What is a semiconductor and what is it eaten with?
Semiconductor- a material without which the modern world of technology and electronics is unthinkable. Semiconductors exhibit the properties of metals and non-metals under certain conditions. In terms of electrical resistivity, semiconductors occupy an intermediate position between good conductors and dielectrics. Semiconductor differs from conductors in a strong dependence of 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 a few electron volts (eV). For example, diamond can be attributed to wide-gap semiconductors, and indium arsenide - to narrow-gap ones. 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 an electron.
The band gap value is of great importance in the generation of 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 all inorganic substances of 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 donates 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 of the crystal lattice it replaces, in which crystallographic plane it is embedded.
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.
According to the type of conductivity, semiconductors are divided into n-type and p-type
n-type semiconductor
According to 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 obtain 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 arsenic As, is added to tetravalent Si silicon. During the interaction, each arsenic atom enters into a covalent bond with silicon atoms. But the 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 detach an electron from an atom. The electron breaks off and turns into a free one, able to carry a charge. Thus, charge transfer is carried out by an electron, and not by a hole, that is, this type of semiconductor conducts electric current like metals.
Also, antimony Sb 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", denoting the positive charge of the majority carriers.
For example, in a semiconductor, tetravalent Si silicon, a small amount of trivalent Indium atoms is added. In our case, indium will be an impurity element whose atoms 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 a covalent bond between neighboring silicon atoms and becomes a negatively charged ion, forming a so-called hole and, accordingly, a hole junction.
According to the same scheme, In ndium imparts hole conductivity to Ge germanium.
Exploring the properties of semiconductor elements and materials, studying the properties of the contact between a conductor and a semiconductor, experimenting in the manufacture of semiconductor materials, O.V. Losev created a prototype of the modern LED in the 1920s.
5. Conductors and insulators
All substances, objects, bodies can be divided into two groups - conductors of electricity and electrical insulators.
How are conductors different from insulators?
To answer this question, we will make the following experiment with an electroscope. Take two electroscopes and put them side by side on the table. We charge one of the electroscopes with electricity, and leave the other uncharged (Fig. 5, top). Now let's touch both balls at once with a copper stick. We will see that the angle between the leaves of a charged electroscope will decrease slightly, and the leaves of an uncharged electroscope will move apart (Fig. 5, left). This is because part of the electricity from one electroscope went through the copper rod to another. Copper is a conductor of electricity.
Rice. 5. Electricity passes through a conductor from one electroscope to another, but cannot pass through an insulator.
Let us now do the same experiment again, but this time we will connect the balls of both electroscopes with a stick made of porcelain (Fig. 5, right). The leaves of the electroscope will remain in the same position: nothing will happen to them. Through porcelain, electricity could not pass from one electroscope to another. Porcelain does not conduct electricity. He is an insulator.
Conductors of electricity are, first of all, metals (copper, iron and others), water and earth. The human body is also a conductor. Examples of electrical insulators are porcelain, glass, rubber, air.
Conductors have their name from the fact that they conduct electricity, that is, they pass it through themselves, and insulators do not conduct - they do not pass electricity through themselves.
The main part of electrical devices are conductors that carry electricity to a certain place, and insulators that do not allow electricity to go to places that are not intended for it. Anyone who has seen a telephone line or a transmission line for electrical energy (Fig. 6) has noticed that the wires that serve to transmit electricity are stretched on porcelain or glass insulators. Wires (transmission lines) carry electricity from the power station (where it is generated by machines) to factories, plants, MTS and homes. Large porcelain insulators support the wires and allow electricity to flow through them. Insulators are needed precisely in order to prevent electricity from leaving the wires through the poles into the ground, to protect, or, as they say, “isolate” it from the ground.
Rice. 6. Electricity transmission line.
The electricity flowing in the wires forms an electric current. The more electricity flows in one second through the wire, the more current flows through it.
All substances are made up of atoms and molecules that have positively charged nuclei and negatively charged electrons. Atoms and molecules are electrically neutral, since the charge of the nucleus is equal to the total charge
electrons surrounding the nucleus. In the presence of external factors (temperature increase, electric field, etc.), an atom or molecule loses an electron. This atom turns into a positive ion, and an electron that has broken away from the atom can join another atom, turning it into a negative ion, and remain free. The process of formation of ions is called ionization. The number of free electrons or ions per unit volume of a substance is called the concentration of charged particles. Thus, in a substance that was placed in an electric field, under the influence of field forces, a process of movement of free electrons or ions in the direction of field forces occurs, called an electric current.
The property of a substance to conduct current under the influence of an electric field is called the electrical conductivity of a substance, which depends on the concentration of free electrically charged particles. The greater the concentration of charged particles, the greater the electrical conductivity of the substance. All substances, depending on the electrical conductivity, are divided into:
1 Explorer. They have very high electrical conductivity. Conductors are divided into two groups. The conductors of the first group include metals (copper, aluminum, silver, etc.) and their alloys, in which only electrons can move. That is, in metals, electrons are very weakly bound to the nuclei of atoms and are easily separated from them. In metals, the phenomenon of electric current is associated with the movement of free electrons, which have very high mobility and are in a state of thermal motion. This electrical conductivity is called electronic. Conductors are used for the manufacture of wires, power lines, windings of electrical machines, etc. The conductors of the second group include aqueous solutions of salts, acids, etc., which are called electrolytes. Under the influence of a solution, the molecules of a substance decompose into positive and negative ions, which, under the action of an electric field, begin to move. Electrolyte ions during the passage of current will begin to settle on the electrodes immersed in the electrolyte. The process of separation of substances from electrolytes by electric current is called electrolysis. It is used for the extraction of non-ferrous metals from solutions of their compounds (copper, aluminum), as well as for coating metals with a protective layer of another metal (for example, chromium plating).
2 Dielectrics (or electrically insulating substances). Substances with very low electrical conductivity (gases, rubber substances, mineral oils, etc.). In these substances, electrons are very strongly bound to the nuclei of atoms and are rarely separated from the nuclei under the action of an electric field. Those. dielectrics do not conduct electricity. This property is used in the production of electrical protective equipment: dielectric gloves, shoes, rugs, insulating stands, linings, caps, insulators on electrical equipment, etc.
Dielectrics can be: solid, gaseous, liquid.
3 Semiconductor (germanium, selenium, silicon). These are substances that, in addition to electronic conductivity, have "hole" conductivity, which largely depends on the presence of external factors: light, temperature, electric or magnetic field. These substances have a covalent bond (it is a chemical bond between two electrons of neighboring atoms in the same orbit). The covalent bond is very weak. In the presence of an external factor, it is destroyed and free electrons appear (electronic conductivity). At the moment of formation of a free electron in a covalent bond, a free city appears - an “electron hole” (equivalent to a proton), which attracts an electron from a neighboring covalent bond. But then a new "hole" is formed, which again attracts an electron from a neighboring covalent bond, and so on. Those. under the action of an electric field, "holes" move in the direction of the field (towards electrons) - the movement of protons. Thus, with electronic conduction, an electron travels the entire path, and with “hole” conduction, electrons are alternately replaced by bonds, each electron travels a fraction of the path. When bonds are broken in semiconductors, the same number of electrons and "holes" appear simultaneously. That is, the conductivity consists of electronic and "hole" and is called the intrinsic conductivity of the semiconductor. The properties of semiconductors can be changed by introducing impurities of other substances into them. Thereby increasing one or another conductivity. It is used in industrial electronics: diodes, transistors, thyristors. They are used as amplifiers, rectifiers, electronic generators, stabilizers and the like. Their advantages: low energy loss, cost, size and weight, ease of operation, long life. Disadvantage: dependence of conductivity on temperature.
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.
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, just the same due to the large number of free charge carriers in their structure. Under the influence of an electric field, the 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, electrical appliances, electrical switches, plugs, sockets, and so on are made from them. 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 its breakdown voltage.
What is a semiconductor
A semiconductor conducts electric current, but not like metals, but under certain conditions - the communication of energy to the 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 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, 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.
conductor resistance. Conductivity. Dielectrics. The use 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- the presence of free charge carriers that participate in thermal motion and can move throughout the volume of matter.
As a rule, such substances include salt solutions, melts, water (except distilled water), moist soil, the human body and, of course, metals.
Metals considered to be the best conductors of electric charge.
There are also very good conductors that are not metals.
Among such conductors, carbon is the best example.
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 conductivity ( G).
G = 1/R
That is, the conductivity – is the property or ability of a conductor to conduct an electric current.
You need to understand that good conductors represent a very small resistance to the flow of electric charges and, accordingly, have high conductivity. The better the conductor, the greater its conductivity. For example, a copper conductor has b about
greater conductivity than an aluminum conductor, and the conductivity of a silver conductor is higher than that of a copper conductor.
Dielectrics
The dielectrics are, in the first place, gases that conduct electrical charges very poorly. As well as glass, porcelain, ceramics, rubber, cardboard, dry wood, various plastics and resins.
Items made of dielectrics are called insulators. It should be noted that the dielectric properties of insulators largely depend on the state of the environment. So, in conditions of high humidity (water is a good conductor), some dielectrics may partially lose their dielectric properties.
On the use of conductors and insulators
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 outlet 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 terms "conductor" or "insulator" do not reflect qualitative characteristics: the characteristics of these materials in fact are in a wide 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 the price is less important compared to the function of the product (space, defense industry).
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 infusibility, predetermined their use in incandescent lamps and high-temperature heating elements.
insulators there are also very good ones, just good ones and bad ones. This is due to the fact that in real dielectrics there are also free electrons, although there are very few of them. The appearance of free charges even in insulators is due to thermal vibrations of electrons: under the influence of high temperature, some electrons still manage to break away from the nucleus and the insulating properties of the dielectric deteriorate. In some dielectrics, there are more free electrons and the quality of their insulation is, accordingly, worse. It is enough to compare, for example, ceramics and cardboard.
The best insulator is an ideal vacuum, but it is practically unattainable on Earth. Absolutely pure water would also be a great insulator, but has anyone seen it in real life? And water with the presence of any impurities is already a fairly good conductor.
The quality criterion of an insulator is its compliance with the functions that it must perform in a given circuit. If the dielectric properties of a material are such that any leakage through it is negligible (does not affect the operation of the circuit), then such a material is considered a good insulator.
Semiconductors
There are substances, which in their conductivity occupy an intermediate position between conductors and dielectrics.
Such substances are called semiconductors.
They differ from conductors in the strong dependence of the conductivity of electric charges on temperature, as well as on the concentration of impurities, and can have the properties of both conductors and dielectrics.
Unlike metallic conductors, in which the conductivity decreases with increasing temperature, for semiconductors, the conductivity increases with increasing temperature, and the resistance, as the reciprocal of conductivity, decreases.
At low temperatures semiconductor resistance, as seen from rice. one, tends to infinity.
This means that at a temperature of absolute zero, a semiconductor has no free carriers in the conduction band and, unlike conductors, behaves like a dielectric.
With an increase in temperature, as well as with the addition of impurities (doping), the conductivity of the semiconductor increases and it acquires the properties of a conductor.
Rice. one. The dependence of the resistance of conductors and semiconductors on temperature