Physical Vapor Transport (PVT) Growth · Physical Vapor Transport (PVT) Growth (with focus on SiC...
Transcript of Physical Vapor Transport (PVT) Growth · Physical Vapor Transport (PVT) Growth (with focus on SiC...
15th International Summer School on Crytsal Growth – ISSCG -15
Physical Vapor Transport (PVT) Growth (with focus on SiC and brief review on AlN & GaN)
Peter J. WellmannCrystal Growth Lab, Materials Department 6
University of Erlangen, [email protected]
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
SiC – wide bandgap semiconductorEg=2.3eV...3.3eV (Si: Eg=1.1eV)
power & high frequency electronicsSiC with high
break-down voltage (10 x Si)heat conductivity (3 x Si)e– saturation velocity (2 x Si)
� applications: computer power supplywithout cooling parts
SiC Schottky diodes with low switching losses
Application Field of Silicon Carbide
blue opto-electronicsn-SiC substrate
(InGaN-based LEDs und LDs)
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Application Field of Silicon Carbide
chemically resistent� sensors in „aggressive“ environments � automobile gas sensor
„visible blind“ photo diodes� sensors: temperature measurement in ovens, UV-exposure, ...
x-ray & γγγγ-ray detectors
bio-compatible� coatings of implantation parts in medicine
© S-SENCE,Sweden
© Istituto Nazionaledi Fisica Nucleare (INFN)
Trento, Italien
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
SiC Polytypes4H-SiC 6H-SiC 3C-SiC
Bandlücke [eV] 3,265 3,023 2,390
Gitterparameter[Å]
a = 3.08c = 10.05
a = 3.08c = 15.12
a = 4.36
Eff. Masse [me] me = 0.37mh = 0.94
me = 0.69mh = 0.92
me||/⊥ =0.68/0.25
Bewegl. µT=300K cm2/Vs]
µe = 500µh = 50
µe = 300µh = 50
µe = 900µh = 20
4H-SiC6H-SiC
Eg=2.4eV
Ec=2.4eV
Ec=0eV
3C-SiC
Eg=3.0eV
Ec=3.04eV
Ec=0.04eV
6H-SiC
Eg=3.0eV
Ec=3.05eV
Ec=0.05eV
15R-SiC
Eg=3.2eV
Ec=3.27eV
Ec=0.07eV
4H-SiC
Eg=3.3eV
Eg=3.43eV
Eg=0.13eV
2H-SiC
Hexagonality 0% 33% 40% 50% 100%
15th International Summer School on Crytsal Growth – ISSCG -15
SiC crystal growth processPVT = physical vapor transport
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Phase diagram of SiC
T1<T2
T
z
Ttop, Pcoil, pArgon
PVTPhysical Vapor TransportSUBLIMATION SiC powderCRYSTALLIZATION at colder seed
0 20 40 60 80 100
0
1000
2000
3000
4000
T [°
C]
carbon [at%]
SiC+C
Si+SiC
L+SiC
L+C
G+CG
L
L+G
Peritecticum(≈ 13% C)
2830°C±40°C
1414°C
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
8hgraphitization/powder consumpt.
40h
2h
0hSiC crystal
Graphite crucible
SiC source
1h
formation ofdisk
15h
X-ray source
Patent with SiCrystal AG, DE 199 15 473.2-51Wellmann, Straubinger and Winnacker.
Wellmann et al. JCG 216 (2000) & JCG 275 (2005).
Digital x-ray imaging – insitu visualization of SiC PVT growth
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
global PVT growth process
t=15h
graphitedust ?→C inclusions
mass transferlimitationby diffusion
δδδδT/δδδδx drop at disk(stable needle like surface)
SiC crystal
SiC source
SiCcrystal
SiC source
crystallization(kinetics)sublimation
diffusion
disk-like structure
heatdissipation
15th International Summer School on Crytsal Growth – ISSCG -15
review on SiC crystal growth (historic remarks)
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
SiC crystal growth – a little bit of history
Acheson technique (today e.g. for SiC polishing powder applications)
greatcurrent
graphite
SiO2/C-powder
SiC
druse
T = ca. 1800°CSiO2 + 2C � Si + 2COSi + C � SiChighly Al-contaminated
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
SiC crystal growth – a little bit of history
Lely technique (SiC platelets) T=2200°C...2800°Cinert gas = Argonpressure = ca.1000mbar
SiCplatelets
porousgraphite
SiC powder
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
SiC crystal growth – a little bit of historyTairov & Ziegler technique (modyfied Lely ~, seeded sublimation)
T=2200°C...2400°Cinert gas = Argonpressure = ca. 15mbar...50mbar
SiC seed
SiC powderporous graphite
15th International Summer School on Crytsal Growth – ISSCG -15
mass transport model& gas phase composition
• chemistry
• mass transport • simple PVT model
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
© Selder, JCG 211 (2000)
Fundamental of PVT Growth 1• Sublimation & Gas Phase Composition
© Lilov, 1995
I,
II,
III,
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Fundamental of PVT Growth 2• SiC Deposition (assumption: no silicon droplets or carbon inclusions)
• Kinetic Side Wall Reactions (experiment: no Si or SiC deposition)
• T-field, Partial Pressures & Mass Transport Driving Force � Super-Saturation,
© Selder, JCG 211 (2000)
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Fundamental of PVT Growth 3• Diffusion limited growth mode
• “Convection” issues© 1D-model, St. Müller, Dissertation Erlangen 1995
15th International Summer School on Crytsal Growth – ISSCG -15
application of numerical modeling for process optimization
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
In-Situ Growth Control Tools
Numerical Modeling of T-fieldstate-of-the-art
Temperature Measurementstate-of-the-art
SiC powder
SiCseed
pyrometer
pyrometer
In-Situ X-ray VisualizationWellmann et al. (ICSCRM1999)
X-ray source
SiC crystalGraphite crucible
SiC source
In-Situ X-ray DiffractionYamaguchi et al. (ICSCRM1999)Konias et al. (ECSCRM2006)Wellmann et al. (ECSCRM2008)
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Numerical ModelingTemperature field• Inductive heating• heat transfer by
• conduction• radiation• convection
Hofmann et al. J.Cryst.Growth (1995)Pons et al. J.Electrochem.Soc. (1996)
Mass transport - crystal growth• mass transport by diffusion and
convection• heterogeneous chemical reactions of
Si- and C- containing gas species with crucible etc.
• sublimation: SiC+C system (graphitization)
• crystallization: SiCSelder et al. J.Cryst.Growth (2000)
sketch PVTgrowth cell
T-field (3h) &mass transportpaths
SiC powder
SiCseed
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
SiC source material – granule core-shell model
Evolution source material
granular morphology - spheres• mean granular radius r• porosity ε• SiC core r• graphite shell r-rcore• graphitization γ = 1-(rcore/r)3
sublimation / recrystallization• C-shell porous for Si-C vapor• co-existence SiC & C• constant granule concentration
species transport in SiC source• convection & diffusion
Kulik et al., Mat.Sci.Forum 2004.Virtual Reactor Sofware,© SoftImpact Ltd.
Porosity ε after 3h Graphitization γ after 3h
SiSi2C
SiC2
Si-Cvapor
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Doping of SiC – overview dopants
Leitungs-band
Valenz-band
NP
AlAkzeptoren
Donatoren
6H-SiC
(1100)(0120)
(000
1)
N(V) auf C(IV)-Platz
P(V) auf Si(IV)-Platz
Al(III) auf Si(IV)-Platz
Er(3+) auf Si(IV)-Platz
C(IV)
Si(IV)
(1120)
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Doping of SiC – “Face”-competition effect
Al NSi-face
AlN
C-face
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Modified-PVT – process principle
Al
doping species(i.e. N, P, Al , ...)
T1<T2
T
x
sourcedepletion
continuousdopantsupply
only gasesinert tographite(T>2000°°°°C)
... solid source ... additionalgas pipe
Doping by... gas supply
PVT setup
dopant gas(i.e. N2)
M-PVT setup
Straubinger, Wellmann et al. JCG 240 (2002)Wellmann et al. JCG 275 (2005)
n-type SiC:Np-type SiC:Al
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Defects in SiC – 0-dim (point defects)
INTRINSICe.g. Si-Vacancy
as well as related complexesC-Vacancy, CSi Antisite
EXTRINSICunintentional doping!e.g. Ti, B, N
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Defects in SiC – 1-dim (Dislocations)revealed by KOH-defect etching & light microscopy
p-type
p=3⋅⋅⋅⋅1017cm -3
Screw Dislocations
EdgeDislocations
p=2⋅⋅⋅⋅1019cm -3
n≈≈≈≈2⋅⋅⋅⋅1017cm -3
“Basal-Plane”Dislocations
n-type
x3 x2
φα
br
Ix3 x2
φα
brx3 x2
φα
br
I© Mark Ramm
x2
br
x3
α=φ
IIIx2
br
x3
α=φ
x2
br
x3
α=φ
III
“Basal-Plane”Dislocations
Screw orEdgeDislocations
Sakwe, Wellmann et al. JCG 289 (2006)
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Defects in SiC – 1-dim (Dislocations)micropipes
density = 1cm-2 ... 50 cm-2
[000
1]
(0001)
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Basal plane dislocations (BPDs) Dissociation & Stacking faults (SFs)
SF is formed from a 60°complete dislocation.
Twigg et al.APL vol. 82 (2003)
Deflected dislocation dissolves into two partial dislocations with a stacking fault in-between
Jacobson et al.JAP vol.91 (2002)
plane view
x3 x2
φα
br
Ix3 x2
φα
brx3 x2
φα
br
I© Mark Ramm
partial dislocationb=1/3·a � stacking fault
dislocation dissociation
© Blumenau, PhD-thesis 2002. (here: cubic lattice)
side view
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
TEM: Collaboration Prof. Strunk (Materials Science 7, Uni-Erlangen)
© Iwata et al. J.Phys.Cond.Matt. 2002.
100nm
gliding directionSFs
[0001]
Basal-Plane Dislocations& Stacking Faults
8° off oriented (0001)n-type 4H-SiC
“Basal-Plane“ Dislocations � Stacking Faults
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Defects in SiC – 2-dim(Stacking Faults, Polytype Changes)
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Defects in SiC – 3-dim (Si-droplets, C-inclusions, hollow cores, also polytype inclusions)
15th International Summer School on Crytsal Growth – ISSCG -15
Group-III-Nitrides
AlN � PVT
GaN � mainly HVPEInN � no bulk growth succeeded
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
PVT growth of AlN
Chemistry & crucible• Al + 1/2 N2 � AlN• tungsten crucible
challenges• purity AlN source (oxygen free)• small process window
Low T � needlesHigh T � decompositionIdeal = ca. 2200°C
• seedingcurrently often on 6H-SiCin future on AlN
© Crystal-N @ www.crystal-n.com© Bickermann, Epelbaum, Winnacker, Erlangen.
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
Heaters of 3-Zone Oven
Ga melt
N2/H2 + NH3
N2/H2 + GaCl3
AbgasN2/H2 + NH3
N2/H2 + HCl Susceptor &Substrate ( ↔↔↔↔)
Quarz TubeT=900°C T=1050°C
Hydrogenated Vapor Phase Epitaxy• great growth velocity
~ 50µm/h (Lit: ~100µm/h)• 6H-SiC Substrate
GaN HVPE growth process –
15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth
GaN Vapor Growth - HVPE
Lit: Ilegems, vapor epitaxy of GaN, J.Cryst.Growth 13/14 (1972), p.360.
Carrier:H, He or N2H-passivation of dislocations?
Ga-source:6HCl + 2Ga ↔ 2GaCl3 + 3H2Ga source @ 950°Cefficiency ~100%
N-source:NH3problem: formation of N radicals
Chemistry:2GaCl3 ↔ 2Ga3+ + 3Cl22NH3 ↔ 2N3- + 3H2Ga3+ + N3- ↔ GaNsubstrate @ 1050 °°°°C
„step flow“ instead of „3dim. nucleation“n = 2x1017cm-3
µ = 380 cm2/Vs
pyramidal growth with hexagonal symmetryn > 1018cm-3
NO GRWOTH