It is known that in a substance placed in an electric field, when exposed to the forces of this field, a movement of free electrons or ions is formed in the direction of the field forces. In other words, an electric current occurs in the substance.

A property that determines the ability of a substance to conduct electric current is called "electrical conductivity". Electrical conductivity is directly dependent on the concentration of charged particles: the higher the concentration, the more electrical conductivity it is.

According to this property, all substances are divided into 3 types:

  1. Conductors.
  2. Semiconductors.

Description of conductors

Conductors have highest electrical conductivity from all types of substances. All conductors are divided into two large subgroups:

  • Metals(copper, aluminum, silver) and their alloys.
  • Electrolytes (aqueous solution salts, acids).

In substances of the first subgroup, only electrons are capable of moving, since their connection with the nuclei of atoms is weak, and therefore they are quite easily detached from them. Since the occurrence of current in metals is associated with the movement of free electrons, the type of electrical conductivity in them is called electronic.

Of the conductors of the first subgroup, they are used in windings of electric machines, power lines, and wires. It is important to note that the electrical conductivity of metals is influenced by its purity and the absence of impurities.

In substances of the second subgroup, when exposed to a solution, the molecule disintegrates into positive and negative ions. Ions move due to exposure electric field. Then, when current passes through the electrolyte, ions are deposited on the electrode, which is lowered into this electrolyte. The process when a substance is released from an electrolyte under the influence of an electric current is called electrolysis. The electrolysis process is usually used, for example, when a non-ferrous metal is extracted from a solution of its compound, or when covering the metal with a protective layer of other metals.

Description of dielectrics

Dielectrics are also commonly called electrical insulating substances.

All electrical insulating substances have the following classification:

  • Depending on state of aggregation dielectrics can be liquid, solid and gaseous.
  • Depending on the methods of production - natural and synthetic.
  • Depending on chemical composition– organic and inorganic.
  • Depending on the structure of the molecules - neutral and polar.

These include gas (air, nitrogen, SF6 gas), mineral oil, any rubber and ceramic substance. These substances are characterized by the ability to polarization in an electric field. Polarization is the formation of charges with different signs on the surface of a substance.

Dielectrics contain a small number of free electrons, while electrons have a strong connection with the nuclei of atoms and are only rarely detached from them. This means that these substances do not have the ability to conduct current.

This property is very useful in the production of products used for protection against electric current: dielectric gloves, mats, boots, insulators for electrical equipment, etc.

About semiconductors

The semiconductor acts as intermediate substance between conductor and dielectric. The most prominent representatives This type of substances are silicon, germanium, selenium. In addition, these substances are usually classified as elements of the fourth group of Dmitry Ivanovich Mendeleev’s periodic table.

Semiconductors have additional "hole" conductivity, in addition to electronic conductivity. This type of conductivity depends on a number of environmental factors, including light, temperature, electric and magnetic fields.

These substances contain weak covalent bonds. When exposed to one of external factors the bond is destroyed, after which free electrons are formed. Moreover, when an electron is detached, in the composition covalent bond a free “hole” remains. Free “holes” attract neighboring electrons, and so this action can be carried out indefinitely.

The conductivity of semiconductor substances can be increased by introducing various impurities into them. This technique is widespread in industrial electronics: in diodes, transistors, thyristors. Let us consider in more detail the main differences between conductors and semiconductors.

What is the difference between a conductor and a semiconductor?

The main difference between a conductor and a semiconductor is its ability to conduct electric current. For the conductor it is an order of magnitude higher.

When the temperature value rises, the conductivity of semiconductors also increases; The conductivity of conductors becomes less as it increases.

In pure conductors in normal conditions When current passes, a much larger number of electrons are released than in semiconductors. At the same time, the addition of impurities reduces the conductivity of conductors, but increases the conductivity of semiconductors.

Often, novice amateur craftsmen (there are also professional electricians), when performing electrical installation work, call a wire a cable and vice versa. It is worth considering that these are completely different products with different purposes and characteristics. To understand how a cable differs from a wire, it is necessary to resort to studying GOST standards and a detailed consideration of the actual differences between them.

Cables and their classification

A cable is one core or a group of cores with an insulating layer, which are woven together in a certain way and enclosed in a single or several shells. They can be installed on the façade of buildings, in the air on supports (pillars), underground and even at the bottom of reservoirs (sea).

The outer shell can be made of various materials: cross-linked polyethylene, rubber, and even an alloy of metals (armor) and other substances. This general insulating layer of the cable is designed to protect the cores from mechanical damage, impacts environment and various chemicals.

Cables are divided into groups according to application. The following classes of these products are distinguished:

  1. Communication cable. Such products are intended for alarm systems (alerts) and wired telecommunications (landline telephone communications);
  2. Power products. This class is designed to move electrical energy from source to final consumer. They are usually laid permanently, forming different types of power transmission lines (PTL). The cores are mainly made of aluminum and copper. They are distinguished by a huge variety of models and a long service life - up to 40 years;
  3. Installation electrical cables (control). These products are necessary for inter-device installation of electrical devices. The conductors are usually made from a copper compound. The main advantage is high resistance to operation at elevated temperatures;
  4. Control cable. These products are used for lighting and control circuits in complex mechanisms and machine tools. Maximum voltage – 600V;
  5. Optical and RF options. Such electrical cables are used to transmit signals and energy in the established optical range or at specific radio frequencies. An example of use is the Internet, modern telephone communications, location equipment.

Just a note. Sometimes communication cables, optical and radio frequency analogues are classified into one large group - communication electrical cables.

Cable products also differ from each other in the following ways:

  • material of manufacture and properties of the insulating layer (layers);
  • shielding parameters;
  • technical characteristics expressed by electrophysical quantities;
  • material of manufacture and number of conductive cores;
  • general cross-section of the product, core diameter, etc.

Wires and their classification

GOST 15845-80 explains what a wire is. A cable connection that contains one or a group of wires (or strands) having a light sheath of non-metallic alloys is called a wire. Also, this technical regulation characterizes the wire according to the installation method - it cannot be installed underground, this is the first difference between a cable and a wire.

Wires are classified according to a number of characteristics and properties:

  • type of material and characteristics of the insulating layer;
  • wire manufacturing material;
  • diameter (section) of the product;
  • conductivity and others.

These characteristics predetermine the scope of application of conductor products. Wires can be:

  • automobile;
  • winding;
  • insulated and non-insulated (the latter are used in overhead power lines);
  • connecting;
  • installation and others.

Important! More details about the qualitative and quantitative characteristics, classification of electrical products, including wires and cables, can be found in GOST 15845-80 and the international standard ISO11801-2002.

Differences between cable and wire

By appearance Electrical cables and wires have a certain similarity, but there are differences between them that are clearly visible to a professional.

Core insulation layer

The main difference between the products under consideration is the presence in the cable of a separate insulating layer for each conductor. While the wire or twist of conductors has a common sheath or does not have it at all. This distinction is described in GOST 15845-80.

Thus, if each individual conductor has its own insulation, then the product is called a cable. And when there is no insulation, or a certain number of bare conductor elements (wires) are enclosed in a common insulation, then the product is called a wire.

Product marking

You can also distinguish cable products from ordinary wires by correct reading notation. Each electrical product has its own marking, which is expressed in alphabetic, numerical symbols and color.

The marking of conductors can tell not only what type they belong to, but also about the material of manufacture of the insulating sheath and core, the number and diameter of cores, scope of application and other information.

For example, if a product has the mark AVVGng 3x2.5, then it is deciphered as follows:

  • A – aluminum core;
  • B – insulating layer of cores made of PVC material (polyvinyl chloride);
  • B – the general insulating shell is also made of PVC;
  • G – no armor;
  • ng – the product does not support combustion;
  • 3x2.5 – three cores with a cross-section of 2.5 mm2.

From the decoding it is clear that each core has its own insulation and a common sheath, respectively, this product is a cable. The presence of the symbol “E” in the marking means that the cable has a screen, P – protection made of rubber material, B – armor from combustion and aggressive environments, Ш – the protective sheath of the cable is presented in the form of a hose, and so on.

The marking of wires differs from cables only in the different meaning of some symbols. For example, if a person has a product of the PuGV brand in front of him, then this is an installation wire that has insulation made of PVC material and is characterized by increased flexibility characteristics.

Important! Due to the huge number of various combinations of symbols in the labeling of electrical cable products, it can sometimes be difficult to read. In such cases, it is recommended to resort to the help of special reference books or resources on the Internet.

Terms of Use

The cable has found wider use in special conditions, in contrast to the wire, as it has enhanced protection against various damages. All underground and underwater communications are carried out only by him. They are also laid in fire-hazardous facilities, mines, rooms with high corrosive activity and others.

Wires, due to their lower protection, are used mainly inside electrical devices, electrical distributors, and as residential wiring; outside of them, it is recommended to use conductive busbars or cables.

Interesting to know. Cable products have a longer service life and greater throughput (higher current strength and voltage) due to multilayer insulation, the possible presence of screens and layers of armor.

It is extremely important to distinguish cables from wires, since their incorrect use is unsafe. Knowing the concepts described above and the differences between cable and conductor products, the question “is it a wire or a cable” will definitely not arise.

Video

Conductors- substances that conduct electric current due to the presence of large quantity charges that can move freely (unlike insulators). They are of I (first) and II (second) kind. The electrical conductivity of type I conductors is not accompanied by chemical processes; it is caused by electrons. Type I conductors include: pure metals, i.e. metals without impurities, alloys, some salts, oxides and a number organic matter. On electrodes made of type I conductors, the process of transfer of a metal cation into a solution or from a solution to the metal surface occurs. Type II conductors include electrolytes. The passage of current in them is associated with chemical processes and is caused by the movement of positive and negative ions.

Electrodes of the first kind. In the case of metal electrodes of the first kind, such ions will be metal cations, and in the case of metalloid electrodes of the first kind, metalloid anions. Silver electrode of the first kind Ag + /Ag. It is answered by the reaction Ag + + e-= Ag and electrode potential

E Ag + /Ag = Ag + / Ag+ b 0 lg a Ag+.

After substituting numerical values E 0 and b 0 at 25 o C:

An example of metalloid electrodes of the first kind is the selenium electrode Se 2- /Se, Se + 2 e-= Se 2 ; at 25 o C E Se 2- /Se 0 = -0.92 - 0.03lg a Se 2- .

Electrodes of the second kind- half-cells consisting of a metal coated with a layer of a sparingly soluble compound (salt, oxide or hydroxide) and immersed in a solution containing the same anion as the sparingly soluble compound of the electrode metal. Schematically, an electrode of the second kind can be represented as follows: A Z-/M.A., M, and the reaction occurring in it is MA + ze = M + A Z - .

Hence the equation for electrode potential will:

Calomel electrodes is mercury coated with calomel paste and in contact with a KCl solution.

Cl - / Hg 2 Cl 2 , Hg.

The electrode reaction boils down to the reduction of calomel to metallic mercury and chlorine anion:

The potential of the calomel electrode is reversible with respect to chlorine ions and is determined by their activity:

At 25 o C, the potential of the calomel electrode is found using the equation:

Mercury sulfate electrodes SO 4 2 - /Hg 2 SO 4 , Hg are similar to calomel with the only difference that the mercury here is covered with a layer of paste of Hg and mercuric sulfate, and H 2 SO 4 is used as a solution. The potential of a mercury sulfate electrode at 25 o C is expressed by the equation:

Silver chloride electrode is a system Cl - /AgCl, Ag, and its potential corresponds to the equation:

E Cl - /AgCl, Ag = E 0 Cl - /AgCl, Ag - b lg a Cl-

or at 25 o C:

E Cl - /AgCl, Ag = 0.2224 - 0.0592 lg a Cl - .

Various materials are used in electrical engineering. Electrical properties substances are determined by the number of electrons in the outer valence orbit. The fewer electrons there are in this orbit, the weaker they are bound to the nucleus, the easier they can travel.

Under the influence of temperature fluctuations, electrons are separated from the atom and move in the interatomic space. Such electrons are called free, and they create electric current in conductors. Is the interatomic space large, is there room for free electrons to travel inside the substance?

The structure of solids and liquids appears continuous and dense, resembling a ball of thread in structure. But in fact even solids more like a fishing or volleyball net. Of course, this cannot be seen at the everyday level, but it is accurate scientific research It has been established that the distances between electrons and the nuclei of atoms are much greater than their own sizes.

If the size of the nucleus of an atom is represented as a ball the size of a football, then the electrons in such a model will be the size of a pea, and each such pea is located from the “nucleus” at a distance of several hundred or even thousands of meters. And between the nucleus and the electron there is emptiness - there is simply nothing! If we imagine the distances between the atoms of a substance on the same scale, the dimensions will be absolutely fantastic - tens and hundreds of kilometers!

Good conductors of electricity are metals. For example, gold and silver atoms have only one electron in their outer orbit, so they are the best conductors. Iron also conducts electricity, but somewhat worse.

They conduct electricity even worse high resistance alloys. These are nichrome, manganin, constantan, fechral and others. Such a variety of high-resistivity alloys is due to the fact that they are designed to solve various tasks: heating elements, strain gauges, standard resistors for measuring instruments and much more.

In order to evaluate the ability of a material to conduct electricity, the concept was introduced "electrical conductivity". Reverse meaning - resistivity. In mechanics, these concepts correspond to specific gravity.

Insulators, unlike conductors, do not tend to lose electrons. In them, the bond between the electron and the nucleus is very strong, and there are almost no free electrons. More precisely, there is, but very little. At the same time, in some insulators there are more of them, and their insulation quality is correspondingly worse. It is enough to compare, for example, ceramics and paper. Therefore, insulators can be divided into good and bad.

The appearance of free charges even in insulators is due to thermal vibrations of electrons: under the influence of high temperatures, the insulating properties deteriorate; some electrons still manage to break away from the nucleus.

Similarly, the resistivity of an ideal conductor would be zero. But fortunately there is no such guide: imagine what Ohm’s law would look like ((I = U/R) with zero in the denominator!!! Goodbye mathematics and electrical engineering.

And only at a temperature of absolute zero (-273.2C°) thermal fluctuations completely stop, and the worst insulator becomes quite good. In order to numerically determine “this” is bad or good, they use the concept of resistivity. This is the resistance in Ohms of a cube with an edge length of 1 cm, the dimension of resistivity is obtained in Ohms/cm. The resistivity of some substances is shown below. Conductivity is the reciprocal of resistivity, - Siemens unit of measurement, - 1Sm = 1 / Ohm.

Good conductivity or low resistivity have: silver 1.5*10^(-6), read as (one and a half to ten to the power minus six), copper 1.78*10^(-6), aluminum 2.8* 10^(-6). The conductivity of alloys with high resistance is much worse: constantan 0.5*10^(-4), nichrome 1.1*10^(-4). These alloys can be called poor conductors. After all these complex numbers, you should substitute Ohm/cm.

Next in separate group semiconductors can be distinguished: germanium 60 Ohm/cm, silicon 5000 Ohm/cm, selenium 100,000 Ohm/cm. The resistivity of this group is greater than that of bad conductors, but less than that of bad insulators, not to mention good ones. Probably, with the same success, semiconductors could be called semi-insulators.

After such a short acquaintance with the structure and properties of the atom, one should consider how atoms interact with each other, how atoms interact with each other, how molecules are obtained from them, from which various substances are composed. To do this, we will again have to remember about the electrons in the outer orbit of the atom. After all, they are the ones who participate in the connection of atoms into molecules and determine the physical and chemical properties substances.

How molecules are made from atoms

Any atom is in a stable state if there are 8 electrons in its outer orbit. It does not seek to take electrons from neighboring atoms, but it does not give up its own. To verify the validity of this, it is enough to look at the inert gases in the periodic table: neon, argon, krypton, xenon. Each of them has 8 electrons in the outer orbit, which explains the reluctance of these gases to enter into any relationships ( chemical reactions) with other atoms, build molecules of chemical substances.

The situation is completely different for those atoms that do not have the coveted 8 electrons in their outer orbit. Such atoms prefer to unite with others in order to supplement their outer orbit with up to 8 electrons and achieve a calm, stable state.

For example, here is the well-known water molecule H2O. It consists of two hydrogen atoms and one oxygen atom, as shown in Figure 1.

Figure 1

At the top of the figure, two hydrogen atoms and one oxygen atom are shown separately. There are 6 electrons in the outer orbit of oxygen and two electrons in two hydrogen atoms nearby. Oxygen lacks just two electrons in its outer orbit to reach the coveted number 8, which it will receive by attaching two hydrogen atoms to itself.

Each hydrogen atom lacks 7 electrons in its outer orbit to be completely happy. The first hydrogen atom receives 6 electrons from oxygen into its outer orbit and one more electron from its twin, the second hydrogen atom. There are now 8 electrons in its outer orbit along with its electron. The second hydrogen atom also completes its outer orbit to the coveted number 8. This process is shown in the lower part of Figure 1.

Figure 2 shows the process of combining sodium and chlorine atoms. The result is sodium chloride, which is sold in stores under the name table salt.

Figure 2. The process of combining sodium and chlorine atoms

Here, too, each of the participants receives from the other the missing number of electrons: chlorine adds a single sodium electron to its own seven electrons, while it gives its own to the sodium atom. Both atoms have 8 electrons in the outer orbit, which ensures complete agreement and well-being.

Valence of atoms

Atoms that have 6 or 7 electrons in their outer orbit tend to attach 1 or 2 electrons to themselves. Such atoms are said to be monovalent or divalent. But if there are 1, 2 or 3 electrons in the outer orbit of an atom, then such an atom tends to give them away. In this case, the atom is considered to be one, two or three valent.

If the outer orbit of an atom contains 4 electrons, then such an atom prefers to unite with the same one, which also has 4 electrons. This is how germanium and silicon atoms are combined to make transistors. In this case, the atoms are called tetravalent. (Germanium or silicon atoms can also combine with other elements, such as oxygen or hydrogen, but these compounds are not interesting for our story.)

Figure 3 shows an atom of germanium or silicon wanting to combine with a similar atom. The small black circles are the atom's own electrons, and the light circles indicate the places where the electrons of the four neighboring atoms will fall.

Figure 3. Germanium (silicon) atom.

Crystal structure of semiconductors

The germanium and silicon atoms are in the same group as carbon in the periodic table ( chemical formula diamond C, are simply large crystals of carbon obtained under certain conditions) and therefore, when combined, form a diamond-like crystal structure. The formation of such a structure is shown, in a simplified form, of course, in Figure 4.

Figure 4.

There is a germanium atom in the center of the cube, and 4 more atoms are located in the corners. The atom depicted in the center of the cube is connected with its valence electrons to its nearest neighbors. In turn, the corner atoms give up their valence electrons to the atom located in the center of the cube and to its neighbors - atoms not shown in the figure. Thus, the outer orbits are completed to eight electrons. Of course, there is no cube in the crystal lattice, it is simply shown in the figure so that the relative, volumetric arrangement of atoms is clear.

But in order to simplify the story about semiconductors as much as possible, the crystal lattice can be depicted as a flat schematic drawing, despite the fact that interatomic bonds are still located in space. Such a diagram is shown in Figure 5.

Figure 5. Germanium crystal lattice in flat form.

In such a crystal, all the electrons are tightly bound to the atoms by their valence bonds, so there are apparently simply no free electrons here. It turns out that what we see in the figure is an insulator, since there are no free electrons in it. But, in fact, this is not so.

Self conductivity

The fact is that under the influence of temperature, some electrons still manage to break away from their atoms, and for some time free themselves from connection with the nucleus. Therefore, a small number of free electrons exist in a germanium crystal, due to which it is possible to conduct electric current. How many free electrons exist in a germanium crystal under normal conditions?

There are only no more than two such free electrons per 10^10 (ten billion) atoms, so germanium is a poor conductor, or, as they say, a semiconductor. It should be noted that just one gram of germanium contains 10^22 (ten thousand billion billion) atoms, which allows you to “get” about two thousand billion free electrons. It seems to be enough to pass a large electric current. To understand this issue, it is enough to remember what a current of 1 A is.

A current of 1 A corresponds to passing through a conductor in one second. electric charge in 1 Coulomb, or 6*10^18 (six billion billion) electrons per second. Against this background, two thousand billion free electrons, and even scattered throughout a huge crystal, can hardly ensure the passage of large currents. Although, due to thermal movement, small conductivity exists in germanium. This is the so-called intrinsic conductivity.

Electronic and hole conductivity

As the temperature increases, additional energy is imparted to the electrons, their thermal vibrations become more energetic, as a result of which some electrons manage to break away from their atoms. These electrons become free and, in the absence of an external electric field, perform chaotic movements and move in free space.

Atoms that have lost electrons cannot perform random movements, but only oscillate slightly relative to their normal position in the crystal lattice. Such atoms that have lost electrons are called positive ions. We can assume that in place of electrons torn out of their atoms, free spaces are obtained, which are usually called holes.

In general, the number of electrons and holes is the same, so a hole can grab an electron that happens to be nearby. As a result, the atom changes from a positive ion to neutral again. The process of combining electrons with holes is called recombination.

The separation of electrons from atoms occurs with the same frequency, therefore, on average, the number of electrons and holes for a particular semiconductor is equal, is a constant value and depends on external conditions, primarily temperature.

If a voltage is applied to a semiconductor crystal, the movement of electrons will become ordered, and a current will flow through the crystal due to its electron and hole conductivity. This conductivity is called intrinsic conductivity, it was already mentioned a little higher.

But semiconductors in their pure form, which have electronic and hole conductivity, are unsuitable for the manufacture of diodes, transistors and other parts, since the basis of these devices is a p-n (read “pe-en”) junction.

To obtain such a transition, two types of semiconductors are needed, two types of conductivity (p - positive - positive, hole) and (n - negative - negative, electronic). These types of semiconductors are made by doping, adding impurities to pure germanium or silicon crystals.

Although the amount of impurities is very small, their presence in to a large extent changes the properties of the semiconductor, allows you to obtain semiconductors of different conductivity. This will be discussed in the next part of the article.

Boris Aladyshkin,

What is a semiconductor and what is it eaten with?

Semiconductor- a material we can’t imagine without modern world technology and electronics. Semiconductors exhibit properties of metals and non-metals under certain conditions. According to the specific value electrical resistance semiconductors occupy an intermediate position between good conductors and dielectrics. Semiconductor differs from conductors in the strong dependence of specific conductivity on the presence of impurity elements (impurity elements) in the crystal lattice and the concentration of these elements, as well as on temperature and exposure to various types of radiation.
Basic property of a semiconductor- increase in electrical conductivity with increasing temperature.
Semiconductors are substances whose band gap is on the order of several electron volts (eV). For example, diamond can be classified as a wide-gap semiconductor, and indium arsenide can be classified as a narrow-gap semiconductor. The band gap is the width of the energy gap between the bottom of the conduction band and the top of the valence band, in which there are no allowed states for the electron.
The magnitude of the band gap is important when generating light in LEDs and semiconductor lasers and determines the energy of the emitted photons.

Semiconductors include many chemical elements: Si silicon, Ge germanium, As arsenic, Se selenium, Te tellurium and others, as well as all kinds of alloys and chemical compounds, for example: silicon iodide, gallium arsenide, mercury tellurite, etc.). In general, almost everything inorganic substances the world around us are semiconductors. The most common semiconductor in nature is silicon, which, according to rough estimates, makes up almost 30% of the earth's crust.

Depending on whether an atom of an impurity element gives up an electron or captures it, impurity atoms are called donor or acceptor atoms. The donor and acceptor properties of an atom of an impurity element also depend on which atom crystal lattice it replaces which crystallographic plane it is embedded in.
As mentioned above, the conductive properties of semiconductors strongly depend on temperature, and when the temperature reaches absolute zero (-273 ° C), semiconductors have the properties of dielectrics.

Based on the type of conductivity, semiconductors are divided into n-type and p-type

n-type semiconductor

Based on the type of conductivity, semiconductors are divided into n-type and p-type.

An n-type semiconductor has an impurity nature and conducts electric current like metals. Impurity elements that are added to semiconductors to produce n-type semiconductors are called donor elements. The term "n-type" comes from the word "negative", which refers to the negative charge carried by a free electron.

The theory of the charge transfer process is described as follows:

An impurity element, pentavalent As arsenic, is added to tetravalent Si silicon. During the interaction, each arsenic atom enters into a covalent bond with silicon atoms. But a fifth free arsenic atom remains, which has no place in saturated valence bonds, and it moves to a distant electron orbit, where less energy is needed to remove an electron from the atom. The electron breaks away and becomes free, capable of carrying charge. Thus, charge transfer is carried out by an electron, not a hole, that is, this type of semiconductor conducts electric current like metals.
Antimony Sb also improves the properties of one of the most important semiconductors - germanium Ge.

p-type semiconductor

A p-type semiconductor, in addition to the impurity base, is characterized by the hole nature of conductivity. The impurities that are added in this case are called acceptor impurities.
“p-type” comes from the word “positive,” which refers to the positive charge of the majority carriers.
For example, a small amount of trivalent indium atoms is added to a semiconductor, tetravalent Si silicon. In our case, indium will be an impurity element, the atoms of which establish a covalent bond with three neighboring silicon atoms. But silicon has one free bond while the indium atom does not have a valence electron, so it captures a valence electron from the covalent bond between neighboring silicon atoms and becomes a negatively charged ion, forming a so-called hole and, accordingly, a hole transition.
According to the same scheme, In ndium imparts hole conductivity to Ge germanium.

Investigating the properties of semiconductor elements and materials, studying the properties of contact between a conductor and a semiconductor, experimenting in the manufacture of semiconductor materials, O.V. Losev created the prototype of the modern LED in the 1920s.