Micro- and Nanoelectronics. Учебное пособие

Unit 2. Semiconductors

TEXT 3

Vocabulary:

important advances – важные достижения resistivity, n [rɪzɪsˈtɪvɪtɪ] – удельное сопротивление compound, n [ˈkɔmpaʊnd] – соединение crystalline, adj [ˈkrɪstәlaɪn] – кристаллический

amorphous, adj [әˈmɔːfәs] – аморфный, бесформенный, некристаллический

intrinsic and extrinsic, adj [ɪnˈtrɪnsɪk],[eksˈtrɪnsɪk] – внутренний и внешний

silicon, n [ˈsɪlɪkәn] – кремний germanium, n [ʤɜːˈmeɪnɪәm] – германий gallium, n [ˈgælɪәm] – галлий

arsenide, n [ˈɑːsnaɪd] – арсенид aluminium, n [æljʊˈmɪnjәm] – алюминий

cadmium sulfide [ˈkædmɪәm ˈsʌlfaɪd] – сульфид кадмия copper oxide [ˈkɔpә ˈɔksaɪd] – оксид меди

charge carrier [ʧɑːʤ ˈkærɪә] – носитель заряда vacant, adj [ˈveɪkәnt] – вакантный

bulky vacuum tubes [ˈbʌlkɪ ˈvækjʊәm tjuːbz] – громоздкие вакуумные трубки

indispensable, adj [ɪndɪsˈpensәbl] – необходимый ruggedness, n [ˈrʌgɪdnәs] – прочность magnitude, n [ˈmægnɪtjuːd] – величина

doping, g [dәʊpɪŋ] – легирование oscillator, n [ˈɔsɪleɪtә] – осциллятор superior, adj [sjuːˈpɪәrɪә] – превосходный

TRANSISTORS AND SEMICONDUCTORS

One of the important advances in the development of electronics is the invention of semiconductor materials, a form of matter situated between metals and insulators in their ability to conduct electricity.

The semiconductor is an electric conductor with resistivity in the range between metals and insulators, in which the electric charge – carrier concentration increases with the increasing temperature range. Semiconductors are

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usually materials which have energy – band gaps smaller than 2 e V. Semiconductors can be crystalline or amorphous and are classified as elemental and compound, intrinsic and extrinsic semiconductors.

Elemental semiconductors are single-element semiconductor materials such as silicon or germanium. Compound semiconductors are materials containing more that one element, for example, III-V compounds such as gallium, arsenide, aluminium, arsenide, cadmium sulfide and copper oxide.

Unlike the vacuum tube where current flow arises from the motion of charge carriers within a vacuum, semiconductor devices develop current flow from the motion of charge carriers within a crystalline solid.

Electrical conduction is possible by the motion of electrons or holes. A perfect semiconductor is essentially an insulator at absolute zero temperature, since its conduction band is vacant. As the temperature increases electrons are thermally excited from the valence into the conduction band and the conductivity increases. The electrons are negative charge carriers, while the holes are positive carriers.

An important property of semiconductors is the ability to change their resistivity over several orders of magnitude by doping.

A transistor is an active semiconductor device with three or more electrodes. It is called active since the transistor is capable of amplification and current, voltage and power gain. A transistor is an electron device in which electronic conduction takes place within a semiconductor.

Transistors revolutionized radioengineering and electronics replacing bulky vacuum tubes and becoming indispensable in many applications. Having small size, great mechanical ruggedness, long lifetime and high reliability, transistors make it possible to design compact, small-dimensioned electronic devices which consume very little power and to produce devices which cannot be made with vacuum tubes.

High-frequency applications of transistors include amplifiers, oscillators and mixers in communications system. They provide useful power gains with noise performance superior to that of vacuum tubes.

1. Read the text and answer the questions:

1.What is a semiconductor?

2.Can you name the types of semiconductors?

3.What is the difference between a vacuum tube and a semiconductor?

4.How do semiconductors change their resistivity over several orders of magnitude?

5.What is a transistor?

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6.How many electrodes can it have?

7.Why is it called active?

8.When is electrical conduction possible?

9.Why did transistors revolutionize radioengineering and electronics?

10.What do high-frequency applications of transistors include?

2. Complete the sentences:

1. An important property of semiconductors is….

a) the ability to change their resistivity over several orders of magnitude by doping.

b) low secondary emission

c) the ability to recreate an original image on a screen of a television 2. A transistor is….

a)a glass tube that has its gas removed, creating a vacuum.

b)an elementary particle that has a negative electric charge.

c)an electron device in which electronic conduction takes place. 3. Electrical conduction is possible…

a)by carring an electrical current.

b)by the motion of electrons or holes.

c)by shifting the energy bands relative to the Fermi level. 4. Semiconductors can be…

a)crystalline or amorphous.

b)recognized from their appearance.

c)cooled with forced air or water cooling. 5. A perfect semiconductor is…

a)essentially an insulator at absolute zero temperature.

b)a material whose internal electric charges do not flow freely.

c)an idealized material exhibiting infinite electrical conductivity or, equivalently, zero resistivity.

6. Transistors make it possible…

a)to reduce the general electromagnetic equations to electrostatic equa-

tions.

b)to carry direct current with 100% efficiency.

c)to design compact electronicdevices which consume very littlepower. 7. Transistors revolutionized radioengineering and electronics…

a)replacing bulky vacuum tubes.

b)taking advantage of many properties.

c)giving us a better understanding of the atomic-scale behavior of some materials.

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8. Transistors provide useful power gains…

a)using density functional based methods.

b)enabling high field electromagnets to be made out of superconducting

wire.

c)with noise performance superior to that of vacuum tubes.

3. Match the synonyms:

4. Find related words and place them in a row:

e.g.: present presentation presenter presentment presenting presentable presented presently presence presentee reliableness powerful consumption performer crystal performed amorphously currently superioress consumable superiorly powered perform reliance consumer operated crystallite operation powerfully superior operative amorphous operate consume operational powerhouse reliable operational powerhouse reliable consumerism operable current operating performance powering superiority powerless relied consumed reliably operationally currency operator reliability consuming

5.Compare transistors and vacuum tubes. List their advantages and disadvantages.

TEXT 4

Vocabulary:

pure silicon [pjʊә ˈsɪlɪkәn] – чистый кремний

undesirable traces [ˈʌndɪˈzaɪәrәbl ˈtreɪsɪz] – нежелательные следы extrinsic, adj [eksˈtrɪnsɪk] – внешний

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intrinsic, adj [ɪnˈtrɪnsɪk] – свойственный, внутренне присущий dopant, n [ˈdәʊpeɪnt] – легирующая примесь

large-scale, adj – крупномасштабный impurity, n [ɪmˈpjʊәrɪtɪ] – примесь

acceptor, n [әkˈseptә] – акцептор, получатель compound, n [ˈkɔmpaʊnd] – соединение

EXTRINSIC SEMICONDUCTORS

Extrinsic semiconductors are partially conductive and partially insulating materials that have been chemically altered to bear a non-neutral electrical charge. They are the building blocks of semiconductor devices. The production of extrinsic semiconductors follows a successful production of intrinsic semiconductors and their transformation into positive (P)-type or negative (N)-type semiconductors.

When silicon dioxide undergoes removal of oxygen atoms, extraction of pure silicon is possible. This pure silicon, while in liquid form, easily reacts with oxygen to revert to a variation of ordinary sand. By using a special production environment, such as in a vacuum or a non-reacting gas, the silicon material has a chance of having high purity. Any undesirable traces of other elements and compounds are also separated to achieve pure silicon. Silicon melts at about 2,577°F (about 1,414°C), thus special equipment and technology are required toward producing extrinsic semiconductors.

Pure silicon by itself has to be doped so that it does not permanently stay as an intrinsic semiconductor. Doping involves introducing additional controlled impurities into the intrinsic semiconductor while it is in liquid form. In the electronics industry, pure silicon functioning as an intrinsic semiconductor needs to be converted into an extrinsic semiconductor in order to be used. If it has solidified as intrinsic, it needs to be molten again to create an extrinsic semiconductor. Once the intrinsic semiconductor is in liquid form, creating a P-type or N-type semiconductor is the next choice, and with the right dopant elements or correct choice of controlled impurities, the intrinsic semiconductor becomes an extrinsic semiconductor or a doped semiconductor.

Extrinsic semiconductors are either N-type or P-type, depending on the dopant used. A dopant, such as boron, may have three electrons on the outer atom shell, or valence, to produce a P-type semiconductor. Those with five valence electrons, such as phosphorus, are used as dopants to produce an N-type semiconductor. Adding boron to molten pure silicon in a non-

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reacting environment makes it a P-type semiconductor, or an electron acceptor, while doping intrinsic silicon with phosphorus creates an N-type semiconductor, or an electron donor. One boron atom to as many as 10 million silicon atoms is the typical ratio of the, of impurity in an intrinsic semiconductor.

A semiconductor plant delivers components with various combinations of extrinsic semiconductors. The two-terminal diode has a single P-N junction, or a joined P-type and N-type semiconductor. Very large-scale integration chips have thousands of junctions of P-type and N-type semiconductors.

1. Read the text and answer the questions:

1.What are extrinsic semiconductors?

2.When is extraction of pure silicon possible?

3.When does it easily react with oxygen to revert to a variation of ordinary sand?

4.What is the process of achieving pure silicon?

5.Why does pure silicon have to be doped?

6.What does doping involve?

7.How many electrons may have a dopant, such as boron, on the outer atom shell to produce a P-type semiconductor?

8.What are the conditions to produce a P-type semiconductor and an N- type semiconductor?

9.Can you name the difference between an electron acceptor and an electron donor?

10.What is the typical ratio of the amount of impurity in an intrinsic semiconductor?

2.Read the following statements and decide if they are true or false or not mentioned. In case the statement is false, correct it.

1.The building blocks of semiconductor devices are partially conductive and partially insulating materials.

2.The extraction of pure silicon is possible, when silicon dioxide undergoes removal of hydrogen atoms.

3.The silicon material has a chance of having high purity in a vacuum or a non-reacting gas.

4.Silicon melts at about 5,577°F.

5.Silicon carbide (SiC) is a semiconductor containing silicon and carbon with chemical formula SiC.

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6.The intrinsic semiconductor becomes an extrinsic semiconductor, when it is in its solid form.

7.A dopant, such as boron, may have three electrons on the outer atom shell to produce an H-type semiconductor.

8.Silicon carbide is used as an abrasive, as well as a semiconductor and diamond simulant.

3. Find the odd word:

1.break carry out remove build destroy demolish break down eliminate

2.extrinsic unusual intrinsic outer external

3.expand enlarge reduce multiply extend add

4.neatness cleanness purity pureness cleanliness clarity impurity fineness whiteness

5.contrast diff equality distinction difference unlikeness diversity

dissimilarity

6.manufacture handicraft production industry manufacturing

7.correlation ratio parity proportion rate inequality

8.magnitude quantity amount quality value number

4.Define the following words as parts of speech and give the initial words of the following derivatives. Make up sentences with some of them:

Partially, amounting, dopant, impurity, choicely, liquidize, difference, possibly, introduction, correctable, valency, highly, undergone, compounding, conductive, solidified, phosphorus, meltable, environing, achievable, follower, siliceous.

5.Prepare a report about a scientist, who contributed to the development of semiconductors.

TEXT 5

Vocabulary:

Impurities, n [ɪmˈpjuːrɪtɪz] – примеси, шлаки Confined, pII [kәnˈfaɪnd] – ограниченный

chemical composition [ˈkemɪkәl kɔmpәˈzɪʃn] – химический состав either… or, conj [ˈaɪðә ɔː] – или... или

compound, n [ˈkɔmpaʊnd] – соединение, смесь

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purposely, adv [ˈpɜːpәslɪ] – преднамеренно accidentally, adv [æksɪˈdentәlɪ] – случайно inevitably, adv [ɪnˈevɪtәblɪ] – неизбежно incidentally,adv [ɪnsɪˈdentlɪ] – кстати dopant, n [ˈdәʊpeɪnts] – легирующая примесь

pentavalent, adj [ˈpentәveɪlәnt] – пентавалентная

substitutional, adj [ˈsʌbstɪtjuːʃnәl] – субституционный, замещающий minority carriers [maɪˈnɔrɪtɪ ˈkærɪә] – неосновной носитель average, adj [ˈævәrɪʤ] – средний, обычный

velocity, n [vɪˈlɔsɪtɪ] – скорость phosphorus, n [ˈfɔsfәrәs] – фосфор arsenic, n [ˈɑːsnɪk] – мышьяк antimony, n [ˈæntɪmәnɪ] – сурьма

caused, pII [kɔːzd] – причиненный, вызванный imperfection, n [ɪmpәˈfekʃn] – несовершенство

TYPES OF IMPURITIES

Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound.

Impurities are either naturally occurring or added during synthesis of a chemical or commercial product. During production, impurities may be purposely, accidentally, inevitably, or incidentally added into the substance.

Impurities can be added to semiconductors to modify their electrical properties. This addition is termed doping. Silicon doped with pentavalent substitutional impurities such as phosphorus, arsenic, and antimony will have a higher electron density due to the easily ionized fifth electrons of the impurities. The hole concentration in such a silicon crystal is reduced since the np product remains constant. Dopants which increase the electron density are called donors. Dopant concentration is denoted Np.

The addition of trivalent dopants such as boron, gallium, and indium to silicon will attract electrons and reduce the electron density. Again, since the np product remains constant, the hole density must increase. Dopants which reduce the electron density are called acceptors. Acceptor concentration is denoted Na.

In an extrinsic (doped) semiconductor the current-carrier type introduced by doping predominates. Donor-doped material is called n-type because the majority of carriers are electrons. The electrons in such semicon-

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ductors are the majority carriers, while the holes are the majority carriers. Acceptor-doped materials are called p-type. Here the holes are the majority carriers and electrons are the minority carriers.

Resistivity is determined by the concentration of majority carriers. Lifetime is the average time required for excess minority carriers to re-

combine with majority carriers. Recombination occurs at “traps” caused by impurities and imperfections in the semiconductor crystal. Semiconductor junctions are formed in material grown as a single continuous crystal to obtain the lattice perfection required, and extreme precautions are taken to ensure exclusion of unwanted impurities during processing. However, in some applications short lifetime is desired, and in such cases gold doping is used to achieve this.

Carrier mobility is the property of a charge carrier which determines its velocity in an electric field. Mobility also determines the velocity of a minority carrier in the diffusion process. High mobility yields a short transit time and good frequency response.

1. Read the text and answer the questions:

1.Can you explain what impurities are?

2.How can impurities be added into a substance?

3.Why are impurities added to semiconductors?

4.How is this addition called?

5.What happens to silicon doped with pentavalent substitutional impuri-

ties?

6.How are dopants which increase the electron density called?

7.How are semiconductor junctions formed in a material?

8.Why are extreme precautions taken during this process?

9.What is gold doping used for?

10.What determines carrier mobility?

2. Put the sentences in the order they follow in the text:

1.Dopants which reduce the electron density are called acceptors.

2.However, in some applications short lifetime is desired, and in such cases gold doping is used to achieve this.

3.Impurities can be added to semiconductors to modify their electrical properties.

4.Semiconductor junctions are formed in material grown as a single continuous crystal.

5.Resistivity is determined by the concentration of majority carriers.

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6.Dopants which increase the electron density are called donors.

7.Impurities are either naturally occurring or added during synthesis of a chemical or commercial product.

8.Donor-doped material is called n-type because the majority of carriers are electrons.

3. Match the words to make word partners using the text:

4. Complete the sentences using the word partners from ex.3:

1.To some degree, water can dissolve every ____________substance on the earth.

2.Does electric current _________ in a circuit?

3.It is essential to get rid of these __________, and make the oil achieves the standards of industrial use.

4.In this lecture we are talking about the structure and characteristics of

___________.

5.It`s important to __________ of this material.

6.A __________ is the identity, and relative number, of the elements that make up any particular compound.

7.In reality, however, we have a ____________ of usable fresh water.

8.It was found that the semiconductors experience large temperature cycles leading to a ___________.

5. Speak about the use of impurities in semiconductor production.

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