Baca A.G., Ashby C.I.H. Fabrication of GaAs Devices
Подождите немного. Документ загружается.
Contents
6.4 Ohmic contacts to n-type GaAs 195
6.4.1 GeAuNi ohmic contacts 196
6.4.2 Limited Au contacts for improved
thermal stability 197
6.4.3 Ohmic contacts to heavily doped surfaces 199
6.4.4 Refractory metals and contacts based
on reducing the surface bandgap 199
6.5 Ohmic contacts to p-type GaAs 200
6.6 Conclusion 201
References 202
7 Schottky contacts 205
7.1 Chapter scope 205
7.2 Physics and characterisation of Schottky
contacts 205
7.2.1 Physics of Schottky contacts 205
7.2.2 Interfacial properties of Schottky
contacts 210
7.3 Fabrication of Schottky contacts 214
7.3.1 Basic recessed gate fabrication 214
7.3.2 Self-aligned Schottky gates 217
7.3.3 Schottky gate structures 219
7.4 Electrical characteristics of GaAs Schottky
contacts 223
7.5 Reliability of GaAs Schottky contacts 225
7.6 Conclusion 227
References 227
8 Field effect transistors 229
8.1 Chapter scope 229
8.2 Field effect transistor basics 229
8.2.1 Field effect transistor tutorial 230
8.2.2 Field effect transistor performance and
reliability issues 236
8.2.3 Field effect transistor structures and
materials 240
8.2.4 Overview of field effect transistor
fabrication 244
8.3 Doping FETs 247
8.4 Isolation of FETs 251
8.5 Source and drain ohmic contacts 253
8.6 Gate metal contacts 254
8.7 Passivation 254
8.8 Degradation of FETs 256
8.8.1 Definition and characterisation of hot
electrons 257
x
Contents
8.8.2 Hot electron degradation 260
8.8.3 Other types of degradation 264
8.9 Conclusion 265
References 265
9 Heterojunction bipolar transistors 267
9.1 Chapter scope 267
9.2 HBT basics 267
9.2.1 Bipolar transistor tutorial 268
9.2.2 Other GaAs HBT performance and
reliability issues 272
9.2.3 HBT device structure and material
issues 275
9.2.4 Overview of HBT fabrication 279
9.3 MESA etching for GaAs-based HBTs 281
9.3.1 Emitter mesa etch 281
9.3.2 Base mesa etch 285
9.3.3 Collector mesa etch 286
9.4 Ohmic contacts for GaAs-based HBTs 286
9.4.1 Emitter metal ohmic contacts 286
9.4.2 Base metal ohmic contacts 287
9.4.3 Collector metal ohmic contacts 289
9.5 Passivation of GaAs-based HBTs 289
9.5.1 Ledge passivation 290
9.5.2 Dielectric passivation 291
9.5.3 Sulphur passivation 294
9.6 Variations on HBT processing 294
9.7 Reliability of HBTs 299
9.8 Conclusions 303
References 303
10 Wet oxidation for optoelectronic and MIS GaAs
devices 305
10.1 Chapter scope 305
10.2 Mechanism of wet oxidation processes 305
10.2.1 Chemistry of wet and dry oxidation of
AlGaAs 306
10.2.2 Electronic consequences of oxidation
processes 307
10.3 Rates and profile evolution 308
10.3.1 Al-mole-fraction effects 310
10.3.2 Layer thickness effects 313
10.3.3 Proximity enhancement effect 314
10.3.4 Wet oxidation of other materials 315
10.3.5 Miscellaneous observations 317
10.4 Practical wet oxidation 319
xi
Contents
10.5 Applications in optoelectronic devices 321
10.5.1 Structural issues for oxide VCSELs 321
10.5.2 Defect-related issues for optoelectronic
devices 324
10.6 Applications in electronic GaAs devices 325
10.6.1 Problems with wet and dry oxidation
for MIS devices 325
10.6.2 GaAs-on-insulator applications 326
10.7 Conclusion 326
References 327
Glossary 329
Index 347
xii
ACKNOWLEDGMENT
We would like to acknowledge all who helped in the preparation
and proofing of this book. Many thanks to Marcelino G.
Armendariz, Matthew G. Blain, William G. Breiland, Ronald
D. Briggs, Melissa Cavaliere, Jeffrey G. Cederberg, Ping-Chih
(Pablo) Chang, Michael J. Cich, Kent M. Geib, Leonardo Griego,
YoungMin Kim, Geraldine M. Lopez, Phil F. Marsh, Carolyn
M. Matzke, Cedric Monier, Mark E. Overberg, Dennis J. Rieger,
Carlos Sanchez, Charlie E. Sandoval, Randy J. Shul, Charles T.
Sullivan, John P. Sullivan, Jeffrey Y. Tsao, and W. Graham Yelton.
Many thanks also to all of our colleagues and collaborators, past
and present, whose interactions we greatly value, and who are too
numerous to mention individually.
xiii
xiv
ABBREVIATIONS
Acronym Chapter Meaning
2DEG 1 two-dimensional electron gas
AES 3 Auger electron spectroscopy
ALE 2 atomic layer epitaxy
AR 3 anti-reflection
AUD 3 advanced unified defect (model)
BJT 1, 9 bipolar junction transistor
BOE 8 buffered-oxide etch
CAIBE 5 chemically assisted ion-beam etching
CBM 3 conduction band minimum
CMOS 1, 3, 8, 10 complementary metal oxide
semiconductor
CRT 2 cathode-ray tube
C-V 2, 3, 7 current-voltage
CZ 1 Czochralski
DBR 10 distributed Bragg reflector
DC 2, 3, 5, 7–9 direct current
DFB 3, 4, 10 distributed feedback
DH 1 double heterostructure
DHBT 9 double heterojunction bipolar
transistor
DI 3, 4 de-ionised
DIGS 3 disorder-induced gap state (model)
DLTS 2 deep level transient spectroscopy
EBIC 2 electron-beam-induced current
ECR 3, 5, 8, 9 electron-cyclotron resonance
EDS 2 energy-dispersive spectrometer
EDX 3, 9 energy-dispersive X-ray analysis
EMP 2 electron microprobe (analysis)
EW 1 electronic warfare
EWF 3 effective work function (model)
FET 1–4, 6–9 field effect transistor
FIB 2, 5 focused ion beam
FWHM 2 full width at half maximum
xv
Abbreviations
Acronym Chapter Meaning
GMR 3 giant magnetoresistance
GOI 10 GaAs-on-insulator
HBT 1–6, 8, 9 heterojunction bipolar transistor
HDP 3 high-density plasma
HDPE 5 high-density-plasma etching
HEMT 1, 2, 5, 7, 8 high electron mobility transistor
IBAE 5 ion-beam-assisted etching
IBE 5 ion-beam etching
IC 1 integrated circuit
ICP 3, 5, 9 inductively coupled plasma
IMPATT 1 impact avalanche and transit time
IR 6, 7 infrared
JFET 1 junction field effect transistor
LCR 2 inductance, capacitance, resistance
LD 1, 9 laser diode
LDD 7, 8 lightly doped drain
LEC 1, 2 liquid encapsulated Czochralski
LED 1, 2, 9 light-emitting diode
LEED 3 low-energy electron diffraction
LPE 1, 2 liquid phase epitaxy
MBE 1–3, 6, 8, 9 molecular beam epitaxy
MESFET 1, 5–8, 10 metal-semiconductor field effect
transistor
MHEMT 8 metamorphic high electron
mobility transistor
MIGS 3 metal-induced gap state (model)
MIS 3, 8–10 metal-insulator-semiconductor
MMIC 2 monolithic microwave integrated
circuit
MOCVD 1–3, 5, 7–9 metal organic chemical vapour
deposition
MODFET 4, 5 modulation doped field effect
transistor
MOS 2, 3, 8 metal-oxide-semiconductor
MOSFET 1, 7, 10 metal-oxide-semiconductor field
effect transistor
MTTF 9 median/mean time to failure
OEM 1, 2 original equipment manufacturer
OES 5 optical emission spectroscopy
PA 1 power amplifier
PE 5 plasma etching
PECVD 3, 7–9 plasma-enhanced chemical
vapour deposition
xvi
Abbreviations
Acronym Chapter Meaning
PHEMT 1, 7, 8 pseudomorphic high electron
mobility transistor
PL 2, 3 photoluminescence
PLE 3 photoluminescence excitation
PMA 3 post-metallisation annealing
PR 5, 7 photoresist
QW 10 quantum well
RBIBE 5 radical-beam-ion-beam etching
RBS 2, 8 Rutherford backscattering
spectroscopy
REDR 9 recombination-enhanced-
defect-reaction
RF 1, 3, 5–9 radio frequency
RHEED 2, 3 reflection high-energy electron
diffraction
RIBE 5 reactive-ion-beam etching
RIE 5, 7–9 reactive ion etching
RMS 5 root mean square
RTA 3, 6–8 rapid thermal annealer/annealing
SAN 1 storage area network
SBH 3 Schottky barrier height
SEM 2 scanning electron microscope/
microscopy
SIMS 2, 3, 6, 8 secondary-ion mass spectrometry
STEM 2 scanning transmission electron
microscopy
STM 3 scanning tunnelling microscopy
TEM 2, 6–10 transmission electron microscope/
microscopy
TPD 3 temperature-programmed desorption
UDF 3 unified defect (model)
UHV 3 ultra-high vacuum
UV 1, 3, 4, 6–9 ultraviolet
VB 2 vertical Bridgman
VBM 3 valence band maximum
VCSEL 1, 10 vertical cavity surface emitting laser
VGF 2 vertical gradient freeze
VPE 1, 2 vapour phase epitaxy
WDM 1 wavelength division multiplexing
WDS 2 wavelength-dispersive spectrometer
XPS 2, 3 X-ray photoelectron spectroscopy
xvii
Chapter 1
Introduction to GaAs devices
Scope of this book p.1
GaAs materials p.2
Types of GaAs devices p.4
Electronic devices p.4
Photonic devices p.5
A brief history of GaAs devices p.6
History of GaAs electronic
devices p.6
History of GaAs photonic devices p.9
Applications of GaAs devices p.10
Photonic device applications p.11
Electronic device applications p.15
References p.19
1.1 SCOPE OF THIS BOOK
One might ask why another book about GaAs processing is needed.
In every field, there are two bodies of knowledge required for true
mastery. This is especially true in the field of device enginee-
ring. The first is related to understanding the ideal behaviour of
devices predicted by fundamental laws of physics. This is the sub-
ject of many textbooks and courses and is readily accessible to
every engineer. However, as we soon discover as we fabricate real-
world devices, behaviour often deviates from that ideal. When that
occurs, the questions “Why?” and “How can I fix it or avoid it next
time?” must be answered or the same problems will continue to
plague our devices.
The second body of knowledge helps us answer these chal-
lenging questions. It is that vast body of practical, even anec-
dotal, knowledge gradually accumulated by a practising engineer
through everyday experiences with successes and failures in
designing and fabricating devices. It is some of this second body
of knowledge that we hope to provide in writing this book. While
even the 30-year veteran will not have fully mastered this second
body of knowledge, the aim of this book is to share many of the
insights and solutions that we have learned during our combined
years working with devices made of GaAs and related materials.
In addition, many books on GaAs devices contain sections or
chapters on processing methods. However, most books provide
only a part of the knowledge required to actually make high-
quality devices and almost all of the previous books neglect some
aspects of processing as specifically related to device operation
and reliability.
Most books on GaAs devices are mainly concerned with a
logical and educational presentation of the device operation,
naturally focusing on the physics of the devices and the deriv-
ation of equations that describe device operation. Some good
books on advanced processing techniques in general [1–5] and
even on modern GaAs processing [6] are available. The GaAs pro-
cessing book by Williams focuses on process techniques for GaAs
1