The difference between semiconductors and metals. Electrical materials: semiconductors, dielectrics, conductors, superconductors

Solid bodies are metals, semiconductors and dielectrics. They differ from each other in their electronic properties. The electrical conductivity of solid bodies is determined by the properties of electrons.

What is semiconductors and metals

Semiconductors refer to metals to solid bodies. Their number belongs to Germany, silicon, arsenic, etc., as well as various alloys and chemical compounds.
Metals These are solid bodies that have a certain structure.

Comparison of semiconductors and metals

What is the difference between semiconductors and metals?
Semiconductors differ from metals with a mechanism electric current.
Consider how electric current occurs in semiconductors.
In atoms, Germany on the outer shell contains four slightly related valence electrons. IN crystal lattice Near each atom there are four more. Atoms in a semiconductor crystal are bound by valence electron vapors. Each valence electron belongs to two atoms. If the temperature is raised, some part of the valence electrons will receive energy, which is sufficient to break the covalent bonds. The crystal will appear free electrons called conduction electrons. At the same time, vacancies, holes are formed on the site of the departed electrons. A vacant place can take the valence electrons of the neighboring pair, then the hole will be in a new place in the crystal. At a certain temperature in a semiconductor, there is a certain amount of electron-hole pairs. Free electron, meeting with a hole, restores electronic communication. The holes are similar to positively charged particles. If a electric field No, the holes and electrons of the conductivity are chaotic. If the semiconductor is placed in an electric field, then the holes and free electrons will begin to move ordered. Therefore, the current in the semiconductor consists of electronic and hole currents. The number of carriers of free charge changes, does not remain constant and depends on temperature. With its increase, the resistance of semiconductors increases.
Metals have a crystal structure. They consist of molecules and atoms that occupy a certain, ordered position. The metal is presented in the form of a crystal lattice, in the nodes of which are atoms, or ions, or molecules that oscillate near their location. Between them in space there are free electrons that are chaotic moving in different directions. But when the electric field appears, they begin to move ordered in the direction of the positive pole, an electric current appears in metals. The number of electrons is constant. When the temperature decreases, the speed of the electron movement slows down, the metal resistance drops.

Imgist determined that the difference between the semiconductors from metals is as follows:

Semiconductors differ from metals with electric current mechanism.
Electric current in metals is the directional movement of electrons.
In pure semiconductors, the electron-hole mechanism of conductivity.
The resistivity of semiconductors and metals depends on the temperature in different ways.

Metal	Biological circulation on land	Metal mass, 1 0 6 t / year
River Stock	Transfer - with dust from continents to the water area	Transfer from a water area to land with atmospheric precipitation	Biological cycle of photosynthesis of the ocean
soluble form	Fixed on suspension
FE.	34,0	27,4	963,0	65,0	0,132	47,3
Mn.	35,0	0,41	20,5	4,0	0,176	0,99
Zn.	5,2	0,82	5,86	0,90	0,240	4,40
Cu	1,3	0,28	1,51	0,11	0,141	0,77
Ni.	0,34	0,12	1,58	0,18	0,057	0,33
SG	0,31	0,041	2,46	0,19	-	0,16
V.	0,26	0,040	2,30	0,25	-	0,33
RB.	0,21	0,041	2,87	0,040	0,44	0,011
SO	0,086	0,011	1,51	0,038	-	0,110
MO	0,085	0,037	0,057	0,004	-	0,220
CD	0,008	0,009	0,013	0,0006	-	0,055
Hg.	0,002	0,003	-	0,0008	-	0,017

Na large quantity Metals migrates in the system of a large biological cycle, which is due to the photosynthesis of the vegetation of sushi and destruction of the dieting organic Invertebrate and microorganisms of the pedosphere. Significant masses of metals are taken out in the river suspension, but this material almost completely goes into precipitation upon admission freshwater In the World Ocean.

The involvement of heavy metals in the biological circulation on land is accompanied by selective differentiation of their masses. The proportionality between the amount of metals in the earth's crust and the relative intensity of their absorption of vegetation is absent. The coefficient of biological absorption To 6.the vegetation of sushi for most metals is from 1 to 9, for zinc, molybdenum and silver - more than 9, for iron, vanadium and chromium - less than 1. As a result of selective absorption of metals in biomass of vegetation, the ratios of metals existing in the earth's crust are noticeably changed. The ratio of iron with other metals is particularly reduced. Biological cycle and differentiation of metals carried out by photosynthesis of the ocean have their own characteristics. Metal masses, passing throughout the year through biological circulation on land and in the ocean, are commensurate, but their ratio is not the same. The vegetation of the world sushi captures more manganese and lead, photosynthesizing ocean organisms - more molybdenum and cobalt.

From sushi to the ocean with a river flow, large masses of water-soluble and fixed in the suspended forms of metals are made. Water migration coefficient values To B.metals indicate that soluble silver forms, mercury, zinc are most actively involved in water migration. (K\u003e10), as well as molybdenum, cadmium and copper, To B.from 2 to 9. Fixed in suspensions of iron, manganese, chromium, vanadium, lead, cobalt are taken out in the amount of 97-98% of the total mass of the metals endured with the river flow. In addition, the ocean is carried out by the wind significant masses of metals fixed on dust particles.

In turn, water-soluble forms of metals are transferred from the water area by air masses. This process is not sufficiently studied, and there are no data on the transfer of mass of individual metals. Nevertheless, it is obvious that the migration flow of mass of heavy metals from the ocean to the land is significantly less than in the opposite direction. For this reason, the annual cycles of metals in the dry system - the ocean is strongly unclipped. Significant masses of metals accumulate in the water of the seas and oceans and go into precipitation. Repeated involvement of metals from sedimentary thickness in mass transfer cycles is due to tectonic cycles. At the same time, mobilization of metals from sedimentary rocks is often more difficult than from depth crystalline rocks.

From the surface of the ocean, gaseous organic compounds of metals are released into the atmosphere. As noted in ch. 3, higher plants Select volatile organic compounds (terpenes, isopranes) containing metals. More large masses of metals are released into the air in the composition of gaseous metabolites of bacteria. Especially important role Play metals biometylization processes. The wind in the troposphere is captured by small soil particles, also containing metals. All listed forms of metals are part of aerosols and washed away by atmospheric precipitation.

In the mass transfer system in the Pedosphere biosphere, the role of a global regulator of the mass of heavy metals is played. In the process of transformation of the organic matter, the metals received in the soil are included in the composition of lightweight complex compounds and are at the same time firmly fixed in the sustainable components of soil humus. Mercury is most firmly fixed, which forms very stable complexes with functional groups of humus acids. Lead is firmly associated, less firmly copper, weaker - zinc and cadmium.

The close conjugation of migration cycles of heavy metals, as well as the regulating role of the pedosphere provide high resistance of the biosphere with respect to the flow of additional masses of natural or technogenic origin.

Literature:

1. Basics of Biogeochemistry - V.V. Dobrovolsky, 2003.

Than semiconductors differ from metals

What is semiconductors and metals
Semiconductors belong to metals, to solid bodies. Their number belongs to Germany, silicon, arsenic, etc., as well as various alloys and chemical compounds.

Metals are solid bodies that have a certain structure.

Comparison of semiconductors and metals
What is the difference between semiconductors and metals?

Consider how electric current occurs in semiconductors.

In atoms, Germany on the outer shell contains four slightly related valence electrons. In the crystal lattice near each atom there are four more. Atoms in a semiconductor crystal are bound by valence electron vapors. Each valence electron belongs to two atoms. If the temperature is raised, some part of the valence electrons will receive energy, which is sufficient to break the covalent bonds. The crystal will appear free electrons called conduction electrons. At the same time, vacancies, holes are formed on the site of the departed electrons. A vacant place can take the valence electrons of the neighboring pair, then the hole will be in a new place in the crystal. At a certain temperature in a semiconductor, there is a certain amount of electron-hole pairs. Free electron, meeting with a hole, restores electronic communications. The holes are similar to positively charged particles. If there is no electrical field, the holes and electrons of the conductivity are chaotic. If the semiconductor is placed in an electric field, then the holes and free electrons will begin to move ordered. Therefore, the current in the semiconductor consists of electronic and hole currents. The number of carriers of free charge changes, does not remain constant and depends on temperature. With its increase, the resistance of semiconductors increases.

Metals have a crystal structure. They consist of molecules and atoms that occupy a certain, ordered position. The metal is presented in the form of a crystal lattice, in the nodes of which are atoms, or ions, or molecules that oscillate near their location. Between them in space there are free electrons that are chaotic moving in different directions. But when the electric field appears, they begin to move ordered in the direction of the positive pole, an electric current appears in metals. The number of electrons is constant. When the temperature decreases, the speed of the electron movement slows down, the metal resistance drops.

Thedifference.ru determined that the difference between semiconductors from metals is as follows:
Semiconductors differ from metals with electric current mechanism.
Electric current in metals is the directional movement of electrons.
In pure semiconductors, the electron-hole mechanism of conductivity.
The resistivity of semiconductors and metals depends on the temperature in different ways.

What is the difference between the dielectric and the conductor? In conductors, in contrast to dielectrics, high concentration of free electrical charges. In metals are free electrons that are capable of moving throughout the volume of the substance. The occurrence of free electrons is due to the fact that valence electrons in metals atoms are very poorly interacting with the nuclei and easily lose touch with them.

Dielectrics, on the contrary, electrons with atoms are firmly connected and are not able to move freely under the influence of the electric field. And since the number of free charged carriers in dielectrics is negligible, it follows from this that there is no electrostatic induction in them, and the tension of the electric field inside dielectrics does not turn into zero, but only decreases.

Strength can not be raised endless, because at a certain amount, all charges can shift so much that the structure of the material structure occurs, in other words, a dielectric breakdown will occur. In this case, he will lose its insulation properties.

Thedifference.ru determined that the difference between the dielectric from the conductor lies in the following:
In the conductor, free electrons that are affected by the electric field forces are moved throughout the volume.
Unlike the conductor, there are no free charges in the dielectric (insulator). Insulators consist of neutral molecules or atoms. The charges in a neutral atom with each other are strongly connected and cannot move under the influence of the electric field through the entire volume of the dielectric.

According to the structure of P. m. They are divided into crystalline, amorphous, liquid. A number of organic. Substances also exhibit semiconductor properties and makes up an extensive group of organic semiconductors. Naib. Relationships have inorganic. Crystalleg. P. m., Khhim. The composition is divided into elementary, double, triple and quadier chemical. Connections, solutions and alloys. Semiconductor compounds are classified by group numbers. Table. Elements, to-ryy belong to the elements included in their composition.

The main groups of crystalline semiconductor materials (see Table 1):

1. Elementary P. M.: GE, SI, C (Diamond ) , IN, SN, those SE and others. The most important representatives of this group are GE and SI - OSN. Materials semiconductor electronics. Possessing 4 valence electrons, GE and Si atoms form crystalleg. A diamond type grid, where each atom has 4 nearest neighbor, with each of the to-rye connected covalent, Communication (Coordination of neighbors - tetrahedral). They form a continuous series of solid solutions among themselves, which are also important P. m.

2. Type connections are in the OSN. Crystalleg. Safellerite type structure. Communication of atoms in crystalline. The grille is wearing. Covalent character with some fraction (5-15%) ion component (see. Chemical relationship). The most important representatives of this group: GaAs, InP, Inas, Insb, Gap. MN. P. M.

form a continuous series of solid solutions of triple Ps more complex (n, d.), which are also important P.M. (see HeteroWork, heterostrth tours).

3. Compounds of elements VI g R y and -p s (o, S, SE, those) with elements I - V groups, as well as with transitional and rare earth metals. Among these P. m. Naib, interest is of type connections. They have crystalleg. The structure of the type of sphalerite or wurcite, less commonly - type NaCl. The relationship between atoms is covalently and sochy character (the fraction of the ion component of about 45-60%). For P. M. Type of characteristicsPolymorphism and the presence of politicizes of cubic and hexagonal modifications. The most important representatives: CDTE, CDS, ZNTE, ZNSE, ZNO, ZNS. MN. P. M. Type form a continuous series of solid solutions among them; The most important of them:

Phys. Properties to meaning are determined by the concentration of their own point defects of the structure exhibiting the electric. Activity (scattering and recombination centers).

Type compounds have crystal. NaCl type structure or orthorhombic. The connection between atoms is covalently ion. Typical representatives: PBS, PBTE, SNTE. They form a continuous series of solid solutions among themselves, among them are Naib, important their own. Point defects in structure in have low ionization energy and manifest electrical. activity.

Type compounds have crystal. Soflerite type structure with unfilled cationic nodes. In terms of its properties occupy an intermediate position between and. They are characterized by low lattice thermal conductivity and mobility of carriers charge . Typical representatives:

In semiconductors, when a change in temperature changes not only

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

an unpremutable semiconductor, then some atoms are ionized, as a result

there are free electrons and holes in the same quantity. Addiction

the concentrations of electrons and holes are determined by the formula:

Hole [edit | edit source text]

Main article: Hole

During the discontinuation of communication between the electron and the core, a free place appears in the electron shell of the atom. This causes an electron transition from another atom to an atom with a free place. The atom, from where the electron passed, includes another electron from another atom, etc. This process is caused by covalent bonds of atoms. Thus, a positive charge is moving without moving the atom itself. This conditional positive charge is called a hole.

Usually the mobility of holes in the semiconductor is below the mobility of electrons.

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

The process of forming a pair "Electric conductivity - Conductivity hole" is called the generation of charge carriers (1 to 16.6). It can be said that the own electrical conductivity of the semiconductor is the electrical conductivity caused by the generation of the conduction pairs of the conduction hole. The formed electron-hole pairs may disappear if the hole is filled with an electron: the electron will become non-free and loses the possibility of moving, and an excessive positive charge of an atom ion will be neutralized. At the same time, the hole and an electron disappear. The process of reunification of an electron and a hole is called recombination (2 to 16.6). Recombination in accordance with the zone theory can be viewed as the transition of electrons from the conduction zone on free space in the valence zone. Note that the transition of electrons with a higher energy level To the lower is accompanied by the release of energy, which is either emitted in the form of quanta light (photons), or is transmitted to the crystal lattice in the form of thermal oscillations (phonons).

The impurity conductivity of semiconductors is an electrical conductivity due to the presence in the semiconductor donated with acceptor impurities.

The impurity conductivity, as a rule, is much higher than its own, and therefore the electrical properties of semiconductors are determined by the type and quantity of allocating impurities entered into it.

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

The impurity conductivity of semiconductors is the conduction due to the presence of impurities in the semiconductor.

Impurity centers can be:

1. Atoms or ions chemical elementsembedded in the semiconductor lattice;

2. Excess atoms or ions embedded in lattice interstices;

3. Different kinds of other defects and distortion in the crystal lattice: empty knots, cracks, shifts arising during crystal deformations, etc.

By changing the concentration of impurities, it is possible to significantly increase the number of carriers of charges of a sign of a sign and create semiconductors with a predominant concentration or negative, or positively charged carriers.

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

Consider the mechanism of electrical conductivity of the semiconductor with a donor five-meant admixture of arsenic AS 5+.which is injected into the crystal, for example, silicon. A five-flowered arsenic atom gives four valence electrons to the formation of covalent bonds, and the fifth electron turns out to be unoccupied in these connections.

The separation energy (ionization energy) of the fifth valence electron of arsenic in silicon is 0.05 eV \u003d 0.08 · 10 -19 J, which is 20 times less than the energy of the electron separation from the silicon atom. Therefore, at room temperature, almost all arsenic atoms lose one of their electrons and become positive ions. Positive arsenic ions cannot capture electrons of neighboring atoms, since all four connections are already equipped with electrons. In this case, the movement of the electronic vacancy - "holes" does not occur and the hole conductivity is very small, i.e. Practically absent. A small part of its own semiconductor atoms is ionized, and part of the current is formed by holes, i.e. Donor impurities are impurities supplying conduction electrons without an equal number of rolling holes. As a result, we obtain a semiconductor with predominantly electronic conductivity, called the N-type semiconductor.

In the case of acceptor impurities, for example, trivalent india In 3+. An impurity atom can give its three electrons to implement covalent Communication Only with three neighboring silicon atoms, and one electron "lacks". One of the electrons of neighboring silicon atoms can fill this relationship, then the inlet in will become a fixed negative ion, and a hole formed from one of the silicon atoms of silicon atoms is formed. Acceptor impurities, capturing electrons and thus creating moving holes, do not increase the number of conductivity electrons. The main charge carriers in a semiconductor with an acceptor admixture are holes, and non-core - electrons.

Semiconductors - a wide class of substances characterized by the values \u200b\u200bof the electrical conductivity lying in the range between the specific electrical conductivity of metals and good dielectrics, that is, these substances cannot be attributed to dielectrics (since they are not good isol-torches) and to metals (are not good electrical current conductors). To semiconductors, for example, include substances such as germanium, silicon, selenium, tellurium, as well as some oxides, sulphides and metal alloys.

Properties:

1) with an increase in temperature, the specific resistance of semiconductors decreases, in contrast to metals, in which the resistivity with increasing temperature increases. Moreover, as a rule, in a wide range of temperatures, this is exponentially exponentially. The resistivity of semiconductor crystals can also decrease when exposed to light or strong electronic fields.

2) The property of one-sided conductivity of the contact of two semiconductors. It is this property that is used in creating a variety of semiconductors-channel instruments: diodes, transistors, thyristors, etc.

3) Contacts of various semiconductors under certain conditions during dime or heating are sources of photo - e. d. s. Or, accordingly, thermo - e. d. s.

Semiconductors differ from other solid classes by many specific features, the most important of which are:

1) the positive temperature coefficient of electrical conductivity, that is, with an increase in temperature, the electrical conductivity of semiconductors is growing;

2) the specific conductivity of semiconductors is less than that of metals, but more than the insulators;

3) large values thermoelectribution force compared with metals;

4) high sensitivity of semiconductor properties to ionizing radiation;

5) ability to sharp change physical properties under the influence of insignificantly small concentrations of impurities;

6) The effect of rectifying current or neomic behavior on contacts.

3. Physical processes in the P-N - transition.

The main element of most semiconductor devices is an electronic-hole transition ( p-N.-The act), which is a transition layer between the two semiconductor regions, one of which has electronic electrical conductivity, and the other - hole.

Education p-N. Transition. P-N. equilibrium

Consider a Read more Education Process p-N. Transition. The equilibrium is called such a state of transition when there is no external voltage. Recall that in r-domain with two types of majority carriers: the fixed negatively charged ions acceptor impurity atoms and free positively charged holes; A B. n.The region also has two types of key charge carriers: fixed positively charged ions of acceptor impurity atoms and free negatively charged electrons.

To contact p. and n. Regions Electrons holes and ions impurities are distributed evenly. When contacting on the border p. and n. Regions arise a gradient of the concentration of free charge carriers and diffusion. Under the action of diffusion electrons from n.- Registration goes in p. And recombining there with holes. Holes out r- Registration transition B. n.- Regard and recombine there with electrons. As a result of such a movement of free chargers of charge in the border region, their concentration decreases to almost zero and at the same time in r The region is formed by a negative spatial charge of the ions of the acceptor impurity, and in n.- The positive spatial charge of the ions of the donor impurity. Contact potential difference arises between these charges φ K. and electric field E K. which prevents diffusion of free charge carriers from depth r- and n-regions through p-N-transition. Thus, the area combined with free charge carriers with its electric field and is called p-N-transition.

P-N.- The transformation is characterized by two basic parameters:

1. The height of the potential barrier. It is equal to the contact difference potential φ K. . This is the difference in potentials in the transition due to a gradient of the concentration of charge carriers. This is the energy that the free charge must be posted to overcome the potential barrier:

where k. - Permanent Boltzmann; e. - electron charge; T. - temperature; N a. and N D. - concentrations of acceptors and donors in hole and electronic regions, respectively; r R. and p N. - Concentration of holes in r- and n-regions, respectively; n i - Own concentration of charge carriers in an unlicited semiconductor,  T \u003d CT / E - Temperature potential. At a temperature T.\u003d 27 0 s  T.\u003d 0.025V, for Germany Transition  K.\u003d 0.6V, for a silicon transition  K.\u003d 0.8V.

2. Width P-N-Transition (Fig. 1) is a cross-border area danced by charge carriers, which is located in p. and n. regions: l P-N \u003d L P + L N:

Hence

where ε - relative dielectric permeability of the material of the semiconductor; ε 0 - dielectric constant of free space.

The thickness of the electron-hole transitions has an order (0.1-10) μm. If, then p-N.-thod is called symmetrical if, then p-N.- The transfer is called asymmetric, and it is mainly located in the field of semiconductor with a smaller concentration of impurities.

In equilibrium condition (without external voltage) through p-N. The transition moves two oncoming charge streams (two currents flow). This drift current of non-core charge carriers and diffusion current, which is associated with the main charge carriers. Since the external pressure is absent, and there is no current in the external circuit, then the drift current and the diffusion current are mutually balanced and the resulting current equal to zero.

I DR + I DIF \u003d 0.

This ratio is called the condition of dynamic equilibrium diffusion and drift processes in an isolated (equilibrium) p-N.-There.

The surface on which is in contact p. and n. Oblast is called the metallurgical border. Really, it has a finite thickness - Δ M. . If a Δ M.<< l p-n T. p-N.-Translate is called sharp. If Δ m \u003e\u003e l P-N T. p-N.-There is called smooth.

P-N. transition with external voltage applied to it

The external voltage disrupts the dynamic equilibrium of currents in p-N.-There. P-N.- The transformation goes into a nonequilibrium state. Depending on the polarity of the voltage applied to the regions in p-N.-The order is possible two modes of operation.

1) Direct displacementp-N. transition. P-N-the transition is considered shifted in the forward direction if the positive pole of the power supply is connected to r- Registration, and negative to n.- Registration (Fig.1.2)

With direct displacement, voltage  K and U are directed on the resulting voltage to p-N.- larch decreases to magnitude  K. - U. . This leads to the fact that the electric field strength decreases and the diffusion process of the main charge carriers is resumed. In addition, the direct displacement reduces the width p-N. transition, because l P-N ≈( K - U) 1/2. Diffusion current, current of the main charge carriers, becomes much more drift. Through p-N.-The line proceeds direct current

I P-N \u003d I PR \u003d I DIF + I DR i dyph. .

When direct current leaks, the main charge carriers of the R-region are moving to the N-region, where it becomes non-core. The diffusion process of introducing the main charge carriers to the area where they become non-core, called injection, and direct current - diffusion current or injection current. To compensate for the minority carriers accumulated in the p and n-regions in the external circuit arises electron current from the voltage source, i.e., The principle of electrophetralism is preserved.

With increasing U. The current increases sharply, - temperature potential, and can reach large quantities. Located with the main carriers of which the concentration is large.

2) Reverse displacementoccurs when to r- Registry is made minus, and to n.- Registration plus, external voltage source (Fig. 1.3).

Such an external tension U.included according to  K. . It: increases the height of the potential barrier to magnitude  K. + U. ; The electric field strength increases; width p-N. transition increases, because l p-n ≈ ( to + U) 1/2. ; The diffusion process is completely stopped and through p-N. The transition flows the drift current, current of non-core charge carriers. Such current p-N.- Transfers are called back, and since it is associated with non-core charge carriers, which arise due to thermogeneration, then it is called thermal current and denote - I 0. .

I P-N \u003d I arr \u003d I DIF + I DR i et \u003d i 0.

This current is small in size. Located with non-core charge carriers, the concentration of which is small. In this way, p-N. The transition has one-sided conductivity.

With reverse displacement, the concentration of non-core charge carriers on the transition boundary is somewhat decreased compared to the equilibrium. This leads to diffusion of non-minor charge carriers from depth p. and n.-Belands to the border p-N. Transition. Having achieved its non-core carriers fall into a strong electric field and transferred through p-N. The transition where the main charge carriers are becoming the main charge carriers. Diffusion of non-core charge carriers to the border p-N. transition and drift through it to the area where they become the main charge carriers are called extraction. Extraction and creates a reverse current p-N. Transition is a current of non-core charge carriers.

The countdown value is highly dependent: on temperature ambient, semiconductor material and square p-N. Transition.

Temperature dependence of the reverse current is given by where - the nominal temperature - actual temperature - temperature heat doubling current.

The thermal current of the silicon transition is much less than the thermal current of transition based on Germany (by 3-4 orders). It's connected with  K. material.

With an increase in the crossing area, it increases by volume, and, therefore, the number of non-core carriers appearing as a result of thermogeneration and thermal current increases.

So, the main property p-N.- Transformation is its one-sided conductivity.

4. Voltamper characteristic P-N - transition.

We get a volt-ampere characteristic p-N Transition. To do this, write the equation of continuity in general:

We will consider the stationary case dp / dt \u003d 0.

Consider the current in the quasi-lane semiconductor N-type to the right of the depleted p-N regions Transition (x\u003e 0). The rate of generation G in a quasi-linear volume is zero: G \u003d 0. The electric field E is also zero: E \u003d 0. The drift current component is also zero: I e \u003d 0, therefore, the diffusion current. The rate of recombination R with a small level of injection is described by the relation:

We use the following relationship between the diffusion coefficient and diffusion length of the minority carrier lifetime: Dτ \u003d L p 2.

Taking into account the above assumptions, the continuity equation is:

The boundary conditions for the diffusion equation in the P-N transition are:

Decision differential equation (2.58) with boundary conditions (*) has the form:

The ratio (2.59) describes the law of distribution of injected holes in the Quasi-Matnic volume of the N-type semiconductor for the electron-hole transition (Fig. 2.15). In the current P-n of the transition, all carriers are involved, crossed the border of the OPZ with a quasi-larger volume of the P-N of the transition. Since the entire current diffusion, substituting (2.59) to the expression for the current, we obtain (Fig. 2.16):

The relation (2.60) describes a diffusion hole current component of the p-n transition, occurring during the injection of minority carriers when forward biased. For the electronic component, the transition current is similar to:

When V G \u003d 0, drift and diffusion components bassize each other. Hence, .

Full current P-N The transition is the sum of all four components of the P-N transition current:

The expression in brackets has the physical meaning of the reverse current of the P-N of the transition. Indeed, with negative voltages V G< 0 ток дрейфовый и обусловлен неосновными носителями. Все эти носители уходят из цилиндра длиной L n со скоростью L n /τ p . Тогда для дрейфовой компоненты тока получаем:

Fig. 2.15. The distribution of non-equilibrium injected from the issuer of carriers by quasi-neutral volume p-N base Transition

It is easy to see that this ratio is equivalent to previously obtained when analyzing the continuity equation.

If you want to implement a unilateral injection condition (for example, only the hole injection), the relation (2.61) that is necessary to choose a small value of the minority carrier density n p0 in the p-region. It follows that the P-type semiconductor must be strongly doped compared to the N-type semiconductor: n a \u003e\u003e n d. In this case, the P-n transition current will dominate the hole component (Fig. 2.16).

Fig. 2.16. Currents in the asymmetric P-n lantern with direct displacement

Thus, the P-N of the transition is:

The density of the saturation current J s is equal to:

P-n transition passes described by relation (2.62), shown in Figure 2.17.

Fig. 2.17. Volt-ampere characteristics perfect P-N Transition

As follows from the relation (2.16) and figure 2.17, the current-voltage characteristic of an ideal p-n junction has a pronounced asymmetric form. In the area of \u200b\u200bdirect voltages, the transition current of the transition diffusion and exponentially increases with an increase in the applied voltage. In the region of negative voltages, the P-N transition current is drift and does not depend on the applied voltage.

5. Capacity P-N - Transition.

Any system in which, with a change in the potential φ, the electrical charge q is changing, has a container. The value of the capacity C is determined by the ratio :.

For the P-n of the transition, two types of charges can be distinguished: the charge in the spatial charge of ionized donors and the Q b and the charge of the injected media into the base from the q p emitter. With different displacements on the P-N, the transition when calculating the container will dominate this or that charge. In this connection, for the tank P-n of the transition, the barrier container C B and the diffusion container C d were isolated.

Barrier CB CB - this capacity P-N Transition with reverse displacement V G< 0, обусловленная изменением заряда ионизованных доноров в области пространственного заряда.

The amount of charge of ionized donors and receptors Q B per unit area for the asymmetric P-n of the transition is:

Differentiating expression (2.65), we get:

From equation (2.66) it follows that the barrier capacity C B is a container of a flat capacitor, the distance between the plates of which is equal to the width of the spatial charge of W. Since the width of the OPZ depends on the applied voltage V g, then the barrier container also depends on the applied voltage. Numerical estimates of the values \u200b\u200bof the barrier capacity show that its value is tens or hundreds of picofrades.

The diffusion capacity C d is the P-n transition capacity with a direct displacement V G\u003e 0, due to a change in the charge of Q P of the injected carriers to the base from the q p emitter.

The dependence of the barrier container with b from the applied reverse voltage V g is used for instrumental implementation. Semiconductor diode that implements this dependence is called varicap. Maximum value Capacities Varicap has at zero voltage V g. With an increase in the reverse bias, the varicap container decreases. The functional dependence of the container of the voltage varicap is determined by the docking profile of the varicap base. In the case of homogeneous doping, the capacity is inversely proportional to the root from the applied voltage V g. By setting the doping profile in the Varicap Base n D (x), you can get various dependencies The capacity of the varicap from voltage C (V g) is linearly decreasing, exponentially decreasing.

6. Semiconductor diodes: classification, design features, legend and labeling.

Semiconductor diode - semiconductor device with one electrical transition and two conclusions (electrodes). Unlike other types of diodes, the principle of action of the semiconductor diode is based on the phenomenon p-N.- Transformation.

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

The property that determines the ability of the substance to carry out the electric current has the name "Electrical conductivity". The electrical conductivity is directly dependent on the concentration of charged particles: the higher the concentration, the electrical conductivity.

For this property, all substances are divided into 3 types:

Conditions.
Semiconductors.

Description of conductors

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

Metals (copper, aluminum, silver) and their alloys.
Electrolytes (water solution Salts, acids).

In the substances of the first subgroup, only electrons are capable of moving, since their connection with the nuclei of atoms is weak, in connection with which they are simply disconnected from them. Since in metals, the appearance of current is associated with the movement of free electrons, the type of electrical conductivity in them is called electronic.

From the conductors of the first subgroup are used in the windings of electromasitis, power lines, wires. It is important to note that its cleanliness and no impurities affect the electrical conductivity of metals.

In the substances of the second subgroup, when exposed to the solution, the semiconduvement of the molecule on a positive and negative ion. The ions are moved due to the effects of the electric field. Then, when the current passes through the electrolyte, the ions are precipitated on the electrode, which is lowered into this electrolyte. The process is separated from the electrolyte under the influence of an electric current, the electrolysis was obtained. The electrolysis process is taken to apply, for example, when a non-ferrous metal is produced from a solution of its compound, either when coating a metal protective layer Other metals.

Description of dielectrics

Dielectrics are also called electrical insulating substances.

All electrical insulating substances have the following classification:

Depending on the aggregate state, the dielectric can be liquid, solid and gaseous.
Depending on the methods of producing - natural and synthetic.
Depending on the chemical composition - Organic and inorganic.
Depending on the structure of molecules - neutral and polar.

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

In dielectrics there is a small amount of free electrons, and electrons have a strong connection with the nuclei of atoms and only in rare cases Disconnect from them. This means that these substances do not have the ability to carry out the current.

This property is very useful in the production of funds used when protected from electric current: dielectric gloves, rugs, shoes, insulators on electrical equipment etc.

About semiconductors

Semiconductor acts as a role intermediate between conductor and dielectric. SAME bright representatives This type of substances are silicon, germanium, selenium. In addition, these substances are made to attribute elements of the fourth group of the periodic table of Dmitry Ivanovich Mendeleev.

Semiconductors have additional "hole" conductivity, in addition to electronic conductivity. This type of conductivity dependent on a number of factors external environment, among which the light, temperature, electric and magnetic field.

In these substances there are fragile covalent bonds. When exposed to one of external factors Communication is destroyed, after which the formation of free electrons is the formation. At the same time, when the electron is disconnected, a free "hole" remains in the covalent bond. Free "holes" attract neighboring electrons, and so this action can be carried out infinitely.

Increase the conductivity of semiconductor substances by entering various impurities. This technique is widespread in industrial electronics: in diodes, transistors, thyristors. Consider in more detail the main differences between the conductors from semiconductors.

What is the difference between the conductor from the semiconductor?

The main difference of the conductor from the semiconductor is the ability to conduct an electric current. The conductor is an order of magnitude higher.

When the temperature is raised, the conductivity of semiconductors is also increasing; The conductivity of the conductors when increasing becomes less.

In pure conductors under normal conditions when the current is released much larger number of electrons than in semiconductors. At the same time, the addition of impurities reduces the conductivity of the conductors, but increases the conductivity of semiconductors.