Gold-doped diodes

Compactrons are a type of thermionic valve, or vacuum tube, which contain arrangements of diodes, triodes, or pentodes in multiple combination arrays, as well as high or low-voltage and power types.

This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, including extraction of modulation from radio signals in radio receivers — these diodes are forms of rectifiers.

These are exploited in special-purpose diodes that perform many different functions.

For example, diodes are used to regulate voltage ( Zener diodes ), to protect circuits from high voltage surges ( avalanche diodes ), to electronically tune radio and TV receivers ( varactor diodes ), to generate radio frequency oscillations ( tunnel diodes, Gunn diodes, IMPATT diodes ), and to produce light ( light emitting diodes ).

Today most diodes are made of silicon, but other semiconductors such as germanium are sometimes used.

Thermionic diodes are thermionic-valve devices ( also known as vacuum tubes, tubes, or valves ), which are arrangements of electrodes surrounded by a vacuum within a glass envelope.

In thermionic-valve diodes, a current through the heater filament indirectly heats the thermionic cathode, another internal electrode 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.

There are several types of p – n 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, are usually made of doped silicon or, more rarely, germanium.

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.

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.

However, diodes can have more complicated behavior than this simple on – off action.

Before the development of silicon power rectifier diodes, cuprous oxide and later selenium was used ; its low efficiency gave it a much higher forward voltage drop ( typically 1. 4 to 1. 7 V per " cell ", with multiple cells stacked to increase the peak inverse voltage rating in high voltage rectifiers ), and required a large heat sink ( often an extension of the diode ’ s metal substrate ), much larger than a silicon diode of the same current ratings would require.

They have a lower forward voltage drop than p – n junction diodes.

They can also be used as low loss rectifiers, although their reverse leakage current is in general higher than that of other diodes.

They also tend to have much lower junction capacitance than p – n diodes, which provides for high switching speeds and their use in high-speed circuitry and RF devices such as switched-mode power supply, mixers, and detectors.

They also have less reverse-current leakage than Schottky diodes ( but not as good as other p – n diodes ).

Negative resistance diodes can amplify signals, and often perform better at microwave frequencies than two-port devices.

On average, but not in every case, the OFL bandwidth measured using a mode scrambler is lower than that produced by excitation of a partial mode volume ( restricted mode launch or RML ), such as occurs with directly coupled laser diodes.

Many diodes designed for use specifically as a photodiode use a PIN junction rather than a p-n junction, to increase the speed of response.

Some non-laser printers expose by an array of light emitting diodes spanning the width of the page, rather than by a laser (" exposing " is also known as " writing " in some documentation ).

Some wire-ended components, such as 1N4148 small-signal switch diodes, are actually significantly cheaper than SMD equivalents.

The penalty isn't as severe as first assumed though, because at the higher voltages where IGBT usage dominates, discrete diodes are of significantly higher performance than the body diode of a MOSFET.

The spontaneous and stimulated emission processes are vastly more efficient in direct bandgap semiconductors than in indirect bandgap semiconductors ; therefore silicon is not a common material for laser diodes.

Vertical-cavity surface-emitting lasers ( VCSELs ) have the optical cavity axis along the direction of current flow rather than perpendicular to the current flow as in conventional laser diodes.

Where in a p-n diode the reverse recovery time can be in the order of hundreds of nanoseconds and less than 100 ns for fast diodes, Schottky diodes do not have a recovery time, as there is nothing to recover from ( i. e. no charge carrier depletion region at the junction ).

This is another reason why Schottky diodes are useful in switch-mode power converters ; the high speed of the diode means that the circuit can operate at frequencies in the range 200 kHz to 2 MHz, allowing the use of small inductors and capacitors with greater efficiency than would be possible with other diode types.

Schottky diodes constructed from silicon carbide have a much lower reverse leakage current than silicon Schottky diodes, and higher reverse voltage.

: These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltage transients.

As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction.

the vast majority of transistors now are produced in integrated circuits ( often shortened to IC, microchips or simply chips ), along with diodes, resistors, capacitors and other electronic components, to produce complete electronic circuits.

The name triode appeared later, when it became necessary to distinguish it from other generic kinds of vacuum tubes with more or fewer elements ( e. g. diodes, tetrodes, pentodes, etc .).

Because of their inefficiency, incandescent light bulbs are gradually being replaced in many applications by other types of electric lights, such as fluorescent lamps, compact fluorescent lamps ( CFL ), cold cathode fluorescent lamps ( CCFL ), high-intensity discharge lamps, and light-emitting diodes ( LEDs ).

Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, solid-state diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches.

These are thyristors or other controlled switching solid-state switches which effectively function as diodes to pass current in only one direction.

High-power laser diodes are used in industrial applications such as heat treating, cladding, seam welding and for pumping other lasers, such as diode-pumped solid-state lasers.

A series of new experimental systems followed, including the Plasmatron and experiments with Organic light-emitting diodes and other technologies, but Sony's attempts to introduce a best-of-breed system all failed.

Thin-film transistors are usually used for constructing an active matrix so that the two terms are often interchanged, even though a thin film transistor is just one component in an active matrix and some active-matrix designs have used other components such as diodes.

: This term is used both for conventional p – n diodes used to monitor temperature due to their varying forward voltage with temperature, and for Peltier heat pumps for thermoelectric heating and cooling .. Peltier heat pumps may be made from semiconductor, though they do not have any rectifying junctions, they use the differing behaviour of charge carriers in N and P type semiconductor to move heat.

: 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.

This transfer of charge causes a " built-in " electric field, which is central to how p – n diodes and photovoltaics work.

These diodes have a heavily doped p – n junction only some 10 nm ( 100 Å ) wide.

p – n junctions are elementary " building blocks " of most semiconductor electronic devices such as diodes, transistors, solar cells, LEDs, and integrated circuits ; they are the active sites where the electronic action of the device takes place.

By manipulating this non-conductive layer, p – n junctions are commonly used as diodes: circuit elements that allow a flow of electricity in one direction but not in the other ( opposite ) direction.

Any diode exhibits this effect ( including p / n junctions in transistors ), but devices specifically sold as variable capacitance diodes ( also called varactors or varicaps ) are designed with a large junction area and a doping profile specifically designed to maximize capacitance.