Physics and technology of heterojunction devices

326 Pages·1991·15.341 MB·English

by  D. Veron Morgan, Robin H. Williams

IET Materials and Devices Series 8
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Physics and Technology of Heterojunction Devices brings together the physics h
of engineering aspects of heterojunction semiconductor devices in one volume. nn
The book draws on the knowledge of various experienced academics, and Do
covers aspects of the physics of heterojunctions, resonant tunnelling effects
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in semiconductor heterojunction devices, characterisation of heterojunctions, eo
high electron mobility transistors, heterojunction bipolar transistors, and vg
heterostructures in semiconductor lasers. icy
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D. Vernon Morgan
and Robin H. Williams
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The Institution of Engineering and Technology m
www.theiet.org s
0 86341 204 1
978-0-86341-204-2
IET MaTErIals and dEvIcEs sErIEs 8
Series Editors: Prof. D.V. Morgan
Dr N. Parkman
Prof. K. Overshott
Physics and Technology
of Heterojunction
Devices
Other volumes in this series:
Volume 4 Semiconductor lasers for long-wavelength optical fibre communications
systems M.J. Adams, A.G. Steventon, W.J. Devlin and I.D. Henning
Volume 5 Semiconductor device modelling C. M. Snowden
Volume 6 Optical fibre C.K. Kao
Volume 8 Physics and technology of hetrojunction devices D.V. Morgan and
R.H. Williams (Editors)
Volume 9 Electrical degradation and breakdown in polymers L.A. Dissado and
J.C. Fothergill
Volume 10 Electrical resistivity handbook G.T. Dyos and T. Farrell (Editors)
Volume 11 III-V quantum system research K. Ploog (Editor)
Volume 12 Handbook of microlithography, micromachining and microfabrication,
2 volumes P. Rai-Choudhury (Editor)
Physics and Technology
of Heterojunction
Devices
Edited by
D. Vernon Morgan
and Robin H. Williams
The Institution of Engineering and Technology
Published by The Institution of Engineering and Technology, London, United Kingdom
First edition © 1991 Peter Peregrinus Ltd
Reprint with new cover © 2006 The Institution of Engineering and Technology
First published 1991
Reprinted 2006
This publication is copyright under the Berne Convention and the Universal Copyright
Convention. All rights reserved. Apart from any fair dealing for the purposes of research
or private study, or criticism or review, as permitted under the Copyright, Designs and
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While the author and the publishers believe that the information and guidance given
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The moral rights of the author to be identified as author of this work have been
asserted by him in accordance with the Copyright, Designs and Patents Act 1988.
British Library Cataloguing in Publication Data
Physics and technology of heterojunction devices.
I. Morgan, D.V. II. Williams, R.H.
621.3815
ISBN (10 digit) 0 86341 204 1
ISBN (13 digit) 978-0-86341-204-2
Printed in the UK by Short Run Press Ltd, Exeter
Reprinted in the UK by Lightning Source UK Ltd, Milton Keynes
Contents
Preface ix
The Editors xi
The Authors xii
1 Aspects of the physics of heteroj unctions;
C Matthai and R. H. Williams 1
1.1 Introduction 1
1.2 Electronic structure of bulk semiconductors 5
1.2.1 Elemental and binary semiconductors 5
1.2.2 Semiconductor alloys 7
1.3 Lattice matched systems 8
1.3.1 Physics of band alignment 9
1.3.2 Macroscopic models 10
1.3.3 Linear4 models 10
1.3.4 Microscopic models 11
1.3.5 Self consistent interface calculation 12
1.3.6 Determination of band offsets 13
1.3.7 Factors influencing band offsets 15
1.4 Strained systems 17
1.4.1 Atomic structure of strained layers 18
1.4.2 Critical thickness of strained layers 18
1.4.3 Effect of strain on bulk band structures 20
1.4.4 Band offsets in strained heteroj unctions 21
1.4.5 Si,_,GeySi 21
1.4.6 InGaAs/GaAs 22
1.5 Superlattices and multi-quantum wells 23
1.5.1 Superlattice band structure 23
1.5.2 Quantum wells 24
1.6 Limits of heteroj unctions 24
1.7 Modifying band offsets 28
1.8 References 31
vi Contents
2 Resonant tunnelling effects in semiconductor
heterostructures. L. Eaves, M. L. Leadbeater, E. S. Alves, F. W.
Sheard and G. A. Toombs 33
2.1 Introduction 33
2.2 Fabry-Perot electron resonances in wide quantum wells 36
2.3 Resonant tunnelling studies of magneto-electric
quantisation in wide quantum wells 38
2.4 Charge build-up and intrinsic bistability 44
2.5 Conclusions 50
2.6 Acknowledgments 50
2.7 References 51
3 Simulation of semiconductor heterojunction devices.
P. A. Mawby 53
3.1 Introduction 53
3.2 Physical basis of simulation programs 53
3.2.1 Drift-diffusion model 53
3.2.2 Hydrodynamic equations 57
3.2.3 Quantum mechanical effects 60
3.3 Heterojunction device structures 63
3.3.1 Heterojunction diodes, solar cells and photodiodes 63
3.3.2 Heterojunction bipolar transistors 72
3.3.3 High electron mobility transistors 86
3.4 Heterojunction lasers 99
3.5 Quantum devices 101
3.6 Summary 104
3.7 References 104
4 Characterisation of heterojunctions: Electrical methods.
H. Thomas 111
4.1 Introduction 111
4.2 Transport properties of AlGaAs-GaAs heterojunctions 112
4.2.1 Hall effect 113
4.2.2 Hall measurements 114
4.2.3 Magnetic field dependent Hall data 116
4.2.4 Mobility spectrum 118
4.2.5 Shubnikov-de Haas effect 120
4.3 Transport properties of heterojunction devices 122
4.3.1 Geometric magneto-resistance 122
4.3.2 Geometric magneto-transconductance (GMT) 123
4.4 Heterojunction band discontinuities 124
4.4.1 Capacitance-voltage measurements 125
4.4.2 Current—voltage measurements 130
4.5 Deep level spectroscopy 135
4.5.1 DX centres in A^Ga^As 135
4.6 Acknowledgments 143
4.7 References 143
Contents vii
5 High electron mobility transistors. P. J. Tasker 146
5.1 Introduction 146
5.1.1 Motivation for modulation doping as gate length is scaled 146
5.1.2 Heterojunction field effect transistors 147
5.2 Performance of HEMT transistors 150
5.3 Characterisation of HEMT transistors 154
5.3.1 Material characterisation 154
5.3.2 Transistor characterisation 155
5.4 Basic physical model 168
5.4.1 Fundamental definition of current gain cut-off frequency f 168
T
5.4.2 Excess charge modulation in HEMT structures 170
5.4.3 Interaction of two ME mechanisms 177
5.5 Design of HEMT transistors 180
5.5.1 Optimisation of modulation efficiency 180
5.5.2 Optimisation of extrinsic performance 185
5.6 Summary 193
5.7 Acknowledgments 195
5.8 References 195
6 Heterojunction bipolar transistors. P. Ashburn and
D. V. Morgan 201
6.1 Introduction 201
6.2 Homojunction and heterojunction bipolar transistor theory 201
6.2.1 Generation—recombination in the depletion region 205
6.3 Heterojunction design and fabrication 207
6.4 Performance of practical heterojunction systems 208
6.4.1 Si/SiGe heterojunctions 208
6.4.2 AlGaAs/GaAs heteroj unctions 212
6.4.3 InP/InGaAs heteroj unctions 214
6.5 Circuit speed of heterojunction bipolar technologies 219
6.5.1 Self-aligned bipolar processes 219
6.5.2 Heterojunction bipolar transistor design 221
6.5.3 ECL gate delay estimation 223
6.5.4 Gate delay comparison for AlGa/GaAs and Si bipolar
technologies 225
6.6 Conclusions 228
6.7 Acknowledgments 228
6.8 References 228
7 Heterostructures in semiconductor lasers. P. Blood 231
7.1 Introduction 231
7.2 Optical gain in semiconductors 233
7.3 Heterostructures in lasers 237
7.3.1 Functions of heterostructures 237
7.3.2 Band offsets 242
7.3.3 Extrinsic properties of heteroj unctions 244
7.4 Double heterostructure lasers 247
viii Contents
7.5 Quantum well lasers 250
7.5.1 Introduction 250
7.5.2 Properties of ideal quantum wells 251
7.5.3 Gain-current relations 253
7.5.4 Well width dependence of threshold current density 259
7.5.5 Cavity length dependence of threshold current 265
7.5.6 Temperature dependence of threshold current 267
7.5.7 Summary of quantum well laser performance 269
7.6 Other uses of heterojunctions in lasers 271
7.6.1 Short period superlattices 271
7.6.2 Strained layer structures 272
7.6.3 Quantum wire lasers 274
7.7 Future developments 277
7.8 Summary 278
7.9 Acknowledgments 279
7.10 References 280
8 Novel heterojunction devices. M. J. Kelly 283
8.1 Introduction 283
8.2 Forward projections 286
8.3 Applicable physics at 10 nm 288
8.3.1 Ballistic and hot-electron motion 288
8.3.2 Tunnelling 290
8.3.3 Quantum confinement 292
8.3.4 Other exploitable phenomena 293
8.3.5 Special materials possibilities 294
8.3.6 10 nm nuisances 294
8.3.7 Very new effects 294
8.4 New electronic devices 295
8.4.1 Tunnelling devices 295
8.4.2 Hot electron devices 296
8.4.3 Avalanching 297
8.4.4 Planar-doped-barrier diodes 298
8.5 New optical devices 298
8.5.1 Optical modulators and switches 298
8.5.2 Infrared sources and detectors 299
8.5.3 Avalanche photodiodes 300
8.5.4 Other optical devices 300
8.6 Qualitatively new devices 300
8.7 Summary and conclusions 302
8.8 References 302
Preface
The use of heteroj unctions to improve the performance of semiconductor
devices is not a new concept; it was first suggested by William Shockley in
1951*. At that time, however, semiconductor technology was not developed to
the point where such novel concepts could be achieved in the laboratory.
As the name suggests, the semiconductor heterojunction is an idealized
interface between two semiconductors. For device application such an interface
has to be free of contaminants and the two semiconductors must generally be
lattice matched so that no distortion of the epitaxial layers occurs to give rise to
unwanted defects within the layer. In these very special circumstances, the
band diagrams of the separate materials can be joined continuously and
engineered to produce some desired heterojunction behaviour. This new
development has been called "band gap engineering" and has provided a
vehicle for a new understanding of semiconductor interface physics.
The key to these developments has been the rapid advances in the epitaxial
crystal growth techniques; of molecular beam epitaxy (MBE) and metal
organic deposition (MOCVD). The advances of these growth techniques may
be gauged by the number of national and international conferences that have
taken place in the past decade. The growth precision of epitaxial growth
possible using these techniques currently enables single monolayers to be
deposited with a resulting crystal perfection unparalleled by previous tech-
niques and enables ultra thin structures to be grown with in-built strain which
can offer advantages in the behaviour of certain devices.
Apart from the wealth of experience gained in our understanding of interfaces
and interface band diagrams, a new body of basic physical knowledge is
emerging on the behaviour of electrons in low dimensional structures. Potential
wells can be grown where the electrons are confined to two dimensions and in
some circumstances quantization can be achieved in all three dimensions to
form quantum dots. In terms of semiconductor device physics band gap
engineering has opened up new directions for research into high performance
devices. Conduction band notches have been used as hot electron injectors in
bipolar transistors and in transferred electron devices. Quantum wells have
been used to confine electrons in high electron mobility transistors and also in
laser diodes. Whilst heterojunction band discontinuities have been used to
selectively enhance the current gain of bipolar transistors. These and many
* W. Schockley U.S. Patent 2569347 25 September 1951.