英文版电子设备与电路理论——半导体二极管深入解析

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"这是一本全面的英文模拟电子设备与电路理论教材，由Robert Boylestad和Louis Nashelsky合著，由Prentice Hall出版社出版。本书内容涵盖半导体二极管的基本概念、应用以及相关电路分析。" 在本书中，作者深入浅出地介绍了模拟电子技术的基础知识，特别是关于半导体二极管的方方面面。第1章"半导体二极管"首先从介绍入手，讲解了理想二极管的概念，并讨论了半导体材料的性质，如能量级和杂质半导体（n型和p型）。接着，书中详细阐述了半导体二极管的工作原理，包括电阻特性、等效电路、规格表、势垒和扩散电容、反向恢复时间、二极管符号以及二极管的测试方法。此外，还特别提到了稳压二极管（Zener二极管）和发光二极管（LEDs）的应用，以及二极管阵列和集成电路。第2章"二极管应用"则将焦点转向二极管在实际电路中的使用。这部分内容涵盖了负载线分析、二极管近似模型、带有直流输入的串联二极管配置、并联和串并联配置、逻辑门（AND/OR门）、正弦波输入下的半波整流、全波整流、钳位电路以及电压钳位器。此外，Zener二极管在电压调节中的作用也得到了详细阐述。通过这本书，读者不仅可以掌握半导体二极管的基础知识，还能了解到如何在各种电路设计中有效地运用这些知识。无论是对于初学者还是有一定基础的学习者，这本书都提供了丰富的学习材料，有助于提升对模拟电子电路的理解和实践能力。对于想要深入理解和应用模电知识的人来说，这无疑是一本非常有价值的参考资料。

p n

Although the covalent bond will result in a stronger bond between the valence

electrons and their parent atom, it is still possible for the valence electrons to absorb

sufficient kinetic energy from natural causes to break the covalent bond and assume

the “free” state. The term free reveals that their motion is quite sensitive to applied

electric fields such as established by voltage sources or any difference in potential.

These natural causes include effects such as light energy in the form of photons and

thermal energy from the surrounding medium. At room temperature there are approx-

imately 1.5  10

free carriers in a cubic centimeter of intrinsic silicon material.

Intrinsic materials are those semiconductors that have been carefully refined

to reduce the impurities to a very low level—essentially as pure as can be

made available through modern technology.

The free electrons in the material due only to natural causes are referred to as

intrinsic carriers. At the same temperature, intrinsic germanium material will have

approximately 2.5  10

free carriers per cubic centimeter. The ratio of the num-

ber of carriers in germanium to that of silicon is greater than 10

and would indi-

cate that germanium is a better conductor at room temperature. This may be true,

but both are still considered poor conductors in the intrinsic state. Note in Table 1.1

that the resistivity also differs by a ratio of about 10001, with silicon having the

larger value. This should be the case, of course, since resistivity and conductivity are

inversely related.

An increase in temperature of a semiconductor can result in a substantial in-

crease in the number of free electrons in the material.

As the temperature rises from absolute zero (0 K), an increasing number of va-

lence electrons absorb sufficient thermal energy to break the covalent bond and con-

tribute to the number of free carriers as described above. This increased number of

carriers will increase the conductivity index and result in a lower resistance level.

Semiconductor materials such as Ge and Si that show a reduction in resis-

tance with increase in temperature are said to have a negative temperature

coefficient.

You will probably recall that the resistance of most conductors will increase with

temperature. This is due to the fact that the numbers of carriers in a conductor will

1.3 Semiconductor Materials

Figure 1.6 Atomic structure: (a) germanium;

(b) silicon.

Figure 1.7 Covalent bonding of the silicon

atom.

not increase significantly with temperature, but their vibration pattern about a rela-

tively fixed location will make it increasingly difficult for electrons to pass through.

An increase in temperature therefore results in an increased resistance level and a pos-

itive temperature coefficient.

1.4 ENERGY LEVELS

In the isolated atomic structure there are discrete (individual) energy levels associated

with each orbiting electron, as shown in Fig. 1.8a. Each material will, in fact, have

its own set of permissible energy levels for the electrons in its atomic structure.

The more distant the electron from the nucleus, the higher the energy state,

and any electron that has left its parent atom has a higher energy state than

any electron in the atomic structure.

Chapter 1 Semiconductor Diodes

p n

Figure 1.8 Energy levels: (a)

discrete levels in isolated atomic

structures; (b) conduction and

valence bands of an insulator,

semiconductor, and conductor.

Energy

Energy Energy

E > 5 eV

Valence band

Conduction band

Valence band

Conduction band

The bands

overlap

Electrons

"free" to

establish

conduction

Valence

electrons

bound to

the atomic

stucture

E = 1.1 eV (Si)

E = 0.67 eV (Ge)

E = 1.41 eV (GaAs)

Insulator Semiconductor

(b)

Valence band

Conductor

Energy gap

etc.

Valance Level (outermost shell)

Second Level (next inner shell)

Third Level (etc.)

Energy

Nucleus

(a)

Between the discrete energy levels are gaps in which no electrons in the isolated

atomic structure can appear. As the atoms of a material are brought closer together to

form the crystal lattice structure, there is an interaction between atoms that will re-

sult in the electrons in a particular orbit of one atom having slightly different energy

levels from electrons in the same orbit of an adjoining atom. The net result is an ex-

pansion of the discrete levels of possible energy states for the valence electrons to

that of bands as shown in Fig. 1.8b. Note that there are boundary levels and maxi-

mum energy states in which any electron in the atomic lattice can find itself, and there

remains a forbidden region between the valence band and the ionization level. Recall

that ionization is the mechanism whereby an electron can absorb sufficient energy to

break away from the atomic structure and enter the conduction band. You will note

that the energy associated with each electron is measured in electron volts (eV). The

unit of measure is appropriate, since

W  QV eV (1.2)

as derived from the defining equation for voltage V  W/Q. The charge Q is the charge

associated with a single electron.

Substituting the charge of an electron and a potential difference of 1 volt into Eq.

(1.2) will result in an energy level referred to as one electron volt. Since energy is

also measured in joules and the charge of one electron  1.6  10

19

coulomb,

W  QV  (1.6  10

19

C)(1 V)

and 1 eV  1.6  10

19

J (1.3)

At 0 K or absolute zero (273.15°C), all the valence electrons of semiconductor

materials find themselves locked in their outermost shell of the atom with energy

levels associated with the valence band of Fig. 1.8b. However, at room temperature

(300 K, 25°C) a large number of valence electrons have acquired sufficient energy to

leave the valence band, cross the energy gap defined by E

in Fig. 1.8b and enter the

conduction band. For silicon E

is 1.1 eV, for germanium 0.67 eV, and for gallium

arsenide 1.41 eV. The obviously lower E

for germanium accounts for the increased

number of carriers in that material as compared to silicon at room temperature. Note

for the insulator that the energy gap is typically 5 eV or more, which severely limits

the number of electrons that can enter the conduction band at room temperature. The

conductor has electrons in the conduction band even at 0 K. Quite obviously, there-

fore, at room temperature there are more than enough free carriers to sustain a heavy

flow of charge, or current.

We will find in Section 1.5 that if certain impurities are added to the intrinsic

semiconductor materials, energy states in the forbidden bands will occur which will

cause a net reduction in E

for both semiconductor materials—consequently, increased

carrier density in the conduction band at room temperature!

1.5 EXTRINSIC MATERIALS—

n- AND p-TYPE

The characteristics of semiconductor materials can be altered significantly by the ad-

dition of certain impurity atoms into the relatively pure semiconductor material. These

impurities, although only added to perhaps 1 part in 10 million, can alter the band

structure sufficiently to totally change the electrical properties of the material.

A semiconductor material that has been subjected to the doping process is

called an extrinsic material.

There are two extrinsic materials of immeasurable importance to semiconductor

device fabrication: n-type and p-type. Each will be described in some detail in the

following paragraphs.

n-Type Material

Both the n- and p-type materials are formed by adding a predetermined number of

impurity atoms into a germanium or silicon base. The n-type is created by introduc-

ing those impurity elements that have five valence electrons (pentavalent), such as an-

timony, arsenic, and phosphorus. The effect of such impurity elements is indicated in

1.5 Extrinsic Materials—n- and p-Type

p n

–

Antimony (Sb)

impurity

–

––

–

––

–

––

–

––

–

––

–

––

–

––

–

––

–

––

–

Si Si Si

Sb Si

SiSiSi

Fifth valence

electron

of antimony

Chapter 1 Semiconductor Diodes

p n

Figure 1.9 Antimony impurity

in n-type material.

Fig. 1.9 (using antimony as the impurity in a silicon base). Note that the four cova-

lent bonds are still present. There is, however, an additional fifth electron due to the

impurity atom, which is unassociated with any particular covalent bond. This re-

maining electron, loosely bound to its parent (antimony) atom, is relatively free to

move within the newly formed n-type material. Since the inserted impurity atom has

donated a relatively “free” electron to the structure:

Diffused impurities with five valence electrons are called donor atoms.

It is important to realize that even though a large number of “free” carriers have

been established in the n-type material, it is still electrically neutral since ideally the

number of positively charged protons in the nuclei is still equal to the number of

“free” and orbiting negatively charged electrons in the structure.

The effect of this doping process on the relative conductivity can best be described

through the use of the energy-band diagram of Fig. 1.10. Note that a discrete energy

level (called the donor level) appears in the forbidden band with an E

significantly

less than that of the intrinsic material. Those “free” electrons due to the added im-

purity sit at this energy level and have less difficulty absorbing a sufficient measure

of thermal energy to move into the conduction band at room temperature. The result

is that at room temperature, there are a large number of carriers (electrons) in the

conduction level and the conductivity of the material increases significantly. At room

temperature in an intrinsic Si material there is about one free electron for every 10

atoms (1 to 10

for Ge). If our dosage level were 1 in 10 million (10

), the ratio

(10

/10

 10

) would indicate that the carrier concentration has increased by a ra-

tio of 100,0001.

Figure 1.10 Effect of donor impurities on the energy band

structure.

Energy

Conduction band

Valence band

Donor energy level

E = 0.05 eV (Si), 0.01 eV (Ge)

E as before

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英文版电子设备与电路理论——半导体二极管深入解析

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