Module 7—Introduction to Solid-State Devices and Power Supplies
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Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview
of the information you are expected to learn in the chapter. The comprehensive check questions are based on the
objectives. By successfully completing the NRTC, you indicate that you have met the objectives and have learned
the information. The learning objective are listed below.
Upon completion of this chapter, you should be
able to do the following:
1. State, in terms of energy bands, the differences between a conductor, an
insulator, and a semiconductor.
2. Explain the electron and the hole flow theory in semiconductors and
how the semiconductor is affected by doping.
3. Define the term "diode" and give a brief description of
its construction and operation.
4. Explain how the diode can be used as a half-wave rectifier and as a
5. Identify the diode by its symbology, alphanumerical designation, and color code.
List the precautions that must be taken when working with diodes and describe the different ways to test them.
INTRODUCTION TO SOLID-STATE DEVICES
As you recall from previous studies in this series, semiconductors have electrical properties somewhere
between those of insulators and conductors. The use of semiconductor materials in electronic components is not
new; some devices are as old as the electron tube. Two of the most widely known semiconductors in use today are
the JUNCTION DIODE and TRANSISTOR. These semiconductors fall under a more general heading called solid-state
devices. A SOLID-STATE DEVICE is nothing more than an electronic device, which operates by virtue of the movement
of electrons within a solid piece of semiconductor material.
Since the invention of the transistor,
solid-state devices have been developed and improved at an unbelievable rate. Great strides have been made in the
manufacturing techniques, and there is no foreseeable limit to the future of these devices. Solid-state devices
made from semiconductor materials offer compactness, efficiency, ruggedness, and versatility. Consequently, these
devices have invaded virtually every field of science and industry. In addition to the junction diode and
transistor, a whole new family of related devices has been developed: the ZENER DIODE, LIGHT-EMITTING DIODE, FIELD
EFFECT TRANSISTOR, etc. One development that has dominated solid-state technology, and probably has had a greater
impact on the electronics industry than either the electron tube or transistor, is the INTEGRATED CIRCUIT. The
integrated circuit is a minute piece of semiconductor material that can produce complete electronic circuit
As the applications of solid-state devices mount, the need for knowledge of these devices becomes
increasingly important. Personnel in the Navy today will have to understand solid-state devices if they are to
become proficient in the repair and maintenance of electronic equipment. Therefore, our objective in this module
is to provide a broad coverage of solid-state devices and, as a broad application, power supplies. We will begin
our discussion with some background information on the development of the semiconductor. We will then proceed to
the semiconductor diode, the transistor, special devices and, finally, solid-state power supplies.
Although the semiconductor was late in reaching its present development, its story began long before the
electron tube. Historically, we can go as far back as 1883 when Michael Faraday discovered that silver sulfide, a
semiconductor, has a negative temperature coefficient. The term negative temperature coefficient is just another
way of saying its resistance to electrical current flow decreases as temperature increases. The opposite is true
of the conductor. It has a positive temperature coefficient. Because of this particular characteristic,
semiconductors are used extensively in power-measuring equipment.
Only 2 years later, another valuable
characteristic was reported by Munk A. Rosenshold. He found that certain materials have rectifying properties.
Strange as it may seem, his finding was given such little notice that it had to be rediscovered 39 years later by
Toward the close of the 19th century, experimenters began to notice the peculiar characteristics of the chemical
element SELENIUM. They discovered that in addition to its rectifying properties (the ability to convert ac into
dc), selenium was also light sensitive-its resistance decreased with an increase in light intensity. This
discovery eventually led to the invention of the photophone by Alexander Graham Bell. The photophone, which
converted variations of light into sound, was a predecessor of the radio receiver; however, it wasn’t until the
actual birth of radio that selenium was used to any extent. Today, selenium is an important and widely used
Many other materials were tried and tested for use in communications. SILICON was found to
be the most stable of the materials tested while GALENA, a crystalline form of lead sulfide, was found the most
sensitive for use in early radio receivers. By 1915, Carl Beredicks discovered that GERMANIUM, another metallic
element, also had rectifying capabilities. Later, it became widely used in electronics for low-power,
Although the semiconductor was known long before the electron tube was
invented, the semiconductor devices of that time could not match the performance of the tube. Radio needed a
device that could not only handle power and amplify but rectify and detect a signal as well. Since tubes could do
all these things, whereas semiconductor devices of that day could not, the semiconductor soon lost out.
wasn’t until the beginning of World War II that interest was renewed in the semiconductor. There was a dire need
for a device that could work within the ultra-high frequencies of radar. Electron tubes had interelectrode
capacitances that were too high to do the job. The point-contact semiconductor diode, on the other hand, had a
very low internal capacitance. Consequently, it filled the bill; it could be designed to work within the
ultra-high frequencies used in radar, whereas the electron tube could not.
As radar took on greater
importance and communication-electronic equipment became more sophisticated, the demands for better solid-state
devices mounted. The limitations of the electron tube made necessary a quest for something new and different. An
amplifying device was needed that was smaller, lighter, more efficient, and capable of handling extremely high
frequencies. This was asking a
lot, but if progress was to be made, these requirements had to be met. A serious study of
semiconductor materials began in the early 1940’s and has continued since.
In June 1948, a significant
breakthrough took place in semiconductor development. This was the discovery of POINT-CONTACT TRANSISTOR. Here at
last was a semiconductor that could amplify. This discovery brought the semiconductor back into competition with
the electron tube. A year later, JUNCTION DIODES and TRANSISTORS were developed. The junction transistor was found
superior to the point-contact type in many respects. By comparison, the junction transistor was more reliable,
generated less noise, and had higher power-handling ability than its point-contact brother. The junction
transistor became a rival of the electron tube in many uses previously uncontested.
were not to be slighted. The initial work of Dr. Carl Zener led to the development of ZENER DIODE, which is
frequently used today to regulate power supply voltages at precise levels. Considerably more interest in the
solid-state diode was generated when Dr. Leo Esaki, a Japanese scientist, fabricated a diode that could amplify.
The device, named the TUNNEL DIODE, has amazing gain and fast switching capabilities. Although it is used in the
conventional amplifying and oscillating circuits, its primary use is in computer logic circuits.
breakthrough came in the late 1950’s when it was discovered that semiconductor materials could be combined and
treated so that they functioned as an entire circuit or subassembly rather than as a circuit component. Many names
have been given to this solid-circuit concept, such as INTEGRATED CIRCUITS, MICROELECTRONICS, and MICROCIRCUITRY.
So as we see, in looking back, that the semiconductor is not something new, but it has come a long way in a
Q1. What is a solid-state device?
Q2. Define the term negative temperature
In the previous paragraphs, we mentioned just a few of the many different applications of semiconductor
devices. The use of these devices has become so widespread that it would be impossible to list all their different
applications. Instead, a broad coverage of their specific application is presented.
are all around us. They can be found in just about every commercial product we touch, from the family car to the
pocket calculator. Semiconductor devices are contained in television sets, portable radios, stereo equipment, and
Science and industry also rely heavily on semiconductor devices. Research laboratories use these devices in all
sorts of electronic instruments to perform tests, measurements, and numerous other experimental tasks. Industrial
control systems (such as those used to manufacture automobiles) and automatic telephone exchanges also use
semiconductors. Even today heavy-duty versions of the solid- state rectifier diode are being use to convert large
amounts of power for electric railroads. Of the many different applications for solid-state devices, space
systems, computers, and data processing equipment are some of the largest consumers.
The various types of
modem military equipment are literally loaded with semiconductor devices. Many radars, communication, and airborne
equipment are transistorized. Data display systems, data processing units, computers, and aircraft
guidance-control assemblies are also good examples of
electronic equipments that use semiconductor devices. All of the specific applications of semiconductor
devices would make a long impressive list. The fact is, semiconductors are being used extensively in commercial
products, industry, and the military.
It should not be difficult to conclude, from what you already know, that semiconductor devices can and
do perform all the conventional functions of rectification, amplification, oscillation, timing, switching, and
sensing. Simply stated, these devices perform the same basic functions as the electron tube; but they perform more
efficiently, economically, and for a longer period of time. Therefore, it should be no surprise to you to see
these devices used in place of electron tubes. Keeping this in mind, we see that it is only natural and logical to
compare semiconductor devices with electron tubes.
Physically, semiconductor devices are much smaller than
tubes. You can see in figure 1-1 that the difference is quite evident. This illustration shows some commonly used
tube sizes alongside semiconductor devices of similar capabilities. The reduction in size can be as great as 100:1
by weight and 1000:1 by volume. It is easy to see that size reduction favors the semiconductor device. Therefore,
whenever miniaturization is required or is convenient, transistors are favored over tubes. Bear in mind, however,
that the extent of practical size reduction is a big factor; many things must be considered. Miniature electron
tubes, for example, may be preferred in certain applications to transistors, thus keeping size reduction to a
Figure 1-1.—Size comparisons of electron tubes and semiconductors.
Power is also a two-sided story. For low-power applications, where efficiency is a significant factor,
semiconductors have a decided advantage. This is true mainly because semiconductor devices perform very well with
an extremely small amount of power; in addition, they require no filaments or heaters as in the case of the
electron tube. For example, a computer operating with over 4000 solid-state devices may require no more than 20
watts of power. However, the same number of tubes would require several kilowatts of power.
applications, it is a different story — tubes have the upper hand. The high-power tube has no equivalent in any
semiconductor device. This is because a tube can be designed to operate
with over a thousand volts applied to its plate whereas the maximum allowable voltage for a transistor
is limited to about 200 volts (usually 50 volts or less). A tube can also handle thousands of watts of power. The
maximum power output for transistor generally ranges from 30 milliwatts to slightly over 100 watts.
it comes to ruggedness and life expectancy, the tube is still in competition. Design and functional requirements
usually dictate the choice of device. However, semiconductor devices are rugged and long-lived. They can be
constructed to withstand extreme vibration and mechanical shock. They have been known to withstand impacts that
would completely shatter an ordinary electron tube. Although some specially designed tubes render extensive
service, the life expectancy of transistors is better than three to four times that of ordinary electronic tubes.
There is no known failure mechanism (such as an open filament in a tube) to limit the semiconductor’s life.
However, semiconductor devices do have some limitations. They are usually affected more by temperature, humidity,
and radiation than tubes are.
Q3. Name three of the largest users of semiconductor devices.
Q4. State one requirement of an electron tube, which does not exist for semiconductors, that makes the tube less
efficient than the semiconductor.
To understand why solid-state devices function as they do, we will have to examine closely the
composition and nature of semiconductors. This entails theory that is fundamental to the study of solid- state
Rather than beginning with theory, let’s first become reacquainted with some of the basic information you studied
earlier concerning matter and energy (NEETS, Module 1).
The universe, as we know it today, is divided into two parts: matter and energy. Matter, which is our main concern
at this time, is anything that occupies space and has weight. Rocks, water, air, automobiles, clothing, and even
our own bodies are good examples of matter. From this, we can conclude that matter may be found in any one of
three states: SOLIDS, LIQUIDS, and GASES. All matter is composed of either an element or combination of elements.
As you know, an element is a substance that cannot be reduced to a simpler form by chemical means. Examples of
elements with which you are in contact everyday are iron, gold, silver, copper, and oxygen. At present, there are
over 100 known elements of which all matter is composed.
As we work our way down the size scale, we come
to the atom, the smallest particle into which an element can be broken down and still retain all its original
properties. The atoms of one element, however, differ from the atoms of all other elements. Since there are over
100 known elements, there must be over 100 different atoms, or a different atom for each element.
us consider more than one element at a time. This brings us to the term "compound." A compound is a chemical
combination of two or more elements. Water, table salt, ethyl alcohol, and ammonia are all examples of compounds.
The smallest part of a compound, which has all the characteristics of the compound, is the molecule. Each molecule
contains some of the atoms of each of the elements forming the compound.
Consider sugar, for example.
Sugar in general terms is matter, since it occupies space and has weight. It is also a compound because it
consists of two or more elements. Take a lump of sugar and crush
it into small particles; each of the particles still retains its original identifying properties of
sugar. The only thing that changed was the physical size of the sugar. If we continue this subdividing process by
grinding the sugar into a fine power, the results are the same. Even dissolving sugar in water does not change its
identifying properties, in spite of the fact that the particles of sugar are now too small to be seen even with a
microscope. Eventually, we end up with a quantity of sugar that cannot be further divided without its ceasing to
be sugar. This quantity is known as a molecule of sugar. If the molecule is further divided, it is found to
consist of three simpler kinds of matter: carbon, hydrogen, and oxygen. These simpler forms are called elements.
Therefore, since elements consist of atoms, then a molecule of sugar is made up of atoms of carbon, hydrogen, and
As we investigate the atom, we find that it is basically composed of electrons, protons, and
neutrons. Furthermore, the electrons, protons, and neutrons of one element are identical to those of any other
element. There are different kinds of elements because the number and the arrangement of electrons and protons are
different for each element.
The electron carries a small negative charge of electricity. The proton carries a positive charge of electricity
equal and opposite to the charge of the electron. Scientists have measured the mass and size of the electron and
proton, and they know how much charge each possesses. Both the electron and proton have the same quantity of
charge, although the mass of the proton is approximately 1,827 times that of the electron. In some atoms there
exists a neutral particle called a neutron. The neutron has a mass approximately equal to that of a proton, but it
has no electrical charge.
According to theory, the electrons, protons, and neutrons of the atoms are thought to be arranged in a manner
similar to a miniature solar system. Notice the helium atom in figure 1-2. Two protons and two neutrons form the
heavy nucleus with a positive charge around which two very light electrons revolve. The path each electron takes
around the nucleus is called an orbit. The electrons are continuously being acted upon in their orbits by the
force of attraction of the nucleus. To maintain an orbit around the nucleus, the electrons travel at a speed that
produces a counterforce equal to the attraction force of the nucleus. Just as energy is required to move a space
vehicle away from the earth, energy is also required to move an electron away from the nucleus. Like a space
vehicle, the electron is said to be at a higher energy level when it travels a larger orbit. Scientific
experiments have shown that the electron requires a certain amount of energy to stay in orbit. This quantity is
called the electron’s energy level. By virtue of just its motion alone, the electron contains kinetic energy.
Because of its position, it also contains potential energy. The total energy contained by an electron (kinetic
energy plus potential energy) is the main factor that determines the radius of the electron’s orbit. For an
electron to remain in this orbit, it must neither gain nor lose energy.
Figure 1-2.—The composition of a simple helium atom.
The orbiting electrons do not follow random paths, instead they are confined to definite energy
levels. Visualize these levels as shells with each successive shell being spaced a greater distance from the
nucleus. The shells, and the number of electrons required to fill them, may be predicted by using Pauli’s
exclusion principle. Simply stated, this principle specifies that each shell will contain a maximum of 2n2
electrons, where n corresponds to the shell number starting with the one closest to the nucleus. By this
principle, the second shell, for example, would contain 2(2) 2 or 8 electrons when full.
In addition to
being numbered, the shells are also given letter designations starting with the shell closest to the nucleus and
progressing outward as shown in figure 1-3. The shells are considered to be full, or complete, when they contain
the following quantities of electrons: 2 in the K(1st) shell, 8 in the L(2nd) shell, 18 in the M(3rd) shell, and
so on, in accordance with the exclusion principle. Each of these shells is a major shell and can be divided into
subshells, of which there are four, labeled s, p, d, and f. Like the major shells, the subshells are also limited
as to the number of electrons they contain. Thus, the
"s" subshell is complete when it contains 2 electrons,
the "p" subshell when it contains 6, the "d" subshell when it contains 10, and the "f" subshell when it contains
Figure 1-3.—Shell designation.
Inasmuch as the K shell can contain no more than 2 electrons, it must have only one subshell, the s
subshell. The M shell is composed of three subshells: s, p, and d. If the electrons in the s, p, and d subshells
are added together, their total is found to be 18, the exact number required to fill the M shell. Notice the
electron configuration of copper illustrated in figure 1-4. The copper atom contains 29 electrons, which
completely fill the first three shells and subshells, leaving one electron in the "s" subshell of the N shell. A
list of all the other known elements, with the number of electrons in each atom, is contained in the PERIODIC
TABLE OF ELEMENTS. The periodic table of elements is included in appendix 2.
Figure 1-4.—Copper atom.
Valence is an atom’s ability to combine with other atoms. The number of electrons in the outermost shell
of an atom determines its valence. For this reason, the outer shell of an atom is called VALENCE SHELL, and the
electrons contained in this shell are called VALENCE ELECTRONS. The valence of an atom determines its ability to
gain or lose an electron, which in turn determines the chemical and electrical properties of the atom. An atom
that is lacking only one or two electrons from its outer shell will easily gain electrons to complete its shell,
but a large amount of energy is required to free any of its electrons. An atom having a relatively small number of
electrons in its outer shell in comparison to the number of electrons required to fill the shell will easily lose
these valence electrons. The valence shell always refers to the outermost shell.
Q5. Define matter and
list its three different states.
Q6. What is the smallest particle into which an element can be broken
down and still retain all its original properties?
Q7. What are the three particles that comprise an
atom and state the type of charge they hold?
Q8. What is the outer shell of an atom called?
Now that you have become reacquainted with matter and energy, we will continue our
discussion with electron behavior.
As stated earlier, orbiting electrons contain energy and are confined
to definite energy levels. The various shells in an atom represent these levels. Therefore, to move an electron
from a lower shell to a higher shell a certain amount of energy is required. This energy can be in the form of
electric fields, heat, light, and even bombardment by other particles. Failure to provide enough energy to the
electron, even if the energy supplied is just short of the required amount, will cause it to remain at its present
energy level. Supplying more energy than is needed will only cause the electron to move to the next higher shell
and the remaining energy will be wasted. In simple terms, energy is required in definite units to move electrons
from one shell to the next higher shell. These units are called QUANTA (for example 1, 2, or 3 quanta).
Electrons can also lose energy as well as receive it. When an electron loses energy, it moves to a
lower shell. The lost energy, in some cases, appears as heat.
If a sufficient amount of energy is absorbed
by an electron, it is possible for that electron to be completely removed from the influence of the atom. This is
called IONIZATION. When an atom loses electrons or gains electrons in this process of electron exchange, it is
said to be ionized. For ionization to take place, there must be a transfer of energy that results in a change in
the internal energy of the atom. An atom having more than its normal amount of electrons acquires a negative
charge, and is called a NEGATIVE ION. The atom that gives up some of its normal electrons is left with fewer
negative charges than positive charges and is called a POSITIVE ION. Thus, we can define ionization as the process
by which an atom loses or gains electrons.
Up to this point in our discussion, we have spoken only of
isolated atoms. When atoms are spaced far enough apart, as in a gas, they have very little influence upon each
other, and are very much like lone atoms. But atoms within a solid have a marked effect upon each other. The
forces that bind these atoms together greatly modify the behavior of the other electrons. One consequence of this
close proximity of atoms is to cause the individual energy levels of an atom to break up and form bands of energy.
Discrete (separate and complete) energy levels still exist within these energy bands, but there are many more
energy levels than there were with the isolated atom. In some cases, energy levels will have disappeared. Figure
1-5 shows the difference in the energy arrangement between an isolated atom and the atom in a solid. Notice that
the isolated atom (such as in gas) has energy levels, whereas the atom in a solid has energy levels grouped into
Figure 1-5.—The energy arrangement in atoms.
The upper band in the solid lines in figure 1-5 is called the CONDUCTION BAND because electrons in this
band are easily removed by the application of external electric fields. Materials that have a large number of
electrons in the conduction band act as good conductors of electricity.
Below the conduction band is the
FORBIDDEN BAND or energy gap. Electrons are never found in this band, but may travel back and forth through it,
provided they do not come to rest in the band.
The last band or VALENCE BAND is composed of a series of
energy levels containing valence electrons. Electrons in this band are more tightly bound to the individual atom
than the electrons in the conduction band. However, the electrons in the valence band can still be moved to the
conduction band with the application of energy, usually thermal energy. There are more bands below the valence
band, but they are not important to the understanding of semiconductor theory and will not be discussed.
The concept of energy bands is particularly important in classifying materials as conductors,
semiconductors, and insulators. An electron can exist in either of two energy bands, the conduction band or the
valence band. All that is necessary to move an electron from the valence band to the conduction band so it can be
used for electric current, is enough energy to carry the electron through the forbidden band. The width of the
forbidden band or the separation between the conduction and valence bands determines whether a substance is an
insulator, semiconductor, or conductor. Figure 1-6 uses energy level diagrams to show the difference between
insulators, semiconductors, and conductors.
Figure 1-6.—Energy level diagram.
The energy diagram for the insulator shows the insulator with a very wide energy gap. The wider this
gap, the greater the amount of energy required to move the electron from the valence band to the conduction band.
Therefore, an insulator requires a large amount of energy to obtain a small amount of current. The insulator
"insulates" because of the wide forbidden band or energy gap.
The semiconductor, on the other hand, has a
smaller forbidden band and requires less energy to move an electron from the valence band to the conduction band.
Therefore, for a certain amount of applied voltage, more current will flow in the semiconductor than in the
The last energy level diagram in figure 1-6 is that of a conductor. Notice, there is no forbidden band or energy
gap and the valence and conduction bands overlap. With no energy gap, it takes a small amount of energy to move
electrons into the conduction band; consequently, conductors pass electrons very easily.
Q9. What term
is used to describe the definite discrete amounts of energy required to move an electron from a low shell to a
Q10. What is a negative ion?
Q11. What is the main difference in the energy
arrangement between an isolated atom and the atom in a solid?
Q12. What determines, in terms of energy
bands, whether a substance is a good insulator, semiconductor, or conductor?
chemical activity of an atom is determined by the number of electrons in its valence shell. When the valence shell
is complete, the atom is stable and shows little tendency to combine with other atoms to form solids. Only atoms
that possess eight valence electrons have a complete outer shell. These atoms are
Introduction to Matter, Energy, and Direct Current, Introduction
to Alternating Current and Transformers, Introduction to Circuit Protection,
Control, and Measurement, Introduction to Electrical Conductors, Wiring Techniques,
and Schematic Reading, Introduction to Generators and Motors,
Introduction to Electronic Emission, Tubes, and Power Supplies,
Introduction to Solid-State Devices and Power Supplies,
Introduction to Amplifiers, Introduction to
Wave-Generation and Wave-Shaping Circuits, Introduction to Wave Propagation, Transmission
Lines, and Antennas, Microwave Principles,
Modulation Principles, Introduction to Number Systems and Logic Circuits, Introduction
to Microelectronics, Principles of Synchros, Servos, and Gyros,
Introduction to Test Equipment, Radio-Frequency
Communications Principles, Radar Principles, The Technician's Handbook,
Master Glossary, Test Methods and Practices, Introduction to Digital Computers,
Magnetic Recording, Introduction to Fiber Optics