Baca A.G., Ashby C.I.H. Fabrication of GaAs Devices

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Glossary

Schottky

Contact

a rectifying contact made from a

metal-semiconductor interface

self-aligned an alignment of a feature to an active structure

in a device without lithography

semiconductor

parameter

analyser

an instrument that provides or measures the

voltages and currents in a device

sheath the boundary region between the plasma and

the electrodes; the plasma potential is

determined by the sheaths; a region of a

plasma where electrical neutrality does not

prevail

sidewall the side of an etched feature

SIMS secondary-ion mass spectroscopy, an analysis

technique where a sample is sputtered and the

mass of the back-sputtered ions is analysed to

identify elements and impurities of a sample

source the electrode that acts as the origin of electrons

in an FET during normal current ﬂow

space-charge

region

a region of a doped semiconductor that is

depleted of free carriers

S-parameter scattering parameter. Describes a method of

testing where reﬂected or transmitted signals

are measured as an alternative to I-V testing

spectrometer an instrument used to determine (detect) light

intensity as a function of the wavelength of

the light

sputtering the process of material removal by ions

accelerated toward the sample in a vacuum;

momentum transfer from the ions to the

surface ejects surface atoms

STEM scanning transmission electron microscopy

stepper a lithography tool that repeats a pattern across

many sites of a wafer

STM scanning tunnelling microscopy

stoichiometry the ratio of various elements of a chemical

compound

stress test a test that subjects a device beyond its normal

operating conditions (bias, temperature,

ambient), usually to accelerate a failure

mechanism

subcollector the part of the collector in an HBT that is

highly doped for ohmic contact formation

surface states electronic states speciﬁc to the surface of a

semiconductor

342

Glossary

surface

potential

the energy difference between the bottom of

the conduction band (or top of the valence

band) at the surface and energy of the bottom

of the conduction band (or top of the valence

band) in the bulk of the semiconductor

surface recom-

bination

velocity

S (units of cm/sec); 2D surface analog of 1/τ

where τ is the 3D carrier lifetime; essentially

the inverse lifetime of a carrier at

the surface

TCE trichloroethane; 1,1,1-trichloroethane

TEM transmission electron microscopy, a

method of high-resolution imaging of

solids

tetrahedral a chemical bonding geometry where four

atoms are each bonded to a ﬁfth atom

and are equally spaced on the surface of

a sphere with the ﬁfth atom at the centre;

the characteristic

bonding geometry for GaAs and Si

thermionic

emission

transport of an electron (hole) across a

potential barrier with a probability

related to its thermal energy

thermionic ﬁeld

emission

transport of an electron (hole) across a

potential barrier with signiﬁcant

probability of either tunnelling or

thermionic emission

threshold voltage the gate voltage of an FET that turns on

the current from source to drain

threading

dislocation

a structural defect in a semiconductor that

extends through the crystal in the

irregular shape of a thread; examples are

edge, screw and mixed (screw + edge)

dislocations

TLM transmission line method (structure) for

ohmic contact testing; refer to

Section 6.3.2 for details of the test

(structure)

TPD temperature-programmed desorption; a

surface analytical technique where a

sample is heated at a controlled rate and

the chemical species released at different

temperatures are measured by mass

spectroscopy

343

Glossary

transconductance the differential of the drain current versus

gate voltage in an FET, noted by the

symbol g

transfer length refers to the typical distance that electrons

(holes) traverse laterally in the

semiconductor before crossing the metal

semiconductor interface of an ohmic

contact

trap a midgap electronic state, usually

localised, that can be ﬁlled by electrons

(holes)

trenching deeper etching at feature edges due to

reﬂection of ions from a sidewall that

locally increases ion ﬂux on the surface

near the feature edge

tunnelling the passage of a particle across a potential

barrier with probability related to the

amplitude of its quantum-mechanical

wave function on the other side of the

barrier

UHV ultrahigh vacuum (pressures ≤ 10

−8

torr)

undercutting etching underneath a mask edge

UV ultraviolet

vacancy a type of defect consisting of a lattice site

in a crystal with no atom residing at

that site

vacuum a pressure below atmospheric pressure:

conventional ranges are low = 760

to 10

−2

torr (overlaps medium range);

medium = 1–10

−2

torr

high = 10

−2

− 10

−8

torr; ultrahigh

≤ 10

−8

torr

valence band the energy bands whose electrons

are involved in chemical bonding in

a solid

valence band offset,

E

the abrupt energy difference in the valence

band at a heterointerface

valence electrons the electrons in the outermost shells of an

atom. These electrons can participate in

chemical bonding

VBM valence band maximum = E

VCSEL vertical-cavity surface-emitting laser

344

Glossary

GS,

CE,

) the drain-source (or gate-source, or

collector-emitter, or base-emitter)

voltage of a transistor

VPE vapour-phase epitaxy, an older technique

for GaAs epitaxial growth with source

materials that are created by ﬂowing

gas over solid, heated Ga and

As sources

WDM wavelength-division multiplexing. A method of

sending multiple communication channels along

an optical ﬁbre by using (slightly) different

wavelengths for each channel

WDS wavelength-dispersive spectrometer, a

high-resolution X-ray detector used for electron

microprobe analysis

work

function

the minimum amount of energy required to

remove an electron from the surface of a metal;

the amount of energy required to take an

electron from the Fermi level within a material

and remove it to inﬁnity

XPS X-ray photoelectron spectroscopy, a technique

where X-rays are absorbed by a sample and

emitted electrons are detected. Also called

ESCA (electron spectroscopy for chemical

analysis)

zinc blende the crystal structure of GaAs with each atom

tetrahedrally bonded to four atoms of the

opposite type

345

INDEX

absorption coefﬁcient 82

acceptor impurities 29

airbridge 329

airbridge emitter process 286

angled evaporation 221

anti-reﬂection coatings 112, 330

antisite defects 78, 308, 324, 329

Arrhenius equation 64

asher 152, 187–8, 330

atomic displacement threshold 330

atomic layer epitaxy 43

atomic-force microscopy 329

Auger spectroscopy 52–3, 329

avalanche breakdown 258

back end processing 60–6

backside metallisation 62–3

backside processing 61

band bending 81, 90–1, 330

band structure 22–7, 330

bandgap 26, 82, 330

bandgap engineering 26, 39

barrier layers 324

base 330

base mesa etch 285–6

base metal ohmic contacts 287–9

bilayer gate process 222–3

bipolar junction transistor 268–9

bipolar transistor 4–5, 267–71

history 7

breakdown 330

breakdown voltage 260–2, 278

breakdown walkout 261–2, 330

Bridgman methods 34–8

horizontal 34

vertical 35

vertical gradient freeze 35

buffer 330

burn-in 65, 257, 330

burn-out 256, 330

capacitance-voltage proﬁling 57–9

capture cross-section 84

carrier capture 31

carrier concentration 27–8

carrier distributions 27

carrier generation 31

carrier transport 32–3

carrier transport equations 33

cell phones 15–16

characterisation 46–59

electrical 56–60

electron-beam techniques 49–53

ionic techniques 53–6

light-based techniques 47–9

chemical bonds 23–4

chemical dry etching 149, 151–2

rates 151

chemically assisted ion-beam etching

149–50, 163–7

rates 165–6

collector 331

collector depletion width 277

collector mesa etch 286

collector metal ohmic contacts 289

collector undercut 298–9

conduction band 25, 331

conduction band offset 331

conduction band spike 275

conductors 25–6

consumer products 10–11

contact resistance 180, 191–3

ohmic contacts to n-type GaAs 196,

198–9

ohmic contacts to p-type GaAs 201

contactless resistivity 57

contaminants 69–71

continuity equations 33

crystal growth 8, 33–8

crystal plane conventions 124

crystal structure 123

crystallographic etchant 123, 305, 331

crystallographic planes 123

current gain 234–5

HBT 268–72, 281, 293, 300

current-voltage techniques 59

cutoff frequency 233, 235, 237, 271

Czochralski method 8, 34–8

liquid encapsulated 8, 34–6

deep levels 31

deep-level transient spectroscopy

59–60, 331

degreasing 69–70, 132

density of states 23, 331

depletion depth 182

depletion region 207, 230–2, 331

dicing 63

die separation 63

dielectric constant 29, 277

dielectric deposition 109–14

dielectric passivation 109–14

HBTs 291–4

diffusion current 32–3

dimensional scaling 8

dimer formation 78

direct semiconductors 26

dislocation density 35–7

dislocations 302, 331

distributed Bragg reﬂector 321–2

distributed feedback Bragg grating 102

distributed feedback lasers 124, 305

donor binding energy 29–30

donor impurities 29

dopant diffusion 302

dopant passivation 170

dopants 29

double heterojunction bipolar transistor 286

double heterostructure laser 9–10

double-mesa process 295

double-recess structure 219

drain 332

drain lag 238, 262–3, 332

drift 32, 332

drift mobility 32

measurements 57

drift velocity 32

dry etching 147–78

chamber cleaning 176–7

chamber

materials 177

damage

168–70

end-point determination 174–6

proﬁles 148–50, 155–6, 166

rates 150–2, 154–7, 159, 162, 164–6

uniformity 167–8

DX centre 170

edge-emitting laser 6, 14, 124

applications 12–14

EL2 31, 36–7, 86, 239–40

luminescence quenching 324

347

Index

electrical passivation 264

electrical resistivity 36–7

measurement 56

electrochemical etching 142–4, 216,

283–4, 332

electroluminescence 53, 332

electron beam evaporation 188–9

electron beam lithography 246

electron conduction 28–9

electron cyclotron resonance 149, 160–2

electron cyclotron resonance deposition

111–14

electron microprobe analysis 50–1

energy-dispersive spectrometers 51

wavelength-dispersive spectrometers 51

electron velocity 32

electron wavelength 49

electronic devices 4–5

applications 15–18

fabrication 325–6

history 6–9

ellipsometry 47–8

emitter 332

emitter mesa etch 281–5

AlGaAs 282–4

InGaP 284–5

emitter metal ohmic contacts 286–7

end resistance method 193–4

energy levels 22–3

atom 22–3

molecule 23

enterprise sector 11

epitaxy 38–40, 333

doping 248

equivalent circuit model 333

etch selectivity 136–41, 157–8, 161–3

GaAs/AlGaAs 137–9, 157–8, 162

InGaAs/InAlAs 140–1

InGaP/GaAs 139, 163

etching: see dry etching, wet etching

etching solutions, aging 124–5

evaporation 188–9

excitons 82

bound 30

unbound 30

extrinsic base regrowth 296

failure analysis 47, 51, 66

Faraday’s constant 137

Fermi function 27

Fermi level 27, 30, 333

Fermi level pinning 78–81, 170, 333

disorder-induced-gap state

model 80–1

effective work function model 80–1

metal-induced-gap state model 80–1

uniﬁed defect models 80–1

ﬁbre-optic communications 12–13, 17–18

ﬁeld effect transistor 5, 229–65

degradation 256–65

doping 247–51

drain I-V characteristics 231–2

equivalent circuit 235–6

fabrication 244–7

gate metal contacts 254

history 7, 229

hydrogen poisoning 226–7

isolation 251–3

lightly-doped drain 218–19

ohmic contacts 253–4

passivation 254–6

performance 236–40

reliability 225–7

structures 240–4

substrate speciﬁcations 38

testing 215

threshold voltage 231

transconductance 233