Designation system for photoelectronic and optoelectronic devices. Moscow State University of Printing Arts

Optical radiation sources used in optoelectronics, generally speaking, are very diverse. However, most of them (subminiature incandescent and gas-discharge light bulbs, powder and film electroluminescent emitters, vacuum cathodoluminescent and many other types) do not satisfy the entire set of modern requirements and are used only in certain devices, mainly in indicator devices and partly in optocouplers.

When assessing the prospects of a particular source, the determining role is played by the state of aggregation of the active luminous substance (or the substance filling the working volume). Of all the possible options (vacuum, gas, liquid, solid), preference is given to a solid-state substance, and “inside” it to a monocrystalline substance as it provides the greatest durability and reliability of devices.

The foundation of optoelectronics is formed by two groups of emitters:

1) optical generators of coherent radiation (lasers), among which semiconductor lasers should be distinguished;

1) light-emitting semiconductor diodes based on the principle of spontaneous injection electroluminescence.

An optoelectronic semiconductor device is a semiconductor device thatemitting or converting electromagnetic radiation, sensitive to this radiation in the visible, infrared and (or) ultraviolet regions of the spectrum, or using such radiation for the internal interaction of its elements.

Optoelectronic semiconductor devices can be divided into semiconductor emitters, radiation receivers, optocouplers and optoelectronic integrated circuits (Fig. 2.1).

A semiconductor emitter is an optoelectronic semiconductor device that converts electrical energy into the energy of electromagnetic radiation in the visible, infrared and ultraviolet regions of the spectrum.

Many semiconductor emitters can only emit incoherent electromagnetic waves. These include semiconductor emitters in the visible region of the spectrum - semiconductor information display devices (light-emitting diodes, semiconductor sign indicators, scales and screens), as well as semiconductor emitters in the infrared region of the spectrum - infrared emitting diodes.

Coherent semiconductor emitters– these are semiconductor lasers with various types of excitation. They can emit electromagnetic waves with a certain amplitude, frequency, phase, direction of propagation and polarization, which corresponds to the concept of coherence.

Optoelectronics is a branch of electronics devoted to the theory and practice of creating instruments and devices based on the conversion of electrical signals into optical signals and vice versa.

Optoelectronics uses a wavelength range of 0.2 µm - 0.2 mm. An optoelectronic device is a combination of a radiation source and receiver. GaAs-based LEDs are used as a radiation source, and Si-based photodiodes and phototransistors are used as photodetectors.

A distinctive feature of optoelectronic devices (OED) from others is that they are optically connected, but electrically isolated from each other. This makes it easy to ensure consistency between high and low voltage and high frequency circuits.

Optoelectronics is developing in two independent directions:

  1. Optical;
  2. Electro-optical.

The optical direction is based on the effects of interaction of a solid with electromagnetic radiation (holography, photochemistry, electro-optics). Electro-optical direction uses the principle of photoelectric conversion with internal photoelectric effect on the one hand, and photoluminescence on the other (replacing galvanic and magnetic communication with optical, fiber-optic communication lines).

Based on the optoelectronic principle, vacuum-free analogues of electronic devices and systems can be created:

  • discrete and analog converters of electrical signals (amplifiers, generators, key elements, memory elements, logic circuits, delay lines, etc.)
  • optical signal converters (light and image amplifiers, flat screens that transmit and reproduce images)
  • playback devices (display screens, digital displays, picture logic, etc.).

The main factors that determine the development of optoelectronics are:

  • development of ultrapure materials,
  • development of perfect technology for new modern instruments and devices,
  • training of highly qualified personnel.

The following are widely used for the manufacture of active and passive optoelectronic elements:

  • semiconductor materials, rare earths and their alloys,
  • dielectric connections,
  • film materials,
  • photoresists,
  • diffusants.

Currently, the range of materials used in optoelectronics is quite wide. These include high-purity substances, pure metals and alloys with special electrophysical properties, diffusants, various semiconductor compounds in the form of powders and single crystals, single-crystalline wafers of silicon, gallium arsenide and phosphide, indium phosphide, sapphire, garnet, various auxiliary materials - process gases , photoresists, abrasive powders, etc.

The most important materials for optoelectronics are substances such as: GaAs, BaF 2, CdTe (for the manufacture of substrates), GaAlAs / GaAs / GaAlAs structures (electro-optical modulators), SiO 2 (insulation material), Si, CdHgTe, PbSnSe (photodiodes, phototransistors). Some ICs use Ni, Cr, and Ag. The production technology of optoelectronic integrated circuits (OEIMC) is constantly being improved based on the development of new physical and technological processes.

OEPs have the following advantages:

  • the possibility of spatial modulation of light beams and their significant intersection in the absence of galvanic connections between channels;
  • greater functional load of light beams due to the possibility of changing many of their parameters (amplitude, direction, frequency, phase, polarization).

Optoelectronic devices are devices whose operating principle is based on the use of electromagnetic radiation in the optical range.

The main groups of optoelectronic devices include the following:

  • light-emitting diodes and lasers;
  • photoelectric radiation detectors - photoresistors and photodetectors with p-n junction;
  • devices that control radiation - modulators, deflectors, etc.; devices for displaying information - indicators;
  • devices for electrical insulation - optocouplers;
  • optical communication channels and optical storage devices.

The above groups of devices generate, transform, transmit and store information. Information carriers in optoelectronics are electrically neutral particles - photons, which are insensitive to the effects of electric and electromagnetic fields, do not interact with each other and create unidirectional signal transmission, which ensures high noise immunity and galvanic isolation of input and output circuits. Optoelectronic devices receive, convert and generate radiation in the visible, infrared and ultraviolet regions of the spectrum.

The operating principle of optoelectronic devices is based on the use of external or internal photoelectric effect.

The external photoelectric effect is the release of free electrons from the surface layer of the photocathode into the external environment under the influence of light.

The internal photoelectric effect is the free movement of electrons inside a substance, freed from bonds under the influence of light, and changing its electrical conductivity or even causing the appearance of an emf at the boundary of two substances (p-n junction).

OEPs are widely used in automatic control and measuring systems, computer technology, phototelegraphy, sound-reproducing equipment, cinematography, spectrophotometry, for converting light energy into electrical energy, and in automation for solving electrical circuits.

Optocoupler

An optocoupler is a semiconductor device in which a radiation source and receiver are structurally combined, connected by optical communication. In the radiation source, electrical signals are converted into light signals that act on the photodetector and again create electrical signals in it. If an optocoupler has only one emitter and one radiation receiver, then it is called an optocoupler or an elementary optocoupler.

A microcircuit consisting of one or more optocouplers with additional devices for matching and amplifying the signal is called an optoelectronic integrated circuit. Electrical signals are always used at the input and output of an optocoupler, and the connection between the input and output occurs due to a light signal.

Photoresistor

Photoresistors are semiconductor resistors that change their resistance under the influence of light. Depending on the spectral sensitivity, photoresistors are divided into two groups: for the visible part of the spectrum and for the infrared part of the spectrum. For the manufacture of photoresistors, compounds are used Cd And Pb. Sensitive elements are made from single crystals or polycrystals of these compounds.

Designation of photoresistors of early releases:

  • 1 element - letters indicating the type of device (FS - photoresistance),
  • 2 element - a letter indicating the material of the photosensitive element (A - lead sulfide, K - cadmium sulfide, D - cadmium selenium),
  • Element 3 is a number that indicates the type of design.
  • the letter B before the number is a sealed version,
  • P - film material of the photosensitive element,
  • M - monocrystalline material of the photosensitive element.
  • letter T - tropical version, intended for use in conditions of high temperatures and humidity.
The principle of structure and connection diagram of a photoresistor

Designation of modern photoresistors:

  • 1 element - letters indicating the type of device (SF - photosensitive resistance),
  • 2 element - a number that means the material of the photosensitive element (2 - cadmium sulfide, 3 - cadmium selenide, 4 - lead selenide),
  • The 3rd element is a number that indicates the serial number of the development.

Photoresistors have high parameter stability. The change in photocurrent is a fairly accurate characteristic of its state. During long-term operation, stabilization of the photocurrent is observed, while its value can change by 20 - 30%. Photoresistors are sensitive to rapid temperature changes. Photoresistors should be stored at 5 - 35 o C and humidity no more than 80%.

The main parameters of photoresistors include:

  1. Dark current ( IT) is the current passing through the photoresistor at an operating voltage 30 s after removing the illumination of 200 lux.
  2. Luminous current ( I c) is the current passing through the photoresistor at an operating voltage and illumination of 200 lux from a light source with a color temperature of 2850 K.
  3. Photocurrent temperature coefficient ( TKIf) - change in photocurrent when the temperature of the photoresistor changes by 1 o C.
  4. Operating voltage ( Uf) - voltage that can be applied to a photoresistor during long-term operation without changing its parameters beyond the permissible limits.
  5. Dark resistance ( RT) - the resistance of the photoresistor at a temperature of 20 o C 30 s after removing the illumination of 200 lux.
  6. Specific sensitivity ( K 0) is the ratio of the photocurrent to the product of the magnitudes of the light flux incident on it and the applied voltage: K 0 =If / (FUf) , Where F— luminous flux, lm.
  7. Time constant ( t) is the time during which the photocurrent changes by a normalized value when illuminated.
  8. Power dissipation ( R race.) - the maximum permissible power that the photoresistor can dissipate under continuous electrical loading and ambient temperature, without changing the parameters beyond the norm established by the technical specifications.
  9. Insulation resistance ( RAnd).
  10. Long wavelength boundary ( l).

The main characteristics of photoresistors are:

  1. Volt-ampere ( I= f(U)) — dependence of light, dark or photocurrent (with F =const) from the applied voltage.
  2. Light or lux-amp (I= f(E))— dependence of the photocurrent on the luminous flux, incident or illumination (at U= const).
  3. Spectral (I= f(l)) — dependence of the photocurrent on the wavelength of the light flux (at U= const).
  4. Frequency (I Ф = f (F Ф)) - dependence of the photocurrent on the modulation frequency of the light flux (at U = const).

High integral sensitivity allows the use of resistors even without amplifiers, and their small dimensions are the reasons for their widespread use. The main disadvantages of photoresistors are their inertia and the strong influence of temperature, which leads to a wide range of characteristics.

Photodiode

Photodiodes — These are semiconductor diodes that use an internal photoelectric effect. The luminous flux controls the reverse current of the photodiodes. Under the influence of light on the electron-hole junction, pairs of charge carriers are generated, the conductivity of the diode increases and the reverse current increases. This mode of operation is called photodiode mode. The second type of mode is photogenerator. Unlike the photogenerator mode, the photodiode mode requires the use of an external power source.

Photodiode connection circuit for operation in photodiode mode

Main parameters of photodiodes:

  • integral sensitivity (~ 10 mA / lm): operating voltage (10 - 30 V);
  • dark current (~ 2 - 20 µA).

Main characteristics of photodiodes:

  • volt-ampere (I = f (U)) - dependence of light, dark or photocurrent (at Ф = const) on the applied voltage;
  • energy ( IF = f(F))— dependence of the photocurrent on the luminous flux (at U= const) - linear, depends little on voltage.

Current-voltage characteristics of a photodiode for photodiode mode

In avalanche photodiodes, avalanche multiplication of carriers occurs in the pn junction and due to this, the sensitivity increases tens of times. Photodiodes with a Schottky barrier have high performance. Photodiodes with heterojunctions work as emf generators. Germanium photodiodes are used as indicators of infrared radiation; silicon - for converting light energy into electrical energy (solar batteries for autonomous power supply of various equipment in space); selenium - for the manufacture of photo exposure meters and lighting technical measurements, since their spectral characteristics are close to the spectral characteristics of the human eye.

Phototransistor

Phototransistors are semiconductor devices with two p-n junctions designed to convert light flux into electric current. A phototransistor is structurally different from a conventional bipolar transistor in that its body has a transparent window through which light can enter the base area.

The supply voltage is supplied to the emitter and collector, its collector junction is closed, and the emitter junction is open. The base remains free. When a phototransistor is illuminated, electrons and holes are generated in its base. In the collector junction, there is a distribution of electron-hole transitions that, as a result of diffusion, have reached the transition boundary. Holes (minority charge carriers in the semiconductor) are transferred by the transition field to the collector, increasing its own current, and electrons (majority charge carriers) remain in the base, reducing its potential. A decrease in the base potential leads to the formation of additional forward voltage at the emitter junction and increased injection of holes from the emitter into the base. The holes injected into the base, reaching the collector junction, cause an additional increase in the collector current.


Block diagram of a bipolar phototransistor with a free base (a) and connection circuit of the phototransistor (b)

The collector current of the illuminated phototransistor turns out to be quite large; The ratio of light current to dark current reaches several hundred.

There are two options for turning on phototransistors:

  • diode- using only two pins (emitter and collector)
  • transistor- using three terminals, when not only a light, but also an electrical signal is supplied to the input.

In optoelectronics, automation and telemechanics, phototransistors are used for the same purposes as photodiodes, but they are inferior to them in terms of sensitivity threshold and temperature range. The sensitivity of phototransistors increases with the intensity of their illumination.

Photothyristor

A photothyristor is a semiconductor device with a four-layer p-n-p-n structure that combines the properties of a thyristor and a photodetector and converts light into electricity.

In the absence of a light signal and control current, the photothyristor is closed and only dark current passes through it. The photothyristor is opened by a light flux that enters the bases p 2 and n 1 through a “window” in its body and creates electron-hole pairs. This leads to the emergence of primary photocurrents and the formation of a total photocurrent. It follows from this that when a light flux arrives at the bases p 2 and n 1, the emitter current increases, the current transfer coefficient α from the emitter to the collector is a function of illumination, which changes the p-n current. The resistance of the photothyristor varies from 0.1 Ohm (in the open state) to 10 8 Ohm (in the closed state), and the switching time is 10 -5 - 10 -6 s.


Photothyristor structure

From the light characteristics Ietc. = F(F) at Uetc. = Const it can be seen that when the photothyristor is turned on, the current through it increases to Ietc.= E pr. /Rload and does not change anymore, that is, the photothyristor has two stable states and can be used as a memory element. According to the current-voltage characteristic Ietc. = F(Uetc.) at F =const(F 2 > F1 > Fo) It can be seen that as the luminous flux increases, the voltage and on-time decrease.


Characteristics of the photothyristor: a - light, b - current-voltage characteristic, c - dependence of the switching time on the luminous flux

The advantages of photothyristors are:

  • high loading capacity with low control signal power;
  • the ability to obtain the required source signal without additional amplification stages;
  • presence of memory, that is, maintaining an open state after removing the control signal;
  • greater sensitivity;
  • high performance.

The above properties of photothyristors make it possible to simplify circuits by eliminating amplifiers and relay elements, which is very important in industrial electronics, for example, in high-voltage converters. Most often, photothyristors are used to switch powerful electrical signals with a light signal.

Thus, despite the fact that optoelectronics was one of the first areas of radio electronics, it has retained its importance to the present day, unlike many technologies that have sunk into oblivion.

Optoelectronic devices are devices that are sensitive to electromagnetic radiation in the visible, infrared and ultraviolet regions, as well as devices that produce or use such radiation.

Radiation in the visible, infrared and ultraviolet regions is classified as the optical range of the spectrum. Typically, this range includes electromagnetic waves with a length of 1 nm up to 1 mm, which corresponds to frequencies from approximately 0.5 10 12 Hz up to 5·10 17 Hz. Sometimes they talk about a narrower frequency range - from 10 nm up to 0.1 mm(~5·10 12 …5·10 16 Hz). The visible range corresponds to wavelengths from 0.38 µm to 0.78 µm (frequency about 10 15 Hz).

In practice, radiation sources (emitters), radiation receivers (photodetectors) and optocouplers (optocouplers) are widely used.

An optocoupler is a device in which there is both a source and a receiver of radiation, structurally combined and placed in one housing.

LEDs and lasers are widely used as radiation sources, and photoresistors, photodiodes, phototransistors and photothyristors as receivers.

Optocouplers are widely used, in which LED-photodiode, LED-phototransistor, LED-photothyristor pairs are used.

The main advantages of optoelectronic devices:

· high information capacity of optical information transmission channels, which is a consequence of the high frequencies used;

· complete galvanic isolation of the radiation source and receiver;

· no influence of the radiation receiver on the source (unidirectional information flow);

· immunity of optical signals to electromagnetic fields (high noise immunity).

Emitting Diode (LED)

An emitting diode that operates in the visible wavelength range is often called a light-emitting diode, or LED.

Let's consider the device, characteristics, parameters and designation system of emitting diodes.

Device. A schematic representation of the structure of the emitting diode is shown in Fig. 6.1,a, and its symbolic graphic designation is in Fig. 6.2, b.

Radiation occurs when direct diode current flows as a result of the recombination of electrons and holes in the region p-n-transition and in areas adjacent to the specified area. During recombination, photons are emitted.

Characteristics and parameters. For emitting diodes operating in the visible range (wavelengths from 0.38 to 0.78 µm, frequency about 10 15 Hz), the following characteristics are widely used:

· dependence of radiation brightness L from diode current i(brightness characteristic);

light intensity dependence I v from diode current i.

Rice. 6.1. Light Emitting Diode Structure ( A)

and its graphic representation ( b)

The brightness characteristic for a light-emitting diode of type AL102A is shown in Fig. 6.2. The glow color of this diode is red.

Rice. 6.2. LED brightness characteristic

A graph of the dependence of luminous intensity on current for an AL316A light-emitting diode is shown in Fig. 6.3. The glow color is red.

Rice. 6.3. Dependence of luminous intensity on LED current

For emitting diodes operating outside the visible range, characteristics are used that reflect the dependence of the radiation power R from diode current i. Zone of possible positions of the graph of the dependence of radiation power on current for an AL119A type emitting diode operating in the infrared range (wavelength 0.93...0.96 µm), is shown in Fig. 6.4.

Here are some parameters for the AL119A diode:

· radiation pulse rise time – no more than 1000 ns;

radiation pulse decay time – no more than 1500 ns;

· constant forward voltage at i=300 mA– no more than 3 IN;

· constant maximum permissible forward current at t<+85°C – 200 mA;

· ambient temperature –60…+85°С.

Rice. 6.4. Dependence of radiation power on LED current

For information about possible values ​​of the efficiency factor, we note that emitting diodes of the ZL115A, AL115A type, operating in the infrared range (wavelength 0.95 µm, spectrum width no more than 0.05 µm), have an efficiency factor of at least 10%.

Notation system. The designation system used for light-emitting diodes involves the use of two or three letters and three numbers, for example AL316 or AL331. The first letter indicates the material, the second (or second and third) indicates the design: L - single LED, LS - row or matrix of LEDs. Subsequent numbers (and sometimes letters) indicate the development number.

Photoresistor

A photoresistor is a semiconductor resistor whose resistance is sensitive to electromagnetic radiation in the optical range of the spectrum. A schematic representation of the photoresistor structure is shown in Fig. 6.5, A, and its conventional graphic representation is in Fig. 6.5, b.

A stream of photons incident on a semiconductor causes pairs to appear. electron-hole, increasing conductivity (decreasing resistance). This phenomenon is called the internal photoelectric effect (photoconductivity effect). Photoresistors are often characterized by a current dependence i from illumination E at a given voltage across the resistor. This is the so-called lux-amp characteristic (Fig. 6.6).

Rice. 6.5. Structure ( A) and schematic designation ( b) photoresistor

Rice. 6.6. Lux-ampere characteristic of photoresistor FSK-G7

The following photoresistor parameters are often used:

· nominal dark (in the absence of light flux) resistance (for FSK-G7 this resistance is 5 MOhm);

· integral sensitivity (sensitivity determined when a photoresistor is illuminated with light of a complex spectral composition).

Integral sensitivity (current sensitivity to light flux) S is determined by the expression:

Where i f– the so-called photocurrent (the difference between the current when illuminated and the current when there is no illumination);

F- light flow.

For photoresistor FSK-G7 S=0,7 A/lm.

Photodiode

Structure and basic physical processes. The simplified structure of the photodiode is shown in Fig. 6.7, A, and its conventional graphic representation is in Fig. 6.7, b.

Rice. 6.7. Structure (a) and designation (b) of a photodiode

The physical processes occurring in photodiodes are the opposite in nature with respect to the processes occurring in LEDs. The main physical phenomenon in a photodiode is the generation of pairs electron-hole in area p-n-transition and in the areas adjacent to it under the influence of radiation.

Pair generation electron-hole leads to an increase in the reverse current of the diode in the presence of reverse voltage and to the appearance of voltage u ak between the anode and cathode with an open circuit. Moreover u ak>0 (holes go to the anode, and electrons go to the cathode under the influence of an electric field p-n-transition).

Characteristics and parameters. It is convenient to characterize photodiodes by a family of current-voltage characteristics corresponding to different light fluxes (luminous flux is measured in lumens, lm) or different illumination (illuminance is measured in lux, OK).

The current-voltage characteristics (volt-ampere characteristics) of the photodiode are shown in Fig. 6.8.

Rice. 6.8. Current-voltage characteristics of the photodiode

Let the luminous flux be zero at first, then the current-voltage characteristic of the photodiode actually repeats the current-voltage characteristic of a conventional diode. If the luminous flux is not zero, then photons penetrating into the region p-n– transition, cause the generation of pairs electron-hole. Under the influence of an electric field p-n– transition, current carriers move to the electrodes (holes - to the layer electrode p, electrons – to the layer electrode n). As a result, a voltage arises between the electrodes, which increases with increasing luminous flux. With a positive anode-cathode voltage, the diode current can be negative (fourth quadrant of the characteristic). In this case, the device does not consume, but produces energy.

In practice, photodiodes are used both in the so-called photogenerator mode (photovoltaic mode, valve mode) and in the so-called photoconverter mode (photodiode mode).

In photogenerator mode, solar cells operate to convert light into electricity. Currently, the efficiency of solar cells reaches 20%. So far, energy obtained from solar cells is approximately 50 times more expensive than energy obtained from coal, oil or uranium.

The photoconverter mode corresponds to the current-voltage characteristic in the third quadrant. In this mode, the photodiode consumes energy ( u· i> 0) from some external voltage source necessarily present in the circuit (Fig. 6.9). Graphical analysis of this mode is performed using a load line, as for a conventional diode. In this case, the characteristics are usually conventionally depicted in the first quadrant (Fig. 6.10).

Rice. 6.9 Fig. 6.10

Photodiodes are faster-acting devices compared to photoresistors. They operate at frequencies 10 7 –10 10 Hz. Photodiode is often used in optocouplers LED-photodiode. In this case, different characteristics of the photodiode correspond to different currents of the LED (which at the same time creates different light fluxes).

Optocoupler (optocoupler)

An optocoupler is a semiconductor device containing a radiation source and a radiation receiver, combined in one housing and interconnected optically, electrically, and simultaneously by both connections. Optocouplers are very widespread, in which a photoresistor, photodiode, phototransistor and photothyristor are used as a radiation receiver.

In resistor optocouplers, the output resistance can change by a factor of 10 7 ... 10 8 when the input circuit mode changes. In addition, the current-voltage characteristic of the photoresistor is highly linear and symmetrical, which makes resistive optocouplers widely applicable in analog devices. The disadvantage of resistor optocouplers is their low speed - 0.01...1 With.

In circuits for transmitting digital information signals, mainly diode and transistor optocouplers are used, and for optical switching of high-voltage, high-current circuits, thyristor optocouplers are used. The performance of thyristor and transistor optocouplers is characterized by switching time, which often lies in the range of 5...50 mks.

Let's take a closer look at the LED-photodiode optocoupler (Fig. 6.11, A). The emitting diode (left) must be connected in the forward direction, and the photodiode must be connected in the forward direction (photogenerator mode) or reverse direction (photoconverter mode). The directions of currents and voltages of the optocoupler diodes are shown in Fig. 6.11, b.

Rice. 6.11. Diagram of an optocoupler (a) and the direction of currents and voltages in it (b)

Let us depict the current dependence i out from current i input at u out=0 for optocoupler AOD107A (Fig. 6.12). The specified optocoupler is designed to operate in both photogenerator and photoconverter modes.

Rice. 6.12. Transfer characteristic of optocoupler AOD107A

    Optoelectronic devices

    Main characteristics of visible light-emitting diodes

    Main characteristics of infrared light-emitting diodes

    Optoelectronic devices in a broad sense

    List of sources used

Optoelectronic devices

The operation of optoelectronic devices is based on electron-photonic processes of receiving, transmitting and storing information.

The simplest optoelectronic device is an optoelectronic pair, or optocoupler. The operating principle of an optocoupler, consisting of a radiation source, an immersion medium (light guide) and a photodetector, is based on converting an electrical signal into an optical one, and then back into an electrical one.

Optocouplers as functional devices have the following advantages over conventional radioelements:

complete galvanic isolation “input – output” (insulation resistance exceeds 10 12 – 10 14 Ohms);

absolute noise immunity in the information transmission channel (information carriers are electrically neutral particles - photons);

unidirectional flow of information, which is associated with the characteristics of light propagation;

broadband due to the high frequency of optical vibrations,

sufficient speed (a few nanoseconds);

high breakdown voltage (tens of kilovolts);

low noise level;

good mechanical strength.

Based on the functions it performs, an optocoupler can be compared to a transformer (coupling element) with a relay (key).

In optocoupler devices, semiconductor radiation sources are used - light-emitting diodes made from materials of compounds of the group A III B V , among which the most promising are gallium phosphide and arsenide. The spectrum of their radiation lies in the region of visible and near-infrared radiation (0.5 - 0.98 microns). Light-emitting diodes based on gallium phosphide have a red and green glow. LEDs made of silicon carbide are promising because they have a yellow glow and operate at elevated temperatures, humidity and in aggressive environments.

LEDs, which emit light in the visible range of the spectrum, are used in electronic watches and microcalculators.

Light-emitting diodes are characterized by a spectral composition of radiation that is quite wide, a directivity pattern; quantum efficiency, determined by the ratio of the number of emitted light quanta to the number of those passing through p-n-transition of electrons; power (with invisible radiation) and brightness (with visible radiation); volt-ampere, lumen-ampere and watt-ampere characteristics; speed (increase and decay of electroluminescence during pulsed excitation), operating temperature range. As the operating temperature increases, the brightness of the LED decreases and the emission power decreases.

The main characteristics of light-emitting diodes in the visible range are given in table. 1, and the infrared range - in table. 2.

Table 1 Main characteristics of visible light-emitting diodes

Diode type

Brightness, cd/m 2, or luminous intensity, mcd

Glow color

Direct forward current, mA

KL101 A – B

AL102 A – G

AL307 A – G

10 – 20 cd/m2

40 – 250 mcd

150 – 1500 mcd

Red Green

Red Green

Light-emitting diodes in optoelectronic devices are connected to photodetectors by an immersion medium, the main requirement for which is signal transmission with minimal losses and distortion. In optoelectronic devices, solid immersion media are used - polymeric organic compounds (optical adhesives and varnishes), chalcogenide media and optical fibers. Depending on the length of the optical channel between the emitter and the photodetector, optoelectronic devices can be divided into optocouplers (channel length 100 - 300 microns), optoisolators (up to 1 m) and fiber-optic communication lines - fiber-optic lines (up to tens of kilometers).

Table 2. Main characteristics of infrared light-emitting diodes

Diode type

Total radiation power, mW

Constant forward voltage, V

Radiation wavelength, microns

Radiation pulse rise time, ns

Radiation pulse decay time, ns

AL106 A – D

0.6 – 1 (at current 50 mA)

0.2 – 1.5 (at current 100 mA)

6 – 10 (at current 100 mA)

1.5 (at 100 mA current)

0.2 (at 20 mA current)

10 (at current 50 mA)

Photodetectors used in optocoupler devices are subject to requirements for matching the spectral characteristics with the emitter, minimizing losses when converting a light signal into an electrical signal, photosensitivity, speed, size of the photosensitive area, reliability and noise level.

For optocouplers, the most promising are photodetectors with an internal photoelectric effect, when the interaction of photons with electrons inside materials with certain physical properties leads to electron transitions in the volume of the crystal lattice of these materials.

The internal photoelectric effect manifests itself in two ways: in a change in the resistance of the photodetector under the influence of light (photoresistors) or in the appearance of photo-emf at the interface between two materials - semiconductor-semiconductor, metal-semiconductor (switched photocells, photodiodes, phototransistors).

Photodetectors with internal photoelectric effect are divided into photodiodes (with p-n-junction, MIS structure, Schottky barrier), photoresistors, photodetectors with internal amplification (phototransistors, compound phototransistors, photothyristors, field-effect phototransistors).

Photodiodes are based on silicon and germanium. The maximum spectral sensitivity of silicon is 0.8 microns, and germanium - up to 1.8 microns. They operate at reverse bias p-n-transition, which makes it possible to increase their performance, stability and linearity of characteristics.

Photodiodes are most often used as photodetectors for optoelectronic devices of varying complexity. p- i-n-structures where i– depleted region of high electric field. By changing the thickness of this region, it is possible to obtain good performance and sensitivity characteristics due to the low capacitance and time of flight of the carriers.

Avalanche photodiodes have increased sensitivity and performance, using amplification of the photocurrent when multiplying charge carriers. However, these photodiodes are not stable enough over a temperature range and require high voltage power supplies. Photodiodes with a Schottky barrier and a MIS structure are promising for use in certain wavelength ranges.

Photoresistors are made mainly from polycrystalline semiconductor films based on a compound (cadmium with sulfur and selenium). The maximum spectral sensitivity of photoresistors is 0.5 - 0.7 microns. Photoresistors are usually used in low light conditions; in sensitivity they are comparable to photomultipliers - devices with an external photoelectric effect, but require low-voltage power. The disadvantages of photoresistors are low performance and high noise levels.

The most common internally amplified photodetectors are phototransistors and photothyristors. Phototransistors are more sensitive than photodiodes, but slower. To further increase the sensitivity of the photodetector, a composite phototransistor is used, which is a combination of photo and amplification transistors, but it has low performance.

In optocouplers, a photothyristor (a semiconductor device with three p- n- transitions, switching when illuminated), which has high sensitivity and output signal level, but insufficient speed.

The variety of types of optocouplers is determined mainly by the properties and characteristics of photodetectors. One of the main applications of optocouplers is the effective galvanic isolation of transmitters and receivers of digital and analog signals. In this case, the optocoupler can be used in converter or signal switch mode. The optocoupler is characterized by the permissible input signal (control current), current transfer coefficient, speed (switching time) and load capacity.

The ratio of the current transfer coefficient to the switching time is called the quality factor of the optocoupler and is 10 5 – 10 6 for photodiode and phototransistor optocouplers. Optocouplers based on photothyristors are widely used. Photoresistor optocouplers are not widely used due to low time and temperature stability. Diagrams of some optocouplers are shown in Fig. 4, a – d.

Lasers with high stability, good energy characteristics and efficiency are used as coherent radiation sources. In optoelectronics, for the design of compact devices, semiconductor lasers are used - laser diodes, used, for example, in fiber-optic communication lines instead of traditional information transmission lines - cable and wire. They have high throughput (bandwidth of units of gigahertz), resistance to electromagnetic interference, low weight and dimensions, complete electrical insulation from input to output, explosion and fire safety. A special feature of FOCL is the use of a special fiber-optic cable, the structure of which is shown in Fig. 5. Industrial samples of such cables have an attenuation of 1 – 3 dB/km and lower. Fiber-optic communication lines are used to build telephone and computer networks, cable television systems with high quality transmitted images. These lines allow the simultaneous transmission of tens of thousands of telephone conversations and several television programs.

Recently, optical integrated circuits (OICs), all elements of which are formed by deposition of the necessary materials onto a substrate, have been intensively developed and become widespread.

Liquid crystal-based devices, widely used as indicators in electronic watches, are promising in optoelectronics. Liquid crystals are an organic substance (liquid) with the properties of a crystal and are in a transition state between the crystalline phase and a liquid.

Liquid crystal indicators have high resolution, are relatively cheap, consume low power and operate at high light levels.

Liquid crystals with properties similar to single crystals (nematics) are most often used in light indicators and optical memory devices. Liquid crystals that change color when heated (cholesterics) have been developed and are widely used. Other types of liquid crystals (smectics) are used for thermo-optical recording of information.

Optoelectronic devices, developed relatively recently, have become widespread in various fields of science and technology due to their unique properties. Many of them have no analogues in vacuum and semiconductor technology. However, there are still many unsolved problems associated with the development of new materials, improvement of the electrical and operational characteristics of these devices and the development of technological methods for their manufacture.

Optoelectronic semiconductor device - a semiconductor device whose operation is based on the use of radiation, transmission or absorption phenomena in the visible, infrared or ultraviolet regions of the spectrum.

Optoelectronic devices in a broad sense are devices , using optical radiation for their work: generating, detecting, converting and transmitting an information signal. As a rule, these devices include one or another set of optoelectronic elements. In turn, the devices themselves can be divided into standard and special, considering standard those that are mass-produced for wide use in various industries, and special devices are produced taking into account the specifics of a particular industry - in our case, printing.

The entire variety of optoelectronic elements is divided into the following product groups: radiation sources and receivers, indicators, optical elements and light guides, as well as optical media that allow the creation of control elements, display and storage of information. It is known that any systematization cannot be exhaustive, but, as our compatriot, who discovered the periodic law of chemical elements in 1869, Dmitry Ivanovich Mendeleev (1834-1907), correctly noted, science begins where counting appears, i.e. assessment, comparison, classification, identification of patterns, determination of criteria, common features. Taking this into account, before proceeding to the description of specific elements, it is necessary to give, at least in general terms, a distinctive characteristic of optoelectronic products.

As mentioned above, the main distinguishing feature of optoelectronics is the connection with information. For example, if laser radiation is used in some installation for hardening steel shafts, then it is hardly natural to classify this installation as an optoelectronic device (although the source of laser radiation itself has the right to do so).

It was also noted that solid-state elements are usually classified as optoelectronics (the Moscow Energy Institute published a textbook for the course “Optoelectronics” entitled “Instruments and Devices of Semiconductor Optoelectronics”). But this rule is not very strict, since certain publications on optoelectronics discuss in detail the operation of photomultipliers and cathode ray tubes (they are a type of electric vacuum devices), gas lasers and other devices that are not solid-state. However, in the printing industry, the mentioned devices are widely used along with solid-state ones (including semiconductor ones), solving similar problems, so in this case they have every right to be considered.

It is worth mentioning three more distinctive features, which, according to the famous expert in the field of optoelectronics, Yuri Romanovich Nosov, characterize it as a scientific and technical direction.

The physical basis of optoelectronics consists of phenomena, methods, and means for which the combination and continuity of optical and electronic processes are fundamental. An optoelectronic device is broadly defined as a device that is sensitive to electromagnetic radiation in the visible, infrared (IR), or ultraviolet (UV) regions, or a device that emits and converts incoherent or coherent radiation in these same spectral regions.

The technical basis of optoelectronics is determined by the design and technological concepts of modern microelectronics: miniaturization of elements; preferential development of solid planar structures; integration of elements and functions.

The functional purpose of optoelectronics is to solve computer science problems: generation (formation) of information by converting various external influences into corresponding electrical and optical signals; transfer of information; processing (transforming) information according to a given algorithm; information storage, including processes such as recording, storage itself, non-destructive reading, erasing; display of information, i.e. converting the output signals of an information system to a human-perceivable form.

List of sources used

    http://www.hi-edu.ru/e-books/xbook138/01/index.html?part-004.htm

    http://www.hi-edu.ru/e-books/xbook138/01/index.html?part-003.htm

    http://revolution.allbest.ru/radio/00049966_0.html

    http://revolution.allbest.ru/radio/00049842.html

FEDERAL AGENCY FOR EDUCATION

State educational institution of higher professional education

TYUMEN STATE OIL AND GAS UNIVERSITY

INSTITUTE OF TRANSPORT

Essay

on the topic “Optoelectronic devices.”

Completed:

OBD groups - 08

Chekardinn

Checked:

Sidorova A.E.

Tyumen 2010


  1. Elements optoelectronic devices

    Abstract >> Communications and communications

    According to the circuit of a composite transistor. Optoelectronic devices Job optoelectronic devices based on electron-photonic... transmission and storage of information. The simplest optoelectronic device is optoelectronic pair, or optocoupler. Operating principle...

  2. Application of optocouplers and devices to display information

    Abstract >> Communications and communications

    Definitions Optocouplers are called such optoelectronic devices, in which there is a source and... 2. V. I. Ivanov, A. I. Aksenov, A. M. Yushin “Semiconductor optoelectronic devices." / Directory.” - M.: Energoatomizdat, 2002 3. Baluev V.K. "Development...

  3. Signs of classification of semiconductors devices

    Abstract >> Physics

    By what criteria are semiconductor devices classified? devices? Semiconductor devices classified depending on the mechanism... optically transparent window. LED Semiconductor optoelectronic device, converting the energy of the flowing direct...

The elements of optoelectronic devices are the photoelectronic devices discussed above, and the connection between the elements is not electrical, but optical. Thus, in optoelectronic devices, galvanic coupling between input and output circuits is almost completely eliminated, and feedback between input and output is almost completely eliminated. By combining the elements included in optoelectronic devices, it is possible to obtain a wide variety of their functional properties. In Fig. Figure 6.35 shows the designs of various optocouplers.

The simplest optoelectronic device is an optocoupler.

Optocoupler is a device that combines an LED and a photoradiation receiver, for example a photodiode, in one housing (Fig. 6.36).

The input amplified signal enters the LED and causes it to glow, which is transmitted through the light channel to the photodiode. The photodiode opens and current flows in its circuit under the influence of an external source E. Effective optical communication between the elements of the optocoupler is carried out using fiber optics - light guides made in the form of a bundle of thin transparent threads, through which the signal is transmitted due to total internal reflection with minimal losses and with high resolution. Instead of a photodiode, the optocoupler may contain a phototransistor, photothyristor, or photoresistor.

In Fig. 6.37 shows the symbolic graphic symbols of such devices.

A diode optocoupler is used as a switch and can switch current with a frequency of 10 6 ... 10 7 Hz and has a resistance between the input and output circuits of 10 13 ... 10 15 Ohms.

Transistor optocouplers, due to the greater sensitivity of the photodetector, are more economical than diode ones. However, their speed is lower; the maximum switching frequency usually does not exceed 10 5 Hz. Just like diodes, transistor optocouplers have low resistance in the open state and high resistance in the closed state and provide complete galvanic isolation of input and output circuits.

Using a photothyristor as a photodetector allows you to increase the output current pulse to 5 A or more. In this case, the turn-on time is less than 10 -5 s, and the input turn-on current does not exceed 10 mA. Such optocouplers allow you to control high-current devices for various purposes.

Conclusions:

1. The operation of optoelectronic devices is based on the principle of internal photoelectric effect - the generation of a pair of charge carriers "electron - hole" under the influence of light radiation.

2. Photodiodes have a linear light characteristic.

3. Phototransistors have greater integral sensitivity than photodiodes due to the amplification of photocurrent.

4. Optocouplers – optoelectronic devices that provide electrical insulation



input and output circuits.

5. Photomultipliers make it possible to sharply increase the photocurrent through the use of secondary electron emission.

Control questions

1. What is external and internal photoelectric effect?

2. What parameters are the photoresistor characterized by?

3. What physical factors affect the light characteristics of a photoresistor at high luminous fluxes?

4. What are the differences in the properties of a photodiode and a photoresistor?

5. How does a photocell directly convert light energy into electrical energy?

6. What are the differences in the operating principle and properties of a photodiode and a bipolar phototransistor?

7. Why can a thyristor control relatively higher powers than the permissible power dissipation of the photothyristor itself?

8. What is an optocoupler?

APPLICATION. CLASSIFICATION AND DESIGNATIONS OF SEMICONDUCTOR DEVICES

To unify the designations and standardize the parameters of semiconductor devices, a system of symbols is used. This system classifies semiconductor devices according to their purpose, basic physical and electrical parameters, structural and technological properties, and type of semiconductor materials. The symbol system for domestic semiconductor devices is based on state and industry standards. The first GOST for the designation system for semiconductor devices - GOST 10862–64 was introduced in 1964. Then, as new classification groups of devices emerged, it was changed to GOST 10862–72, and then to the industry standard OST 11.336.038–77 and OST 11.336.919–81. With this modification, the basic elements of the alphanumeric code of the symbol system were preserved. This notation system is logically structured and allows itself to be supplemented as the element base further develops.

Basic terms, definitions and letter designations of the main and reference parameters of semiconductor devices are given in GOSTs:

§ 25529–82 – Semiconductor diodes. Terms, definitions and letter designations of parameters.

§ 19095–73 – Field-effect transistors. Terms, definitions and letter designations of parameters.

§ 20003–74 – Bipolar transistors. Terms, definitions and letter designations of parameters.

§ 20332–84 – Thyristors. Terms, definitions and letter designations of parameters.



 

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