What semiconductors differ from metals. Examples of semiconductors

In electricity, three main groups of materials are distinguished - these are conductors, semiconductors and dielectrics. Their differences are the ability to carry out current. In this article, we will consider what the differences in these types of materials and how they behave in the electric field.

What is a conductor

The substance in which there is free charge carriers are called the conductor. The movement of free carriers is called thermal. The main characteristic of the conductor is its resistance (R) or conductivity (G) - the reverse resistance value.

Speaking simple words - The conductor spends the current.

Such substances include metals, but if we talk about non-metals, for example, carbon is a great conductor, found an application in sliding contacts, for example, an electric motor brushes. Wet soil, solutions of salts and acids in water, human body - also conducts current, but their electrical conductivity is often less than in copper or aluminum, for example.

Metals are excellent conductors, just because big number free chargers of charges in their structure. Under influence electric field The charges begin to move, as well as redistributed, the phenomenon of electrostatic induction is observed.

What is dielectric

Dielectrics call substances that do not conduct current, or spend, but very bad. They do not have free chargers of charges, because the connection of the particles of the atom is quite strong, for the formation of free media, therefore, under the influence of the electric field, there is no current in the dielectric.

Gas, glass, ceramics, porcelain, some resins, textolite, carb, distilled water, dry wood, rubber - are dielectrics and do not conduct an electric current. In everywhere, dielectrics are found everywhere, for example, the electrical appliances enclosures are made of them, electrical switches, Fork housings, sockets, etc. In power lines, insulators are performed from dielectrics.

However, in the presence of certain factors, such as an increased level of humidity, the electric field strength above the permissible value and other - lead to the fact that the material begins to lose its dielectric functions and becomes the conductor. Sometimes you can hear phrases of the type of "test of the insulator" - this is the phenomenon described above.

If you say briefly, the main properties of the dielectric in the field of electricity are electrical insulating. It is the ability to prevent the flow of current protects a person from electric traumamum and other troubles. The main characteristic of the dielectric is electrical strength - The value is equal to the voltage of its breakdown.

What is a semiconductor

The semiconductor conducts electric current, but not as metals, but when complying with certain conditions - the message of the energy substance in the necessary quantities. This is due to the fact that there are no free carriers (holes and electrons) of charges too little or there is no, but if you make some kind of energy - they will appear. Energy can be various shapes - Electric, thermal. Also, free holes and electrons in the semiconductor may occur under the influence of radiation, for example in the UV spectrum.

Where are semiconductors apply? Of these, transistors, thyristors, diodes, chips, LEDs, and so on are manufactured. Such materials include silicon, germanium, mixtures different materials, for example, Arsenide Galia, selenium, arsenic.

To understand why the semiconductor conducts electric current, but not as metals, you need to consider these materials from the point of view of the zone theory.

Zone theory

The zone theory describes the presence or absence of free charge carriers, relative to certain energy layers. The energy level or layer is called the amount of electron energy (atomic nuclei, molecules - simple particles), they are measured in the amount of electron-slot (eV).

The image below shows three types of materials with their energy levels:

Please note that the conductor has energy levels from the valence zone to the conduction zone are combined into an inseparable diagram. Conductivity zone and valence zones are superimposed on each other, this is called the overlap zone. Depending on the presence of an electric field (voltage), temperature and other factors, the number of electrons may vary. Thanks to the above, electrons can move in conductors, even if you inform them some minimum amount of energy.

The semiconductor between the valence zone and the conduction zone there is a certain forbidden. The width of the forbidden zone describes how much energy must be reported to the semiconductor in order to begin to flow.

The dielectric diagram is similar to the one that describes semiconductors, but the difference is only in the width of the forbidden zone - it is many times large here. Differences are due to the inner structure and substances.

We reviewed the main three types of materials and led their examples and features. The main difference is the ability to carry out the current. Therefore, each of them found its scope: conductors are used to transmit electricity, dielectrics - for insulation of current-handing parts, semiconductors - for electronics. We hope that the information provided helped you understand what guides, semiconductors and dielectrics in the electric field are represented, as well as their difference between themselves.

Kikoin A.K. Dielectrics, semiconductors, semimetals, metals // Kvant. - 1984. - № 2. - P. 25-29.

According to a special agreement with the editorial board and the editors of the magazine "Kvant"

In classical physics, all substances were taken on their electrical properties to divide on conductors and dielectrics ("Physics 9", §§44 and 46). Modern physics distinguishes two more intermediate states - semiconductors ("Physics 9", § 78) and semimetals. Only with the advent of quantum mechanics it became clear what the differences between all these types of substances. In this note, we will try to briefly describe the essence of a modern quantum-mechanical theory explaining the electrical properties of solids.

The solid consists of atoms forming a crystal lattice. Atoms are held in the lattice by the interaction of electrically charged atomic particles - positively charged nuclei and adversely charged electrons. The electric current in the crystal is the movement of electrons, which obeys the laws of quantum mechanics. According to these laws, electrons and in a separate atom, and in the crystal can only have certain (authorized energy values, or, in other words, to be on certain energy levels. The higher the level, the greater the energy it corresponds to.

In atom, these levels are located fairly far from each other - it is customary to say that the levels form a discrete energy spectrum (Fig. 1). Under certain conditions, electrons can move from one level to another, allowed, level. An electron with this energy can only move on a closed trajectory - orbit - around the kernel.

When atoms are combined into a crystal, part of the electrons still remains on its atomic orbits, but the electrons are most distant from the core be able to move throughout the crystal due to the fact that the external orbits of neighboring atoms overlap. And this means that the energy levels previously belonged to individual atoms become "common" for the entire crystal. Instead of discrete levels in the crystal are formed energy zonesconsisting of very closely located levels. Electrons that are on these "common" levels are called valence electrons.

Valence electrons move along orbits covering the entire crystal, and seemingly electric currents. However, if everything was so simple, all solid bodies would be good conductors (metals). The laws of quantum mechanics make a picture much more complex and diverse.

First, the energy zones are separated by the intervals in which there is not a single energy level. These gaps are called forbidden zones. Secondly, electrons are subject to the so-called Pauli principle, according to which every level in this state There may be only one electron. With the lowest possible temperature (equal to absolute zero), the energy levels are sequentially at the bottom up (that is, starting with the smallest energy values) are filled with electrons according to the principle of Pauli, and levels with higher energies remain free. Various degree Filling the energy zones, as well as differences in their relative location and allow you to divide all solid bodies on dielectrics, semiconductors, semimetals and metals.

Dielectrics.

For T. \u003d 0 valence electrons fully fill the lowest zone called valence zone (Fig. 2). There are no free levels in it, and the next allowed zone - conductory zone - separated from it a widely prohibited zone. If this sample is attached to electric fieldIt will not be able to accelerate electrons, that is, to create an electric current, as it will accelerate the electron - it means to inform it additional energy, and, according to the laws of quantum mechanics, it can be done only by moving it to a higher energy level. But the principle of Pauli prohibits electrons to occupy the already occupied levels, and to get into the following allowed zone, which is completely empty, they cannot, because the energy obtained from the electric field is much smaller than the width Δ of the prohibited zone.

At a temperature other than zero, electrons, in principle, can go to the conduction zone and become carriers electric current. However, in order for the number of electrons moving to this zone to be quite large, you need to heat the dielectric to such high temperaturesthat he melts before the current reaches a measurable value. For room temperature The current in the dielectric is practically not flowing.

Semiconductors.

A semiconductor differs from the dielectric only by the fact that the width δ of the prohibited zone separating the valence zone from the conduction zone is much less (he is ten times). For T. \u003d 0 The valence zone in the semiconductor, as in the dielectric, is entirely filled, and the current in the sample cannot flow. But due to the fact that the energy Δ is small, already with a slight increase in temperature, the part of the electrons can go to the conduction zone (Fig. 3). Then the electrical current in the substance will be possible, and immediately in two "channels".

First, in the conduction zone, electrons, acquiring energy in the electric field, are moving to higher energy levels. Secondly, the contribution to the electric current is given ... Empty levels left in the valence zone by electrons who have left the conduction zone. Indeed, the Pauli principle allows any electron to take the liberated level in the valence zone. But, taking this level, it leaves its own level, etc. If you monitor the movement of electrons by levels in the valence zone, but for the movement of the empty levels themselves, it turns out that these levels having a scientific name hole, also become current carriers. The number of holes is obviously equal to the number of electrons deployed in the conduction zone (so-called electric conductivity), But the holes have a positive charge, because the hole is the missing electron.

Thus, in the semiconductor, the electric current is the electrons current in the conduction zone and holes in the valence zone. Such a semiconductor conductivity is called own.

Electrons and holes when moving along a crystal interact with the atoms of a crystal lattice, while losing its energy. With these losses, the electrical resistance of the substance is associated. With increasing temperature, energy loss increases, so that the resistance of the semiconductor would have to increase the temperature with increasing temperature. But when the temperature is raised, the number is growing electronspassing into the conduction zone, and therefore, the number of holes R valence zone. This means that it grows (and very quickly) the total number of current carriers. Because of this, the resistance of the semiconductor with an increase in temperature does not grow, but falls. Semiconductor and can be defined as substance, practically non-conducting current at an absolute zero temperatures, but the resistance of which with increasing temperature drops sharply.

In nature, however, semiconductors with their own conductivity does not exist: they always have impurities of other substances that determine their electrical properties. The presence of impurities leads to the prohibited zone of the semiconductor appear additional energy levels, from which or to which electronic transitions are also possible. The wide use of semiconductors in the technique has become possible only after the technologists have learned to control the content of impurities in semiconductors and at its discretion to make their conductivity ( adjustable conductivity) Almost purely electronic or pure hole.

It turns out that these impurities can be selected, the atoms of which easily give electrons. Additional energy levels are released within the prohibited semiconductor zone near its upper edge (Fig. 4, a). Such impurities are called donor impurities, and levels - donor levels. From Figure 4, but it can be seen that at the same temperature of electrons at such levels, it is much easier to switch to the conduction zone than electrons from the valence zone, so impurity levels will become the main electrons in the conductivity zone. But at the same time in the valence zone of holes will not appear, and the conductivity of the semiconductor will become almost purely electronic. Such semiconductors are called semiconductors. n.-Type.

There are also such impurities whose atoms easily attach electrons ( acceptor impurities). Additional levels of their electrons (acceptor levels) are also located inside the prohibited semiconductor zone, but near its bottom (Fig. 4, b). In this case, electrons from the valence zone are easier to go to acceptor levels of impurities than in the conductivity zone. Then the holes will appear in the valence zone without electrons appear in the conduction zone. It turns out a semiconductor with almost pure hole conductivity, or semiconductor p.-Type.

Electrons in metals finally "forget" their atomic origin, their levels form one very wide zone. It is always filled only partially (the number of electrons is less than the number of levels) and therefore may be called the conduction zone (Fig. 6). It's clear that in metals, the current can flow and at zero temperature. Moreover, with the help of quantum mechanics, you can prove that ideal Metal (the lattice of which does not have defects) when T. \u003d 0 Current must flow without resistance!

Unfortunately, there are no ideal crystals, and it is impossible to achieve zero temperature. In fact, electrons lose energy, interacting with the oscillating lattice atoms, so Real metal resistance grows with temperature (Unlike the resistance of the semiconductor). But the most important thing is that at any temperature, the electrical conductivity of the metal is significantly higher than the electrical conductivity of the semiconductor because there are much more electrons in the metal capable of conducting an electric current.

The most famous semiconductor is silicon (Si). But, besides him, there are many others. An example is such natural semiconductor materials such as zinc destruction (ZNS), buy (Cu 2 O), Galenit (PBS) and many others. The family of semiconductors, including semiconductors synthesized in laboratories, is one of the most versatile classes of materials known to humans.

Characteristics of semiconductors

Of the 104 elements of the Mendeleev table 79 are metals, 25 - non-metals, of which 13 have semiconductor properties and 12 - dielectric. The main difference between semiconductors is that their electrical conductivity increases significantly when temperatures increase. For low temperatures They behave like dielectrics, and at high - as conductors. These semiconductors differ from metals: metal resistance increases in proportion to temperature increase.

Another distinction of the semiconductor from the metal is that the resistance of the semiconductor falls under the action of light, while the latter does not affect the metal. The conductivity of semiconductors is also changing when an insignificant amount of impurity is introduced.

Semiconductors are found among chemical compounds With a variety of crystal structures. It may be elements like silicon and selenium, or double connectionslike arsenide gallium. Many polyacetylene (CH) N, - semiconductor materials. Some semiconductors exhibit magnetic (CD 1-x Mn X TE) or ferroelectric properties (SBSI). Others with sufficient doping become superconductors (GETE and SRTIO 3). Many of the recently open high-temperature superconductors have non-metallic semiconducting phases. For example, La 2 CuO 4 is a semiconductor, but when the alloy is formed with SR becomes a superioron (La 1-x SR X) 2 Cuo 4.

Physics textbooks give the semiconductor as a material with electrical resistance from 10 -4 to 10 7 ohms · m. An alternative definition is possible. The width of the forbidden semiconductor zone is from 0 to 3 eV. Metals and semi-metals are materials with a zero energy gap, and substances that it exceeds from eV is called insulators. There are exceptions. For example, a semiconductor diamond has a prohibited zone 6 eV wide, semi-insulating GaAs - 1.5 eV. GAN, Material for in the blue area has a prohibited zone of 3.5 eV width.

Energy clearance

Valence orbital atoms in a crystal lattice are divided into two groups energy levels - free zone located on summit and the determining electrical conductivity of semiconductors, and the valence zone located below. These levels, depending on the symmetry of the crystal lattice and the composition of atoms, can intersect or be located apart from each other. In the latter case, an energy gap or, in other words, a prohibited zone arises between the zones.

The location and level filling determines the electrically conductive properties of the substance. Therefore, the substance is divided into conductors, insulators and semiconductors. The width of the forbidden semiconductor zone varies within 0.01-3 eV, the energy gap of the dielectric exceeds 3 eV. Metals due to overlapping levels of energy breaks do not have.

Semiconductors and dielectrics, as opposed to metals, have a valented zone filled with electrons, and the nearest free zone, or conduction zone, fell apart from the valence energy gap - a portion of the prohibited energies of electrons.

In dielectric thermal energy or a minor electric field, it is not enough to make a jump through this gap, electrons in the conduction zone do not fall. They are not able to move along the crystal lattice and become electric current carriers.

To initiate electrical conductivity, an electron on the valence level should be given the energy that would be enough to overcome the energy gap. Only when absorbing the amount of energy that is not less than the magnitude of the energy gap, the electron will switch from the valence level to the conduction level.

In the event that the width of the energy gap exceeds 4 eV, the excitation of the conductivity of the semiconductor by irradiation or heating is almost impossible - the electron excitation energy at a melting point is insufficient for the jump through the energy break zone. When heated, the crystal is melted until electronic conductivity occurs. Such substances include quartz (de \u003d 5.2 eV), diamond (DE \u003d 5.1 EV), many salts.

Impurity and own conductivity of semiconductors

Clean semiconductor crystals have their own conductivity. Such semiconductors are referred to as their own. Own semiconductor contains equal number holes and free electrons. When heated, the own conductivity of semiconductors increases. At a constant temperature, the state of dynamic equilibrium of the amount of generated electron-hole pairs and the amount of recombining electrons and holes that remain constant under these conditions are arisen.

The presence of impurities has a significant effect on the electrical conductivity of semiconductors. Adding them allows much to increase the amount of free electrons with a small number of holes and increase the number of holes with a small number of electrons at the conductivity level. The impurity semiconductors are conductors with impurity conductivity.

Impurities that easily give electrons are called donor. Donor impurities can be chemical elements with atoms whose valence levels contain large quantity electrons than base substance atoms. For example, phosphorus and bismuth are silicon donor impurities.

The energy required to jump an electron into the conduction area is called the activation energy. Impurity semiconductors need much less than its main substance. With a slight heating, either the lighting is predominantly electron atoms of impurity semiconductors are released. The location of an electron atom occupies a hole. But the recombination of electrons in holes is practically not happening. The punch conductivity of the donor is insignificant. This is because the small number of impurity atoms does not allow free electrons often approach the hole and occupy it. Electrons are near holes, but they are not able to fill them due to the insufficient energy level.

A minor additive of the donor impurity by several orders increases the number of conduction electrons compared to the number of free electrons in its own semiconductor. Electrons here are the main carriers of charges of atoms of impurity semiconductors. These substances relate to N-type semiconductors.

Impurities that bind the semiconductor electrons, increasing the number of holes in it, is called acceptor. Acceptor impurities are chemical elements with a smaller number of electrons on the valence level than the base semiconductor. Bor, Gallium, India - acceptor impurities for silicon.

The characteristics of the semiconductor are depending on the defects of its crystal structure. This is the reason for the need to grow extremely pure crystals. The parameters of the semiconductor conductivity are controlled by adding alloying additives. Silicon crystals are doped with phosphorus (element V subgroup), which is a donor to create a N-type silicon crystal. An acceptor boron is introduced to obtain a crystal with hole conductivity in silicon. Semiconductors with a compensated Fermi level to move it in the middle of the forbidden zone are created in a similar way.

Single-element semiconductors

The most common semiconductor is, of course, silicon. Together with Germany, he became a prototype of a wide class of semiconductors with similar structures of the crystal.

Si and Ge is the same as the diamond and α-tin. In it, each atom surrounds 4 closest atoms that form a tetrahedron. Such coordination is called fourfold. Crystals with a tetradrical connection were basic to the electronic industry and play a key role in modern technology. Some elements of the Mendeleev table group V and VI are also semiconductors. Examples of semiconductors of this type - phosphorus (P), sulfur (S), selenium (SE) and TVLUR (those). In these semiconductors, atoms may have three-time (P), two-time (S, SE, those) or fourfold coordination. As a result, such elements may exist in several different crystal structures, as well as be obtained in the form of glass. For example, SE was grown in monoclinic and trigonal crystalline structures or in the form of glass (which can also be considered a polymer).

Almaz has excellent thermal conductivity, excellent mechanical and optical characteristics, high mechanical strength. The width of the energy break - de \u003d 5.47 eV.

Silicon - semiconductor used in solar panels, and in amorphous form - in thin-winged solar panels. It is the most used semiconductor in photocells, easy to manufacture, has good electrical and mechanical qualities. DE \u003d 1.12 EV.

Germanium is a semiconductor used in gamma spectroscopy, highly efficient photocells. Used in the first diodes and transistors. It requires less cleaning than silicon. DE \u003d 0.67 EV.

Selenium - semiconductor, which is used in selenium rectifiers with high radiation resistance and self-healing ability.

Two-element compounds

The properties of semiconductors formed by elements 3 and 4 groups of the Mendeleev table resemble 4 groups. Transition from 4 group of elements to compounds 3-4 gr. Makes communication partially ion due to the transfer of electron charge from an atom 3 of the group to the atom of 4 groups. Ionality changes the properties of semiconductors. It is the cause of an increase in the Coulomb mea interaction and energy of the energy rupture of the zone structure of electrons. An example of a binary connection of this type - an antimonide India Insb, Gaas Gallium arsenide, Gallium Gallium Antimid, India InP Phosphid, AlsB Aluminum Antimonide, Gallium Phosphide GaP.

Ionality increases, and its value is even more growing in compounds of substances of 2-6 groups, such as cadmium selenide, zinc sulfide, cadmium sulfide, cadmium television, zinc selenide. As a result, in most compounds 2-6 groups, the prohibited zone is wider than 1 eV, except for mercury compounds. Mercury teleuride is a semiconductor without an energy gap, semi-metall, like α-tin.

Semiconductors 2-6 groups with a large energy gap are used in the production of lasers and displays. Binary compounds 2-6 groups with a narrowed energy gap are suitable for infrared receivers. Binary compounds of elements 1-7 groups (CUBR copper bromide, AGI silver iodide, copper chloride) due to high ionicity have a prohibited zone wider than s. They are actually not semiconductors, but insulators. The growth of the clutch energy of the crystal due to the Coulomb mea interaction contributes to the structuring of atoms with six-time, and not quadratic coordination. Compounds 4-6 groups - sulfide and lead televaride, tin sulfide - also semiconductors. The degree of ionicity of these substances also contributes to the formation of six-time coordination. Significant ionicity does not prevent the presence of very narrow forbidden zones, which allows them to use them for intra-radiation. Gallium nitride is a compound of 3-5 groups with a wide energy gap, found the use of B and LEDs operating in the blue part of the spectrum.

GaAs, Gaas Arsenide - the second in demand after silicon semiconductor, commonly used as a substrate for other conductors, for example, Gainnas and Ingaas, in IR networks, high-frequency chips and transistors, highly efficient photocells, laser diodes, nuclear cure detectors. DE \u003d 1.43 EV, which allows you to increase the power of the instruments compared to silicon. The fragile contains more impurities, complicated in the manufacture.

ZNS, zinc sulfide - a zinc hydrogen sulfide salt with a range of a prohibited zone 3.54 and 3.91 eV, is used in lasers and as a phosphor.

SNS, tin sulphide - semiconductor used in photoresistors and photodiodes, DE \u003d 1.3 and 10 eV.

Oxides.

Metal oxides are predominantly excellent insulators, but there are exceptions. Examples of semiconductors of this type - nickel oxide, copper oxide, cobalt oxide, copper dioxide, iron oxide, europe oxide, zinc oxide. Since copper dioxide exists in the form of a cuprite mineral, its properties have studied hard. The procedure for growing semiconductors of this type is not yet completely clear, so their use is still limited. The exception is zinc oxide (ZnO), compound 2-6 groups used as a converter and in the production of adhesive tapes and patches.

The situation has changed dramatically after in many compounds of copper with oxygen, superconductivity was opened. The first high-temperature superconductor, open Muller and the Bistzen, was a compound based on the LA 2 Cuo 4 semiconductor with an energy gap of 2 eV. Naturally tiled lanthanum in bivalent barium or strontium, in the semiconductor introduces solar charge carriers. The achievement of the necessary concentration of holes turns LA 2 Cuo 4 to the superconductor. At this time, the largest transition temperature to the superconducting state belongs to the HGBACA 2 Cu 3 O 8 compound. For high pressure Its value is 134 K.

ZnO, zinc oxide, used in varistors, blue LEDs, gas sensors, biological sensors, windows coatings for reflection of infrared light, as a conductor in LCD displays and solar panels. DE \u003d 3.37 EV.

Layered crystals

Double compounds such as lead dioiodide, gallium selenide and molybdenum disulfide are distinguished by a layered structure of the crystal. There are significant strength in the layers, much stronger van der Waals bonds between the layers themselves. Semiconductors of this type are interesting in that electrons behave in the layers of quasi-two-dimensional. The interaction of the layer is changed by the introduction of third-party atoms - intercalation.

MOS 2, Molybdenum Disulfide is used in high-frequency detectors, rectifiers, membranes, transistors. DE \u003d 1.23 and 1.8 EV.

Organic semiconductors

Examples of semiconductors based on organic compounds - naphthalene, polyacetylene (CH 2) N, anthracene, polydiaacetylene, phthalocyanids, polyvinyl carbazol. Organic semiconductors have an advantage over inorganic: they can easily give the right qualities. Substances with conjugate bonds of the like-С - C-C \u003d, have significant optical nonlinearity and, due to this, are used in optoelectronics. In addition, the zone of the energy gap of organic semiconductors is changed by changing the compound formula, which is much easier than the ordinary semiconductors. Crystalline altrotrops of carbon Fullerene, graphene, nanotubes are also semiconductors.

Fullerene has a structure in the form of a convex closed polyhedron from former number atoms of carbon. And the alloying of fullerene with 60 alkaline metal turns it into the superconductor.

The graphene is formed by a single-cattle layer of carbon connected in a two-dimensional hexagonal grid. It has record thermal conductivity and electron mobility, high rigidity

Nanotubes are a graphite plate rolled into the tube having several nanometers in diameter. These carbon forms have a great perspective in nanoelectronics. Depending on the clutch, metal or semiconductor qualities can be exhibited.

Magnetic semiconductors

Connections with magnetic ions of Europe and manganese have curious magnetic and semiconductor properties. Examples of semiconductors of this type are Europium sulphide, europe selenide and solid solutions, similar to CD 1-X-MN x TE. The content of magnetic ions affects how magnetic properties such as antiferromagnetism and ferromagnetism appear in substances. Magnetic semiconductors are solid magnetic solutions of semiconductors that contain magnetic ions in a small concentration. Such hard solutions draw attention to their promising and high potential of possible applications. For example, in contrast to non-magnetic semiconductors, they can be achieved in a million times of larger Faraday rotation.

Strong magneto-optical effects of magnetic semiconductors allow you to use them for optical modulation. Perovskites, similar to Mn 0.7 Ca 0.3 o 3, are superior to the transition of a metal-semiconductor, the direct dependence of which from the magnetic field has a consequence of the phenomenon of giant magnet-resistivity. Apply in radio engineering, optical devices that are managed magnetic field, in the waveguides of microwave devices.

Semiconductor segroelectrics

This type of crystals is distinguished by the presence of electrical moments and the occurrence of spontaneous polarization. For example, semiconductors Titanate PBTIO 3 Titanate, Barium Titanate Batio 3, Germany Telluride GEETE, SNTE Trucride, which at low temperatures have the properties of a ferroelectric at low temperatures. These materials are used in nonlinear optical, storage devices and piezodators.

Variety of semiconductor materials

In addition to the above semiconductor substances mentioned above, there are many others that do not fall under one of the listed types. Compounds of elements according to formula 1-3-5 2 (aggas 2) and 2-4-5 2 (ZNSIP 2) form crystals in the structure of the chalcopyrite. Communications of tetrahedral compounds, similar to semiconductors 3-5 and 2-6 groups with a crystalline structure of zinc decking. Compounds that form elements of semiconductors 5 and 6 groups (like AS 2 SE 3), - semiconductor in the form of a crystal or glass. Bismuth and antimony chalcogenides are used in semiconductor thermoelectric generators. The properties of semiconductors of this type are extremely interesting, but they have not gained popularity due to limited use. However, what they exist, confirms the presence of still not studied areas of semiconductor physics.

Solid bodies are metals, semiconductors and dielectrics. They differ from each other in their electronic properties. The electrical conductivity of solid bodies is determined by the properties of electrons.

Definition

Semiconductorsrefer to metals to solid bodies. Their number belongs to Germany, silicon, arsenic, etc., as well as various alloys and chemical compounds.

Metals These are solid bodies that have a certain structure.

Comparison

Consider how electric current occurs in semiconductors. In atoms, Germany on the outer shell contains four slightly related valence electrons. IN crystal lattice Near each atom there are four more. Atoms in a semiconductor crystal are bound by valence electron vapors. Each valence electron belongs to two atoms. If the temperature is raised, some part of the valence electrons will receive energy that is sufficient for breaking covalent ties. The crystal will appear free electrons called conduction electrons. At the same time, vacancies, holes are formed on the site of the departed electrons. A vacant place can take the valence electrons of the neighboring pair, then the hole will be in a new place in the crystal. At a certain temperature in a semiconductor, there is a certain amount of electron-hole pairs. Free electron, meeting with a hole, restores electronic communications. The holes are similar to positively charged particles. If there is no electrical field, the holes and electrons of the conductivity are chaotic. If the semiconductor is placed in an electric field, then the holes and free electrons will begin to move ordered. Therefore, the current in the semiconductor consists of electronic and hole currents. The number of carriers of free charge changes, does not remain constant and depends on temperature. With its increase, the resistance of semiconductors increases.

Metals have a crystal structure. They consist of molecules and atoms that occupy a certain, ordered position. The metal is presented in the form of a crystal lattice, in the nodes of which are atoms, or ions, or molecules that oscillate near their location. Between them in space there are free electrons that are chaotic moving in different directions. But when the electric field appears, they begin to move ordered in the direction of the positive pole, an electric current appears in metals. The number of electrons is constant. When the temperature decreases, the speed of the electron movement slows down, the metal resistance drops.

Conclusions Site

1. Semiconductors differ from metals with electric current mechanism.
2. Electric current in metals is the directional movement of electrons.
3. In pure semiconductors, the electron-hole mechanism of conductivity.
4. The resistivity of semiconductors and metals depends on the temperature in different ways.

All substances consist of molecules, molecules from atoms, atoms from positively charged cores around which negative electrons are located. Under certain conditions, electrons are able to leave their kernel and move to the neighboring. At the same time, the atom becomes positively charged, and the neighboring gets a negative charge. The movement of negative and positive charges under the action of the electric field received the name of the electric current.

Depending on the properties of materials, the electric current is divided into:

1. Semiconductors.

Properties of conductors

Conductors are different good electrical conductivity. This is due to the presence of a large amount of free electrons that do not belong specifically by any of the atoms, which under the action of the electric field can freely move.

Most conductors have low resistivity and conduct electric current with very small losses. Due to the fact that perfectly clean chemical composition Elements in nature does not exist, any material in its composition contains impurities. The impurities in the conductors occupy space in the crystal lattice and, as a rule, prevent the passage of free electrons under the action of the applied voltage.

Impurities worsen the properties of the conductor. The more impurities, the stronger they affect the parameters of the conductivity.

Good conductor with low resistivity are such materials:

• Gold.
• Silver.
• Copper.
• Aluminum.
• Iron.

Gold and silver are good conductors, but due to high costs are used where you need to get good high-quality conductors with a small volume. This is basically electronic circuits, chips, conductors of high-frequency devices in which the conductor itself is made of cheap material (copper), which is covered with a thin layer of silver or gold from above. This makes it possible at minimal consumption. precious metal Good frequency characteristics of the conductor.

Copper and aluminum - cheaper metals. With a slight decrease in the characteristics of these materials, their price is about the order below, which makes it possible for their mass application. Apply in electronics, in electrical engineering. In electronics are tracks printed circuit board, legs of radio elements, radiators, etc. The electrical engineering is very widely used in the windings of the engines, for laying electrical networks high and low voltage, wiring of electricity in apartments, houses, in transport.

The conductivity parameter is very dependent on the temperature of the material itself. With an increase in the crystal temperature, electrons fluctuations in the crystal lattice increases, preventing the free passage of free electrons. With a decrease - on the contrary, the resistance decreases and at some value close to the absolute zero, the resistance becomes zero and the effect of superconductivity occurs.

Properties of dielectrics

Dielectrics in their crystal lattice contain very little free electronscapable of transferring charge under the action of an electric field. In this regard, when creating the difference in potentials on a dielectric, the current passing through it is so insignificant, which is considered equal to zero - Dielectric does not conduct electric current. Along with this, impurities contained in any dielectric usually worsen its dielectric properties. The current passing through the dielectric under the action of the applied voltage is mainly determined by the amount of impurities.

The greatest distribution of dielectrics was obtained in electrical engineering where it is necessary to protect the service personnel from harmful effects electric current. This is insulating handles different devices, measuring equipment devices. In electronics - gaskets of capacitors, insulation of wires, dielectric pads necessary for the heat sink of active elements, instrument housings.

Semiconductors - materials that conduct electricity under certain conditions, in another case behave like dielectrics.

Table: What is the differences and dielectrics?