Hot Carriers in Semiconductor Nanostructures. Physics and Applications

498 Pages·1992·12.567 MB·English

by  Jagdeep Shah (Auth.)

HOT CARRIERS IN SEMICONDUCTOR
NANOSTRUCTURES:
Physics and
Applications
Jagdeep Shah
AT&T Bell Laboratories
Holmdel, New Jersey
AT&T
ACADEMIC PRESS, INC.
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copyright © 1992 by American Telephone and Telegraph Company
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Library of Congress Cataloging-in-Publication Data:
Hot carriers in semiconductor nanostructures: physics and applications
Jagdeep Shah [editor].
p. cm.
Includes bibliographical references and index.
ISBN 0-12-638140-2 (acid-free paper)
1. Hot carriers—Congresses. 2. Semiconductors—Congresses.
I. Shah, J. (Jagdeep) II. Title: Nanostructures.
QC611.6. H67H66 1992
621.38Γ 52—dc20 91-15684
CIP
PRINTED IN THE UNITED STATES OF AMERICA
92 93 94 95 9 8 7 6 5 4 3 2 1
To the memory of my parents
PREFACE
The success of various epitaxial growth techniques such as molecular-
beam epitaxy, vapor-phase epitaxy and chemical vapor deposition
techniques has made it possible to grow a large class of high-quality
semiconductor structures where the composition and doping can be
controlled down to a single monolayer (~3 Ä). Furthermore, remarkable
advances in semiconductor processing technology have allowed fabrica­
tion of structures with lateral dimensions of tens of nanometers. It is no
exaggeration to state that these nanostructures have revolutionized the
world of semiconductor physics and devices, by leading to novel physical
phenomena and to smaller and faster devices.
The field of hot carriers in semiconductors occupies a pivotal position
in semiconductor science. Investigation of hot carriers provides important
information about many fundamental scattering processes that determine
high-field transport in semiconductors, and such knowledge is invaluable
in understanding high-speed electronic and optoelectronic devices opera­
ting at high electric fields.
There are several excellent books covering hot-carrier effects in bulk
semiconductors, e.g., by Conwell, by Nag and by Reggiani. Various
aspects of growth and fabrication of semiconductor nanostructures,
physics of semiconductor heterostructures and devices made from such
structures have also been covered in several excellent books, e.g., by
Dingle, by Capasso and Margaritondo and by Capasso. References to
these books are provided in the Overview (Chapter I). There are,
however, no books dealing with hot carriers in semiconductor nanostruc­
tures. This book attempts to fill this gap and reviews the most exciting
recent developments in the field of hot carriers in semiconductor
nanostructures, a field that is important from fundamental as well as
device points of view.
It is hoped that this book will be useful to a wide range of researchers:
to specialists as a source of references and of information on subfields
related to their interests, to nonspecialists as an overview of the field, to
researchers interested in the basic physics of semiconductor nanostruc­
tures as a source of information about scattering processes in quasi-2D
systems, and to researchers interested in nanostructures devices as an
overview of some of these devices and as a source of information about
the basic physics governing them. It is indeed fortunate that each chapter
is written by an internationally recognized expert or group of experts who
have played leading roles in the advancement of their fields.
There are some topics that logically should be a part of a book of this
xiii
XIV PREFACE
kind but are omitted either because the subject has just been reviewed or
because it is not yet ripe for a review. The books on heterostructures
mentioned above include excellent reviews on resonant tunneling bipolar
and unipolar transistors, ballistic transport in vertical structures, tran­
sport in quasi-ID mosfets, and modulation-doped field-effect transistors.
The recent work on coherent spectroscopy of free carriers in semicon­
ductors and their nanostructures, and on one- and zero-dimensional
nanostructures, might well form the subject matter of future books.
I am grateful to AT&T Bell Laboratories for permission to publish
this book and for providing an intellectually stimulating environment
conducive to successful and productive research in a rapidly developing
field. I would like to thank many colleagues, both within and outside
AT&T Bell Laboratories, with whom I have collaborated and interacted
in the course of research on hot-carrier relaxations in semiconductor and
their nanostructures, the colleagues who have contributed to this volume,
the colleagues who provided valuable feedback on the scope and the
content of this volume, and Mr. Robert Kaplan of Academic Press for
encouragement to undertake this project and for providing a smooth
interface with the publishers. Last but not least, I wish to express my
appreciation to my wife and children for their encouragement, under­
standing and support.
Jagdeep Shah
Holmdel, New Jersey
CONTRIBUTORS
Numbers in parentheses indicate the pages on which the authors’
contributions begin.
E. R. Brown (469), Lincoln Laboratory, Massachusetts Institute of
Technology, Lexington, MA 02173-9108
Rossella Brunetti (153), Dipartimento di Fisica, Universitä di Modena,
Via Campi 213/A, 41100 Modena, Italy
S. Das Sarma (53), Department of Physics, University of Maryland,
College Park, MD 20742-4111
Stephen M. Goodnick (191), Department of Electrical and Computer
Engineering, Oregon State University, Corvallis, OR 97331
M. Heiblum (411), Weizmann Institute of Sciences, Rehovot, Israel
76100
Karl Hess (235), Beckmann Institute, Department of Electrical and
Computer Engineering, University of Illinois, Urbana, IL 61801
Ralph A. Höpfel (379), Institut für Experimentalphysik, Universität
Innsbruck, A-6020 Innsbruck, Austria
Kenichi Imamura (443), Fujitsu Limited, Fujitsu Laboratories Ltd., 10-1
Morinosato-Wakamiya, Atsugi 243-01, Japan
Carlo Jacoboni (153), Dipartimento di Fisica, Universitä di Modena,
Via Campi 213/A, 41100 Modena, Italy
A. P. Jauho (121), Physics Laboratory, H.C. 0rsted Institute, University
of Copenhagen, DK-2100 Copenhagen 0, Denmark
Simon Juen (379), Institut für Experimentalphysik, Universität Inns­
bruck, A-6020 Innsbruck, Austria
Isik C. Kizilyalli (235), AT&T Bell Laboratories, Allentown, PA 18103
Wayne H. Knox (313), AT&T Bell Laboratories, Holmdel, NJ 07733
P. Kocevar (87), Institut für Theoretische Physik, Universität Graz,
Universitätsplatz 5, A-8010 Graz, Austria
Paolo Lugli (191), Dipartimento di Ingegneria Meccanica, II Universitä
di Roma, Via O. Raimondo, 00173 Roma, Italy
XV
xvi CONTRIBUTORS
Toshihiko Mori (443), Fujitsu Limited, Fujitsu Laboratories Ltd., 10-1
Morinosato-Wakamiya, Atsugi 243-01, Japan
Shunichi Muto (443), Fujitsu Limited, Fujitsu Laboratories Ltd., 10-1
Morinosato-Wakamiya, Atsugi 243-01, Japan
Hiroaki Ohnishi (443), Fujitsu Limited, Fujitsu Laboratories Ltd., 10-1
Morinosato-Wakamiya, Atsugi 243-01, Japan
W. Pötz (87), Department of Physics, University of Illinois at Chicago,
Chicago, IL 60680
B. K. Ridley (17), Department of Physics, University of Essex,
Colchester, United Kingdom
Fausto Rossi (153), Dipartimento di Fisica, Universitä di Modena, Via
Campi 213/A, 41100 Modena, Italy
J. F. Ryan (345), Clarendon Laboratory, University of Oxford, Oxford,
England
Jagdeep Shah (3, 279, 379), AT&T Bell Laboratories, Holmdel, NJ
07733
Akihiro Shibatomi (443), Fujitsu Limited, Fujitsu Laboratories Ltd.,
10-1 Morinosato-Wakamiya, Atsugi 243-01, Japan
U. Sivan (411), IBM Research Division, T. J. Watson Research Center,
Yorktown Heights, NY 10598
Motomu Takatsu (443), Fujitsu Limited, Fujitsu Laboratories Ltd., 10-1
Morinosato-Wakamiya, Atsugi 243-01, Japan
M. C. Tatham (345), Clarendon Laboratory, University of Oxford,
Oxford, England
Naoki Yokoyama (443), Fujitsu Limited, Fujitsu Laboratories Ltd., 10-1
Morinosato-Wakamiya, Atsugi 243-01, Japan
LI
OVERVIEW
JAGDEEP SHAH
AT&T Bell Laboratories
Holmdel, New Jersey
1. Introduction 3
2. Fundamental Aspects of Quasi-2D Systems 5
2.1. Electron-Phonon Interaction in Quasi-2D Systems 6
2.2. Many-Body Effects 7
2.3. Hot-Phonon Effects 7
2.4. Scattering Processes Specific to Quasi-2D Systems 8
2.5. Tunneling Times 8
2.6. Quantum Transport 8
3. Monte Carlo Simulations 9
3.1. Monte Carlo Simulations of Ultrafast Optical Studies 9
3.2. Monte Carlo Simulations of Submicron Devices 10
4. Optical Studies of Hot Carriers in Semiconductor Nanostructures 10
4.1. Ultrafast Luminescence Studies of Carrier Relaxation and Tunneling . . . 11
4.2. Femtosecond Pump-and-Probe Transmission Studies 11
4.3. Ultrafast Pump-and-Probe Raman Scattering Studies 11
4.4. Electron-Hole Scattering 12
5. Transport Studies and Devices 12
5.1. Ballistic Transport in Nanostructures 12
5.2. Resonant Tunneling Hot-electron Transistors 13
5.3. Resonant Tunneling Diodes 13
6. Summary 13
References 14
1. INTRODUCTION
In thermal equilibrium, all elementary excitations in a semiconductor
(e.g., electrons, holes, phonons) can be characterized by a temperature
that is the same as the lattice temperature. Under the influence of an
external perturbation such as an electric field or optical excitation, the
distribution functions of these elementary excitations deviate from those
in thermal equilibrium. In general, the nonequilibrium distribution
functions are nonthermal (i.e. cannot be characterized by a temperature).
But, under special conditions, they can be characterized by a temperature
that may be different for each elementary excitation and different from
Hot Carriers in Semiconductor Nanostructures: 3 Copyright © 1992 by American Telephone and
Physics and Applications Telegraph Company
All rights of reproduction in any form reserved.
ISBN 0-12-638140-2
4 JAGDEEP SHAH
the lattice temperature. The term “hot carriers” is often used to describe
both these nonequilibrium situations.
Investigation of hot-carrier effects plays a central role in modern
semiconductor science. Properties of hot carriers are determined by
various interactions between carriers and other elementary excitations in
the semiconductor. Therefore, investigations of hot-carrier properties
provide information about scattering processes that are of fundamental
interest in the physics of semiconductors. Furthermore, these processes
determine high-field transport phenomena in semiconductors and thus
form the basis of many ultrafast electronic and optoelectronic devices.
The field of hot carriers in semiconductors thus provides a link between
fundamental semiconductor physics and high-speed devices.
Although some theoretical work on high-field transport in semiconduc­
tors dates from 1930s, experimental investigations started in 1951 with
the high-field experiments of Ryder and Shockley (the early work is
referenced by Conwell [1]). These and other investigations that followed
in the next quarter of a century concentrated on bulk semiconductors and
semiconductor devices, and provided quantitative understanding of many
phenomena and new insights into the high-field transport processes in
semiconductors. This work is extensively covered in excellent books by
Conwell [1], Nag [2,3], and Reggiani [4]. The topic has also been the
subject of NATO Advanced Study Institutes [5,6].
The direction of the field changed considerably in 1970s and 1980s
because of several developments. The quasi-two-dimensional nature of
carriers in the conducting channels in Si mosfets brought into play new
physical phenomena [7]. The mid 1970s brought the first high-quality
quantum-well heterostructures, consisting of thin layers of semiconduc­
tors with different bandgaps and grown using the techniques of
molecular-beam epitaxy (for a recent review, see, for example, Mad-
hukar in [8]). Semiconductor nanostructures have led to many exciting
developments in the physics of semiconductors [8-10]. Furthermore, the
ability to grow and fabricate semiconductor structures on nanometer
scales has led to the development of many new devices, such as
modulation-doped field-effect transistors and resonant tunneling diodes.
Nonequilibrium transport of carriers is a common thread in these
ultrasmall, ultrafast devices operating at high electric fields. Ballistic
transport in nanonstructures provided another focal point of interest.
These developments have led to considerable interest in the investigation
of hot-carrier effects in semiconductor nanostructures.
An important milestone in the field of hot carriers in semiconductors
was the demonstration in late 1960s that optical excitation can create hot
carriers and optical spectroscopy can provide information about the
distribution function of hot carriers. Although transport measurements
OVERVIEW 5
provide considerable information about various scattering processes in
semiconductors, they are averaged over the carrier distribution functions.
In contrast, optical techniques, by providing the best means of determin­
ing the carrier distribution functions, allow one to investigate the
microscopic scattering processes. Another development that has sig­
nificantly altered the course of this field is the recent availability of
ultrafast lasers with pulsewidths as short as 6 fs (for a recent review of the
field of ultrafast lasers and their applications to physics, chemistry and
biology, see [11]). These lasers allowed the investigation of the time
evolution of the carrier distribution functions on ultrashort time scales.
Since different scattering processes occur on different time scales, it
became possible to isolate various scattering processes by appropriate
choices of time windows.
The availability of high-speed computers has made it possible to carry
out ensemble Monte Carlo simulations of submicron devices and ultrafast
carrier relaxation in semiconductors. Detailed comparison of these
simulations with the device performance or with experimental observa­
tions of carrier relaxations obtained with ultrafast lasers has provided
valuable new information.
Finally, the ability to grow nanostructures has led to interesting new
transport phenomena such as ballistic transport of electrons and led to
devices based on nonequilibrium transport through such nanostructures.
Examples of the devices are resonant tunneling diodes, resonant tunnel­
ing hot-electron transistors and modulation-doped field-effect transistors.
As one can see from this brief historical survey, the field of hot carriers
in semiconductors and their nanostructures has been a dynamic field with
many important developments in the past decade. The purpose of this
book is to review the most exciting of these developments in the four
areas discussed above. The book is divided into four parts, with several
chapters in each part. Part II deals with the fundamental aspects of
hot-carrier physics in quasi-2D systems. Part III deals with Monte Carlo
simulations of ultrafast optical experiments in quasi-2D systems and of
submicron devices. Part IV discusses optical studies of hot carriers in
quasi-2D systems, and Part V deals with ballistic transport, resonant
tunneling transistors and diodes. In the remainder of this chapter, I will
present an overview of these developments.
2. Fundamental Aspects of Quasi-2D Systems
Hot-carrier effects are determined by many different scattering processes,
such as carrier-carrier scattering, carrier-phonon scattering, intervalley