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Materials Magic: Semiconductors Introduction
Material Magic: Semiconductors
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Materials Magic: Semiconductors Introduction
Table of Contents
An Introduction to Semiconductors and Their Use
3
Symbol List
6
Semiconductors: A Brief History of the Industry
8
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Materials Magic: Semiconductors Introduction
An Introduction to Semiconductors and Their Use
Semiconductors have many unique properties that make them useful,
especially in the manufacture of electronic and optical devices. During the
last 40 years or so improvements in our understanding of the physics of
semiconductors and developments in materials science have made possible
electronic and optical devices that were inconceivable earlier. During this
short period the semiconductor industry has grown into a multibillion dollar
business and in the process changed the way we do science and engineering,
the way we do business and even the way we learn. Of course, one could still
ask, why has this incredible expansion in the semiconductor industry
occurred? The answer to this question is that humankind has an insatiable
desire for information and for energy. By employing semiconductor
technology it has been possible to manufacture the extremely complicated
electronic circuits necessary for high capacity computer, telecommunication
and entertainment systems. Another contribution to this remarkable
expansion of the semiconductor industry lies in the fact that semiconductor
devices have been invented that are capable of generating electricity and
light.
In this short summary of semiconductor materials and technology, we will
first be concerned with the basic properties of semiconductors (Chapter 1).
The most important electrical, optical, thermal and magnetic properties will
be reviewed first. Also, a short summary will be given of some important
mechanical and acoustic properties. No attempt is made to give a rigorous
mathematical treatment of the materials science of semiconductors here or
discuss the properties of all the different types of semiconductors; there are
almost 200 different semiconductors! Rather, the focus is on the physical
principles involved, though every attempt is made to present accurate data in
the text.
Without the invention of the p-n junction all the electronic and optoelectronic
devices that we have come to be so dependent on would not have been
possible. Because of this, a chapter on the principles of semiconductor
devices (Chapter 2) will follow. The principles of operation of electronic
devices such as the bipolar transistor and the metal oxide semiconductor field
effect transistor (MOSFET), as well as optical devices such as the light
emitting diode (LED) and lasers are discussed. In addition, a short
introduction to integrated circuits (microelectronics), sensors and actuators
(microsystems) and finally a short discussion of what nanotechnology is, will
be presented. By nanotechnology is meant the study of devices and systems
having dimensions in the range 1 x 10-9 m, i.e. one billionth of a meter.
Thereafter, a brief introduction to materials and device fabrication
technology (Chapter 3 ) will be given. After discussing the very important
subjects of the growth of semiconductor single crystals and basic device
fabrication, integrated circuit technology will be reviewed. In fig. C1 a cross
section through an advanced Complimentary Metal Oxide Semiconductor
(CMOS) inverter circuit is shown [1]. As it can be seen it is very complicated
and consists of many layers of different materials; a substrate of silicon,
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Materials Magic: Semiconductors Introduction
insulators such as silicon dioxide and silicon nitride, conductors such as
aluminium and copper, as well as highly doped silicon are employed. It is
then surprising to realize that this complicated device is actually made with
the repetitive application of relatively few processes. How this is done will
be explained in the discussion on device fabrication.
Fig. 1 A cross
sectional view of an
advanced CMOS
inverter circuit [1].
Also a very brief presentation of some of the important aspects of the
fabrication of photonic devices, microsystems and, finally, nanoelectronic
devices will be given. In addition to improving our understanding of
advanced semiconductor processing technology, it will be shown that,
"nanotechnology", is not new! It is just one more step on the road to the
ultimate in smallness of devices and systems. What is new in this respect is
all the unexpected new physics and chemistry we meet along the way!
In order to illustrate the level to which the technology has risen, fig. C2
shows a photograph of a 200 mm diameter slice of silicon on which
approximately 200 microprocessor chips have been fabricated. The total
number of transistors on the slice is about 2 billion. It should also be
mentioned that the perfection and purity of the silicon crystal slice used far
exceeds any natural or synthesized material made until now.
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Materials Magic: Semiconductors Introduction
Fig. 2 On this 200
mm diameter slice of
silicon approximately
200 microprocessor
chips have been
made. The total
number of transistors
on the slice is
approximately 2
billion.
Finally, some of the special measurement techniques used to characterize
semiconductor materials and devices (Chapter 4) will be discussed. The
reason why an extra chapter on material testing is included is that some of
the methods employed for semiconductors are not found elsewhere.
In order to make these chapters as useful as possible, the material of each
section will include enough physical theory to give the reader an
understanding of how semiconductor devices work and how they are
manufactured. We will see that although integrated circuits can be very
complicated, the manufacture of these is based on relatively few processes as
stated above. It is hoped that this sort of presentation will help to make the
basic principles more easily understood and, thus, give the reader a basis for
a more quantitative study of semiconductors. Again it should be mentioned
that for specific mathematical details, data, and advanced theory, reference
should be made to the references cited.
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Materials Magic: Semiconductors Introduction
Symbol List
Symbol
Description
Unit
A
B
C
C
D
E
E
EC
EF
Eg
EV
E
Ec
Em
F
F
F(E)
G
H
Ħ
h
I
IC
J
Jth
K
K
kT
L
Le
m0
mn
mp
mi
N
N
ni
n0
NA
NC
ND
NV
p
p0
P
Lattice Constant
Magnetic Induction
Speed of Light in Vacuum
Capacitance
Diffusion coefficient
Magnitude of Electronic Charge
Energy
Energy, bottom of conduction band
Energy, Fermi level
Energy, bandgap
Energy, Top of Valance Band
Electric Field
Critical Field at Breakdown
Maximum Field
Frequency
Force
Fermi - Dirac Distribution Function
Generation Rate
Planck’s Constant
=h/2
Photon energy
Current
Collector Current
Current Density
Threshold Current Density
Boltzmann constant
Wave Vector
Thermal Energy
Length
Diffusion Length
Electron Rest Mass
Effective Mass, Electron
Effective Mass, Hole
Direction Cosines
Index of Refraction
Free Electron Concentration
Intrinsic Carrier Concentration
Equilibrium Electron Concentration
Acceptor Impurity Concentration
Effective Density of States, Conduction Band
Donor Impurity Concentration
Effective Density of States, Valance Band
Free Hole Concentration
Equilibrium Hole Concentration
Pressure
Å
T
cm / s
F
cm2/s
C
eV
eV
eV
eV
eV
V/cm
V/cm
V/cm
Hz (cps)
N
6
pairs/cm2s
J-s
eV
A
A
A/cm2
A/cm2
J/K
eV
cm or m
cm
kg
kg
kg
cm-3
cm-3
cm-3
cm-3
cm-3
cm-3
cm-3
cm-3
cm-3
Pa
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Materials Magic: Semiconductors Introduction
P
R
R
Ri (n0,p0,T)
ri (T)
t
T
vn
vs
vth
V
Vbi
VEB
VB
W
WB
Y
0
s
ox
s / 0 or
0
n
p
d
s
i
Bn
Bp
e
m
c
Power
Resistance
Reflection Coefficient
Recombination Rate
Recombination Rate
Time
Absolute Temperature
Carrier Velocity
Saturation Velocity
Thermal Velocity
Voltage
Built in Potential
Emitter - Base Voltage
Breakdown Voltage
Thickness
Base Thickness
Young’s Modulus
Absorbtion Coefficient
Linear Coefficient of Expansion
Permittivity in Vacuum
Semiconductor Permittivity
Oxide Permittivity
ox/ 0 Dielectric Constant
Lifetime or decay time
Angle
Wavelength
Frequency of Light
Permeability in Vacuum
Electron Mobility
Hole Mobility
Resistivity
Specific Density
Space Charge Density
Stress Coefficients
Schottky
Barrier
Height,
semiconductor
Schottky
Barrier
Height,
semiconductor
Metal Work Function
Angular Frequency (2 f or 2 )
= eB/m = cyclotron frequency
Ohm
Extinction Coefficient
7
W
cm-2 s-1
cm-2 s-1
s
K
cm/s
cm/s
cm/s
V
V
V
V
cm or m
cm or m
cm-1
1/ C
F/cm
F/cm
F/cm
s
rad
m, nm, Å
Hz
H/cm
cm2/V - s
cm2/V - s
- cm
atoms/cm-3
cm-3
n-type
V
p-type
V
eV
Hz
Hz
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Materials Magic: Semiconductors Introduction
Semiconductors: A Brief History of the Industry
Today it is possible to manufacture semiconductors with a purity and
perfection that was unheard of until a few years ago. However, the
importance of semiconductors is not just based on perfection of the
semiconductor crystals we can grow but, in large measure, on advances in
the design of electronic and optical devices, as well as the tremendous
advances that have been made in the area of semiconductor manufacturing
technology. Thus, the history of semiconductors is not just the history of
semiconductor materials manufacture, but also the history of the great strides
made in the invention of new electronic and optical devices and integrated
circuits. It is the interplay between semiconductor materials technology and
the fantastic inventiveness of electronic and optical systems designers that
has made possible the microelectronic revolution that has taken place during
the last 50 years. For those who are interested in economics, it should also be
mentioned, of course, that not only technology push but also market pull has
been decisive in expansion of the semiconductor industry as we have already
mentioned before. Today the semiconductor industry is the largest in the
world, in terms of economy!
From the very beginnings of the electronics and radio era in the early 1900's
it was realized that to make complex electronic systems it would be
necessary to find ways of interconnecting thousands or even millions of
electronic devices in reliable and inexpensive circuits. Although the use of
electron tubes was dominant all the way up through the 1950's, the vision
was to somehow make a system of integrated electronic circuits that could be
employed to make reliable electronic systems cheaply. This took more than
75 years to achieve and the solution was very much different than what
scientists and engineers first envisioned.
The era of semiconductors started in a modest way even before the turn of
the 19th century with the discovery that a point contact to selenium exhibited
rectifying properties and that the material was photosensitive. By the mid
1930's point contact selenium rectifiers and photodetectors, silicon carbide
varistors, and lead sulfide (naturally occurring Galena) point contact diodes
for radios were on the market [2].
During the second world war radio detection and ranging (RADAR) was
developed to a high level and began to be used in a variety of distance and
object identification applications. As a consequence, there arose a need for
sensitive mixer and detector diodes for radar detection circuitry. Since silicon
and germanium were the best materials for these applications, a great effort
was established for the production of high purity silicon and germanium.
This effort has continued to this day.
Semiconductors
Germanium,
Silicon and III-V
Compounds
The element germanium was discovered by Winkler in 1886 in the mineral
argyrodite. For half a century after it remained very much a scientific
curiosity, although it's properties were studied extensively. In 1935 studies
were begun at the Eagle Picher plant in the United States, on recovery of the
element from zinc smelting operations. In 1941 a pilot plant production of
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99.9% germanium oxide was achieved. At that time there was no commercial
application for this material, but in 1942 the National Defense Research
Council initiated a search for materials that could be used for microwave
detectors in radar. Germanium and silicon were found to be well suited.
Germanium occurs as a minor constituent of a number of ores. Argyrodite
(4AgS-GeS2) occurs in Germany and contains about 6-7% of the metal.
Germanite (7CuS-FeS-GeS2) containing 5-10% Ge and renierite (a complex
of Cu, Fe, Ge and As) are both found in Africa in zinc ores . None of these
minerals has been found in sufficient quantity to be of significance
commercially. Most of the supply of germanium is obtained as a bi-product
from other smelting operations.
In contrast to germanium, silicon is one of the most abundant elements,
second only to oxygen. Silica has been recognized from the earliest times and
glass manufacture has been depicted in Egyptian frescoes from
approximately 2000 B.C. However, the quartz form of silica was long
believed to be the element and it was not until comparatively modern times
that the element silicon was discovered. As is well known, early interest in
silicon was generated by the use of silicon as an alloying element in the steel
industry. Originally the element was prepared as ferrosilicon by heating a
mixture of silica, carbon and ferric oxide in a blast furnace. Later electric arc
furnaces were used in the refining of silicon and purities up to 99.8% were
obtained.
The III-V compounds are stoichiometric compounds prepared from elements
of group IIIA in combination with elements of group VA. Although most of
the combinations have been examined, only the gallium and indium
compounds with arsenic, antimony and phosphor are of commercial
significance. The III-V compounds are always grown as single crystals so
that their preparation will be discussed later in the text. Highly purified
elements must be used in the growth of crystals, of course.
The Invention of
the Transfer
Resistor =
Transistor!
Moving over to the work on electronic devices, in December of 1947 a
fantastic discovery was made. The first point contact bipolar transistor was
made by a group of scientists at Bell Laboratories in the United States. The
inventors were John Bardeen and Walter Brattain [3]. The first point contact
transistor was made using polycrystalline germanium. Shortly after the
transistor effect was demonstrated using silicon and by 1949 single crystal
material was used instead of polycrystalline. This conversion from
polycrystalline to single crystal material was primarily the work of Gordan
Teal and Morgan Sparks, also from Bell Laboratories. They were also
responsible for the fabrication of the first junction transistor, which W.
Shockley invented [4,5]. The conversion from polycrystalline to single
crystal source material has been one of the most significant advances in
semiconductor materials technology, because without a source of large single
crystals with uniform properties, the commercial production of small devices
would had been difficult and the development of complex large area
integrated circuits impossible.
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In spite of the fact that point contact transistors were relatively expensive and
unreliable, they were in most respects superior to vacuum tubes. Because of
the advantages they were put into production in 1951 as replacements for
vacuum tubes in telephone exchanges. After that, the technological advances
came rapidly and were followed by a gigantic expansion of the market. First
came the grown junction transistor, then the germanium alloyed transistor.
Silicon alloyed transistors were difficult to manufacture and never became a
commercial success.
The next important development in materials technology was the use of
gaseous diffusion, again developed at Bell Laboratories [6]. This technique
gave rise to the diffused, "mesa", transistors. These were commercially
available using germanium substrates in 1957 and silicon substrates in 1958
[7, 8]. The mesa transistor represented a considerable improvement over the
grown junction or the alloy junction transistor because higher operational
frequencies and less expensive devices could be made due to the much
narrower and more reproducible base widths that could be produced using
diffusion. Since many transistors could be made at one time on each slice of
semiconductor material and many slices could be cut from a crystal, mesa
transistors were less expensive to manufacture. In spite of the fact that the
development of these three types of transistor represented a great
advancement in manufacturing, they all had the same serious flaw. The p-n
junctions were exposed at the semiconductor surface. Many types of coatings
were developed in order to reduce the electrical leakage at these surfaces, but
none were completely successful.
The Planar
Process
Fortunately, a solution to this serious problem was found in 1959 by Jean
Hoerni at Fairchild Semiconductor Corporation [9, 10]. This was called the
planar process and it solved this problem very effectively by terminating the
p-n junctions under a thermally grown silicon dioxide layer on the surface of
the silicon slice. There is no other semiconductor that has an oxide that can
be grown in situ and that possess the near ideal electrical characteristics of
silicon dioxide. The introduction of the planar process, which increased
reliability and improved yields, along with the inherently better high
temperature performance of silicon, marked the beginning of the decline of
germanium devices. Thus, the four year period between 1957 and 1961
included first the introduction of large scale production with introduction of
the mesa process and then the beginning of the conversion from germanium
to silicon because of the advent of planar processing.
Invention of the
Integrated
Circuit
Until the invention of the integrated circuit, complete circuits, whether they
used transistors or vacuum tubes, were made by individually connecting the
various components, i.e. tubes or transistors, diodes, capacitors, resistors and
inductors, together. Although, many improvements were introduced to
increase packing density, simplify fabrication and increase reliability of the
electronic circuits, they all continued to depend on the wiring together of
discrete and separately packaged devices.
During February of 1959 came the great breakthrough. Jack Kilby of Texas
Instruments Corporation filed a patent application describing a concept that
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allowed, using relatively simple steps, the fabrication of all the necessary
components of the desired circuit, both active and passive components, in a
single piece of semiconductor and their interconnection in situ [11]. Because
of the manner in which the integrated circuit (IC) construction was described
in the Kilby patent, a separate patent on an IC using the planar process was
awarded to Robert Noyce of Fairchild Semiconductor [12]. That award was
the subject of a heated legal battle, but in the end both inventors were
awarded a patent, each for a different aspect of the integrated circuit. Kilby
was credited for conceiving and constructing the first working monolithic
circuit in 1959 and Noyce for his sophistication of the monolithic circuit for
more specialized use, particularly in industry.
The Metal Oxide
Semiconductor
Transistor
(MOST)
In 1960 D. Kahng and M.M. Atalla presented a paper on the silicon insulated
gate field effect transistor at the IRE-AIEE Solid State Device Conference in
Pittsburg, Pennsylvania, U.S.A [13]. Three years later S.R. Hofstein and F.P.
Heiman published a paper describing the fabrication of integrated circuits IC
based on this device. Today, these devices are called Metal Oxide
Semiconductor Transistors (MOST). The MOST is actually the same device
described in O. Heil's British patent entitled, "Improvement in or Relating to
Electrical Amplifiers and Other Control Arrangements and Devices", of 1939
[14]. It is interesting to note that the device that Bardeen, Brattain and
Shockley were trying to make at Bell Laboratories when they almost by
chance invented the bipolar transistor was the MOST [15]! The MOST is by
far the most important semiconductor device since the vast majority of all
integrated circuits manufactured today are based on this device.
Semiconductor
materials and
processing
technology
In addition to the semiconductor devices mentioned above, which are only a
small number of those actually invented, there have been great advances in
semiconductor materials and processing technology. Around 1958 the
primary wafer fabrication steps in the mesa process were 1) diffusion, 2)
metallization, 3) silicon etching and 4) various cleaning procedures. It should
be mentioned also that the first integrated circuits were made employing
these steps. In the planar process invented in 1960 three more steps were
introduced: 4) thermal oxidation of silicon, 5) lithographic printing of
patterns in a photoresist layer on top of the surface of the wafer and 6) the
etching of such patterns in the oxide and the contact metal. Since 1960 there
have been only a few steps added that allow new types of structures or
circuits to be fabricated. Probably the most important were the following: 7)
the use of epitaxial layers in bipolar circuits to provide an easy method of
device isolation. Epitaxial layers are also deposited over previously diffused
areas of the circuit to reduce collector saturation resistance and switching
time, thus resulting in higher speed circuitry, 8) the use of epitaxial
overgrowth of silicon onto insulating substrates, such as sapphire, for the
fabrication of thin film transistors, 9) the use of chemical vapour deposition
(CVD) to deposit materials such as silicon nitride for protective films and as
diffusion masking material and 10) the use of ion implantation for MOST
threshold adjusting and as an alternate technique for diffusion.
In addition to improving processing technology, great imagination has been
used in increasing the achievable complexity of IC circuitry and in reducing
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Materials Magic: Semiconductors Introduction
the cost of each circuit element. However, these advances have been made
possible through the use of more sophisticated equipment and through
processes such as the use of plasma etching instead of wet etching and
optical steppers and the use of electron beam writers or X-ray printing
instead of contact printers. Fig. 3 illustrates how advances in microlithographic techniques has made possible the reduction of the size of
semiconductor devices [16]. However, it must be admitted that the reduction
in device size has required increasing complexity and cost of patterning
equipment. Not surprisingly this trend is also typical for all the other
fabrication processes as well.
Fig. 3 The minimum
line width that
different lithographic
exposure systems
can be used to make
versus the years they
were in use. Notice
that the minimum line
width decreases
during the system's
lifetime [16].
In addition, to the advances in processing equipment the other areas of the
industry have changed also. The increase in circuit complexity can be seen
by comparing the first commercially available IC which consisted of a single
flip-flop with two transistors, four diodes, four capacitors and six resistors
with a MOST memory of today, such as the 1 megabit DRAM chip shown in
fig. 4. This memory chip has an area of approximately 70 mm2 and contains
over 2,200,000 components [17].
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Fig. 4 a) A
photograph of a 100
mm diameter silicon
wafer on which 1
megabit DRAM have
been fabricated. b)
we see the DRAM
itself mounted in a
special ceramic
package [17].
In the IC of the 1960 chip area was approximately 1 mm2; today chip area
can be larger than 200 mm2. However, it should be mentioned that while chip
size has increase tremendously, it has not increased commensurately with
circuit complexity, i.e. while the area has increased 100 times circuit
complexity has increased by more than 10 million times. In addition to all
this, the slice diameter of silicon crystals has steadily increased from 25 mm
to 200 mm due to advances in crystal growing techniques.
Going back to device and circuit design again, it is clear that these have
become much more sophisticated and much smaller. Two or three layers of
interconnections between circuit components are common today, but the
number of active devices required to perform a given function has decreased.
For example, some of the early DRAM cells required six transistors, whereas
today one transistor and one capacitor suffice.
Also in the area of processing much more attention is necessary to make sure
that designs are more tolerant of expected process variations. At the same
time, process control has been continually tightened through better
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understanding of the processes and the introduction of microprocessor
control of most of the equipment. With the recognition that most yield loss is
associated with particulates on the wafer, extensive effort has been expended
to provide better cleaning procedures, purer chemicals and a cleaner
manufacturing environment.
Moore's Law
One way of showing the total effect of all of these improvements is to show
the increase in the number of circuit elements in IC versus year from 1960 up
until today as shown in fig. 5. Note that the increase in complexity of IC has
increased exponentially, at first doubling every year and more recently
roughly every 18 months. This curve is called Moore's Law, after Gordan
Moore whom first noticed this relationship between chip complexity and the
year that the IC was first introduced [18]. Moore was also one of the
founders of Fairchild Semiconductor and Intel Corporations. To dramatize
the effect of the original inventions and the subsequent improvements on our
daily lives we can mentally eliminating all of the things around us that
depend on transistors of one type or another for their successful operation. It
is easy to see that our world would be very different indeed.
Fig. 5 Device density
and minimum feature
size in a IC versus
year. Until about
1975 the device
density per chip
doubled every year.
Since then it has
doubled every 18
months,
approximately [18].
Photonics and
the
Semiconductor
LASER
Paralleling the developments in semiconductor electronics we have the field
of Photonics. Here semiconductor materials technology also plays an
important role.
Lasing action in semiconductors was reported by several research groups in
1962 [19, 20, 21, 22]. The device used was a simple forward biased gallium arsenide (GaAs) p-n junction. Electron hole recombination in the depletion
region of the p-n junction provided the optical gain and the polished facets
perpendicular to the plane of the junction provided the optical feedback by
forming a resonant cavity. Quite soon thereafter, lasing action was reported
in other direct band gap semiconductor materials, among others: InP, InAs,
InAsP, GaAsP, and GaInAs. However, the utility of these early devices was
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limited because, the large value of the threshold current density (Jth ≥ 50
kA/cm2 ) made continuous operation at room temperature impossible.
The following year it was suggested that lasers might be improved if a layer
of one type of semiconductor were sandwiched between two cladding layers
of another semiconductor having a larger bandgap [23]. This configuration is
commonly referred to as a heterostructure laser, in contrast to the
homostructure lasers made of only one type of semiconductor material,
mentioned above. In spite of the reduction in threshold current brought about
by the use of heterostructure lasers, it wasn't until 1969 that a heterostructure
laser that could be operated at room temperature was demonstrated [24]. For
these devices the liquid phase epitaxial technique was employed for growing
the GaAs and AlxGa 1-x As layers. Additional work resulted in
heterostructure lasers operating contiuously at room temperature in 1970
[25]. By 1975 AlGaAs lasers having threshold currents as low as Jth 0.5
kA/cm2 were demonstrated using thin active layers approximately 0.1 m
thick, i.e. about 100 nm thick! This represented a reduction of threshold
current by more than two orders of magnitude over the simple homostructure
lasers first fabricated in 1962. With these advances the semiconductor laser
was changed from being a laboratory curiosity to a practical compact
coherent light source useful for numerous applications.
The room temperature operation of a InGaAsP laser operating in the pulsed
mode at a wavelength of 1.1 m was also reported in1975. By changing the
geometry of the laser to a very narrow stripe geometry continuous operation
was achieved in 1976 [26] . In 1977 the wavelength was extended to 1.3 m.
Since low loss dispersion free optical fibers were already available
considerable effort was made to develop a practical InGaAsP laser for this
wavelength. Around the same time, ultra low loss optical fibers having losses
in the range of approximately 0.2 dB/km at the 1.55 m wavelength were
being developed. As a consequence several groups changed the focus of their
work and started to develop InGaAsP lasers operating at this wavelength.
Since then the effort for developing InGaAsP lasers operating in the
wavelength range of 1.3 to 1.6 m has proceeded very rapidly. The primary
motivation for this is due to their application in fiber optical
communications. Today the use of InGaAsP lasers in long haul optical
communication systems is standard and has been so for several years.
Another important area of photonics in which advances in semiconductor
materials technology and device design has bought about impressive
industrial growth, as well as, important advances in our understanding of the
basic physics is that of photovoltaic devices or solar cells as they are often
called.
Photovoltaic
Diodes
Solar cells are employed in both space and terrestrial applications for the
reliable generation of electricity. This device is unique in that it can convert
sunlight directly into electricity with good efficiency. It has no moving parts,
it can operate at room temperature and is virtually non-polluting. Some of the
very earliest solar cell systems are still operational after 40 years of service.
The solar cell is quite a simple device; actually it is just a large area diode. It
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was first described in a scientific paper by D.M. Chapin, C.S. Fuller and G.L.
Pearson in 1954 [27]. The first devices had a conversion efficiency of 4%.
Today, the most advanced structures are nearly 30% efficient, an efficiency
that earlier was thought to be theoretically impossible!
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References Cited
1.
J.D. Plummer, M.D. Deal and P.B. Griffin, "Silicon VLSI
Technology, Prentice Hall, New Jersey (2000) Chapter 2
2.
G. K. Teal, "Semiconductor Materials", Chapter 6 in "Material
Processes", J.F. Yuong and R. Shane editors, Marcel Dekker, New
York (1985)
3.
J. Bardeen and W.H. Brattain, "The Transistor a Semiconductor
Triode", Phys. Rev. 74, 230 (1948)
4.
W. Shockley, M. Sparks and G.K. Teal, "p-n Junction Transistors",
Phys. Rev. 83 pp 151 - 162 (1951)
5.
W. Shockley, "The Theory of p-n Junctions in Semiconductors and
the Junction Transistor", Bell Sys. Tech. J. 28, 435 (1949)
6.
G.L. Pearson and C.S. Fuller, "Silicon p-n Junction Power
Rectifiers and Lightning Protectors", Proc. IRE 42 760 (1954)
7.
M. Tannenbaum and D.E. Thomas, "Diffused Emitter and Base
Silicon Transistors", Bell Sys. Tech. J. 35 pp 1-22 (1956)
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