How are semiconductors different from metals? Semiconductor examples

In electricity, there are three main groups of materials - these are conductors, semiconductors and dielectrics. Their main difference is the ability to conduct current. In this article, we will look at how these types of materials differ and how they behave in an electric field.

What is a conductor

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

talking in simple terms- A conductor conducts current.

Metals can be attributed to such substances, but if we talk about non-metals, then, for example, carbon is an excellent conductor, it has found application in sliding contacts, for example, motor brushes. Wet soil, solutions of salts and acids in water, the human body also conduct current, but their electrical conductivity is often less than that of copper or aluminum, for example.

Metals are excellent conductors due to a large number free charge carriers in their structure. Under influence electric field charges begin to move, as well as redistribute, the phenomenon of electrostatic induction is observed.

What is a dielectric

Dielectrics are substances that do not conduct current, or conduct, but very poorly. There are no free charge carriers in them, because the bond of the particles of an atom is strong enough to form free carriers, therefore, under the influence of an electric field, no current arises in the dielectric.

Gas, glass, ceramics, porcelain, some resins, textolite, carbolite, distilled water, dry wood, rubber are dielectrics and do not conduct electricity. In everyday life, dielectrics are found everywhere, for example, cases of electrical appliances are made from them, electrical switches, housings for plugs, sockets and more. In power lines, insulators are made of dielectrics.

However, in the presence of certain factors, for example, an increased level of humidity, an electric field strength above the permissible value, and so on, lead to the fact that the material begins to lose its dielectric functions and becomes a conductor. Sometimes you can hear phrases like "breakdown of the insulator" - this is the phenomenon described above.

In short, the main properties of a dielectric in the field of electricity are electrical insulating. It is the ability to prevent the flow of current that protects a person from electrical injuries and other troubles. The main characteristic of a dielectric is dielectric strength- a value equal to the voltage of its breakdown.

What is a semiconductor

A semiconductor conducts electric current, but not like metals, but under certain conditions - the communication of energy to a substance in the right quantities. This is due to the fact that there are too few free charge carriers (holes and electrons) or they do not exist at all, but if you apply some amount of energy, they will appear. Energy can be various forms- electrical, thermal. Also, free holes and electrons in a semiconductor can appear under the influence of radiation, for example, in the UV spectrum.

Where are semiconductors used? Transistors, thyristors, diodes, microcircuits, LEDs, etc. are made from them. Such materials include silicon, germanium, mixtures different materials e.g. gallium arsenide, selenium, arsenic.

To understand why a semiconductor conducts electricity, but not like metals, we need to consider these materials from the point of view of band theory.

Zone theory

The band theory describes the presence or absence of free charge carriers, relative to certain energy layers. The energy level or layer is the amount of energy of electrons (nuclei of atoms, molecules - simple particles), they are measured in the value of Electronvolts (EV).

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

Note that in a conductor, the energy levels from the valence band to the conduction band are combined into a continuous diagram. The conduction band and valence band overlap each other, this is called the overlap band. 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 give them some minimal amount of energy.

A semiconductor has a certain band gap between the valence band and the conduction band. The band gap describes how much energy must be imparted to a semiconductor in order for current to begin to flow.

For a dielectric, the diagram is similar to the one that describes semiconductors, but the difference is only in the band gap - it is many times larger here. Differences are due to the internal structure and substance.

We have reviewed the main three types of materials and given their examples and features. Their main difference is the ability to conduct current. Therefore, each of them has found its own scope: conductors are used to transmit electricity, dielectrics - to isolate current-carrying parts, semiconductors - for electronics. We hope that the information provided has helped you understand what conductors, semiconductors and dielectrics are in an electric field, as well as how they differ from each other.

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

By special agreement with the editorial board and the editors of the journal "Kvant"

In classical physics, it was customary to divide all substances according to their electrical properties into 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 did it become clear what are the differences between all these types of substances. In this note, we will try to briefly describe the essence of the modern quantum mechanical theory that explains the electrical properties of solids.

A solid body is made up of atoms that form a crystal lattice. Atoms are held in the lattice by the forces of interaction of electrically charged atomic particles - positively charged nuclei and negatively charged electrons. Electric current in a crystal is the movement of electrons, which obeys the laws of quantum mechanics. According to these laws, electrons both in an individual atom and in a crystal can have only certain (permitted) energy values, or, in other words, be at certain energy levels. The higher the level, the more energy it corresponds to.

In an atom, these levels are located quite far from one another - 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 a given energy can only move along a closed trajectory - an orbit - around the nucleus.

When atoms combine to form a crystal, some of the electrons still remain in their atomic orbits, but the electrons farthest from the nucleus are able to move throughout the crystal due to the fact that the outer orbits of neighboring atoms overlap. And this means that the energy levels that used to belong to individual atoms become "common" for the entire crystal. Instead of discrete levels in a crystal, energy zones consisting of very closely spaced levels. The electrons that are in these "socialized" levels are called valence electrons.

Valence electrons move in orbits that cover the entire crystal, and, it would seem, can conduct an electric current. However, if things were that simple, all solids would be good conductors (metals). The laws of quantum mechanics make the picture much more complex and varied.

First, the energy zones are separated by gaps in which there is not a single energy level. These intervals are called forbidden zones. Secondly, electrons obey the so-called Pauli principle, according to which at each level in given state there can only be one electron. At the lowest possible temperature (equal to absolute zero), the energy levels sequentially from bottom to top (that is, starting from the lowest energy values) are filled with electrons in accordance with the Pauli principle, and the levels with higher energies remain free. varying degree filling the energy bands, as well as differences in their relative arrangement, and make it possible to divide all solids into dielectrics, semiconductors, semimetals and metals.

Dielectrics.

At T= 0 valence electrons completely fill the lowest band, called valence band(Fig. 2). There are no free levels in it, and the next allowed zone is conduction band- separated from it by a wide bandgap. If we apply to such a sample electric field, it will not be able to accelerate electrons, that is, create an electric current, since accelerating an electron means giving it additional energy, and, according to the laws of quantum mechanics, this can only be done by transferring it to a higher energy level. But the Pauli principle forbids electrons from occupying already occupied levels, and they cannot get into the next allowed band, which is completely empty, because the energy received from the electric field is much less than the width Δ of the band gap.

At a temperature other than zero, electrons, in principle, can go into the conduction band and become carriers electric current. However, in order for the number of electrons that have passed into this zone to be large enough, the dielectric must be heated to such high temperature that it will melt before the current reaches a measurable value. At room temperature practically no current flows in the dielectric.

Semiconductors.

A semiconductor differs from a dielectric only in that the width Δ of the band gap separating the valence band from the conduction band is much smaller (tens of times). At T= 0, the valence band in a semiconductor, as in a dielectric, is completely filled, and the current cannot flow through the sample. But due to the fact that the energy Δ is small, already with a slight increase in temperature, some of the electrons can go into the conduction band (Fig. 3). Then the electric current in the substance will become possible, moreover, through two "channels" at once.

First, in the conduction band, electrons, acquiring energy in an electric field, move to higher energy levels. Secondly, the contribution to the electric current comes from ... empty levels left in the valence band by electrons that have gone into the conduction band. Indeed, the Pauli principle allows any electron to occupy the vacated level in the valence band. But, having occupied this level, it leaves its own level free, and so on. holes, also become current carriers. The number of holes is obviously equal to the number of electrons that have gone into the conduction band (the so-called conduction electrons), but holes have a positive charge because the hole is the missing electron.

Thus, in a semiconductor, electric current is the current of electrons in the conduction band and holes in the valence band. This conductivity of a semiconductor is called own.

Electrons and holes while moving through the crystal interact with the atoms of the crystal lattice, losing their energy. These losses are associated with the electrical resistance of the substance. As the temperature increases, energy losses increase, so the resistance of a semiconductor should also increase with increasing temperature. But as the temperature rises, the number electrons passing into the conduction band, and hence the number of holes r in the valence band. This means that the total number of current carriers is growing (and very rapidly). Because of this, the resistance of a semiconductor does not increase with increasing temperature, but decreases. Semiconductor and can be defined as a substance that practically does not conduct current at absolute zero temperature, but whose resistance decreases sharply with increasing temperature.

In nature, however, semiconductors with intrinsic conductivity do not exist: they always contain impurities of other substances, which determine their electrical properties. The presence of impurities leads to the fact that additional energy levels appear in the band gap of the semiconductor, from which or to which electronic transitions are also possible. The widespread use of semiconductors in technology became possible only after technologists learned to control the content of impurities in semiconductors and make their conductivity at their discretion ( impurity conductivity) is almost purely electronic or purely hole.

It turns out that it is possible to select such impurities whose atoms easily donate electrons. The additional energy levels released in this case are located inside the band gap of the semiconductor near its upper edge (Fig. 4a). Such impurities are called donor impurities, and the levels are donor levels. Figure 4, a shows that at the same temperature it is much easier for electrons from such levels to move into the conduction band than for electrons from the valence band, so the impurity levels will become the main suppliers of electrons to the conduction band. But in this case, no holes will appear in the valence band, and the conductivity of the semiconductor will become almost purely electronic. Such semiconductors are called semiconductors. n-type.

There are also impurities whose atoms easily attach electrons to themselves ( acceptor impurities). Additional levels of their electrons (acceptor levels) are also located inside the band gap of the semiconductor, but near its bottom (Fig. 4b). In this case, it is easier for electrons from the valence band to pass to the acceptor impurity levels than to the conduction band. Then holes will appear in the valence band without electrons appearing in the conduction band. The result is a semiconductor with almost pure hole conductivity, or a semiconductor p-type.

Electrons in metals completely "forget" their atomic origin, their levels form one very wide band. It is always only partially filled (the number of electrons is less than the number of levels) and therefore can be called the conduction band (Fig. 6). It's clear that in metals, current can flow even at zero temperature. Moreover, with the help of quantum mechanics, one can prove that in ideal metal(whose lattice has no defects) at T= 0 current must flow without resistance !

Unfortunately, ideal crystals do not exist, and zero temperature cannot be reached. In reality, electrons lose energy by interacting with vibrating lattice atoms, so that the resistance of real metal increases with temperature(as opposed to semiconductor resistance). But the most important thing is that at any temperature the electrical conductivity of a metal is much higher than the electrical conductivity of a semiconductor, because there are much more electrons in the metal that can conduct electric current.

The best known semiconductor is silicon (Si). But besides him, there are many others. An example is such natural semiconductor materials as zinc blende (ZnS), cuprite (Cu 2 O), galena (PbS) and many others. The semiconductor family, including laboratory-synthesized semiconductors, is one of the most versatile classes of materials known to man.

Characterization of semiconductors

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

Another difference between a semiconductor and a metal is that the resistance of a semiconductor drops under the influence of light, while the latter does not affect the metal. The conductivity of semiconductors also changes when a small amount of impurity is introduced.

Semiconductors are found among chemical compounds with various crystal structures. These may be elements such as silicon and selenium, or double connections like gallium arsenide. 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 discovered high temperature superconductors have non-metallic semiconducting phases. For example, La 2 CuO 4 is a semiconductor, but when alloyed with Sr, it becomes a superconductor (La 1-x Sr x) 2 CuO 4 .

Physics textbooks define a semiconductor as a material with electrical resistance from 10 -4 to 10 7 ohm m. An alternative definition is also possible. The band gap of a semiconductor is from 0 to 3 eV. Metals and semimetals are materials with a zero energy gap, and substances in which it exceeds 3 eV are called insulators. There are also exceptions. For example, semiconductor diamond has a band gap of 6 eV, semi-insulating GaAs - 1.5 eV. GaN, the material for the blue region, has a band gap of 3.5 eV.

Energy gap

The valence orbitals of atoms in the crystal lattice are divided into two groups energy levels- a free zone located on highest level and determining the electrical conductivity of semiconductors, and the valence band located below. These levels, depending on the symmetry of the crystal lattice and the composition of atoms, can intersect or be located at a distance from each other. In the latter case, an energy gap or, in other words, a forbidden zone appears between the bands.

The arrangement and filling of the levels determines the conductive properties of the substance. On this basis, substances are divided into conductors, insulators and semiconductors. The semiconductor bandgap width varies within 0.01-3 eV, the dielectric energy gap exceeds 3 eV. Metals do not have energy gaps due to overlapping levels.

Semiconductors and dielectrics, in contrast to metals, have a valence band filled with electrons, and the nearest free band, or conduction band, is fenced off from the valence band by an energy gap - a region of forbidden electron energies.

In dielectrics, thermal energy or an insignificant electric field is not enough to make a jump through this gap; electrons do not enter the conduction band. They are not able to move along the crystal lattice and become carriers of electric current.

To excite electrical conductivity, an electron at the valence level must be given energy that would be enough to overcome the energy gap. Only when absorbing an amount of energy that is not less than the value of the energy gap, the electron will move from the valence level to the conduction level.

In the event that the width of the energy gap exceeds 4 eV, excitation of semiconductor conductivity by irradiation or heating is practically impossible - the excitation energy of electrons at the melting temperature is insufficient to jump through the energy gap zone. When heated, the crystal will melt until electronic conduction occurs. Such substances include quartz (dE = 5.2 eV), diamond (dE = 5.1 eV), and many salts.

Impurity and intrinsic conductivity of semiconductors

Pure semiconductor crystals have their own conductivity. Such semiconductors are called intrinsic. Intrinsic semiconductor contains equal number holes and free electrons. When heated, the intrinsic conductivity of semiconductors increases. At a constant temperature, a state of dynamic equilibrium arises between the number of formed electron-hole pairs and the number of recombining electrons and holes, which remain constant under given conditions.

The presence of impurities has a significant effect on the electrical conductivity of semiconductors. Adding them makes it possible to greatly increase the number of free electrons with a small number of holes and to increase the number of holes with a small number of electrons at the conduction level. Impurity semiconductors are conductors with impurity conductivity.

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

The energy required for an electron to jump into the conduction region is called the activation energy. Impurity semiconductors need much less of it than the base substance. With a slight heating or illumination, it is predominantly the electrons of the atoms of the impurity semiconductors that are released. The place of the electron leaving the atom is occupied by a hole. But the recombination of electrons into holes practically does not occur. The hole conductivity of the donor is insignificant. This is because the small number of impurity atoms does not allow free electrons to often approach the hole and occupy it. Electrons are located near holes, but are not able to fill them due to insufficient energy level.

An insignificant addition of a donor impurity increases the number of conduction electrons by several orders of magnitude compared to the number of free electrons in the intrinsic semiconductor. Electrons here are the main charge carriers of atoms of impurity semiconductors. These substances are classified as n-type semiconductors.

Impurities that bind the electrons of a semiconductor, increasing the number of holes in it, are called acceptor. Acceptor impurities are chemical elements with fewer electrons at the valence level than the base semiconductor. Boron, gallium, indium - acceptor impurities for silicon.

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

Single element semiconductors

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

Si and Ge is the same as that of diamond and α-tin. In it, each atom is surrounded by 4 nearest atoms, which form a tetrahedron. This coordination is called quadruple. Crystals with tetrahedral bonds have become the basis for the electronics industry and play a key role in modern technology. Some elements of groups V and VI of the periodic table are also semiconductors. Examples of semiconductors of this type are phosphorus (P), sulfur (S), selenium (Se) and tellurium (Te). In these semiconductors, atoms can have three-fold (P), two-fold (S, Se, Te) or four-fold coordination. As a result, such elements can exist in several different crystal structures, and also be obtained in the form of glass. For example, Se has been grown in monoclinic and trigonal crystal structures or as glass (which can also be considered a polymer).

Diamond has excellent thermal conductivity, excellent mechanical and optical properties, high mechanical strength. The energy gap width is dE = 5.47 eV.

Silicon is a semiconductor used in solar panels, and in amorphous form - in thin-film solar cells. It is the most used semiconductor in solar cells, easy to manufacture, and has good electrical and mechanical properties. dE = 1.12 eV.

Germanium is a semiconductor used in gamma spectroscopy, high-performance photovoltaic cells. Used in the first diodes and transistors. Requires less cleaning than silicon. dE = 0.67 eV.

Selenium is a semiconductor that is used in selenium rectifiers, which have high radiation resistance and the ability to self-heal.

Two-piece connections

The properties of semiconductors formed by elements of the 3rd and 4th groups of the periodic table resemble 4 groups. The transition from 4 groups of elements to compounds 3-4 gr. makes the bonds partially ionic due to the transfer of electron charge from the atom of group 3 to the atom of group 4. Ionicity changes the properties of semiconductors. It is the reason for the increase in the Coulomb interion interaction and the energy of the energy gap of the band structure of electrons. An example of a binary compound of this type is indium antimonide InSb, gallium arsenide GaAs, gallium antimonide GaSb, indium phosphide InP, aluminum antimonide AlSb, gallium phosphide GaP.

Ionicity increases, and its value grows even more in compounds of substances of groups 2-6, such as cadmium selenide, zinc sulfide, cadmium sulfide, cadmium telluride, zinc selenide. As a result, for most compounds of groups 2–6, the band gap is wider than 1 eV, except for mercury compounds. Mercury telluride is a semiconductor without an energy gap, a semimetal, like α-tin.

Semiconductors of groups 2-6 with a large energy gap are used in the production of lasers and displays. Binary connections of 2-6 groups with a narrowed energy gap are suitable for infrared receivers. Binary compounds of elements of groups 1-7 (copper bromide CuBr, silver iodide AgI, copper chloride CuCl) due to their high ionicity have a band gap wider than 3 eV. They are actually not semiconductors, but insulators. An increase in the anchoring energy of the crystal due to the Coulomb interionic interaction contributes to the structuring of atoms with sixfold rather than quadratic coordination. Compounds of groups 4-6 - lead sulfide and telluride, tin sulfide - are also semiconductors. The degree of ionicity of these substances also contributes to the formation of six-fold coordination. Significant ionicity does not prevent them from having very narrow band gaps, which allows them to be used to receive infrared radiation. Gallium nitride - a compound of 3-5 groups with a wide energy gap, has found application in LEDs operating in the blue part of the spectrum.

GaAs, gallium arsenide, is the second most demanded semiconductor after silicon, commonly used as a substrate for other conductors, such as GaInNAs and InGaAs, in IR diodes, high-frequency microcircuits and transistors, high-efficiency photovoltaic cells, laser diodes, nuclear cure detectors. dE = 1.43 eV, which makes it possible to increase the power of devices compared to silicon. Fragile, contains more impurities, difficult to manufacture.

ZnS, zinc sulfide - zinc salt of hydrosulfide acid with a band gap of 3.54 and 3.91 eV, is used in lasers and as a phosphor.

SnS, tin sulfide - a semiconductor used in photoresistors and photodiodes, dE= 1.3 and 10 eV.

oxides

Metal oxides are predominantly excellent insulators, but there are exceptions. Examples of semiconductors of this type are nickel oxide, copper oxide, cobalt oxide, copper dioxide, iron oxide, europium oxide, zinc oxide. Since copper dioxide exists as the mineral cuprite, its properties have been extensively researched. The procedure for growing semiconductors of this type is not yet fully understood, so their application is still limited. The exception is zinc oxide (ZnO), a compound of groups 2-6, used as a converter and in the production of adhesive tapes and plasters.

The situation changed radically after superconductivity was discovered in many compounds of copper with oxygen. The first high-temperature superconductor discovered by Müller and Bednorz was a compound based on the semiconductor La 2 CuO 4 with an energy gap of 2 eV. By replacing trivalent lanthanum with divalent barium or strontium, hole charge carriers are introduced into the semiconductor. Reaching the required concentration of holes turns La 2 CuO 4 into a superconductor. At present, the highest transition temperature to the superconducting state belongs to the HgBaCa 2 Cu 3 O 8 compound. At high pressure its value is 134 K.

ZnO, zinc oxide, is used in varistors, blue LEDs, gas sensors, biological sensors, window coatings to reflect infrared light, as a conductor in LCDs and solar panels. dE=3.37 eV.

layered crystals

Binary compounds like lead diiodide, gallium selenide, and molybdenum disulfide are characterized by a layered crystal structure. Significant forces act in the layers, much stronger than the van der Waals bonds between the layers themselves. Semiconductors of this type are interesting in that electrons behave quasi-two-dimensionally in layers. The interaction of the layers is changed by the introduction of foreign atoms - intercalation.

MoS 2, molybdenum disulfide is used in high-frequency detectors, rectifiers, memristors, transistors. dE=1.23 and 1.8 eV.

Organic semiconductors

Examples of semiconductors based on organic compounds are naphthalene, polyacetylene (CH 2) n, anthracene, polydiacetylene, phthalocyanides, polyvinylcarbazole. Organic semiconductors have an advantage over inorganic ones: it is easy to impart the desired qualities to them. Substances with conjugated bonds of the form -С=С-С= have significant optical nonlinearity and, due to this, are used in optoelectronics. In addition, the energy discontinuity zones of organic semiconductors are changed by changing the compound formula, which is much easier than that of conventional semiconductors. Crystalline allotropes of carbon - fullerene, graphene, nanotubes - are also semiconductors.

Fullerene has a structure in the form of a convex closed polyhedron of even number carbon atoms. And doping fullerene C 60 with an alkali metal turns it into a superconductor.

Graphene is formed by a monatomic layer of carbon connected into a two-dimensional hexagonal lattice. It has a record thermal conductivity and electron mobility, high rigidity

Nanotubes are graphite sheets rolled into a tube, several nanometers in diameter. These forms of carbon hold great promise in nanoelectronics. Depending on the coupling, they can exhibit metallic or semiconductor qualities.

Magnetic semiconductors

Compounds with magnetic europium and manganese ions have curious magnetic and semiconductor properties. Examples of semiconductors of this type are europium sulfide, europium selenide and solid solutions like Cd 1-x- Mn x Te. The content of magnetic ions influences how magnetic properties such as antiferromagnetism and ferromagnetism appear in substances. Semimagnetic semiconductors are solid magnetic solutions of semiconductors that contain magnetic ions in a small concentration. Such solid solutions attract attention due to their promise and great potential for possible applications. For example, unlike non-magnetic semiconductors, they can achieve a million times greater Faraday rotation.

The strong magneto-optical effects of magnetic semiconductors make it possible to use them for optical modulation. Perovskites, like Mn 0.7 Ca 0.3 O 3, are superior in their properties to the metal-semiconductor transition, the direct dependence of which on the magnetic field results in the phenomenon of giant magneto-resistance. They are used in radio engineering, optical devices that are controlled magnetic field, in waveguides of microwave devices.

Semiconductor ferroelectrics

This type of crystals is distinguished by the presence of electric moments in them and the occurrence of spontaneous polarization. For example, semiconductors lead titanate PbTiO 3 , barium titanate BaTiO 3 , germanium telluride GeTe, tin telluride SnTe have such properties, which have ferroelectric properties at low temperatures. These materials are used in non-linear optical, storage devices and piezoelectric sensors.

Variety of semiconductor materials

In addition to the semiconductor substances mentioned above, there are many others that do not fall under any of the listed types. Compounds of elements according to the formula 1-3-5 2 (AgGaS 2) and 2-4-5 2 (ZnSiP 2) form crystals in the chalcopyrite structure. The bonds of the compounds are tetrahedral, similar to semiconductors of 3-5 and 2-6 groups with the crystal structure of zinc blende. The compounds that form the elements of semiconductors of groups 5 and 6 (like As 2 Se 3) are 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 application. However, the fact that they exist confirms the presence of areas of semiconductor physics that have not yet been fully explored.

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

Definition

Semiconductors related to metals and solids. These include germanium, silicon, arsenic, etc., as well as various alloys and chemical compounds.

Metals are solids that have a certain structure.

Comparison

Consider how an electric current arises in semiconductors. Germanium atoms have four weakly bound valence electrons in their outer shell. V crystal lattice there are four more around each atom. Atoms in a semiconductor crystal are bound by pairs of valence electrons. Each valence electron belongs to two atoms. If there is an increase in temperature, some of the valence electrons will receive energy that is sufficient to break covalent bonds. Free electrons, called conduction electrons, will appear in the crystal. At the same time, vacancies and holes are formed in place of the departed electrons. The vacant place can be occupied by the valence electrons of the neighboring pair, then the hole will be in a new place in the crystal. At a certain temperature, a certain number of electron-hole pairs exist in a semiconductor. A free electron, meeting with a hole, restores the electronic bond. Holes are like positively charged particles. If there is no electric field, holes and conduction electrons move randomly. If we place a semiconductor in an electric field, then holes and free electrons will begin to move in an orderly manner. Therefore, the current in a semiconductor is the sum of the electron and hole currents. The number of free charge carriers varies, does not remain constant and depends on temperature. As it increases, the resistance of semiconductors increases.

Metals have a crystalline structure. They are made up of molecules and atoms that occupy a specific, ordered position. A metal is represented as a crystal lattice, at the nodes of which there are atoms, or ions, or molecules that vibrate around their location. Between them in space are free electrons that randomly move in different directions. But when an electric field appears, they begin to move in an orderly direction towards the positive pole, an electric current appears in the metals. The number of electrons is constant. As the temperature decreases, the speed of electrons slows down, and the resistance of metals decreases.

Findings site

1. Semiconductors differ from metals in the mechanism of electric current.
2. Electric current in metals is the directed movement of electrons.
3. Pure semiconductors have an electron-hole mechanism of conduction.
4. The resistivity of semiconductors and metals depends on temperature in different ways.

All substances consist of molecules, molecules of atoms, atoms of positively charged nuclei around which are located negative electrons. Under certain conditions, electrons are able to leave their nucleus and move to neighboring ones. In this case, the atom itself becomes positively charged, and the neighboring one receives a negative charge. The movement of negative and positive charges under the influence of an electric field is called an electric current.

Depending on the property of materials to conduct electric current, they are divided into:

1. Semiconductors.

Conductor properties

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

Most conductors have low resistivity and conduct electricity with very little loss. Due to the fact that perfectly clean chemical composition elements do not exist in nature, any material contains impurities in its composition. Impurities in conductors occupy places in the crystal lattice and, as a rule, prevent the passage of free electrons under the action of an applied voltage.

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

Good conductors with low resistivity are the following materials:

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

Gold and silver are good conductors, but due to their high cost, they are used where it is necessary to obtain good quality conductors with a small volume. These are mainly electronic circuits, microcircuits, 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 on top. This gives you the opportunity at the lowest cost. precious metal good frequency characteristics of the conductor.

Copper and aluminum are cheaper metals. With a slight decrease in the characteristics of these materials, their price is orders of magnitude lower, which makes it possible for their mass application. Used in electronics and electrical engineering. In electronics, these are tracks. printed circuit boards, legs of radioelements, radiators, etc. In electrical engineering, it is very widely used in motor windings, for laying electrical networks high and low voltage, electrical wiring in apartments, houses, transport.

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

Properties of dielectrics

Dielectrics in their crystal lattice contain very few free electrons capable of carrying a charge under the action of an electric field. In this regard, when creating a potential difference on a dielectric, the current passing through it is so insignificant that it is considered zero A dielectric does not conduct electricity. Along with this, impurities contained in any dielectric, as a rule, worsen its dielectric properties. The current passing through a dielectric under the action of an applied voltage is mainly determined by the amount of impurities.

Dielectrics are most widely used in electrical engineering where it is necessary to protect operating personnel from harmful effects electric current. These are insulating handles. different devices, measuring devices. In electronics - capacitor gaskets, wire insulation, dielectric gaskets necessary for heat removal of active elements, instrument cases.

Semiconductors are materials that conduct electricity under certain conditions, otherwise behave as dielectrics.

Table: what is the difference between conductors and dielectrics?