Technology of Quantum Devices

569 Pages·2010·20.544 MB·English

by  Manijeh Razeghi (auth.)

Technology of Quantum Devices
Manijeh Razeghi
Technology of Quantum
Devices
123
ManijehRazeghi
WalterP.MurphyProfessorofElectricalEngineering
andComputerScience
NorthwesternUniversity
2220CampusDr.RM4051
Evanston,IL60208–3129
USA
ISBN978-1-4419-1055-4 e-ISBN978-1-4419-1056-1
DOI10.1007/978-1-4419-1056-1
SpringerNewYorkDordrechtHeidelbergLondon
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Foreword
Students commonly think of a textbook as merely a tool to get prepared for
exams. This is not the right way of looking at it! A textbook is the fruit of
long-term studies and experience acquired by the author and reflects her or
his personality. It embodies priorities; knowledge and I dare say even
dreams and life attitudes. Compare the difference in style and content in the
now classic physics textbooks by Landau and Feynman. Both Landau and
Feynman were scientists whose minds were ready to listen to the music of
the heavens. But how very differently! Landau wrote with the authority of a
Zeus and his book sounds like the ultimate message from Heaven, while
Feynman’s style is more modest, and his curiosity and quest for truth could
hardly be matched by anyone. His famous textbook is like an invitation to
travel through the Disneyland of Nature, where he acts as a guide, but a
guide who is also learning during this journey. And there is a third example:
the Chicago lecture notes on quantum mechanics by another Nobel laureate
– Enrico Fermi. At first sight – it appears to be more student friendly,
simple, very much to the point, but what a simplistic, and, indeed, incorrect
interpretation that would be! Fermi made a selection of topics and then
reduced the content to the absolute essence of what has to be understood to
get prepared for a journey into the quantum wonderland. He did it in such a
way that an average student had the impression he or she understood
everything, while a more demanding student would get a sense of much
more: a feeling that a miraculous quantum world was waiting for him
behind invisible doors, full of questions and surprises. Fermi did what
Albert Einstein once said about science in his peculiar English – make
things as simple as possible, but no simpler.
I admire this textbook by Professor Razeghi as much as I respect her
research achievements, which she fulfilled in her personal journey through
this demanding life. She was born in Persia, but left her motherland forever
to join her new country France, the country that gave her the chance to
continue the science she loved so much. In doing so, she followed the
footsteps of Marie Curie, who a century before left oppressed Poland as a
young math-teacher by the name of Skłodowska. Welcomed in France,
Skłodowska completed her studies at the Sorbonne, got married to a brilliant
French physicist Pierre Curie, and then spent endless hours working with
him, processing tons of radioactive ores from Czechoslovakia. Together
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vi Technology of Quantum Devices
they, eventually extracted small grains of the miraculous Polonium and
Radium – two radioactive elements they discovered and named. This superb
technological achievement, of which Marie definitely was the master and
the spiritus movens, opened new avenues for science and finally led her
twice to Stockholm to be awarded the Nobel medal.
Dr Razeghi hopefully was not forced to work in a cold and primitive
warehouse, like the Curies had to. The wise management of the French
electronic giant Thomson spotted her unique talents and gave her proper
resources to realize her visions and dreams. In a short time she became the
First Lady in solid-state physics and made Thomson the leader in modern
III-V compound semiconductor technology. Her laboratory was a dream for
most of us, well before the common excellence of today in many places. But
Razeghi became a technologist by choice. She was driven by the vision of
the ultimate device backed by a deep understanding of the science and full
of curiosity. This is what guided her. No wonder she became a very desired
collaborator for top labs and personalities in the semiconductor world. She
soon reached the peak of the Himalayas and could well have stopped there.
But not for Madame Razeghi. After many years of success, she left friendly
Europe for the next grand tour of her life – to the host of most advanced
material science – the United Sates. Interestingly, not to another industrial
super-organization like Thomson, but to a University, where she could share
her experiences, and shape the next generations. Her energy and visions
attracted money, and the money helped to create one of most advanced
university-based semiconductor labs in the world, visited and applauded by
most Nobel laureates in the field.
So, dear reader, make sure that you learn from this book, but not only
science and technology, which is presented with great clarity, skill and care
(there is even an appendix how to work with dangerous chemicals in the
MOCVD lab!). Maybe you will hear – just as I did – the whisper of the
modestly hidden powerful message from Professor Razeghi: the only thing
to prevent you from performing miracles in the tournament with Nature is
yourself. To win and to have pleasure, learn first, then practice in the lab,
and work with your notebook. If you work hard enough and still enjoy it,
you may have the stuff for the ultimate destiny – real Himalayas – the
discourse with Nature: understand her laws and limitations, but also her
immense and endless frontiers.
Thank you Manijeh for the guidance.

Jerzy M Langer
Professor in Physics, Institute of Physics
Polish Academy of Science, Warsaw, Poland
Fellow of the American Physical Society
Member of Academia Europaea
Preface

The cover of this book shows the beautiful interaction of two streams of
cosmic dust – this serves as a philosophical allegory to the contents of this
book. We start with atoms fixed in a crystalline lattice. When these atoms
are of the right type, and organized correctly, they profoundly influence the
behavior of electrons, similar to the cosmic dust on the cover. Arranging
many atoms together creates an artificial structure within the crystal, whose
electrical and optical properties are entirely within our control. By
understanding the art and science of atomic engineering we can create a
wide array of sophisticated semiconductor devices.
This book is dedicated to the student who is specializing in solid state
engineering especially in the areas of nanotechnology, photonics, and hybrid
devices. He is expected to have a basic knowledge, at undergraduate level,
of the fundamentals of semiconductor physics. The present book was
developed with a view to nanotechnology, which we believe is the subject of
today, tomorrow being perhaps dedicated to the interface between solid state
and soft solids and biology. The reader is expected to have an elementary
knowledge of quantum mechanics. For example he should understand what
is meant by quantum confinement and realize its novelty and importance.
He is expected to have come across such concepts as “the semiconductor
superlattice,” “the quantum dot,” “the heterojunction,” and have learned
why it is interesting to study these systems. In this book he is going to learn
how to make devices which use the new quantum physics which results
from the reduced dimensionality. (You would do well to refer to
Fundamentals of Solid State Engineering as the ideal place to freshen up on
these topics.)
To begin with, Chapter 1 of this book discusses modern single crystal
semiconductor growth technology with a focus on recent development and
technological improvements critical to modern semiconductor devices. In
Chapter 2, we are going to learn the first steps on how to actually fabricate a
bulk semiconductor device, how to prepare the material the substrate and
achieve the doping. Then in Chapter 3, we consider the fabrication of an
actual device structure. This involves patterning the semiconductor, and then
wire bonding it to arrive at the desired circuit configuration. Patterning
involves photolithography and electron beam lithographies. This is a
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specialized topic of great importance also for the new emerging fields of
organic and hybrid electronics. So more recently, scientists and engineers
have also invented the so called nano-imprint lithography in which man-
sized stamps are used to impress an image onto a surface. One can now also
use atomic force microscope tip to move atoms around on surfaces. “Nano-
membranes” can now be fabricated by etching away the substrate and
producing ultra thin free standing semiconductor films which can also be
“glued” onto another surface. These new developments have given device
fabrication another very powerful degree of spatial resolution and flexibility.
In addition, one has to imagine the AFM (atomic force microscope) tip
moving around on surfaces, and placing magnetic atoms, magnetic clusters
and fluorescent molecules and nanoparticles exactly into the location where
they are needed on the surface. This technology will allow us to eventually
make nanomachines, tools, and even surgical instruments. It is already
routine now to implant nanosized metallic particles or fluorescent molecules
of engineered sizes and shapes into cancer tumors, and then to irradiate
them. With metallic particle at their resonance “plasmon” absorption
frequencies for example, the particles get hot and destroy the tumor with
minimal damage to the rest of the tissue. The key discovery here, was that
one can tune the plasmon resonance (collective oscillation frequency of the
charges on the surface of the metal particle) by changing the shape and size
of particles. This requires “nanoengineering” and “nanochemistry.”
Making physically contactable electrical circuits on a micron scale
constitutes what is the well-established chip technology. In Chapter 4 we
review the operation of the p-n junction which constitutes one of the
fundamental building blocks of many modern electronic and opto-electronic
devices. In Chapter 5 we introduce the student to the technology of the
transistor. The concept of switching and amplification is explained. The
various types of transistor architectures are introduced. The focus is here not
so much on absolute miniaturization, as to understanding present day
transistor technology. The absolute miniaturization down to single electron
devices is still very much a research field. We feel that this fascinating topic
should be the subject of a specialized textbook because the present book is a
book for engineers. However small, the devices described in this volume are
ones which have current engineering applications. In Chapter 6, we consider
the principles, design and fabrication of the semiconductor laser. Later in
Chapter 7 the reader will learn how one makes and operates a Quantum
Cascade Laser (QCL), a work of art in the application of quantum
mechanics. But first, he has to learn the principles of light amplification and
light confinement, i.e. waveguiding, and how one can make lasers using
semiconductors. Semiconductors lasers are ideal for the mid-infrared
wavelength regime. Mid-infrared wavelengths (3–12 μ m) have a remarkable
amount of versatility for many new types of applications. Perhaps the most
Preface ix
important aspect of this wavelength range is that all molecules are optically
active in this regime, and quantitative infrared spectroscopy has been an
industrial tool for many years. Most of the time these tools were however
thermal sources, and they were limited in sensitivity and range. Mid-infrared
lasers, use an excitation/illumination source, and have demonstrated very
sensitive real-time and remote sensing capabilities. Besides simple
spectroscopy, the direct absorption of light in the right range by specific
molecules also lends itself to some potentially very useful medical
technologies. Breath analysis, for example, has already been used to monitor
health by checking for abnormal cell metabolism byproducts. In the future,
it may also be possible to target or cauterize specific types of cells by their
chemical or protein content for selective surgery. In addition, mid-infrared
lasers, in some ranges, have very good atmospheric transmission, which
potentially allows for improved, secure, free-space communication, which is
less sensitive to weather conditions than existing near-infrared systems. The
uniqueness of the QCL described in detail in Chapter 7, is that the laser
transition takes place between two quantum “intersubband states”, whose
energy difference can be engineered to produce lasers with different
wavelengths using the same material system.
In Chapter 8 we turn our attention to measuring light intensities, not
creating light. Each wavelength regime has its own characteristics uses and
its own applications: seeing and recording visible daylight (500–700 nm) to
seeing hotter objects in the dark (2–20 μm) and or behind walls, to seeing
through paper for example (THz spectroscopy). Then there is a multitude of
current and potential applications for sensitive detectors in the area of
specific single and multicolor detection, in the field of communication,
sensing security, robotics, artificial intelligence and medical diagnostics. A
sensitive photodetector is a very powerful tool, and research and
development in this field is worldwide. In Chapter 8 we learn about
photoconduction and how to quantify photodetector noise and define figures
of merits. Then in Chapter 9, we review the most important classes of
photodetectors. We explain the special role that semiconductor physics
plays and how these are fabricated using single atom deposition techniques.
In the current detector technologies, three examples take advantage of the
low dimensional properties that are predicted by quantum mechanics. They
include: the Type II InAs/GaSb superlattice photodetectors, the quantum
well intersubband photodetectors QWIP and the quantum dot infrared
photodetector QDIP. From the point of view of dimensionality, strictly
speaking, one has to point out that the Type II superlattice is actually a
three-dimensional system, the same as a bulk semiconductor, while the other
two systems are respectively two and zero dimensional systems. In
Chapter 10, we begin our discussion of photodetectors with Type II
materials.
x Technology of Quantum Devices
The concept of the Type II InAs/GaSb superlattice was first proposed by
Sai-Halasz and Esaki in the 1970s. The superlattice is fabricated by
alternating InAs and GaSb layers over several periods, creating a one-
dimensional periodic structure, in analogy to the periodic atomic chain in
naturally occurring crystals. The special feature of the Type II system is the
bringing together of two materials for which the energy gaps are not aligned
in energy space. The broken gap alignment as in the case InAs/GaSb leads
to the situation in which electrons from the GaSb valence band can wander
into the adjacent conduction band of InAs. The degree of this transfer can
however be controlled by using thin InAs sandwiched layers for which the
conduction band confinement can make the lowest levels again rise up
above the GaSb valence band. The consequences for physics and technology
are understandingly exciting. It took however a decade for this technology
to reach the degree of maturity needed for the realization of the new
predicted applications. Now the material systems we grow are good enough
to give us the detector performance that is comparable to the state-of-the-art
Mercury Cadmium Telluride (MCT) technology.
Chapter 11 is devoted to the important and beautiful area of Quantum
Well (QW) and Quantum Dot (QD) physics and technology. There are
several ways of fabricating small nano-size particles of semiconducting
materials, but the ones we focus on in this chapter are grown using the
“Stranski Krastanov” method. It was discovered by these researchers that
lattice mismatch at semiconducting interfaces, could, beyond a certain point
of strain, give rise to the spontaneous formation of dot like structures. The
fascinating side is that these dots are fairly regularly spaced, and
furthermore, they can be made to grow on top of each other. The chapter
begins by introducing the basic operating principles of the intersubband
detector, which are shared by the Quantum well intersubband detectors
QWIPs and the Quantum Dot intersubband detectors called QDIPs. We
describe how the QDIP operation deviates from the simple principles of
bulk semiconductor operation when we discuss the theoretical advantages of
QDIPs. Next we look at the growth technology for making the QDs that go
into the QDs. The capabilities and limitations of the growth technology
directly relate to whether or not the predicted theoretical advantages of
QDIPs can be achieved. Finally, we finish by reviewing some of the major
accomplishments in QDIP technology to date.
Whereas QDIPs and QWIPs are designed to cover the 2–15 μm range, at
the other extreme, we have the UV photodetectors which operate in the
<250 nm range. The high energy of the photon to be detected makes life
easier, because here, we can use wide band gap materials such as the GaN,
AlN and multilayers thereof materials. Large band gaps means that thermal
excitation of carriers is very difficult even at room temperature, and thus the
noise level is low. The growth of the GaN-AlN is however not
Preface xi
unproblematic and the details of this exciting subject area is covered by a
specialized text book devoted to these materials by the present author
{III-Nitrides Optoelectronic Devices by M Razeghi and M Henini,
published by Elsevier 2004}.
There is another area where GaN is being usefully developed and which
is causing great deal of excitement and that is the detection of single
photons. This has attracted the attention of scientists now for many years.
Applications include Raman spectroscopy, fluorescence spectroscopy, and
importantly now also quantum computing with photons. Photons emitted by
lasers can keep their coherence over long (km) distances bur the detection of
the combined quantum states require the use of devices with very high level
of sensitivity. Initially because of their high internal gain, photomultiplier
tubes were used to demonstrate single-photon counting. However, their high
volume and required voltages made these devices not so practical.
Nowadays, material progress has led to the development of improved
avalanche photodiodes with single-photon detection capabilities in
traditional semiconductors, such as Si or InGaAs, as well as in novel wide-
bandgap technologies. Integrated photon counting systems based on Si
single-photon avalanche diodes (SPADs) are today commercially available
for a wide spectral range from 350 nm to 900 nm; commercial InGaAs/InP
avalanche photodiodes have been successfully tested as single-photon
detectors at telecommunication wavelengths; and in the ultraviolet range,
SiC and GaN avalanche photodiodes have demonstrated single-photon
detection capabilities.
In Chapter 12, we review the basic properties of avalanche photodiodes.
In the second part, we focus on the main characteristics and issues of Geiger
mode operation (operating the device just above breakdown) for photon
counting purposes. Towards the end of the chapter, we provide some
examples of the state-of-the-art of single-photon avalanche diodes in Si,
InGaAs, and GaN.
Finally in Chapter 13 we discuss the interesting developing new area of
terahertz technology. In this chapter we describe recent developments in the
technology of terahertz (THz) emitters. We begin, by presenting a short
description of what can be done in the THz range, and later, some
applications are described in detail. An overview of the different broadband
sources available is presented. Further considerations are restricted to
modern semiconductor THz emitters. Next, the current state of the art of the
semiconductor THz emitter is presented. The Quantum Cascade Laser,
which is one of the most efficient semiconductor emitters in the mid-
infrared range, has now also been developed for the THz range. In this
wavelength range, the device is usually fabricated using multiquantum well
structures of GaAs/AlGaAs. Unfortunately these structures do not operate at
room temperature under continuous wave working conditions. We conclude
by discussing a new generation of THz emitters which are fabricated using