entire SHF band at minimum. Frequencies in the microwave range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations.
Direct current (DC) is the unidirectional flow of electric charge. A battery is a good example of a DC power supply. Direct current may flow in a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.
Gallium arsenide Gunn diodes are made for frequencies up to 200 GHz, gallium nitride materials can reach up to 3 terahertz.
Gallium arsenide (GaAs) is a compound of the elements gallium and arsenic. It is a III-V direct bandgap semiconductor with a zinc blende crystal structure.
Gallium nitride (GaN) is a binary III/V direct bandgap semiconductor commonly used in light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic, high-power and high-frequency devices. For example, GaN is the substrate which makes violet (405 nm) laser diodes possible, without use of nonlinear optical frequency-doubling.
The Gunn diode is based on the Gunn effect, and both are named for the physicist J. B. Gunn who, at IBM in 1962, discovered the effect because he refused to accept inconsistent experimental results in gallium arsenide as "noise", and tracked down the cause. Alan Chynoweth, of Bell Telephone Laboratories, showed in June 1965 that only a transferred-electron mechanism could explain the experimental results.It was realized that the oscillations he detected were explained by the Ridley-Watkins-Hilsum theory, named for British physicists Brian Ridley, Tom Watkins and Cyril Hilsum who in scientific papers in 1961 showed that bulk semiconductors could display negative resistance , meaning that increasing the applied voltage causes the current to decrease.
John Battiscombe "J. B." Gunn, known as Ian or Iain, was a British physicist, who spent most of his career in the United States. He discovered the Gunn Effect, which led to the invention of the Gunn diode, the first inexpensive source of microwave power that did not require vacuum tubes. He was born John Battiscombe Gunn, but only used that name in legal documents.
International Business Machines Corporation (IBM) is an American multinational information technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the Computing-Tabulating-Recording Company (CTR) and was renamed "International Business Machines" in 1924.
Brian Kidd Ridley is a British solid-state physicist specialising in semiconductor theory. He is an emeritus professor at the University of Essex.
The Gunn effect, and its relation to the Watkins-Ridley-Hilsum effect entered electronics literature in the early 1970s, e.g. in books on transferred electron devicesand, more recently on nonlinear wave methods for charge transport.
The electronic band structure of some semiconductor materials, including gallium arsenide (GaAs), have another energy band or sub-band in addition to the valence and conduction bands which are usually used in semiconductor devices. This third band is at a higher energy than the normal conduction band and is empty until energy is supplied to promote electrons to it. The energy comes from the kinetic energy of ballistic electrons, that is, electrons in the conduction band but moving with sufficient kinetic energy such that they are able to reach the third band.
These electrons either start out below the Fermi level and are given a sufficiently long mean free path to acquire the needed energy by applying a strong electric field, or they are injected by a cathode with the right energy. With forward voltage applied, the Fermi level in the cathode moves into the third band, and reflections of ballistic electrons starting around the Fermi level are minimized by matching the density of states and using the additional interface layers to let the reflected waves interfere destructively.
In GaAs the effective mass of the electrons in the third band is higher than those in the usual conduction band, so the mobility or drift velocity of the electrons in that band is lower. As the forward voltage increases, more and more electrons can reach the third band, causing them to move slower, and current through the device decreases. This creates a region of negative differential resistance in the voltage/current relationship.
When a high enough potential is applied to the diode, the charge carrier density along the cathode becomes unstable, and will develop small segments of low conductivity, with the rest of the cathode having high conductivity. Most of the cathode voltage drop will occur across the segment, so it will have a high electric field. Under the influence of this electric field it will move along the cathode to the anode. It is not possible to balance the population in both bands, so there will always be thin slices of high field strength in a general background of low field strength. So in practice, with a small increase in forward voltage, a low conductivity segment is created at the cathode, resistance increases, the segment moves along the bar to the anode, and when it reaches the anode it is absorbed and a new segment is created at the cathode to keep the total voltage constant. If the voltage is lowered, any existing slice is quenched and resistance decreases again.
The laboratory methods that are used to select materials for the manufacture of Gunn diodes include angle-resolved photoemission spectroscopy.
Because of their high frequency capability, Gunn diodes are mainly used at microwave frequencies and above. They can produce some of the highest output power of any semiconductor devices at these frequencies. Their most common use is in oscillators, but they are also used in microwave amplifiers to amplify signals. Because the diode is a one-port (two terminal) device, an amplifier circuit must separate the outgoing amplified signal from the incoming input signal to prevent coupling. One common circuit is a reflection amplifier which uses a circulator to separate the signals. A bias tee is needed to isolate the bias current from the high frequency oscillations.
Gunn diode oscillators are used to generate microwave power for:airborne collision avoidance radar, anti-lock brakes, sensors for monitoring the flow of traffic, car radar detectors, pedestrian safety systems, "distance traveled" recorders, motion detectors, "slow-speed" sensors (to detect pedestrian and traffic movement up to 85 km/h (50 mph)), traffic signal controllers, automatic door openers, automatic traffic gates, process control equipment to monitor throughput, burglar alarms and equipment to detect trespassers, sensors to avoid derailment of trains, remote vibration detectors, rotational speed tachometers, moisture content monitors.
By virtue of their low voltage operation, Gunn diodes can serve as microwave frequency generators for very low powered (few-milliwatt) microwave transceivers called Gunnplexers. They were first used by British radio amateurs in the late 1970s, and many Gunnplexer designs have been published in journals. They typically consist of an approximately 3 inch waveguide into which the diode is mounted. A low voltage (less than 12 volt) direct current power supply, that can be modulated appropriately, is used to drive the diode. The waveguide is blocked at one end to form a resonant cavity and the other end usually feeds a horn antenna. An additional "mixer diode" is inserted into the waveguide, and it is often connected to a modified FM broadcast receiver to enable listening of other amateur stations. Gunnplexers are most commonly used in the 10 GHz and 24 GHz ham bands and sometimes 22 GHz security alarms are modified as the diode(s) can be put in a slightly detuned cavity with layers of copper or aluminium foil on opposite edges for moving to the licensed amateur band. Typically the mixer diode if intact is reused in its existing waveguide and these parts are well known for being extremely static sensitive. On most commercial units this part is protected with a parallel resistor and other components and a variant is used in some Rb atomic clocks. The mixer diode is useful for lower frequency applications even if the Gunn diode is weakened from use, and some amateur radio enthusiasts have used them in conjunction with an external oscillator or n/2 wavelength Gunn diode for satellite finding and other applications.
Gunn oscillators are used as local oscillators for millimeter-wave and submillimeter-wave radio astronomy receivers. The Gunn diode is mounted in a cavity tuned to resonate at twice the fundamental frequency of the diode. The cavity length is changed by a micrometer adjustment. Gunn oscillators capable of generating over 50 mW over a 50% tuning range (one waveguide band) are available.
The Gunn oscillator frequency is multiplied by a diode frequency multiplier for submillimeter-wave applications.
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities. Electrons pass by the openings to these cavities and cause radio waves to oscillate within, similar to the way a whistle produces a tone when excited by an air stream blown past its opening. The frequency of the microwaves produced, the resonant frequency, is determined by the cavities' physical dimensions. Unlike other vacuum tubes such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier in order to increase the intensity of an applied microwave signal; the magnetron serves solely as an oscillator, generating a microwave signal from direct current electricity supplied to the vacuum tube.
A laser diode, (LD), injection laser diode (ILD), or diode laser is a semiconductor device similar to a light-emitting diode in which the laser beam is created at the diode's junction. Laser diodes can directly convert electrical energy into light. Driven by voltage, the doped p-n-transition allows for recombination of an electron with a hole. Due to the drop of the electron from a higher energy level to a lower one, radiation, in the form of an emitted photon is generated. This is spontaneous emission. Stimulated emission can be produced when the process is continued and further generate light with the same phase, coherence and wavelength.
In electronics, a varicap diode, varactor diode, variable capacitance diode, variable reactance diode or tuning diode is a type of diode designed to exploit the voltage-dependent capacitance of a reverse-biased p–n junction.
A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian, which is used as an amplifier for high radio frequencies, from UHF up into the microwave range. Low-power klystrons are used as oscillators in terrestrial microwave relay communications links, while high-power klystrons are used as output tubes in UHF television transmitters, satellite communication, radar transmitters, and to generate the drive power for modern particle accelerators.
In electronics, the dynatron oscillator, invented in 1918 by Albert Hull at General Electric, is an obsolete vacuum tube electronic oscillator circuit which uses a negative resistance characteristic in early tetrode vacuum tubes, caused by a process called secondary emission. It was the first negative resistance vacuum tube oscillator. The dynatron oscillator circuit was used to a limited extent as beat frequency oscillators (BFOs), and local oscillators in vacuum tube radio receivers as well as in scientific and test equipment from the 1920s to the 1940s but became obsolete around World War 2 due to the variability of secondary emission in tubes.
A tunnel diode or Esaki diode is a type of semiconductor diode that has negative resistance due to the quantum mechanical effect called tunneling. It was invented in August 1957 by Leo Esaki, Yuriko Kurose, and Takashi Suzuki when they were working at Tokyo Tsushin Kogyo, now known as Sony. In 1973, Esaki received the Nobel Prize in Physics, jointly with Brian Josephson, for discovering the electron tunneling effect used in these diodes. Robert Noyce independently devised the idea of a tunnel diode while working for William Shockley, but was discouraged from pursuing it. Tunnel diodes were first manufactured by Sony in 1957, followed by General Electric and other companies from about 1960, and are still made in low volume today.
A MESFET is a field-effect transistor semiconductor device similar to a JFET with a Schottky (metal-semiconductor) junction instead of a p-n junction for a gate.
A High-electron-mobility transistor (HEMT), also known as heterostructure FET (HFET) or modulation-doped FET (MODFET), is a field-effect transistor incorporating a junction between two materials with different band gaps as the channel instead of a doped region. A commonly used material combination is GaAs with AlGaAs, though there is wide variation, dependent on the application of the device. Devices incorporating more indium generally show better high-frequency performance, while in recent years, gallium nitride HEMTs have attracted attention due to their high-power performance. Like other FETs, HEMTs are used in integrated circuits as digital on-off switches. FETs can also be used as amplifiers for large amounts of current using a small voltage as a control signal. Both of these uses are made possible by the FET’s unique current-voltage characteristics. HEMT transistors are able to operate at higher frequencies than ordinary transistors, up to millimeter wave frequencies, and are used in high-frequency products such as cell phones, satellite television receivers, voltage converters, and radar equipment. They are widely used in satellite receivers, in low power amplifiers and in the defense industry.
An IMPATT diode is a form of high-power semiconductor diode used in high-frequency microwave electronics devices. They have negative resistance and are used as oscillators and amplifiers at microwave frequencies. They operate at frequencies of about 3 and 100 GHz, or higher. The main advantage is their high-power capability; single IMPATT diodes can produce continuous microwave outputs of up to 3 kilowatts, and pulsed outputs of much higher power. These diodes are used in a variety of applications from low-power radar systems to proximity alarms. A major drawback of IMPATT diodes is the high level of phase noise they generate. This results from the statistical nature of the avalanche process.
A backward wave oscillator (BWO), also called carcinotron or backward wave tube, is a vacuum tube that is used to generate microwaves up to the terahertz range. Belonging to the traveling-wave tube family, it is an oscillator with a wide electronic tuning range.
A resonant-tunneling diode (RTD) is a diode with a resonant-tunneling structure in which electrons can tunnel through some resonant states at certain energy levels. The current–voltage characteristic often exhibits negative differential resistance regions.
A vircator is a microwave generator that is capable of generating brief pulses of tunable, narrow band microwaves at very high power levels. Its application is mainly in the area of electronic warfare, by way of interfering with electronic equipment such as radars or radio equipment.
In solid state physics the Ridley–Watkins–Hilsum theory (RWH) explains the mechanism by which differential negative resistance is developed in a bulk solid state semiconductor material when a voltage is applied to the terminals of the sample. It is the theory behind the operation of the Gunn diode as well as several other microwave semiconductor devices, which are used practically in electronic oscillators to produce microwave power. It is named for British physicists Brian Ridley, Tom Watkins and Cyril Hilsum who wrote theoretical papers on the effect in 1961.
The heterostructure barrier varactor (HBV) is a semiconductor device which shows a variable capacitance with voltage bias, similar to a varactor diode. Unlike a diode, it has an anti-symmetric current-voltage relationship and a symmetric capacitance-voltage relationship, as shown in the graph to the right. The device was invented by Erik Kollberg together with Anders Rydberg in 1989 at Chalmers University of Technology.
The field-effect transistor (FET) is an electronic device which uses an electric field to control the flow of current. FETs are 3-terminalled devices, having a source, gate, and drain terminal. FETs control the flow of current by the application of a voltage to the gate terminal, which in turn alters the conductivity between the drain and source terminals.
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