What are conductors, semiconductors and dielectrics

What is the difference between a conductor and a semiconductor?

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. The 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. Dielectrics.
3. Semiconductors.

Metals.

Rice. 6

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 can be called the conduction band (Fig. 6). It is clear that current can flow in metals at zero temperature

.
Moreover, using quantum mechanics it can be proven that in an ideal metal
(the lattice of which has no defects) at
T
= 0, current should flow without resistance [2]!

Unfortunately, there are no ideal crystals, and zero temperature cannot be achieved. In reality, electrons lose energy by interacting with vibrating lattice atoms, so the resistance of a 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 significantly higher than the electrical conductivity of a semiconductor because the metal contains many more electrons capable of conducting electric current.

Description of conductors

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

• Metals (copper, aluminum, silver) and their alloys.
• Electrolytes (aqueous solution of salt, acid).

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.

Parallel connection of conductors

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.

Movement of electric current

In substances of the second subgroup, when exposed to a solution, the molecule disintegrates into positive and negative ions. Ions move due to the influence of an 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.

Zone theory

Band theory describes the presence or absence of free charge carriers relative to certain energy layers. An energy level or layer is the amount of energy of electrons (atomic nuclei, molecules - simple particles), they are measured in Electron Volts (EV).

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

Note that for 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 zone. Depending on the presence of an electric field (voltage), temperature and other factors, the number of electrons may change. Thanks to the above, electrons can move in conductors, even if they are given 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 supplied to a semiconductor for current to flow.

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

We looked at the main three types of materials and gave their examples and features. Their main difference is their ability to conduct current. Therefore, each of them has found its own field of application: conductors are used to transmit electricity, dielectrics are used to insulate live parts, semiconductors are used for electronics. We hope 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.

Electrical conductivity is the ability of a body to pass electric current under the influence of an electric field. To characterize this phenomenon, the value of specific electrical conductivity σ is used. As the theory shows, the value σ can be expressed through the concentration n of free charge carriers, their charge e, mass m, free path time τ e, free path length λe and the average drift velocity of charge carriers. For metals, free electrons act as free charge carriers, so:

σ = ne 2 · τе / m = (n · e 2 / m) · (λe / ) = e · n · u

where u is the carrier mobility, i.e. a physical quantity numerically equal to the drift velocity acquired by carriers in a field of unit strength, namely

u = / E = (e τ e) / m

Depending on σ, all substances are divided; to conductors - with σ > 10 6 (Ohm m) -1, dielectrics - with σ > 10 -8 (Ohm m) -1 and semiconductors - with an intermediate value of σ.

From the point of view of band theory, the division of substances into conductors, semiconductors and dielectrics is determined by how the valence band of the crystal is filled with electrons at 0 K: partially or completely.

The energy imparted to electrons even by a weak electric field is comparable to the distance between levels in the energy band. If there are free levels in the zone, then electrons excited by an external electric field will fill them. The quantum state of the electron system will change, and a preferential (directional) movement of electrons against the field will appear in the crystal, i.e. electricity. Such bodies (Fig. 10.1, a) are conductors.

If the valence band is completely filled, then a change in the state of the electron system can occur only when they pass through the band gap. The energy of an external electric field cannot carry out such a transition. The rearrangement of electrons within a completely filled zone does not cause a change in the quantum state of the system, because The electrons themselves are indistinguishable.

In such crystals (Fig. 10.1,b), an external electric field will not cause the appearance of an electric current, and they will be non-conductors (dielectrics). From this group of substances, those with a band gap ΔE ≤ 1 eV (1 eV = 1.6 · 10 -19 J) were isolated.

The transition of electrons through the band gap in such bodies can be accomplished, for example, through thermal excitation. In this case, part of the levels—the valence band—is released and the levels of the following free band (conduction band) are partially filled. These substances are semiconductors.

According to expression (10.1), a change in the electrical conductivity (electrical resistance) of bodies with temperature can be caused by a change in the concentration n of charge carriers or a change in their mobility u.

Metals

Quantum mechanical calculations show that for metals the concentration n of free charge carriers (electrons) is equal to:
n = (1 / 3π 2) · (2mE F / ђ 2) 3/2

where ђ = h / 2π = 1.05 · 10 -34 J · s is the normalized Planck constant, EF is the Fermi energy.

Since EF practically does not depend on temperature T, the concentration of charge carriers does not depend on temperature. Consequently, the temperature dependence of the electrical conductivity of metals will be completely determined by the mobility u of electrons, as follows from formula (10.1). Then in the high temperature region

u ~ λ e / ~ T -1

and in the low temperature region

u ~ λ e / ~ const (T).

The degree of charge carrier mobility will be determined by scattering processes, i.e. interaction of electrons with a periodic lattice field. Since the field of an ideal lattice is strictly periodic, and the state of the electrons is stationary, scattering (the appearance of electrical resistance of the metal) can only be caused by defects (impurity atoms, structure distortions, etc.) and thermal vibrations of the lattice (phonons).

Near 0 K, where the intensity of thermal vibrations of the lattice and the phonon concentration are close to zero, scattering by impurities (electron-impurity scattering) predominates. In this case, the conductivity practically does not change, as follows from formula (10.4), and the resistivity

has a constant value, which is called the specific residual resistance ρ rest or the specific impurity resistance ρ approx, i.e.

ρ rest (or ρ approx) = const (T)

At high temperatures in metals, the electron-phonon scattering mechanism becomes dominant. With this scattering mechanism, electrical conductivity is inversely proportional to temperature, as can be seen from formula (10.3), and resistivity is directly proportional to temperature:

The dependence of resistivity ρ on temperature is shown in Fig. 10.2

At temperatures other than 0 K and a sufficiently large amount of impurities, both electron-phonon and electron-impurity scattering can occur; the total resistivity has the form

ρ = ρ approx + ρ f

Expression (10.6) represents Matthiessen’s rule about the additivity of resistance. It should be noted that both electron-phonon and electron-impurity scattering are chaotic in nature.

Description of dielectrics

Dielectrics are also commonly called electrical insulating substances.

All electrical insulating substances have the following classification:

• Depending on their state of aggregation, dielectrics can be liquid, solid or gaseous.
• Depending on the methods of production - natural and synthetic.
• Depending on the 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 polarize 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, and the 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.

Types and types of dielectrics

The classification of dielectrics is quite extensive. There are liquid, solid and gaseous substances here. They are further divided according to certain characteristics. Below is a conditional classification of dielectrics with examples in list form.

• gaseous
• - polar
• - non-polar (air, SF6 gas)

• - polar (water, ammonia)
• - liquid crystals

• - centrosymmetric
• - amorphous
• - resins, bitumen (epoxy resin)
• - glass
• - disordered polymers

• – irregular crystals
• - ceramics
• - ordered polymers
• - glass-ceramics

• - molecular
• - covalent
• - ionic
• — displacement paraelectrics
• — paraelectrics “order-disorder”

• — single crystals
• - pyroelectrics
• — bias ferroelectrics
• — ferroelectrics “order-disorder”
• — linear pyroelectrics

• - with hydrogen bonds
• - covalent
• - ionic

• - electronic defects
• — ionic defects
• - polar molecules
• — macrodipoles
• — ferroelectric domains
• - crystals in the matrix

If we take liquid and gaseous dielectrics, then the main classification lies in the issue of polarity. The difference is in the symmetry of the molecules. In polar molecules the molecules are asymmetrical, in nonpolar ones they are symmetrical. Asymmetrical molecules are called dipoles. Polar liquids have such high conductivity that they cannot be used as insulating substances. Therefore, non-polar, also transformer oil, is used for these purposes. And the presence of polar impurities, even in hundredths, significantly reduces the breakdown level and negatively affects the insulating properties of non-polar dielectrics.

crystals are a cross between a liquid and a crystal, as the name suggests.

Another popular question about the properties and applications of liquid dielectrics is the following: is water a dielectric or a conductor? Pure distilled water contains no impurities that could cause current to flow. Pure water can be created in laboratory and industrial conditions. These conditions are complex and difficult to meet for an ordinary person. There is an easy way to check whether distilled water conducts current.

Create an electrical circuit (current source - wire - water - wire - light bulb - another wire - current source), in which one of the areas for current flow will be a vessel with distilled water. When the circuit is turned on, the light bulb will not light up - therefore no current flows. Well, if it lights up, it means water with impurities.

Therefore, any water that we encounter: from a tap, in a lake, in a bathroom - will be a conductor due to impurities that create the opportunity for current to flow. Do not swim in a thunderstorm or handle electricity with wet hands. Although pure distilled water is a polar dielectric.

For solid dielectrics, classification mainly lies in the question of activity and passivity or something. If the properties are constant, then the dielectric is used as an insulating material, that is, it is passive. If the properties change depending on external influences (heat, pressure), then this dielectric is used for other purposes. Paper is a dielectric; if water is saturated with water, then current is conducted and it is a conductor; if paper is saturated with transformer oil, then it is a dielectric.

Foil is a thin metal plate; metal is known to be a conductor. For example, there is PVC foil on sale, here the word foil is for clarity, and the word PVC is for understanding the meaning - after all, PVC is a dielectric. Although on Wikipedia, foil is a thin sheet of metal.

Amorphous liquids

- this includes resin, glass, bitumen, and wax. As the temperature rises, this dielectric melts, these are frozen substances - these are wild definitions that characterize only one facet of the truth.

Polycrystals

- these are, as it were, fused crystals united into one crystal. For example, salt.

Monocrystal

- this is a solid crystal, unlike the above-mentioned polycrystal, which has a continuous crystal lattice.

Piezoelectrics

- dielectrics in which, under mechanical action (tension-compression), an ionization process occurs. Used in lighters, detonators, ultrasound examinations.

Pyroelectrics

— when the temperature changes, spontaneous polarization occurs in these dielectrics. It also occurs under mechanical influence, that is, pyroelectrics are also piezoelectrics, but not vice versa. Examples are amber and tourmaline.

About semiconductors

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

Semiconductors: silicon, germanium, selenium

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 the external factors, the bond is destroyed, after which free electrons are formed. In this case, when an electron is removed, a free “hole” remains in the covalent bond. 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 a semiconductor

A semiconductor conducts electric current, but not like metals, but subject to certain conditions - imparting energy to the substance in the required quantities. This is due to the fact that there are too few free charge carriers (holes and electrons) or none at all, but if you apply a certain amount of energy, they will appear. Energy can be of 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 of different materials, such as gallium arsenide, selenium, and 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.

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, under normal conditions, when a 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.

Difference Between Conductor, Semiconductor and Insulator

The fundamental difference between a Conductor, a Semiconductor and an Insulator depends on their level of conductivity. Conductors are materials that allow electric current to flow easily, hence have high conductivity, Semiconductors are materials that have moderate conductivity, whereas insulators are materials that prevent charge from flowing through them, and thus have low conductivity.

The conductivity of solids is the main factor that distinguishes these three materials and the differences in their conductivity are explained by Electronic Band Theory. In addition, conductors - have very low resistance, semiconductors - pure semiconductors have very high resistance, and insulators - have extremely high resistance. However, there are some other differences between Conductor, Semiconductor and Insulator.

Content

1. Overview and main differences
2. Band theory of conduction
3. Conductors
4. Insulators
5. Semiconductors
6. What is the difference between Conductor, Semiconductor and Insulator
7. Conclusion

Band theory of conduction

Electrons orbit the positive nucleus of an individual atom at acceptable energy levels, as shown by the gray lines on the left in the diagram below. In a large collection of atoms, such as a metal wire or a semiconductor crystal, the energy levels reorganize into two bands. The conduction band is the zone of higher energy levels of electrons, and the valence band is the zone of lower energy levels of electrons. In the energy “gap” between the bands, electrons cannot exist.

On the left side are horizontal lines that move closer together as energy levels increase

Conduction is the movement of electrons in a solid. For conduction to exist, electrons must move freely in the conduction band and there must be spaces in the energy bands for electrons to move.

Conductors

There are no band gaps between the valence and conduction bands in a conductor. In some metals, the conduction and valence bands partially overlap. This means that electrons can move freely between the valence band and the conduction band.

The conduction band is only partially filled. This means that there are places for electrons to move. When electrons for the valence band move into the conduction band, they are free to move. This allows the conductor to conduct electrical current.

Zones in conductors

Insulators

The insulator has a large gap between the valence band and the conduction band. The valence band is full because no electrons can rise to the conduction band. As a result, the conduction band becomes empty. Since there are no electrons in the conduction band of an insulator, and only electrons can move easily in the conduction band, the material cannot conduct electric current.

Zones in isolation wards

Semiconductors

In a semiconductor, the gap between the valence band and the conduction band is smaller. At room temperature, there is enough energy to move some electrons from the valence band to the conduction band. This allows for some conductivity. Increasing the temperature increases the conductivity of the semiconductor because more electrons will have enough energy to move into the conduction band.

Dielectrics.

Rice. 2

At T

= 0 valence electrons completely fill the lowest band, called
the valence band
(Fig. 2).
There are no free levels in it, and the next allowed band, the conduction band
, is separated from it by a wide band gap. If an electric field is applied to such a sample, it will not be able to accelerate the 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 prohibits electrons from occupying already occupied levels, and they cannot enter 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 temperatures other than zero, electrons, in principle, can move into the conduction band and become carriers of electric current. However, in order for the number of electrons transferred to this zone to be large enough, the dielectric must be heated to such a high temperature that it melts before the current reaches a measurable value. At room temperature, practically no current flows in the dielectric.

Conductors, insulators and semiconductors

Any body consists of molecules and atoms. An atom contains negatively charged electrons and a positively charged nucleus. Electrons in an atom perform orbital rotations around the nucleus. If the sum of negatively charged electrons is equal to the positive charge, then the atom is considered electrically neutral . In the periodic table, the atomic number of an element is determined by the number of electrons of an atom with a neutral charge. The electric charge of an electron is -1.6*10 -19 C. The absolute value of the nuclear charge is equal to the charge of the electron multiplied by the number of electrons of the atom with a neutral charge.

The electrons of atoms are usually located in outer or inner orbits. Those electrons located in the inner orbits are relatively tightly bound to the nucleus of the atom. Valence electrons, i.e. those in outer orbits can break away from the atom and remain in a “free” state until they attach to a new atom. An atom that is missing any number of electrons is called an ion with a positive charge. But an atom to which electrons have attached is called an ion with a negative charge.

The process of ion formation is called ionization . The number of “free” ions or electrons, i.e. charge-carrying particles per unit volume of a substance is called charge carrier concentration . Electric current is the ordered movement of positively and negatively charged particles. Electrical conductivity is the ability of a substance, under the influence of an electric field, to conduct electric current through itself.

The higher the concentration of charge carriers in a substance, the greater its electrical conductivity. Depending on their ability to conduct electric current, substances are divided into 3 groups: conductors, semiconductors and dielectrics.

Conductors of electric current

Conductors are substances with high electrical conductivity. There are 2 types of conductors: with electronic conductivity and ionic conductivity. Electronic conductivity includes metals and their alloys. In metals, electric current is created by the movement of electrons. The current passing through such conductors does not affect the material in any way and does not change its chemical component.

The high level of electrical conductivity of metals is due to the fact that they contain many “free” electrons that are in a state of random motion and fill the volume of the conductor like a gas. With such active movement, electrons collide with ions of a stationary crystal lattice consisting of atoms of the substance. As a result, the electrons change the direction of movement, speed and their kinetic energy.

If there is an electric field in a type 1 conductor, then the forces of this field act on the charges of the conductor, ordering their movement. Free electrons do not move in a chaotic order, but in one direction opposite to the direction of the field (from the negative terminal to the positive terminal). This ordered movement of free charge carriers under the influence of an electric field is an electric current (conduction).

Type 2 conductors are solutions or melts of salts, acids, alkalis, etc. in which electrolytic dissociation is observed, regardless of the passage of current.

Electrolytic dissociation is the process of neutral molecules breaking down into negative and positive ions.

Positive ions are hydrogen and metal ions. Negative - hydroxyl group and acidic residues.

These solutions or melts consisting of ions, partially or completely, are called electrolytes. Without the influence of an external electric field, the molecules and ions of such a conductor will be in a state of chaotic motion.

When an electric field appears in such a conductor, the movement of ions acquires a directed, ordered movement, i.e., a current (conductivity) flows through the conductor. Positive ions move in the direction of the field, and negative ions move against it.

Semiconductors

Semiconductors are substances whose electrical conductivity depends on temperature, light, electric fields and impurities. Such materials include: silicon, tellurium, germanium, selenium, metal compounds with sulfur and metal oxides. Semiconductors also differ in that in addition to electronic conductivity they also have hole conductivity. Hole conductivity is caused by the movement of “holes” due to the influence of an electric field. “Holes” are empty spaces in atoms that are not occupied by valence electrons. This is similar to the fact that positively charged particles move in the same way as charges equal to the charges of electrons. Today, the use of semiconductors is widespread in various devices and devices, for example, in photoresistors and semiconductor diodes.

Electrical dielectrics

Dielectrics are those substances in which, under normal conditions, there is a very small number of free electrically charged particles. As a result, they have low electrical conductivity. Dielectrics include gases, mineral oils, varnishes and solid materials (except metals). However, if the dielectric is exposed to high temperature or a strong electric field, the molecules will begin to split into ions, which will lose their insulating properties as a result of this effect.

Content

• 1 Dielectrics.
• 2 Semiconductors.
• 3 Semi-metals.
• 4 Metals.
• 5 Notes

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 the differences were between all these types of substances. In this note we will try to briefly describe the essence of modern quantum mechanical theory that explains the electrical properties of solids.

A solid is made up of atoms that form a crystal lattice. Atoms are held in a lattice by the 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 only have certain (allowed) energy values, or, in other words, be at certain energy levels

. The higher the level, the more energy it corresponds to.

Rice. 1

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 [1].

When atoms combine to form a crystal, some electrons still remain in their atomic orbits, but the electrons farthest from the nucleus are able to move throughout the crystal due to the overlapping outer orbits of neighboring atoms. This means that energy levels that previously belonged to individual atoms become “common” for the entire crystal. Instead of discrete levels, energy bands

, consisting of very closely spaced levels.
The electrons that are found in these "socialized" levels are called valence electrons
.

The valence electrons move in orbits that span the entire crystal and appear to be able to conduct electrical current. However, if everything were that simple, all solids would be good conductors (metals). The laws of quantum mechanics make the picture much more complex and varied.

Firstly, energy zones are separated by gaps in which there is not a single energy level. These gaps are called forbidden zones

. Secondly, electrons obey the so-called Pauli principle, according to which only one electron can be in a given state at each level. At the lowest possible temperature (equal to absolute zero), energy levels sequentially from bottom to top (that is, starting with the lowest energy values) are filled with electrons in accordance with the Pauli principle, and levels with higher energies remain free. The different degrees of filling of energy bands, as well as differences in their relative location, make it possible to divide all solids into dielectrics, semiconductors, semimetals and metals.

Introduction to Conductors, Semiconductors, and Dielectrics: Specifications

What is the main thing about the materials that are used for electricity? Their main property is conductivity. Such materials are divided into three types - conductors, semiconductors, and dielectrics.

Today's article is dedicated to these materials. We will look in detail at what they are, what they are used for and how they pass current.

So let's start with the conductor

A conductor is matter that consists of free carriers of charged particles. When these particles move, thermal energy is generated, which is why they gave it the name thermal motion.

There are two main parameters of a conductor - resistance, denoted by the letter R, or conductivity, denoted by the letter G. Conductivity is the opposite indicator of resistance - G = 1/R.

That is, a conductor is a material that conducts current.

What is a conductor? Metals are the best conductors, especially copper and aluminum. Also conductors are salt solutions, wet soil, and carbon. The latter has found wide application in working with sliding bonds.

What is a conductor

A substance in which free charge carriers are present 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.

In simple terms, a conductor conducts current.

Such substances include metals, but if we talk about non-metals, then, for example, carbon is an excellent conductor and has found application in sliding contacts, for example, electric motor brushes. Wet soil, solutions of salts and acids in water, and 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, precisely due to the large number of free charge carriers in their structure. Under the influence of an electric field, charges begin to move and also redistribute, and the phenomenon of electrostatic induction is observed.

Let's move on to dielectrics

A dielectric is a matter that is not subject to the influence of an electric field, that is, it does not pass current through itself, and if it does, it is in an insignificant amount.

This happens because they do not have freely moving particles - current carriers, since they have a very strong atomic bond.

In life, such substances are rubber, ceramic components, glass, certain types of resins, distilled water, carbonite, porcelain, textolite, as well as dry wood and so on.

It is thanks to their properties that the above materials are the basis for the housings of various electrical appliances, switches, sockets, plugs and other devices that come into direct contact with electricity.

Insulating elements in networks are also made of dielectric materials.

But not everything is so simple with dielectrics. If you pass a higher current through them, store them or install them in an environment with high humidity, or use them incorrectly, you can cause a phenomenon called “insulator breakdown” - this means that the dielectric material loses its non-conductive functions and becomes a conductor.

That is, to describe the situation in a nutshell, the main thing in a dielectric is its electrical insulating abilities. Thus, these devices help us protect ourselves from the traumatic effects of electricity.

The properties of a dielectric are measured by its electrical strength - this is an indicator that is equal to the breakdown voltage of the dielectric.

And finally we come to semiconductors

Semiconductors are called so because they have the property of conducting current, but not always. To do this, this substance must create special conditions. You need to supply it with energy in a certain amount.

A semiconductor has its properties because in its structure there are very few particles that are free carriers, and it may be that they are not there at all. But once you influence them with a certain energy, they appear and actively move.

Energy can not only be electrical, it can also be influenced by thermal energy, or various radiations. For example, freely moving elements appear under the influence of radiation in the UV spectrum.

Materials with such properties are germanium, silicon, it can also be a mixture of arsenide and helium, arsenic, selenium and others.

The use of semiconductors can be different. Microcircuits, LEDs, transistors, diodes and much more are made from this material.

In order to explain the operation of a semiconductor in more detail, we apply the so-called band theory to it. The theory mentioned explains the existence or non-existence of free charged particles in relation to specific energy levels.

An energy level (layer) is the number of simple particles, such as molecules, atoms, that is, electrons. This indicator is measured in Electronvolts (EV).

It should be noted that the layers of the conductor form a continuous diagram from the valence zone to the conduction zone. If these two zones overlap each other, an overlap zone occurs.

In accordance with the influence of certain influences, such as electric fields, temperature conditions, etc., the number of electrons may change.

Based on the processes described above, electrons with minimal energy impact begin to move in the conductor.

Semiconductors between the two above-mentioned zones also have a band gap. The size of this zone shows the amount of energy that will be sufficient to conduct current.

Dielectrics are similar in structure to semiconductors, but their protective sphere is much larger due to the internal bonds of the material.

We talked about the main properties of conductors, semiconductors and dielectrics. We can conclude that they differ from each other in their current conductivity. It is because of this that each material has its own area of ​​application.

Thus, conductors are used where 100% current conductivity is needed.

The use of dielectrics is necessary for the manufacture of various insulation of conductive sections.

Well, semiconductors are actively used in electronics.

We think that this article has revealed to you all the nuances of the work of conductors, dielectrics and semiconductors, their main differences and areas of application.

ImGist determined that the differences between semiconductors and metals are as follows:

Semiconductors differ from metals in the mechanism of electric current. Electric current in metals is the directed movement of electrons. Pure semiconductors have an electron-hole conduction mechanism. The resistivity of semiconductors and metals varies with temperature differently.

What is the difference between a dielectric and a conductor? Conductors, unlike dielectrics, have a high concentration of free electrical charges. In metals, these are free electrons that are able to move throughout the entire volume of the substance. The appearance of free electrons is due to the fact that valence electrons in metal atoms interact very poorly with nuclei and easily lose contact with them.

In dielectrics, on the contrary, electrons are tightly bound to atoms and are not able to move freely under the influence of an electric field. And since the number of free charged carriers in dielectrics is negligible, it follows that there is no electrostatic induction in them, and the electric field strength inside the dielectrics does not become zero, but only decreases.

The voltage cannot be increased indefinitely, because at a certain value, all charges can shift so much that the structure of the material changes, in other words, a breakdown of the dielectric occurs. In this case, it will lose its insulating properties.

TheDifference.ru determined that the difference between a dielectric and a conductor is as follows: In a conductor, free electrons, influenced by the forces of the electric field, move throughout the entire volume. Unlike a conductor, there are no free charges in a dielectric (insulator). Insulators consist of neutral molecules or atoms. The charges in a neutral atom are strongly bound to each other and cannot move under the influence of an electric field throughout the entire volume of the dielectric.

Based on their structure, polymers are divided into crystalline, amorphous, and liquid. A number of organic substances also exhibit semiconductor properties and constitute a large group of organic semiconductors. The most important are inorganic. crystalline P. m., which are based on chemistry. composition are divided into elementary, double, triple and quaternary chemicals. compounds, solutions and alloys. Semiconductor compounds are classified according to periodic group numbers. table elements, to which the elements included in their composition belong.

Main groups of crystalline semiconductor materials (see Table 1):

1. Elementary materials: Ge, Si, C (diamond)

, B, Sn, Te, Se, etc. The most important representatives of this group are Ge and Si - main.
semiconductor electronics materials. Possessing 4 valence electrons, Ge and Si atoms form crystalline particles. a diamond-type lattice, where each atom has 4 nearest neighbors, each of which is connected by a covalent bond
(neighbor coordination is tetrahedral). They form among themselves a continuous series of solid solutions, which are also important P. m.

2. Connections of the type Mainly have. crystalline sphalerite type structure. The connection of atoms in a crystalline. the grille wears preim. covalent character with a certain proportion (5-15%) of the ionic component (see Chemical bond). The most important representatives of this group: GaAs, InP, InAs, InSb, GaP. Mn. P. m.

form among themselves a continuous series of solid solutions of ternary p more complex ones (etc.), which are also important PMs (see Heterojunction, Heterostrzk-tura)

.

3. Compounds of elements VI r y and -n s (O, S, Se, Te) with elements of groups I - V, as well as with transition and rare earth metals. Among these P. m., compounds of the type are of greatest interest. They are crystalline. structure like sphalerite or wurtzite, less often - like NaCl. The bond between atoms is of a covalent nature (the share of the ionic component is about 45-60%). P. m. type is characterized by the phenomenon of polymorphism and the presence of polytypes of cubic and hexagonal modifications. The most important representatives: CdTe, CdS, ZnTe, ZnSe, ZnO, ZnS. Mn. P. m. type form a continuous series of solid solutions among themselves; the most important of them:

Phys. properties are, to a large extent, determined by the concentration of the structure’s own point defects that exhibit electrical properties. activity (scattering and recombination centers).

Compounds of the type are crystalline. NaCl type or orthorhombic structure. The bond between atoms is covalent-ionic. Typical representatives: PbS, PbTe, SnTe. They form a continuous series of solid solutions among themselves, among them the most important are Own. point defects in the structure have low ionization energy and exhibit electrical properties. activity.

Compounds of the type are crystalline. sphalerite-type structure with unfilled cationic sites. In terms of their properties, they occupy an intermediate position between and. They are characterized by low lattice thermal conductivity and
charge
carrier mobility . Typical representatives:

In semiconductors, when the temperature changes, not only the power

visibility, but also the concentration of charge carriers. If you increase the temperature

pure semiconductor, then some of the atoms are ionized, as a result of which

free electrons and holes appear in equal numbers. Addiction

The concentration of electrons and holes on temperature is determined by the formula:

Hole[edit | edit source text]

Main article: Hole

When the bond between the electron and the nucleus is broken, a free space appears in the electron shell of the atom. This causes the transfer of an electron from another atom to an atom with a free place. The atom from which the electron passed receives another electron from another atom, etc. This process is determined by the covalent bonds of atoms. Thus, a positive charge moves without moving the atom itself. This conditional positive charge is called a hole.

Typically, the mobility of holes in a semiconductor is lower than the mobility of electrons.

Free electrons and holes are called charge carriers, since their directed movement leads to the appearance of a current in the semiconductor. The process of the appearance of free electrons in the conduction band and holes in the valence band in a semiconductor, caused by heating the semiconductor, is called thermal generation of charge carriers. The process of returning free electrons from the conduction band to the valence band, associated with the disappearance of charge carriers, is called recombination. In semiconductor materials, a dynamic equilibrium is established between the processes of thermal generation and recombination of charge carriers, in which the concentration of charge carriers, i.e., the number of free electrons in the conduction band and holes in the valence band per 1 cm3 of the semiconductor, remains unchanged at a constant temperature of the semiconductor.

The process of formation of a conduction electron–conduction hole pair is called the generation of a pair of charge carriers (1 in 16.6). We can say that the intrinsic electrical conductivity of a semiconductor is the electrical conductivity caused by the generation of conduction electron–conduction hole pairs. The resulting electron-hole pairs can disappear if the hole is filled with an electron: the electron will become unfree and lose the ability to move, and the excess positive charge of the atomic ion will be neutralized. In this case, both the hole and the electron disappear simultaneously. The process of reuniting an electron and a hole is called recombination (2 on 16.6). Recombination, in accordance with band theory, can be considered as the transition of electrons from the conduction band to free places in the valence band. Note that the transition of electrons from a higher energy level to a lower one is accompanied by the release of energy, which is either emitted in the form of light quanta (photons) or transferred to the crystal lattice in the form of thermal vibrations (phonons).

Impurity conductivity of semiconductors is electrical conductivity caused by the presence of donor or acceptor impurities in the semiconductor.

Impurity conductivity, as a rule, much exceeds intrinsic conductivity, and therefore the electrical properties of semiconductors are determined by the type and amount of doping impurities introduced into it.

The intrinsic conductivity of semiconductors is usually low, since the number of free electrons, for example, in germanium at room temperature is about 3·10 13 / cm 3. At the same time, the number of germanium atoms in 1 cm 3 ~ 10 23. The conductivity of semiconductors increases with the introduction of impurities, when, along with their own conductivity, additional impurity conductivity appears.

Impurity conductivity of semiconductors is conductivity caused by the presence of impurities in the semiconductor.

Impurity centers can be:

1. atoms or ions of chemical elements embedded in a semiconductor lattice;

2. excess atoms or ions embedded in the interstices of the lattice;

3. various other defects and distortions in the crystal lattice: empty nodes, cracks, shifts that occur during deformation of crystals, etc.

By changing the concentration of impurities, you can significantly increase the number of charge carriers of one sign or another and create semiconductors with a predominant concentration of either negatively or positively charged carriers.

Impurities can be divided into donor (giving away) and acceptor (receiving) impurities.

Let us consider the mechanism of electrical conductivity of a semiconductor with a donor pentavalent arsenic impurity As 5+

, which is introduced into a crystal, for example, silicon. The pentavalent arsenic atom donates four valence electrons to form covalent bonds, and the fifth electron is unoccupied in these bonds.

The abstraction energy (ionization energy) of the fifth valence electron of arsenic in silicon is 0.05 eV = 0.08·10 -19 J, which is 20 times less than the energy of electron abstraction from a silicon atom. Therefore, already at room temperature, almost all arsenic atoms lose one of their electrons and become positive ions. Positive arsenic ions cannot capture electrons from neighboring atoms, since all four bonds are already equipped with electrons. In this case, there is no movement of the electron vacancy—the “hole”—and the hole conductivity is very small, i.e. practically absent. A small part of the semiconductor's own atoms is ionized, and part of the current is generated by holes, i.e. Donor impurities are impurities that supply conduction electrons without producing an equal number of mobile holes. The result is a semiconductor with predominantly electronic conductivity, called an n-type semiconductor.

In the case of an acceptor impurity, for example, trivalent indium In 3+

an impurity atom can give its three electrons to carry out a covalent bond with only three neighboring silicon atoms, and one electron is “missing”. One of the electrons of neighboring silicon atoms can fill this bond, then the In atom will become a stationary negative ion, and a hole will form in the place of the electron that left one of the silicon atoms. Acceptor impurities, capturing electrons and thereby creating mobile holes, do not increase the number of conduction electrons. The majority charge carriers in a semiconductor with an acceptor impurity are holes, and the minority charge carriers are electrons.

Electronic devices use a variety of materials. The main elements used for these devices are conductor and semiconductor products. To use them more effectively, you need to know exactly how conductors differ from semiconductors. The properties of each element, used in combination, make it possible to create devices with unique qualities and characteristics.

We design electrics together

Conductors and dielectrics. Semiconductors

Conductor resistance. Conductivity. Dielectrics. Application of conductors and insulators. Semiconductors.

Physical substances are diverse in their electrical properties. The most extensive classes of matter are conductors and dielectrics.

Conductors

The main feature of conductors is the presence of free charge carriers, which participate in thermal motion and can move throughout the entire volume of the substance. As a rule, such substances include salt solutions, melts, water (except distilled), moist soil, the human body and, of course, metals.

Metals are considered the best conductors of electrical charge. There are also very good conductors that are not metals. Among such conductors, the best example is carbon.

All conductors have properties such as resistance and conductivity . Due to the fact that electric charges, colliding with atoms or ions of a substance, overcome some resistance to their movement in an electric field, it is customary to say that conductors have electrical resistance ( R ). The reciprocal of resistance is called conductance ( G ).

G = 1/R

That is, conductivity is the property or ability of a conductor to conduct electric current. It must be understood that good conductors present very little resistance to the flow of electrical charges and, accordingly, have high conductivity. The better the conductor, the greater its conductivity. For example, a copper conductor has greater conductivity than an aluminum conductor, and the conductivity of a silver conductor is higher than the same conductor made of copper.

Dielectrics

Unlike conductors , in dielectrics at low temperatures there are no free electrical charges. They consist of neutral atoms or molecules. Charged particles in a neutral atom are bound to each other and cannot move under the influence of an electric field throughout the entire volume of the dielectric.

Dielectrics include , first of all, gases that conduct electrical charges very poorly. As well as glass, porcelain, ceramics, rubber, cardboard, dry wood, various plastics and resins.

Objects made from dielectrics are called insulators. It should be noted that the dielectric properties of insulators largely depend on the state of the environment. Thus, in conditions of high humidity (water is a good conductor), some dielectrics may partially lose their dielectric properties.

About the use of conductors and insulators

Both conductors and insulators are widely used in technology to solve various technical problems.

For example , all electrical wires in the house are made of metal (most often copper or aluminum). And the sheath of these wires or the plug that is plugged into the socket must be made of various polymers, which are good insulators and do not allow electrical charges to pass through.

It should be noted that the concepts of “conductor” or “insulator” do not reflect quality characteristics: the characteristics of these materials actually range from very good to very bad. Silver, gold, platinum are very good conductors, but these are expensive metals, so they are used only where price is less important compared to the function of the product (space, defense). Copper and aluminum are also good conductors and at the same time inexpensive, which predetermined their widespread use. Tungsten and molybdenum, on the contrary, are poor conductors and for this reason cannot be used in electrical circuits (they will disrupt the operation of the circuit), but the high resistance of these metals, combined with refractoriness, predetermined their use in incandescent lamps and high-temperature heating elements.

Comparison of semiconductors and metals

What is the difference between semiconductors and metals? Semiconductors differ from metals in the mechanism of electric current. Let's consider how electric current arises in semiconductors. Germanium atoms have four weakly bonded valence electrons in their outer shell. In the crystal lattice, near each atom there are four more. Atoms in a semiconductor crystal are connected by pairs of valence electrons. Each valence electron belongs to two atoms. If there is an increase in temperature, some part 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 lost electrons. The vacant place can be taken 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 encountering a hole restores electronic communication. 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 consists of electron and hole currents. The number of free charge carriers changes, does not remain constant and depends on temperature. As it increases, the resistance of semiconductors increases. Metals have a crystalline structure. They consist of molecules and atoms that occupy a certain, ordered position. A metal is represented in the form of a crystal lattice, at the nodes of which there are atoms, or ions, or molecules that vibrate around their location. Between them in space there are free electrons that move chaotically in different directions. But when an electric field appears, they begin to move in an orderly manner towards the positive pole, and 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.