), and substances [that do not actually conduct electric current (insulators or dielectrics).

Semiconductors are characterized by a strong dependence of their properties and characteristics on the microscopic amounts of impurities they contain. By changing the amount of impurity in a semiconductor from ten millionths of a percent to 0.1-1%, you can change their conductivity by millions of times. Another important property of semiconductors is that electric current is carried into them not only by negative charges - electrons, but also by positive charges of equal magnitude - holes.

If we consider an idealized semiconductor crystal, absolutely free of any impurities, then its ability to conduct electric current will be determined by the so-called intrinsic electrical conductivity.

Atoms in a semiconductor crystal are connected to each other using electrons in the outer electron shell. During thermal vibrations of atoms thermal energy is distributed unevenly between the electrons forming bonds. Individual electrons can receive enough thermal energy to “break away” from their atom and be able to move freely in the crystal, i.e., become potential current carriers (in other words, they move into the conduction band). Such departure of an electron violates the electrical neutrality of the atom; it acquires a positive charge equal in magnitude to the charge of the departed electron. This vacant space is called a hole.

Since the vacant place can be occupied by an electron from a neighboring bond, the hole can also move inside the crystal and become a positive current carrier. Naturally, under these conditions, electrons and holes appear in equal quantities, and the electrical conductivity of such an ideal crystal will be equally be determined by both positive and negative charges.

If in place of an atom of the main semiconductor we place an impurity atom, the outer electron shell of which contains one more electron than the atom of the main semiconductor, then such an electron will turn out to be superfluous, unnecessary for the formation of interatomic bonds in the crystal and weakly connected with its atom. Tens of times less energy is enough to tear it away from its atom and turn it into a free electron. Such impurities are called donor, i.e., donating an “extra” electron. The impurity atom is charged, of course, positively, but no hole appears, since a hole can only be an electron vacancy in an unfilled interatomic bond, and in in this case all connections are complete. This positive charge remains associated with its atom, motionless and, therefore, cannot take part in the process of electrical conductivity.

The introduction of impurities into a semiconductor, the outer electron shell of which contains fewer electrons than in the atoms of the main substance, leads to the appearance of unfilled bonds, i.e. holes. As mentioned above, this vacancy can be occupied by an electron from a neighboring bond, and the hole is able to move freely throughout the crystal. In other words, the movement of a hole is a sequential transition of electrons from one neighboring bond to another. Such impurities that “accept” an electron are called acceptor impurities.

With an increase in the amount of impurities of one type or another, the electrical conductivity of the crystal begins to acquire an increasingly pronounced electronic or hole character. In accordance with the first letters of the Latin words negativus and positivus, electronic electrical conductivity is called i-type electrical conductivity, and hole conductivity is called p-type, indicating which type of mobile charge carriers for a given semiconductor is the main one and which is the minor one.

With electrical conductivity due to the presence of impurities (i.e., impurity), 2 types of carriers still remain in the crystal: major, which appear mainly due to the introduction of impurities into the semiconductor, and minor, which owe their appearance to thermal excitation. The content in 1 cm3 (concentration) of electrons n and holes p for a given semiconductor at a given temperature is a constant value: n- p = const. This means that, increasing due to the introduction

If you apply an n-type voltage (the polarity indicated in the figure) to the metal-dielectric-semiconductor structure, then an electric field arises in the near-surface layer of the semiconductor, repelling electrons. This layer becomes depleted of electrons and will have a higher resistance. When the polarity of the voltage changes, electrons will be attracted by the electric field and an enriched layer with reduced resistance will be created at the surface.

In a p-type semiconductor, where the majority carriers are positive charges - holes, the voltage polarity that repelled electrons will attract holes and create an enriched layer with reduced resistance. The polarity scheme in this case will lead to the repulsion of holes and the formation of a near-surface layer with increased resistance.

The next important property of semiconductors is their strong sensitivity to temperature and radiation. As the temperature rises, the average vibration energy of the atoms in the crystal increases, and more and more bonds will be broken. More and more pairs of electrons and holes will appear. At sufficiently high temperatures, the intrinsic (thermal) conductivity can be equal to the impurity conductivity or even significantly exceed it. The higher the concentration of impurities, the higher the temperatures this effect will occur.

Bonds can also be broken by irradiating the semiconductor, for example, with light, if the energy of light quanta is sufficient to break the bonds. The energy of breaking bonds is different for different semiconductors, so they react differently to certain parts of the irradiation spectrum.

Silicon and germanium crystals are used as the main semiconductor materials, and boron, phosphorus, indium, arsenic, antimony and many other elements that impart the necessary properties to semiconductors are used as impurities. The production of semiconductor crystals with a given impurity content is a complex technological process, carried out in especially clean conditions using high-precision and complex equipment in electronic computer blocks. Engineers today cannot do without semiconductor rectifiers, switches and amplifiers. Replacing lamp equipment with semiconductor equipment has made it possible to reduce the size and weight of electronic devices tenfold, reduce their power consumption and sharply increase

Detector radio receiver.

Regular detector.

Where does a young radio amateur start? From the detector receiver. This amazing device is extremely simple. A wire coil, a nondescript detector pebble, headphones. That's all the wisdom. And what fabulous power is embodied in the combination of simple details! Ask people of the older generation who made the first detector receivers with their own hands. They will say: perhaps a brand new TV these days is less fun than those wooden boxes.

Here the assembled receiver is solemnly placed on the table. Its creator climbs onto the roof and extends a long, thirty to forty meters, antenna. He connects the wire coming from it to the receiver (108) and tinkers with the detector for some time. Resting the end of an elastic spring against a silver crystal placed in a glass tube, you need to feel a sensitive point on it. And as soon as this is achieved, the long-awaited “magic” happens: music or speech sounds in the headphones.

The detector crystal is, perhaps, the very first semiconductor that has found wide practical application. Why is it needed?

Radio waves excite an electric field in the antenna, which quickly changes direction. The electric field sets the electrons in the wire in motion. They fly in the wire, now forward, now back. Such electron oscillations occur hundreds of thousands of times per second. To hear the transmission, you need to cut these vibrations in half, letting through the headphones only those electron movements that are directed in one direction. In this case, the alternating current is said to be rectified, turning into a pulsating direct current. And in the relatively slow changes in its strength (hundreds and thousands of vibrations per second) the transmitted sounds are captured. The greater the strength of the rectified current, which means that the steel membrane of the earphone is pulled stronger by the electromagnet. The current weakens and it moves away from the electromagnet. The membrane vibrates, transmits its vibrations to the air, and sound waves spread around.

This, in brief, is the essence of the operation of the simplest radio receiver. As you can see, in addition to wires, only two devices are required here: headphones and a current rectifier. The detector acts as a rectifier.

The crystal, which is located in a glass tube, is a semiconductor. Its electrical conductivity, as we well understood earlier, can be either electronic or hole. Let's say it is endowed with electronic conductivity. But the crystal is not uniform. On its surface there are areas that are, to one degree or another, clogged with impurities. There are also places among them where, under the influence of impurities, an electronic semiconductor has turned into a hole semiconductor. And at the boundary of the electron and hole regions, the familiar blocking layer necessarily appears - a zone in which there are neither electrons nor holes.

Let us recall the peculiarity of this layer: on one side of it, “border guard” electrons stand guard. They repel all free electrons deep into the electron region. On the other side of the border there is the same guard of holes. They, as you remember, repel other holes deeper into the hole region. In short, a boundary electric field arises in the barrier layer. It counteracts the movement of electrons and holes to the interface between the electron and hole regions of the semiconductor.

Let us apply an external electric field to the blocking layer. Depending on the direction, it will either add its force to the force of the border guards in the semiconductor (expand the barrier layer), or, conversely, weaken and even sweep away the “border guard” electrons and holes.

What if we supply an alternating, that is, changing direction, electric field? Obviously, the blocking layer will periodically expand and disappear, the Border Guard will either strengthen or be removed altogether - in time with changes in the direction of the external field. And the result will be this: at the moments of expansion of the blocking layer, no current will flow through the semiconductor (electrons and holes scatter in different directions); at the moments (110) of the disappearance of the blocking layer, current will flow through the crystal (electrons and holes run towards each other).

Summarize. The sensitive point of the detector is a section of the semiconductor surface where the current carriers are different from those in the rest of the crystal. This means that under the tip of the spring there is a locking layer. The detector is included in the wire leading from the antenna to the headphones. The electric field of the antenna, penetrating the crystal, either expands this layer or destroys it. And the current through the detector flows only in one direction - when electrons and holes move towards each other.

Mercury lamp - AC rectifier. This device is bulky, uneconomical and fragile. Below is a semiconductor germanium rectifier, characterized by its simplicity of design, reliability, and exceptional efficiency.

It must be said that this principle is used to rectify current not only in the simplest radio receiver. Rectifiers made from semiconductors - cuprous oxide, selenium, copper sulphide, and Lately from germanium - are increasingly used in technology. The possibilities for their use are enormous: from simple measuring instruments to radio stations, electrometallurgical installations, and electric locomotives. And in many cases, rectifying semiconductors have proven to be the best rectifying devices available. Their coefficient useful action reaches 98-99 percent. Add to this strength, reliability, small size - and you will understand why the production of semiconductor rectifiers was given special attention in the Directives of the 20th Party Congress.

But let's return to our detector.

At the time when the first detectors appeared, they were still very imperfect. Sometimes it took a lot of effort to find a sensitive point. The spring kept jumping off it. I had to set up the receiver again and again. Engineers put a lot of ingenuity into improving the detector.

Modern semiconductor devices are the heirs of the first primitive detectors and vacuum tube diodes.

In 1919, a young radio amateur, Oleg Vladimirovich Losev, became interested in improving the detector. Dreaming of devoting his life to radio engineering, he began by working as a messenger at the first Nizhny Novgorod radio laboratory in (112) our country. Here they noticed an inquisitive and talented young man. The laboratory staff helped him complete his education, and Losev soon began independent scientific work. He carefully examined natural minerals used as detectors, studied their electrical properties, and in 1922 came to an unexpected discovery. The young scientist proved that if two detectors and an electric battery are included in the receiver circuit in a special way, then the electrical vibrations entering the headphones can be amplified.

For that time, Losev's discovery was very important. After all, an ordinary detector receiver made it possible to listen only to nearby stations. Long-range reception, especially in cities where there is a lot of interference and it is difficult to install a high and long antenna, turned out to be almost impossible. And Losev’s receivers, which he called kristadins, confidently received broadcasts from relatively distant radio stations. The inventor also built other devices using crystals - generators, that is, exciters of electrical oscillations.

Losev immediately published his discoveries without patenting them or demanding any monetary reward for them. In many countries, radio amateurs began to build receivers based on his designs. American magazine wrote: “The young Russian inventor conveyed his invention to the world.” The French magazine echoed: (113) “Scientific glory awaits Losev. He made his discovery public, thinking first of all about his friends - radio amateurs around the world."

For several years the name of the inventor did not leave the pages of magazines, but then it began to appear less and less often. By the end of the 20s, his idea - to use crystals to amplify and excite electrical vibrations - was forgotten. Science is not yet ripe for the creative, constructive development of this plan. There was no theory of semiconductors; there was almost no ability to artificially create such substances. All the hopes of radio engineers focused on another innovation - radio tubes.

Radio amateurs of the older generation remember well the first years of the victorious march of radio tubes. In millions of radios, gleaming glass and metal, these delicate, fragile devices were lined up in proud rows. How perfect they seemed compared to the primitive stone detectors!

The radio tubes really had something to be proud of. After all, with them we got the opportunity to listen to the radio without annoying headphones! It was then that the first loudspeakers began to sound in our homes.

What does a radio tube do?

Remember how you washed your face at the tap this morning. If the tap was well adjusted, it was enough to touch it slightly, and the stream would noticeably decrease or, conversely, increase. Insignificant hand efforts caused sudden changes in the flow of water.

Something similar happens in a radio tube. There, subtle fluctuations in the antenna's electric field change the powerful flow of electrons.

Vacuum triode circuit. On the left - the lamp is “unlocked”; on the right - “locked”.

How is this practically accomplished?

The simplest radio tube is a glass container freed from air. Looking inside, we will see three metal electrodes isolated from each other: the cathode, the grid and the anode. The cathode and anode are included in an external electrical circuit with a high constant voltage. And weak antenna signals are supplied to the grid.

A thin cathode filament is heated by electric current. Therefore, electrons fly out of it. Caught up strong field, they immediately rush to the anode. But in the path of the electrons is a wire mesh spiral. With its small field, it noticeably affects flying electrons nearby: it either allows them to pass freely, or slows down the flight, weakening the current flowing through the lamp, or, finally, throws the electrons back to the cathode - “locks” the lamp. All such changes in the electron flow occur in time with changes in the electric field of the grid. The electron flow is like a water jet in a pipe, and the mesh resembles a faucet. And just as light movements of a faucet create sharp shocks of water in a pipe, so weak signals picked up by an antenna cause noticeable current pulses in a radio tube. (115)

Signals can be amplified many times in several lamps in a row. And not only to strengthen it. Radio tubes with two electrodes (without grid) rectify alternating currents- play the role of detectors. Radio tubes equipped with additional electrodes control electron flows extremely finely. Finally, it is not difficult to excite various electrical vibrations in these devices.

In the hands of scientists and engineers, the radio tube has become a powerful means of technological progress. Continuously improving, in a few years it conquered all radio technology. Thanks to her, television developed, radar and radio navigation appeared, and with her participation, sound cinema, magnetic sound recording and many other wonderful inventions arose. A real technical revolution took place, which brought to life a new vast area of ​​​​knowledge - electronics.

It seemed that the future of radio engineering was inextricably linked with radio tubes. However, decades passed, and it gradually became clear that radio tubes were not so flawless.

During the polar wintering, the radio operator lost his difficultly established connection - another lamp went out. The pilot landed the plane unsuccessfully - the on-board radio lamps could not withstand the shaking and deteriorated. In the vast majority of cases, any radio device failed due to the fragility of the lamps. Their service life, estimated at hundreds and thousands of hours, ceased to satisfy the technology. And little by little they acquired a reputation as the most unreliable, capricious elements of the radio system.

Then the dimensions of the radio tubes turned out to be too large. After all, other modern radio devices number more than one hundred, even more than one thousand of them. It is not easy (116) for the designer to arrange this equipment so that it does not take up too much space.

All this forced radio engineers to seriously think about replacing radio tubes with some other compact and reliable devices.

The search for new solutions began.

Any tube radio, scientists reasoned, combines difficultly compatible structural elements: solids and... emptiness. Wires, capacitors, coils, resistances - all this is solid, all this can be fixed, made firmly, for a long time. What about radio tubes? To increase durability, lamp cylinders are made of metal, special plastics, and ceramics. This certainly helps. However, the main inconvenience - emptiness - remains. It is necessary to install complex electrodes in it and heat the cathode filament. Everything there is tender, delicate, afraid of shocks and shaking.

It would seem that emptiness is irreplaceable. In it, the electronic flows seem to be exposed, become accessible to regulation, and fall under the power of the weak electric field of the radio tube grid.

However, is it only in emptiness that the movement of electrons can be controlled?

What if we try a semiconductor crystal instead of emptiness? Obviously, it is necessary to pass a current through it and change the electrical conductivity of the crystal from the outside. But how can you change it? Is it even possible to achieve this?

The fate of the entire further development of radio technology depended on the solution of these issues.

Thus, O. V. Losev’s idea of ​​amplifiers and oscillators on crystals was revived on a new basis. (117)

Of course, a lot has changed in her. It has become impractical to use conventional detectors for this purpose. They had little effect. The talk was about creating a crystalline device that could confidently compete with a modern radio tube.

We did not immediately find a way to solve the problem. There were many unfortunate failures, breakdowns, and doubts. But in the end the answer was found: yes, the conductivity of the crystal can be controlled, it is possible to create a semiconductor device - a substitute for a radio tube. The theory of the device was developed American physicist William Shockley. His compatriots Bardeen and Brattain created in 1948 the first samples of devices called crystal triodes or transistors.

How are they built? We'll talk about this a little further. First, a few words about the material from which they are made.

Crystal triodes are made mainly from the semiconductor germanium. We have already mentioned the applications of this substance, which played a huge role in the development of physics and semiconductor technology. Another interesting page in the history of natural science is connected with it.

The crystalline element germanium is the most important semiconductor. In front is a single crystal of germanium.

In 1869, when Dmitry Ivanovich Mendeleev created his famous periodic table, no one suspected the existence of germanium. But the brilliant chemist, for purely theoretical reasons, predicted its discovery. The scientist gave it a place in his multi-story table and even described in advance what its main properties might be. According to the periodic law, this substance, unknown at that time, should have been in many ways similar to the known element silicon. Mendeleev (118) therefore assigned it the conventional name ekasilicium (silicon - Latin name silicon, and the prefix “eka” in Sanskrit means “similar”).

Sixteen years later, the remarkable vision came true. The German researcher Winkler found eca-silicon in one of the natural minerals and gave it the name of his homeland. It was a true triumph of scientific thought.

“It is hardly possible,” wrote Winkler, “to find a more striking proof of the validity of the doctrine of periodicity... This is not just a confirmation of a bold theory; here we see... a powerful step in the field of knowledge.”

Practical application again open element At first I almost didn’t get it. For a long time its silver-gray shiny crystals served only as unique exhibits in chemical collections. But for last years germanium became the most important technical material. And he achieved the crown of glory as soon as he became the basis of crystalline devices - substitutes for radio tubes.

Here it is in front of us - a germanium triode, a crystal, replacing emptiness, replacing the glass bubble of a radio tube. It looks like a tiny, pea-sized fungus. Three wires extend from the cap.

Semiconductor triodes. How much smaller are they than a radio tube!

Open it, and you will see that even in a miniature steel device, the overwhelming majority of the volume is occupied (119) by the body, the shell. And the crystal itself is tens of times smaller.

Let's figure out how the device works, how it controls the flow of electrons. On a metal stand called base, a crystalline plate of germanium with electronic conductivity is at rest. On top surface The crystal has been specially processed to create an area with hole conductivity. As always in such cases, a blocking layer appears between the hole and electron regions. The ends of two very thin platinum wires are attached side by side to the surface of the crystal. One of them is called emitter, Other - collector.

Emitter, collector and base are the three electrodes of a crystal amplifier. They correspond to the cathode, anode and grid of the radio tube. But the crystal is introduced into the amplification circuit differently than a radio tube.

The control signal source is connected between the base and emitter. The switching is done in such a way that the blocking layer does not serve as an obstacle to control signals (the electric field of the signals is directed against the electric field of the blocking layer). The relatively high voltage current source to be controlled is fed through a resistor to the collector and base. But it is included in opposite direction so that the blocking layer does not allow current to pass through.

Semiconductor triode circuit.

The scheme is ready. Let's send a control signal.

An electric field pulse enters the hole region of the crystal through the emitter wire. It breaks a hole in the barrier layer and draws holes into it. Thus, holes are, as it were, injected by the emitter into the electronic region of the crystal. Wandering briefly in the crystal, they manage to get under the collector wire. And when the barrier layer is momentarily enriched here with holes, it becomes electrically conductive for the high voltage current connected between the base and the collector. The impulse of this current flies through the barrier layer in the “forbidden” direction. This immediately affects the state of the external circuit of the device. An amplified signal appears there. The closer the ends of the emitter and collector wires are located on the crystal, the more significant it is.

So, we amplified a weak electrical signal using a crystal and did without a radio tube. The crystal is reliable. It is hard and durable. It will not burst or break like a glass container. (121)

Special processing of germanium crystals makes it possible to create so-called planar semiconductor triodes. In them, the crystal is divided into three relatively large areas electron and hole conductivity.

Planar triodes do not require thin lead wires, so they are even stronger and more durable. In addition, they are able to pass more significant currents through themselves and operate more steadily.

Semiconductor amplifiers are distinguished by another remarkable property - efficiency. After all, they do not need to waste energy on heating the cathode or creating a strong electric field. If the efficiency of a radio tube is a fraction of a percent, then in crystal triodes it reaches 50-60 percent.

There is a huge gain in all this. However, semiconductor devices also have disadvantages.

The thinnest inputs and layers, insignificant distances between the electrodes - all this, it would seem, should make the crystal triode exceptionally fast-acting, capable of amplifying extremely frequent electrical oscillations. In fact, just the opposite. In a solid, in a crystal, electrons are not as free as in the emptiness of a radio tube. They seem to be limited in their ability to change their movement, and therefore ultra-high frequencies of electrical oscillations, so important in modern radio engineering, are not yet available to crystalline devices.

In many countries, physicists are striving to make semiconductor devices more agile and faster. Some progress has been made along this path. Quite efficient, for example, are triodes, in which the outer surface is electronic, and the crystal itself is hole-based. Then the emitter injects electrons into the blocking layer, and they are almost twice as mobile as holes. As a result (122), the processes we talked about occur much faster. Modern crystal triodes of this type manage to amplify up to ten million electrical oscillations every second.

Even more advanced crystal amplifiers have appeared - tetrodes- with four areas of semiconductors of different conductivity. Among crystals, these are record holders for the fastest action. They excite or amplify tens, hundreds, even thousands of millions of electrical oscillations per second. More frequent oscillations remain and, obviously, will remain the domain of vacuum electronics,

There are other disadvantages to the new devices. It is not yet possible to make high-power equipment using crystals. Germanium changes its properties greatly when heated. Germanium amplifiers cannot withstand increased temperatures with difficulty. That is why recently people increasingly prefer to make crystalline devices from silicon. They are less capricious.

True, an interesting solution is possible here: to enclose tiny crystalline amplifiers in equally miniature semiconductor electric refrigerators (you read about them above - in the chapter “Chasing Heat”). Such experiments are carried out and give good results.

However, sometimes it happens that a crystal amplifier, despite all possible precautions, suddenly changes its properties for no apparent reason. Devices of the same type do not always work the same way. There is only one reason: the features of semiconductor devices have not been sufficiently studied, and the technology for their production has not been fully developed. Therefore, it is completely wrong to think that radio tubes everywhere will immediately be replaced by semiconductors.

Semiconductors also turn out to be very useful in the development of vacuum electronics. They are used to produce new highly efficient sources of electrons for radio tubes, devices that ignite a discharge in mercury (123) rectifiers, and much more. Not enmity, but friendly competition is unfolding between semiconductors and vacuum devices.

In both areas, there is a lot of research work ahead, the search for new systems, new design solutions. Vacuum electronics is enriched with remarkable inventions. At the same time, semiconductor radio devices are being improved every year. A huge army of scientists, engineers, and radio amateurs works tirelessly, paving the way for crystals with their labor.

Everything about a crystalline device is compact and simple. But this simplicity is not easy. Filigree work has been put into a miniature semiconductor amplifier.

First, the germanium blank was sawed with a diamond saw into the thinnest plates on a special machine. You can’t even take them in your hand - they are so small. Nevertheless, they were sorted and cleaned with chemical solutions. Looking through a microscope, almost invisible tendrils of wires were attached to the crystal, and the opposite ends were soldered to thicker wires. Then they coated the device with a protective varnish, enclosed it in a housing, and filled all the voids with special plastic. Some operations had to be carried out in an airless environment, and the correct assembly was constantly monitored electrical measurements. But this is far from the end of the matter. There will still be a lot of tinkering with the semiconductor amplifier before it is finally ready.

Almost all of this jewelry work is done by hand. And it’s easy to imagine what vast experience, what fine skill assemblers of semiconductor radio devices must have.

Engineers and scientists are now pushing for mechanization and (124) even automation of the production of crystal diodes and triodes.

Instead of a diamond saw, ultrasound began to be used to cut germanium and silicon. The safety razor blade, attached to the frequently vibrating rod of the ultrasonic generator, plunges into the fragile crystal like a table knife into butter. And in the usual way, processing another crystalline semiconductor is as difficult as, say, cutting a patterned star out of a tea cracker. Ultrasound saves materials here (incomparably less sawdust is obtained, no precious diamond is needed), speeds up work, and most importantly, opens up the possibility of its mechanization.

Applies also original way electrochemical processing of crystals. For some types of planar semiconductor triodes, it is necessary to obtain extremely thin (0.005 millimeter) germanium plates. You won't get them with any mechanical finishing. But a way out was still found.

Thin jets of etching solution are directed onto a crystalline germanium plate from both sides. They simultaneously play the role of wires: electric current from the battery is passed through them through the semiconductor layer. For one and a half to two minutes the crystal is corroded by this electrochemical method. Holes are formed on both sides of the germanium plate, between which a thin film of semiconductor remains.

Then the surface of the film is coated with layers of metal using the same electrochemical method.

During processing, it is necessary to constantly and extremely finely regulate the current strength in the solution jets and in the semiconductor. The adjustment is carried out with a light beam directed at the germanium plate. After all, this semiconductor significantly increases its conductivity when illuminated. The stronger the light directed at it - and the greater the electrical conductivity of the plate; consequently, both the current (125) flowing through it and the jets of the etching solution increase.

In the production of planar triodes, the phenomenon of diffusion is also used - the slow penetration of atoms of one substance into the thickness of another.

Other amazing techniques for making crystalline radio devices are also proposed.

Some scientists believe it may be possible to grow crystals with different layers. According to a number of experts, it will be possible to create entire radio-electronic systems in one tiny crystal - just as chemists have long been producing ordinary crystals from solutions. A radio receiver built in a flask or crucible by chemical means! What could be more amazing!

Unique jeweler machines for assembling crystal amplifiers also appear. Technology is moving towards making the production of semiconductor devices truly mass-produced and making them even smaller. Engineers are now seriously talking about creating a matrix with the volume of a child's cube with thousand crystal triodes. And they not only talk, but also work hard on this problem.

A big discovery never remains isolated. It puts forward new tasks and nourishes inventive thought in related fields. This is especially clearly seen in the example of the introduction of semiconductors into radio engineering.

As soon as the first samples of crystalline amplifiers were created, it became clear that the size of radio devices could be dramatically reduced. But the question immediately arose: what about the antenna? Will it really remain as long as before? Or, say, induction coils, capacitors? After all, if they are not reduced, there will be a disproportion (126) - and not only in the size of the parts, but also in their technical level. In fact, placing a bulky wire coil next to a tiny semiconductor amplifier, ideal in simplicity and perfection, is perhaps the same as lighting subway trains with candles. So the task became ripe: to transform literally all radio components, to re-equip all practical radio equipment.

And again, semiconductors came to the rescue here, primarily materials called ferrites.

Everyone has seen a horseshoe magnet. You will find it in a loudspeaker, in any electric generator, in a car magneto. Permanent magnets have a serious drawback - they are heavy. To make them lighter, metal scientists have developed special alloys. Some of them are quite valuable. But you still can’t make metal very light.

Let us note another feature of metal magnetic materials: They are excellent conductors of electricity. This property is used beneficially in a number of cases - for example, during high-frequency hardening. An alternating field accelerates electrons in the metal. There are vortices of electric currents that quickly increase the temperature. This is what is required here. But in other cases, heating is harmful.

Take, for example, the core of a transformer. It doesn't need to be heated at all. After all, this takes extra energy. In addition, eddy currents prevent the magnetic metal from quickly demagnetizing and magnetizing and slow down such processes. And modern radio devices often require very “agile” magnetic substances.

Electricians and radio engineers put a lot of work into getting rid of eddy currents. It was decided to make the cores of transformers, chokes, and coils from thin iron plates coated with insulating varnish. Such cores were made from an insulating mass interspersed with iron filings. This brought some benefit (127), but I wanted more. The ideal would be to find light magnetic substances that conduct almost no electric current.

This is exactly what ferrites turned out to be.

Ferrites have a completely everyday appearance. Gray-black inconspicuous plates, rings, rods. They are made from the most common substances widespread in nature - iron oxides and some other metals. The common ore magnetite also belongs to them.

Even in the last century, chemists knew the composition of such compounds, their internal structure, basic properties. It seemed that science had long ago taken from them everything that they could give to man.

But in reality it turned out differently. Several years ago, physicists began studying ferrites. They began to grind them into powder, mix them in different proportions, press them, burn them, and sinter them. And it turned out that if such materials are processed in a special way, they acquire various and very valuable combinations electrical properties with magnetic ones.

Among ferrites, there are materials that are magnetized with lightning speed even in a weak magnetic field and also quickly change magnetization in time with changes in the magnetic field. A wire-wrapped rod of such material can serve as an excellent antenna.

Such rods can now be seen in many new radios and televisions. The antennas are so small that they are mounted directly into the housing. For example, the Dorozhny receiver is equipped with an antenna the length of a pencil. It replaces many meters of metal wire. A magnetic ferrite antenna can even be the size of a match! (128)

Ferrite cores for coils, transformers, chokes are a wonderful gift for radio engineering. Having such a core, there is no longer any need to contrive in the fight against eddy currents, take care of the speed of magnetization reversal. It is hard to believe that a tiny spiral of electrically conductive substance applied with a brush onto a ferrite plate (in other words, drawn) will play the same role in the receiver that a bulky one usually plays. induction coil made of wire.

Of course, a spiral can not only be drawn, but also printed. It is not difficult to print both connecting conductors and details such as resistances (by the way, they can now be made the size of a dot that a sharply sharpened pencil leaves on paper). Finally, it is even possible to print capacitors, but not on ferrite, but on plates made of other substances - ferroelectrics, for example from the so-called barium titanates.

Barium titanates and other similar substances are also wonderful materials for modern radio engineering. Several years ago their valuable properties were revealed Soviet physicist Corresponding Member of the USSR Academy of Sciences B. M. Bul. Using them, it is possible to make tiny (129) capacitors - variconds - with extraordinary properties, to create miniature antennas and other devices that significantly simplify radio equipment.

The introduction of crystal diodes and triodes, ferrite parts, variconds shows that even complex radio systems - entire radio transmitters or radio receivers - can be reduced to negligible sizes. The opportunity opens up to create them entirely in a unique typographical way, similar to how postcards or postage stamps are produced.

Any radio device must be powered with energy. It takes tens of watts to operate a home receiver. They are taken from the lighting network, from batteries, and more recently from thermoelectric generators that are already familiar to us.

What if radios were the size of a postage stamp and simply sewn onto the lapel of a jacket? Will they also have to be plugged into the network or connected to heavy, bulky batteries?

No, such power supplies are not needed for a miniature semiconductor radio device. It will require tens, hundreds, even many thousands of times less energy than conventional modern radio devices. Therefore, a small battery will be enough for him, which, by the way, they have now learned to make capacious and durable.

Here is one of them - it is half the size of a match. Its weight is 5 grams, service life is more than a year. There are button-sized batteries with a two-year lifespan. There are also tiny batteries.

Perhaps even more interesting is the so-called atomic battery. Its continuous validity period is more than twenty years. (130)

The design of an atomic battery resembles a semiconductor valve photocell, only the source of energy in it is not light, but radioactive radiation. A silicon crystal, in which electron and hole regions are created by special processing, is coated with a layer of radioactive strontium, a substance that is not difficult to obtain in a nuclear boiler. When undergoing decay, strontium atoms emit so-called beta rays, that is, simply a stream of electrons.

Each of them, entering a semiconductor, releases about two hundred thousand conduction electrons in it.

Such a battery can be built into the radio receiver right at the time of its manufacture, and it will serve until the receiver becomes obsolete (you can guarantee that this will happen for sure in twenty years).

However, semiconductor radio devices sometimes do without batteries at all. Energy can be provided to them, for example, by valve photocells - light traps. Recently, a pocket “solar” radio receiver with four crystal amplifiers was built by engineers from an American company. Just keep it in the light for a while, and then it can work for five hundred hours in complete darkness. The weight of this receiver is 280 grams.

Finally, radio amateurs came up with another amazing way to power a radio device without batteries. A tiny semiconductor radio provides electricity... a person's voice is the very sound that is transmitted over the radio.

You are speaking into the microphone. There, voice sounds are converted into electrical impulses. Some of the energy from the resulting pulsating current is sent to a radio transmitter to be amplified and converted into radio waves. And the other fraction of the microphone current is smoothed out in a special device and goes to power the same (131) transmitter, and at the same time the receiver that receives response radio signals. With the help of semiconductor crystals, sound seems to transform itself into radio waves. This entire system is extremely compact: the radio station fits into the microphone housing.

Let's ask a radio engineer and semiconductor enthusiast:

What kind smallest sizes can radio devices on crystals achieve?

The engineer will shrug:

Nowadays, experts will not be surprised to read a report about a radio receiver the size of a grain of wheat!

Admiring this miracle, this amazing achievement of science, we at the same time involuntarily think about the possibilities of its practical service. And if we are talking about a receiver the size of a grain of wheat, the question arises: why such a microscopic radio device? It is only suitable for radio-fication of anthills, it looks like a trinket, like steel flea, which Leskov described in the story “Lefty”. Remember, a tiny “speck” that had to be wound with a key, and then it began to dance. If a tiny radio device is a match for Leskov’s flea, then what good is it? Absolutely none.

Of course, radio engineering based on semiconductors does not strive for the ultimate reduction in radio devices. The goal is not to set miniature records, but to fit the most advanced equipment into convenient volumes.

What is it like?

A complex radio receiver (132) the size of a cigarette case has become not such a rarity. You put it in your pocket and listen to the radio on the trolleybus on your way to work.

The transmitting and receiving radio installation on crystals can be placed in a matchbox. This is a great help, for example, in sports. A parachutist, who for the first time threw himself from an airplane into the abyss of air, talks with his experienced comrade on the ground, listens to his calm advice. The coach gives instructions to the slalom skier, swimmer, and runner via radio.

How useful are such miniature radio stations in the construction industry! The masonry foreman will be able to constantly maintain contact with the crane operator. There will be no need to strain your voice by shouting, the cries of “mine” and “vira” will become a thing of the past, and there will be no need for mouthpieces.

Next are new opportunities. Imagine the telephone of the future. This is either a small record in a jacket pocket, or, say, a specially equipped pen: on one side is a microphone, on the other is an earpiece like an acorn.

The phone will have unnecessary wires. Ultrashort radio waves will connect our apartments, factories and institutions with cars and airplanes, with by railway trains and pedestrians. A person will be able to conduct telephone conversations anywhere, at any time, with any point. This problem is being seriously discussed these days on the pages of special magazines. There is already a generally accepted term for such a connection - “universal”.

Do you think it is possible to play football with a radio transmitter?

A question from a man who has lost his mind, you say.

It turns out that this answer is too hasty.

Semiconductor radio devices are now made so strong and reliable that they can be attached to the tire of a ball without the risk of the devices being damaged by blows from football players. What's the use of this? Why do you need a radio station in the ball?

Common in America sport game golf. They hit a small hard ball with a stick - it jumps up, rolls, hits the holes, but sometimes gets lost in the grass or bushes. Players sometimes have to look for it for a long time. And so, in order to speed up the search so that the balls do not disappear, they proposed installing semiconductor radio transmitters in them. No matter how tight the ball is, the radio transmitter in it operates without ceasing. It emits a radio signal that can be picked up by a receiver with a directional antenna built into the player's stick. If (134) the ball is lost, the player puts a radio stick to his ear and easily finds the direction from which the “voice” of the missing ball is heard. Now it's very easy to find it.

True, this use of semiconductor amplifiers is more of an advertising than practical nature. For the same purpose, radio transmitters on crystals are mounted in an ordinary plumber's hammer. You can hit it with a hammer as much as you like, the device will not stop working.

There are a lot of similar radio engineering oddities and semiconductor toys being made now. They give a particularly clear idea of ​​the greatest practical value of crystal diodes and triodes. The equipment, which we are accustomed to consider delicate and fragile, acquires the strength of stone. It can be installed in a high-altitude rocket, even in an artillery shell - to study its flight. In the most hectic environment it will serve without fail.

How unshakably strong the radio equipment of airplanes, helicopters, and ships becomes with the advent of semiconductors. The sharpest blows and the strongest shaking are no longer scary!

We have given just a few examples of the remarkable service of semiconductor radio technology. Maybe they are not the most revealing.

But now it is still very difficult to foresee all the rich variety of possibilities for using semiconductors in this area. Almost every day brings news of new discoveries, new solutions.

The picture on the right shows the possible appearance of a TV assembled entirely on semiconductors. Instead of a cathode ray tube, it will use a kind of flat luminous screen with a metal mesh.

They are building sound recording devices the size of an inkwell. A TV is created without a vacuum tube, with a flat screen. It can be hung on the wall like a picture, or placed on the table like a desk calendar. Someday there will also be pocket TVs - video phones in the style of a notebook.

The piano was invented about two hundred and fifty years ago. The violin, cello, and various copper and wooden pipes were created even earlier.

Over the centuries, they have all reached the highest perfection. We can say with confidence: you cannot extract a more beautiful sound than in modern musical instruments from strings, reeds and vibrating air columns. But does this mean that it is impossible to create more beautiful sounds? Of course not. Over the past decades, enthusiasts of new music have appeared - electric. They built many instruments with wonderful, previously unknown voices. Electric vibrations there (136) are born, transformed, and amplified in radio tubes. Therefore, all electric musical instruments have the disadvantage of tube radios: they are short-lived, heavy, and bulky. For example, the single-voice instrument emiriton weighs about 90 kilograms. Too much!

Nowadays, electric music enthusiasts are eagerly taking up the development of semiconductors. The first electric organs with crystal oscillators and amplifiers have already been built. Several years will pass - and wonderful electric pipes, bells, and strings will ring in our homes, in parks, and on the streets. Composers will begin to create not only scores, but also new timbres. Light and reliable electric musical instruments will appear, accessible to everyone, and not requiring many years of study to master.

Enriched with science, musical culture will become even closer to the people.

The pinnacle of modern electronics is undoubtedly computing devices. They perform complex mathematical calculations, operate machines, translate texts from one language to another, and solve chess problems. A person gives a machine an “instruction”, and then it itself, in a few hours or even minutes, performs titanic computational work - work that would take long years the work of many hundreds of people.

Electronic computers are extremely complex and cumbersome. They occupy huge halls, sometimes entire buildings. And each has thousands of radio tubes. It is not difficult to understand what a remarkable effect the use of semiconductors gives here. Counting machines on chips require several times less space, are much lighter, incomparably more economical in energy consumption (137), and most importantly - more reliable. A three-millimeter ferrite ring, crossed by several thin wires, can replace a pair of radio tubes and several other parts in a counting machine. Ferrites of other types play the role of unique memory cells of an electronic counting device.

In the future, there will undoubtedly be desktop, and perhaps even pocket-sized, semiconductor-based computers. These will be means of truly comprehensive mechanization of not only physical, but also mental labor of a person.

One of the components of an electronic computer using vacuum tubes. On the left is the same assembly on ferrite parts.

Electronic computing technology will come to the aid of meteorologists, and we will receive astronomically accurate weather forecasts. Accountants, librarians, and dispatchers will instruct machines to compile various catalogs, information reports, schedules, and statistical reports.

Connected with traffic lights, computers will regulate street traffic.

The first experiments were made in automatic control of aircraft movements from the ground. Following commands from an electronic computer, the aircraft independently takes off, takes off, performs maneuvers, and lands in the desired (138) place. How far has this wonderful automation left behind the “sighted” car of the science fiction story!

In industry electronic devices will manage workshops and entire factories. A person will force them to issue raw materials, control and change technology, sort, and count products. And everywhere here semiconductors will provide trouble-free service.

Our time is called the beginning of the atomic age. A justified name, but incomplete. Remaking the planet for the benefit of humanity involves many great victories for science. Here are the achievements nuclear physics, and the rapid development of electronics, and the progress of semiconductor physics, and the amazing successes of chemistry. There is powerful and smart technology in energy, metallurgy, mechanical engineering, construction, and agriculture.

The study of semiconductors moves forward in unison with all the most important branches of precise knowledge and industry, relying on their many years of experience.

In turn, semiconductor physics enriches related fields of science and technology.

It turned out, for example, that semiconductor materials are excellent catalysts - accelerators of chemical processes. Corresponding member of the USSR Academy of Sciences S.Z. Roginsky noted at one scientific conference that until recently chemists were in the position of “petty bourgeois among the nobility.” Moliere's hero did not suspect that he had been speaking in prose all his life, and chemists did not know that in many chemical processes they were dealing with semiconductors, with electronic processes in semiconductors.

The instrument industry has to master one more feature (139) of semiconductors - the displacement of electric current in them under the influence of an external magnetic field. On this basis, it is possible to create unprecedentedly sensitive and accurate compasses, to build devices that are capable of detecting the movement of objects to a ten-millionth of a millimeter!

Semiconductor physics also had to encounter such an unexpected field of knowledge for this science as physiology. It turns out that electronic phenomena play a significant role here too. The Hungarian physiologist E. Ernst not so long ago noticed that a number of characteristic features neural processes find a simple explanation if we assume that some structural formations of nerves are a kind of semiconductor rectifiers. Who knows, maybe surgeons, using some as yet unknown semiconductors, will learn to make artificial nerves!

The mechanical properties of semiconductor substances have not yet been studied enough. Meanwhile, the field of such research is wide and grateful. Some semiconductors are exceptionally strong and heat-resistant—withstanding temperatures of over 4,000 degrees! Perhaps the combustion chambers of interplanetary spacecraft engines and equipment will someday be built from such materials nuclear engines.

Today's study of semiconductors has lifted before us only a corner of the veil of time that hides tomorrow. But even through this crack we saw a lot. In the city of tomorrow we encountered buildings heated by frost, in deserts - amazing traps of radiant energy. We foresaw the birth of solar energy. We saw the universal spread of new radio technology, the victorious march of miniature machines with vision and memory, and caught the sounds of unheard-of musical instruments.

These are the grains of our future. But they are not easy to get. (140) Thousands of large and small obstacles must be overcome, the theory of semiconductors - not only crystalline, but also glassy and liquid - must be further developed, and better ways of purifying and processing them must be found.

Hero of Socialist Labor, Academician A.F. Ioffe, the oldest Soviet scientist who devoted more than a quarter of a century to work in the field of semiconductor physics, says: “We are entering a new era of technical progress. We have enough strength and capabilities, both moral and material, to solve problems of any scale in the coming years, in the coming decades.”

Scientists and engineers of the Soviet country are confidently looking forward. People of bold dreams, clear minds, tireless enthusiasts of science, they are today preparing what will become the property of the people tomorrow, which will be included in the countless centuries of communism to come.

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

Characteristics of semiconductors

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

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

Semiconductors are found among chemical compounds with a variety of crystal structures. These can be elements such as silicon and selenium, or binary compounds such as gallium arsenide. Many polyacetylene (CH) n, - semiconductor materials. Some semiconductors exhibit magnetic (Cd 1-x Mn x Te) or ferroelectric properties (SbSI). Others, with sufficient doping, become superconductors (GeTe and SrTiO 3). Many of the recently discovered high-temperature superconductors have non-metallic semiconducting phases. For example, La 2 CuO 4 is a semiconductor, but upon formation of an alloy with Sr it becomes a superconductor (La 1-x Sr x) 2 CuO 4.

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

Energy gap

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

The location and filling of the levels determines the electrical conductivity properties of the substance. Based on this criterion, substances are divided into conductors, insulators and semiconductors. The band gap of a semiconductor varies between 0.01-3 eV, and the energy gap of the dielectric exceeds 3 eV. Metals do not have energy gaps due to the overlap of levels.

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

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

To initiate electrical conductivity, an electron at the valence level must be given energy that would be sufficient to overcome the energy gap. Only by absorbing an amount of energy no less than the size of the energy gap will the electron move from the valence level to the conduction level.

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

Impurity and intrinsic conductivity of semiconductors

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

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

Impurities that easily give up electrons are called donor impurities. Donor impurities can be chemical elements with atoms whose valence levels contain more electrons than the atoms of the base substance. For example, phosphorus and bismuth are donor impurities of silicon.

The energy required for an electron to jump into the conduction region is called activation energy. Impurity semiconductors need much less of it than the main substance. With slight heating or illumination, mainly the electrons of the atoms of impurity semiconductors are released. A hole takes the place of the electron that leaves the atom. But the recombination of electrons into holes practically does not occur. The hole conductivity of the donor is negligible. This happens because the small number of impurity atoms prevents free electrons from frequently approaching the hole and occupying it. Electrons are located near holes, but are not able to fill them due to insufficient energy level.

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

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

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

Single element semiconductors

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

Si and Ge are the same as diamond and α-tin. In it, each atom is surrounded by 4 nearest atoms, which form a tetrahedron. This coordination is called quadruple coordination. Tetradrical bonded crystals have become fundamental to the electronics industry and play a key role in modern technology. Some elements of group V and VI of the periodic table are also semiconductors. Examples of this type of semiconductor are phosphorus (P), sulfur (S), selenium (Se) and tellurium (Te). In these semiconductors, atoms can have threefold (P), twofold (S, Se, Te) or fourfold coordination. As a result, similar elements can exist in several different crystal structures and can also be produced in the form of glass. For example, Se has been grown in monoclinic and trigonal crystal structures or as glass (which can also be considered a polymer).

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

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

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

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

Two-element connections

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

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

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

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

ZnS, zinc sulfide - zinc salt hydrogen sulfide acid with a bandgap range of 3.54 and 3.91 eV, it is used in lasers and as a phosphor.

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

Oxides

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

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

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

Layered crystals

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

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

Organic semiconductors

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

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

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

Nanotubes are graphite plates rolled into a tube, several nanometers in diameter. These forms of carbon have great promise in nanoelectronics. Depending on the adhesion, they may exhibit metallic or semiconductor qualities.

Magnetic semiconductors

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

The strong magneto-optical effects of magnetic semiconductors allow them to be used for optical modulation. Perovskites like Mn 0.7 Ca 0.3 O 3 have properties superior to the metal-semiconductor transition, the direct dependence of which on the magnetic field results in the phenomenon of giant magnetoresistance. Used in radio engineering, optical instruments, which are controlled by a magnetic field, in the waveguides of microwave devices.

Semiconductor ferroelectrics

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

Variety of semiconductor materials

Apart from the semiconductor substances mentioned above, there are many others that do not fall under any of the listed types. Compounds of elements with the formula 1-3-5 2 (AgGaS 2) and 2-4-5 2 (ZnSiP 2) form crystals in the structure of chalcopyrite. The bonds of the compounds are tetrahedral, similar to semiconductors of groups 3-5 and 2-6 with a zinc blende crystal structure. The compounds that form the elements of semiconductors of groups 5 and 6 (like As 2 Se 3) are semiconductor in the form of a crystal or glass. Bismuth and antimony chalcogenides are used in semiconductor thermoelectric generators. The properties of this type of semiconductor are extremely interesting, but they have not gained popularity due to their limited applications. However, the fact that they exist confirms the presence of still unexplored areas of semiconductor physics.

Let's prepare a semiconductor. You have already succeeded once - when you turned an aluminum spoon into a current rectifier. Now the experience is no less interesting, and with theoretical explanations. It’s better to do it in a chemistry club or in a school laboratory, and not because the experiment is dangerous: you just most likely don’t have the required substances at home.

First - preliminary experience. Prepare a solution of lead nitrate or acetate and pass hydrogen sulfide through it (work under draft!). Dry the precipitated lead sulfide PbS and check how it conducts electricity. It turns out that this is the most common insulator. So what do semiconductors have to do with it?

Let’s not rush to conclusions, but let’s carry out the following, basic experiment. For it you will have to prepare equal quantities, say 15 ml each, of a 3% solution of thiocarbamide NH 2 C(S)NH 2 and a 6% solution of lead acetate. Pour both solutions into a small glass. Using tweezers, introduce a glass plate into the solution and hold it vertically (or secure it in this position). Wearing rubber gloves, pour a concentrated lye solution into the glass almost to the top (carefully!) and stir very carefully with a glass rod, trying not to touch the plate with it. Heat the solution slightly until steam appears; Continue stirring. After about ten minutes, carefully remove the glass plate, wash it under running water and dry it.

And in this case, you got lead sulfide - so what's the difference?

In the second experiment, the reaction proceeds slowly, and the precipitate does not form immediately. If you observed the solution, you noticed that at first it became cloudy and became almost like milk, and only then darkened - these intermediate compounds, decomposing, formed black lead sulfide. And it settles on the glass in the form of a thin black film, which consists of very small crystals that are visible only under a microscope. Therefore, the film appears very smooth, almost mirror-like.

Attach two electrical contacts to the film and pass current. If lead sulfide behaved like a dielectric in the previous experiment, now it conducts current! Connect an ammeter to the circuit, measure the current and calculate the resistance: it will be higher than that of metals, but not so large as to serve as an obstacle to the passage of current.

Bring the lit lamp very close to the plate and turn on the current again. You will immediately find that the resistance of lead sulfide has dropped sharply. Black film will behave in approximately the same way if it is simply heated. But if the conductivity increases with light and heating, then we are dealing with a semiconductor!

Why does lead sulfide have this property? We wrote down its formula as PbS, but the true composition of the crystals of this substance does not quite correspond to it. Some compounds, including lead sulfide, do not obey the law of constant composition. And they are all semiconductors. (The same, by the way, also applies to aluminum oxide, which rectified alternating current.)

In a PbS crystal, the order of arrangement of particles should, it would seem, be strictly repeated. But often, due to the fact that the concentrations of the solutions from which the crystals are obtained fluctuate, the order is disrupted. The influence of temperature and other external causes is felt. However, in a real crystal the ratio of sulfur and lead atoms is not exactly 1:1. Deviations from this ratio are very small, only about 0.0005. But this is enough for the properties to change significantly.

Lead and sulfur atoms are connected in a crystal by two electrons: lead donates them to sulfur. Well, when does the 1:1 ratio break down? If there is no sulfur atom next to the lead atom, the electrons will be free - they will serve as current carriers. And such cases are not as few as it might seem. Of course, the ratio of 1.0005:1 is almost equal to unity, but if you remember how many atoms there are in a crystal, then this minor difference will no longer seem so trivial to you.

The composition of lead sulfide can be adjusted. This is necessary in order to change its conductivity. When there are more sulfur atoms in the crystal, the conductivity decreases, and when there are fewer of them, more free electrons are formed and the conductivity increases. In short, by changing the ratio of sulfur and lead atoms, you can obtain the required conductivity. This experiment is not easy to carry out; If you do not dare to conduct an experiment, take my word for it that it will work.

Take a quartz tube and place a boat of lead sulfide in it. On the other side, insert the same boat with lead into the tube and heat the tube very much so that the lead begins to evaporate. In this case, the sulfide will absorb vapors, it will be enriched in lead, and its electrical conductivity will increase significantly.

It remains only to answer the question why lead sulfide is so sensitive to light. Light quanta impart energy to electrons, and in each specific case, rays with a certain wavelength are most effective. For lead sulfide, this is infrared thermal radiation. That's why we advised you to bring the lamp closer to the film.

By the way, infrared radiation receivers usually use an excellent semiconductor - lead sulfide.

O. Holguin. "Experiments without explosions"
M., "Chemistry", 1986

The crystalline structure is understood as a solid phase of a substance, the arrangement of atoms and molecules of which exhibits a certain pattern, at least in microscopic areas. In this case, the atoms form a crystal lattice, and a certain combination of atoms or unit cells is repeated in any direction. A semiconductor crystal is formed as a result of the grouping of a large number of atoms at certain sites in a crystal lattice, which can be considered large molecule. Properties crystal lattice determine all the properties of semiconductors.

Monocrystal- a single crystal, it is grown artificially from melts and solutions.

Polycrystal- a solid body consisting of many crystals (grains), the crystal lattices of neighboring grains are usually misoriented at angles measured in degrees and tens of degrees. Most of the properties of semiconductors are associated with the ability to change their electrical conductivity under the influence of various factors. The conductivity of semiconductors can be controlled by controlling the introduction small quantity impurity atoms.

Factors that influence the electrical properties of conductors are the effects of heat treatment in an atmosphere of various gases, the structure of the material, as well as the state of the surface of the semiconductor, changes in its properties under the influence of electric and magnetic fields. Germany and Silicon are characterized by diamond-type lattices. The elementary crystal lattice of the diamond type has cubic symmetry, so a rectangular coordinate system (x y z) can be chosen as a basis. In IC manufacturing technology, Miller indices are usually used, which determine the position of crystal planes or crystallographic directions perpendicular to the corresponding planes. For cubic crystals, the Miller indices are 3 digits related to rectangular system coordinates As you can see, the number “1” means that the plane under consideration passes through the point corresponding to the axis with coordinate = “1”. The number "0" means that the crystallographic plane is parallel to the axis. Accordingly, the crystallographic plane (1 0 0) passes through the point x=1 and is parallel to the y and z axes. Maintaining the Miller coefficient is necessary for assessment important property crystal lattice, namely anisotropy, that is, the need for mechanical and electrical properties in different directions.

Basic definitions of technical processes:

Epitaxy- the process of deposition of atomic silicon onto monocrystalline silicon wafers, in which a film is obtained that is a continuation of the structure. Epitaxy makes it possible to create a single-crystal semiconductor film with a given crystallographic orientation of the surface density.

To create layers in a semiconductor with different types conductivity and p-n junctions use 2 methods of introducing impurities - thermal diffusion and ion implantation (doping).

Diffusion- this is the directed movement of atoms that occurs under the influence of a concentration or temperature gradient.

Ion implantation- a method of doping a wafer or epitaxial layer by bombarding it with impurity ions, accelerated to an energy sufficient for their penetration into depth solid.

Thermal oxidation of dielectric- obtaining a SiO2 film performs several important functions:

protection (like a dielectric)

Mask function (through which the necessary impurities are introduced)

Lithography- the process of creating a protective mask necessary for local processing during the formation of the IC structure. The mask contains a set of pre-designed openings - windows.

Etching- a non-mechanical method of changing the surface topography of a solid body. When etching, solutions are used for general and local removal of the surface layer of a solid to a certain depth.

Preparation process: single-crystalline silicon ingots are obtained by zone melting and by crystallization from the melt using the Czochralski method.

In the method, rods with a seed in the form of monocrystalline silicon, after contact with the semiconductor melt, are slowly raised with simultaneous rotation. In this case, following the seed, a growing and solidifying ingot is pulled out. The crystallographic orientation of the ingot (cross section) determines the crystallographic orientation of the seed. The typical diameter of the ingot is 10-15 cm, the length of the ingot is up to a meter. Silicon ingots are cut into many thin wafers - 400-500 microns, on which ICs and devices are then manufactured.

Zone melting- in the presentation of an ingot of polycrystalline silicon and heating at the end of the zone. The molten zone moves and converts polycrystalline silicon into monocrystalline silicon. At the same time, a cleaning process also occurs.