In semiconductors, this is the directed movement of holes and electrons, which is influenced by an electric field.

As a result of the experiments, it was noted that the electric current in semiconductors is not accompanied by the transfer of matter - they do not undergo any chemical changes. Thus, electrons can be considered current carriers in semiconductors.

The ability of a material to form an electric current in it can be determined. According to this indicator, conductors occupy an intermediate position between conductors and dielectrics. Semiconductors are various types of minerals, some metals, metal sulfides, etc. Electricity in semiconductors arises due to the concentration of free electrons, which can move in a direction in a substance. Comparing metals and conductors, it can be noted that there is a difference between the temperature effect on their conductivity. An increase in temperature leads to a decrease In semiconductors, the conductivity index increases. If the temperature in the semiconductor increases, then the movement of free electrons will be more chaotic. This is due to the increase in the number of collisions. However, in semiconductors, in comparison with metals, the concentration of free electrons increases significantly. These factors have an opposite effect on the conductivity: the more collisions, the lower the conductivity, the greater the concentration, the higher it is. In metals, there is no relationship between temperature and the concentration of free electrons, so that with a change in conductivity with increasing temperature, the possibility of an ordered movement of free electrons only decreases. With regard to semiconductors, the effect of increasing the concentration is higher. Thus, the more the temperature rises, the greater the conductivity will be.

There is a relationship between the movement of charge carriers and such a concept as electric current in semiconductors. In semiconductors, the appearance of charge carriers is characterized by various factors, among which the temperature and purity of the material are especially important. By purity, semiconductors are divided into impurity and intrinsic.

As for the intrinsic conductor, the influence of impurities at a certain temperature cannot be considered significant for them. Since the band gap in semiconductors is small, in an intrinsic semiconductor, when the temperature reaches, the valence band is completely filled with electrons. But the conduction band is completely free: there is no electrical conductivity in it, and it functions as a perfect dielectric. At other temperatures, there is a possibility that during thermal fluctuations certain electrons can overcome the potential barrier and find themselves in the conduction band.

Thomson effect

The principle of the thermoelectric Thomson effect: when an electric current is passed in semiconductors along which there is a temperature gradient, in addition to Joule heat, additional amounts of heat will be released or absorbed in them, depending on the direction in which the current flows.

Insufficiently uniform heating of a sample having a homogeneous structure affects its properties, as a result of which the substance becomes inhomogeneous. Thus, the Thomson phenomenon is a specific Pelte phenomenon. The only difference is that different chemical composition sample, and the non-ordinary temperature causes this inhomogeneity.

Yeryutkin Evgeny Sergeevich
physics teacher of the highest qualification category, secondary school №1360, Moscow

If you make a direct connection, then the external field will neutralize the blocking field, and the current will be made by the main charge carriers.

Rice. 9. p-n junction with direct connection ()

In this case, the current of minority carriers is negligible, it is practically non-existent. Therefore, the p-n junction provides one-way conduction of electric current.

Rice. 10. Atomic structure of silicon with increasing temperature

The conduction of semiconductors is electron-hole, and such conduction is called intrinsic conduction. And unlike conductive metals, as the temperature increases, the number of free charges just increases (in the first case, it does not change), so the conductivity of semiconductors increases with increasing temperature, and the resistance decreases

A very important issue in the study of semiconductors is the presence of impurities in them. And in the case of the presence of impurities, one should speak of impurity conductivity.

The small size and very high quality of transmitted signals have made semiconductor devices very common in modern electronic technology. The composition of such devices may include not only the aforementioned silicon with impurities, but also, for example, germanium.

One of these devices is a diode - a device that can pass current in one direction and prevent it from passing in the other. It is obtained by implanting another type of semiconductor into a p- or n-type semiconductor crystal.

Rice. 11. The designation of the diode on the diagram and the diagram of its device, respectively

Another device, now with two pn junctions called a transistor. It serves not only to select the direction of current flow, but also to convert it.

Rice. 12. Scheme of the structure of the transistor and its designation on the electrical circuit, respectively ()

It should be noted that modern microcircuits use many combinations of diodes, transistors and other electrical devices.

In the next lesson, we will look at the propagation of electric current in a vacuum.

1. Tikhomirova S.A., Yavorsky B.M. Physics ( a basic level of) M.: Mnemosyne. 2012
2. Gendenstein L.E., Dick Yu.I. Physics grade 10. M.: Ileksa. 2005
3. Myakishev G.Ya., Sinyakov A.Z., Slobodskov B.A. Physics. Electrodynamics M.: 2010

1. Principles of operation of devices ().
2. Encyclopedia of Physics and Technology ().

1. What causes conduction electrons in a semiconductor?
2. What is intrinsic conductivity of a semiconductor?
3. How does the conductivity of a semiconductor depend on temperature?
4. What is the difference between a donor impurity and an acceptor impurity?
5. * What is the conductivity of silicon with an admixture of a) gallium, b) indium, c) phosphorus, d) antimony?

Electric current in semiconductors The purpose of the lesson: to form an idea of ​​the free carriers of electric charge in semiconductors and the nature of electric current in semiconductors. Type of lesson: lesson learning new material. LESSON PLAN Knowledge check 5 min. 1. Electric current in metals. 2. Electric current in electrolytes. 3. Faraday's law for electrolysis. 4. Electric current in gases Demonstration 5 min. Fragments of the video film "Electric current in semiconductors" Learning new material 28 min. 1. Charge carriers in semiconductors. 2. Impurity conductivity of semiconductors. 3. Electron-hole transition. 4. Semiconductor diodes and transistors. 5. Integrated circuits Consolidation of the studied material 7 min. 1. Qualitative questions. 2. Learning to solve problems STUDYING A NEW MATERIAL 1. Carrying charges in semiconductors The specific resistances of semiconductors at room temperature have values ​​that are in a wide range, i. from 10-3 to 107 Ohm m, and occupy an intermediate position between metals and dielectrics. Semiconductors are substances whose resistivity decreases very rapidly with increasing temperature. Many semiconductors are chemical elements(boron, silicon, germanium, phosphorus, arsenic, selenium, tellurium, etc.), great amount minerals, alloys and chemical compounds. Almost all inorganic substances environment - semiconductors. For enough low temperatures and the absence of external influences of lighting or heating) semiconductors do not conduct electric current: under these conditions, all electrons in semiconductors are bound. However, the bond of electrons with their atoms in semiconductors is not as strong as in dielectrics. And in the case of an increase in temperature, as well as for bright illumination, some electrons break away from their atoms and become free charges, that is, they can move throughout the sample. Due to this, negative charge carriers appear in semiconductors - free electrons. electrons is called an electron. When an electron is detached from an atom, the positive charge of that atom becomes uncompensated, i.e. an extra positive charge appears in this place. This positive charge is called a “hole”. The atom near which a hole has formed can take away a bound electron from a neighboring atom, while the hole will move to the neighboring atom, and that atom, in turn, can “transfer” the hole further. Such a "baton" movement of bound electrons can be considered as the movement of holes, that is, positive charges. The conductivity of a semiconductor due to motion (for example, charge. The conductivity of a semiconductor due to the motion of holes is called hole. The difference between hole conductivity and Thus, electronic conductivity is that electronic conductivity is due to the movement of free electrons in semiconductors, and hole conductivity is due to the movement of bound electrons. In In a pure semiconductor (without impurities), an electric current creates the same number of free electrons and holes.This conductivity is called the intrinsic conductivity of semiconductors.2. Impurity conductivity of semiconductors If you add a small amount of arsenic (about 10-5%) to pure molten silicon, after hardening, ordinary crystalline silicon lattice, but at some lattice sites, instead of silicon atoms, there will be arsenic atoms.Arsenic, as you know, is a pentavalent element. Chotivalent electrons form paired electronic bonds with neighboring silicon atoms. The nth electron will not have enough bonds, while it will be so weakly bound to the Arsenic atom, which easily becomes free. As a result, each impurity atom will give one free electron. Impurities whose atoms easily donate electrons are called donor impurities. Electrons from silicon atoms can become free, forming a hole, therefore, impurities that "capture" the electrons of atoms can simultaneously exist in a crystal, and free electrons and holes are called. However, there will be many times more free electrons than holes. Semiconductors in which the majority charge carriers are electrons are called n-type semiconductors. If a small amount of trivalent indium is added to silicon, then the nature of the conductivity of the semiconductor will change. Since indium has three valence electrons, it can establish a covalent bond with only three neighboring atoms. An electron is not enough to establish a bond with the fourth atom. Indium "borrows" an electron from neighboring atoms, as a result, each atom of India forms one vacant place - a hole. crystal lattice semiconductors, acceptor. In the case of an acceptor impurity, the main charge carriers have holes during the passage of an electric current through a semiconductor. Semiconductors in which holes are the majority charge carriers are called p-type semiconductors. Almost all semiconductors contain both donor and acceptor impurities. The type of semiconductor conductivity determines the impurity with a higher concentration of charge carriers - electrons and holes. 3. Electron-hole transition physical properties inherent in semiconductors, the properties of contacts (p-n-junction) between semiconductors with different types conductivity. In an n-type semiconductor, electrons participate in thermal motion and diffuse through the boundary into the p-type semiconductor, where their concentration is much lower. Similarly, holes will diffuse from a p-type semiconductor to an n-type semiconductor. This happens just as the atoms of a solute diffuse from a strong solution to a weak one in the event of a collision. As a result of diffusion, the near-contact area is depleted of the main charge carriers: in the n-type semiconductor, the concentration of electrons decreases, and in the p-type semiconductor, the concentration of holes. Therefore, the resistance of the contact area is very significant. The diffusion of electrons and holes through the p-n junction leads to the fact that the n-type semiconductor from which the electrons come is charged positively, and the p-type is negatively charged. An electric double layer is formed, which creates an electric field that prevents further diffusion of free current carriers through the semiconductor contact. At a certain voltage between the double charged layer, further impoverishment of the near-contact area by the main carriers stops. If now the semiconductor is connected to a current source so that its electronic region is connected to the negative pole of the source, and the hole region to the positive pole, then the electric field created by the current source will be directed so that it moves the main current carriers in each section of the semiconductor with p- n-junction. Upon contact, the section will be enriched with the main current carriers, and its resistance will decrease. A significant current will flow through the contact. The direction of the current in this case is called throughput, or direct. If, however, an n-type semiconductor is attached to the positive, and a p-type semiconductor to the negative pole of the source, then the near-contact area expands. The resistance of the area is greatly increased. The current through the transition layer will be very small. This direction of current is called closing, or reverse. 4. Semiconductor Diodes and Transistors Therefore, through the interface between n-type and p-type semiconductors, electric current flows in only one direction - from the p-type semiconductor to the n-type semiconductor. This is used in devices called diodes. Semiconductor diodes are used to rectify an alternating current (such a current is called alternating), as well as for the manufacture of LEDs. Semiconductor rectifiers have high reliability and long service life. devices: Semiconductor diodes are widely used in radio receivers, video recorders, televisions, computers. An even more important application of semiconductors has been the transistor. It consists of three layers of semiconductors: at the edges are semiconductors of one type, and between them is a thin layer of another type of semiconductor. The widespread use of transistors is due to the fact that they can be used to amplify electrical signals. Therefore, the transistor has become the main element of many semiconductor devices. 5. Integrated circuits Semiconductor diodes and transistors are the "building blocks" of very complex devices, which are called integrated circuits. Microcircuits work today in computers and televisions, mobile phones and artificial satellites , in cars, airplanes and even in washing machines. An integrated circuit is made on a silicon wafer. The size of the plate is from a millimeter to a centimeter, and one such plate can accommodate up to a million components - tiny diodes, transistors, resistors, etc. Important advantages of integrated circuits are high speed and reliability, as well as low cost. Thanks to this, on the basis of integrated circuits, it was possible to create complex, but accessible to many devices, computers and modern household appliances. QUESTION TO STUDENTS DURING THE PRESENTATION OF NEW MATERIAL First level 1. What substances can be classified as semiconductor? 2. The movement of which charged particles creates a current in semiconductors? 3. Why is the resistance of semiconductors very strongly dependent on the presence of impurities? 4. How is a p-n junction formed? What property does a p-n junction have? 5. Why can't free charge carriers pass through the p-n junction of a semiconductor? Second level 1. After the introduction of arsenic impurities into germanium, the concentration of conduction electrons increased. How did the concentration of holes change in this case? 2. With the help of what experience can one be convinced of the one-sided conductivity of a semiconductor diode? 3. Is it possible to obtain a pn junction by fusing tin into germanium or silicon? CONFIGURATION OF THE STUDYED MATERIAL 1). Qualitative questions 1. Why are the requirements for the purity of semiconductor materials very high (in some cases, the presence of even one impurity atom per million atoms is not allowed)? 2. After the introduction of arsenic impurities into germanium, the concentration of conduction electrons increased. How did the concentration of holes change in this case? 3. What happens in the contact of two n- and p-type semiconductors? 4. In a closed box are a semiconductor diode and a rheostat. The ends of the devices are brought out and connected to the terminals. How to determine which terminals belong to a diode? 2). Learning to solve problems 1. What kind of conductivity (electronic or hole) does silicon doped with gallium have? india? phosphorus? antimony? 2. What conductivity (electronic or hole) will be in silicon if phosphorus is added to it? boron? aluminum? arsenic? 3. How will the resistance of a silicon sample with a phosphorus impurity change if a gallium impurity is introduced into it? The concentration of Phosphorus and Gallium atoms is the same. (Answer: will increase) WHAT WE LEARNED AT THE LESSON · Semiconductors are substances whose resistivity decreases very quickly with increasing temperature. The conductivity of a semiconductor due to the movement of electrons is called electronic. The conductivity of a semiconductor due to the movement of holes is called hole conductivity. Impurities whose atoms easily donate electrons are called donor impurities. · Semiconductors in which the main charge carriers are electrons are called n-type semiconductors. · Impurities that "capture" the electrons of the atoms of the crystal lattice of semiconductors are called acceptor. · Semiconductors in which holes are the main charge carriers are called p-type semiconductors. · The contact of two semiconductors with different types of conductivity has the properties of conducting current well in one direction and much worse in the opposite direction, i.e. has unidirectional conduction. Homework 1. §§ 11, 12.

Hello dear readers of the site. The site has a section dedicated to beginner radio amateurs, but so far I haven’t really written anything for beginners taking their first steps into the world of electronics. I fill this gap, and from this article we begin to get acquainted with the device and operation of radio components (radio components).

Let's start with semiconductor devices. But in order to understand how a diode, thyristor or transistor works, one must understand what semiconductor. Therefore, we will first study the structure and properties of semiconductors on molecular level, and then we will deal with the operation and design of semiconductor radio components.

General concepts.

Why exactly semiconductor diode, transistor or thyristor? Because the basis of these radio components is semiconductors Substances capable of both conducting electrical current and preventing its passage.

This is a large group of substances used in radio engineering (germanium, silicon, selenium, copper oxide), but for the manufacture of semiconductor devices, they mainly use only Silicon(Si) and Germanium(Ge).

By their own electrical properties semiconductors occupy a middle place between conductors and non-conductors of electric current.

Properties of semiconductors.

The electrical conductivity of conductors is highly dependent on the ambient temperature.
At very low temperatures close to absolute zero (-273°C), semiconductors do not carry out electric current, and promotion temperature, their resistance to current decreases.

If you point at the semiconductor light, then its electrical conductivity begins to increase. Using this property of semiconductors, were created photovoltaic appliances. Semiconductors are also capable of converting light energy into electrical current, for example, solar panels. And when introduced into semiconductors impurities certain substances, their electrical conductivity increases dramatically.

The structure of semiconductor atoms.

Germanium and silicon are the main materials of many semiconductor devices and have four valence electron.

Atom Germany is made up of 32 electrons, and an atom silicon out of 14. But only 28 electrons of the germanium atom and 10 electrons of the silicon atom, located in the inner layers of their shells, are firmly held by the nuclei and never come off from them. Just four valence electrons of the atoms of these conductors can become free, and even then not always. And if a semiconductor atom loses at least one electron, then it becomes positive ion.

In a semiconductor, the atoms are arranged in a strict order: each atom is surrounded by four the same atoms. Moreover, they are located so close to each other that their valence electrons form single orbits passing around neighboring atoms, thereby binding the atoms into a single whole substance.

Let us represent the interconnection of atoms in a semiconductor crystal in the form of a flat diagram.
In the diagram, red balls with a plus, conventionally, denote nuclei of atoms(positive ions), and the blue balls are valence electrons.

Here you can see that around each atom are located four exactly the same atoms, and each of these four has a connection with four other atoms, and so on. Each of the atoms is connected to each neighboring two valence electrons, and one electron is its own, and the other is borrowed from a neighboring atom. Such a bond is called a two-electron bond. covalent.

On the other hand, the outer layer electron shell each atom contains eight electrons: four their own, and alone, borrowed from four neighboring atoms. Here it is no longer possible to distinguish which of the valence electrons in the atom is "one's own" and which one is "foreign", since they have become common. With such a bond of atoms in the entire mass of a germanium or silicon crystal, we can assume that a semiconductor crystal is one large molecule. In the figure, pink and yellow circles show the relationship between outer layers shells of two neighboring atoms.

Semiconductor electrical conductivity.

Consider a simplified drawing of a semiconductor crystal, where atoms are denoted by a red ball with a plus, and interatomic bonds are shown by two lines symbolizing valence electrons.

At a temperature close to absolute zero, a semiconductor does not conduct current, since it does not have free electrons. But with an increase in temperature, the bond of valence electrons with the nuclei of atoms weakens and some of the electrons, due to thermal motion, can leave their atoms. The electron escaping from the interatomic bond becomes " free", and where he was before, an empty place is formed, which is conventionally called hole.

How above semiconductor temperature, the more it becomes free electrons and holes. As a result, it turns out that the formation of a "hole" is associated with the departure of a valence electron from the shell of an atom, and the hole itself becomes positive electric charge equal negative charge of an electron.

Now let's look at the figure, which schematically shows the phenomenon of the occurrence of current in a semiconductor.

If you apply some voltage to the semiconductor, the "+" and "-" contacts, then a current will appear in it.
Due to thermal phenomena, in a semiconductor crystal from interatomic bonds will begin be released some number of electrons (blue balls with arrows). Electrons are attracted positive pole of the voltage source will be move towards him, leaving behind holes, which will be filled in by others released electrons. That is, under the influence of an external electric field charge carriers acquire a certain speed of directional movement and thereby create electricity.

For example: the freed electron closest to the positive pole of the voltage source attracted this pole. Breaking the interatomic bond and leaving it, the electron leaves after myself hole. Another freed electron, which is located on some removal from the positive pole, also attracted pole and moving towards him, but having met a hole in its path, is attracted to it core atom, restoring the interatomic bond.

The resulting new hole after the second electron, fills the third released electron, located next to this hole (Figure No. 1). In its turn holes, which are closest to negative pole, filled with other released electrons(Figure No. 2). Thus, an electric current arises in the semiconductor.

As long as the semiconductor operates electric field, this process continuous: interatomic bonds are broken - free electrons appear - holes are formed. The holes are filled with released electrons - interatomic bonds are restored, while other interatomic bonds are broken, from which electrons leave and fill the following holes (Figure No. 2-4).

From this we conclude: electrons move from the negative pole of the voltage source to the positive, and holes move from the positive pole to the negative.

Electron-hole conductivity.

In a "pure" semiconductor crystal, the number released in this moment electrons is equal to the number emerging in this case, there are holes, so the electrical conductivity of such a semiconductor small, since it provides an electric current big resistance, and this electrical conductivity is called own.

But if we add to the semiconductor in the form impurities a certain number of atoms of other elements, then its electrical conductivity will increase significantly, and depending on structures atoms of impurity elements, the electrical conductivity of the semiconductor will be electronic or perforated.

electronic conductivity.

Suppose, in a semiconductor crystal, in which atoms have four valence electrons, we have replaced one atom with an atom in which five valence electrons. This atom four electrons will bond with four neighboring atoms of the semiconductor, and fifth the valence electron will remain superfluous' means free. And than more more will be free electrons, which means that such a semiconductor will approach a metal in its properties, and in order for an electric current to pass through it, it interatomic bonds do not have to be destroyed.

Semiconductors with such properties are called semiconductors with conductivity of the type " n", or semiconductors n-type. Here the Latin letter n comes from the word "negative" (negative) - that is, "negative". It follows that in a semiconductor n-type main charge carriers are - electrons, and not the main ones - holes.

hole conduction.

Let us take the same crystal, but now we will replace its atom with an atom in which only three free electron. With its three electrons, it will only bond with three neighboring atoms, and to bond with the fourth atom, he will not have enough one electron. As a result, it forms hole. Naturally, it will be filled with any other free electron nearby, but, in any case, there will be no such semiconductor in the crystal. grab electrons to fill holes. And than more there will be such atoms in the crystal, so more there will be holes.

In order for free electrons to be released and move in such a semiconductor, must be destroyed valence bonds between atoms. But the electrons will still not be enough, since the number of holes will always be more number of electrons at any given time.

Such semiconductors are called semiconductors with perforated conductivity or conductors p-type, which in Latin "positive" means "positive". Thus, the phenomenon of electric current in a p-type semiconductor crystal is accompanied by a continuous emergence And disappearance positive charges are holes. And this means that in a semiconductor p-type main charge carriers are holes, and not basic - electrons.

Now that you have some understanding of the phenomena occurring in semiconductors, it will not be difficult for you to understand the principle of operation of semiconductor radio components.

Let's stop at this, and in we will consider the device, the principle of operation of the diode, we will analyze its current-voltage characteristic and switching circuits.
Good luck!

A source:

1 . Borisov V.G. - A young radio amateur. 1985
2 . Website academic.ru: http://dic.academic.ru/dic.nsf/es/45172.

Semiconductors include many chemical elements (germanium, silicon, selenium, tellurium, arsenic, etc.), a huge number of alloys and chemical compounds. Almost all inorganic substances of the world around us are semiconductors. The most common semiconductor in nature is silicon, which makes up about 30% of the earth's crust.

The qualitative difference between semiconductors and metals is manifested in temperature dependence of resistivity(fig.9.3)

Band model of electron-hole conductivity of semiconductors

At education solids a situation is possible when the energy band that has arisen from the energy levels of the valence electrons of the initial atoms turns out to be completely filled with electrons, and the nearest ones available for filling with electrons energy levels separated from valence band E V gap unresolved energy states- the so-called forbidden zone E g.Above the band gap is the zone of energy states allowed for electrons - conduction band E c .

The conduction band at 0 K is completely free, while the valence band is completely occupied. Similar band structures are characteristic of silicon, germanium, gallium arsenide (GaAs), indium phosphide (InP) and many other semiconductor solids.

With an increase in the temperature of semiconductors and dielectrics, electrons are able to receive additional energy associated with thermal motion. kT. For some electrons, the energy of thermal motion is sufficient for the transition from the valence band to the conduction band, where electrons under the action of an external electric field can move almost freely.

In this case, in a circuit with a semiconductor material, as the temperature of the semiconductor rises, an electric current will increase. This current is associated not only with the movement of electrons in the conduction band, but also with the appearance vacancies from electrons that have gone into the conduction band in the valence band, the so-called holes . The vacant place can be occupied by a valence electron from a neighboring pair, then the hole will move to a new place in the crystal.

If a semiconductor is placed in an electric field, then not only free electrons are involved in the ordered movement, but also holes, which behave like positively charged particles. Therefore, the current I in a semiconductor is made up of an electronic I n and hole Ip currents: I= I n+ Ip.

The electron-hole mechanism of conduction manifests itself only in pure (i.e., without impurities) semiconductors. It is called own electrical conductivity semiconductors. Electrons are thrown into the conduction band with Fermi level, which turns out to be located in its own semiconductor in the middle of the forbidden zone(Fig. 9.4).

It is possible to significantly change the conductivity of semiconductors by introducing very small amounts of impurities into them. In metals, an impurity always reduces the conductivity. Thus, the addition of 3% phosphorus atoms to pure silicon increases the electrical conductivity of the crystal by a factor of 105.

Slight addition of dopant to the semiconductor called doping.

Necessary condition A sharp decrease in the resistivity of a semiconductor with the introduction of impurities is the difference in the valency of the impurity atoms from the valence of the main atoms of the crystal. The conductivity of semiconductors in the presence of impurities is called impurity conductivity .

Distinguish two types of impurity conduction – electronic And hole conductivity. Electronic conductivity occurs when pentavalent atoms (for example, arsenic, As) are introduced into a germanium crystal with tetravalent atoms (Fig. 9.5).

The four valence electrons of the arsenic atom are included in the formation covalent bonds with four neighboring germanium atoms. The fifth valence electron turned out to be redundant. It easily detaches from the arsenic atom and becomes free. An atom that has lost an electron turns into a positive ion located at a site in the crystal lattice.

An admixture of atoms with a valency greater than the valency of the main atoms of a semiconductor crystal is called donor impurity . As a result of its introduction, a significant number of free electrons appear in the crystal. This leads to a sharp decrease in the resistivity of the semiconductor - by thousands and even millions of times.

The resistivity of a conductor with a high content of impurities can approach the resistivity of a metallic conductor. Such conductivity, due to free electrons, is called electronic, and a semiconductor with electronic conductivity is called n-type semiconductor.

hole conduction occurs when trivalent atoms are introduced into a germanium crystal, for example, indium atoms (Fig. 9.5)

Figure 6 shows an indium atom that has created covalent bonds with only three neighboring germanium atoms using its valence electrons. The indium atom does not have an electron to form a bond with the fourth germanium atom. This missing electron can be captured by an indium atom from a covalent bond of neighboring germanium atoms. In this case, the indium atom turns into a negative ion located at a site of the crystal lattice, and a vacancy is formed in the covalent bond of neighboring atoms.

An admixture of atoms capable of capturing electrons is called acceptor impurity . As a result of the introduction of an acceptor impurity, many covalent bonds are broken in the crystal and vacant sites (holes) are formed. Electrons can jump to these places from neighboring covalent bonds, which leads to random wandering of holes around the crystal.

The concentration of holes in a semiconductor with an acceptor impurity significantly exceeds the concentration of electrons that arose due to the mechanism of intrinsic electrical conductivity of the semiconductor: np>> n n. This type of conduction is called hole conductivity . An impurity semiconductor with hole conductivity is called p-type semiconductor . Major free charge carriers in semiconductors p-type are holes.

Electron-hole transition. Diodes and transistors

In modern electronic technology, semiconductor devices play an exceptional role. Over the past three decades, they have almost completely replaced electrovacuum devices.

Any semiconductor device has one or more electron-hole junctions. . Electron-hole transition (or n–p-transition) - this is the contact area of ​​two semiconductors with different types of conductivity.

At the boundary of semiconductors (Fig. 9.7), a double electric layer is formed, the electric field of which prevents the process of diffusion of electrons and holes towards each other.

Ability n–p-transition to pass current in almost only one direction is used in devices called semiconductor diodes. Semiconductor diodes are made from silicon or germanium crystals. During their manufacture, an impurity is melted into a crystal with a certain type of conductivity, which provides a different type of conductivity.

Figure 9.8 shows a typical volt-ampere characteristic of a silicon diode.

Semiconductor devices with not one but two n-p junctions are called transistors . Transistors are of two types: p–n–p-transistors and n–p–n-transistors. in transistor n–p–n-type basic germanium plate is conductive p-type, and the two regions created on it - by conductivity n-type (Figure 9.9).

in transistor p–n–p- it's kind of the opposite. The plate of a transistor is called base(B), one of the regions with the opposite type of conductivity - collector(K), and the second - emitter(E).