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Xiuju Zhou, Qiang Li, Chak Wah Tang, and Kei May Lau
ECE depart., Hong Kong University of Science & Technology
Clear Water Bay, Kowloon, Hong Kong
Compliant III-V on (001) Si substrates for direct laser growth
UCSB, January 5, 2017
Kei May Lau
Fang Professor of Engineering
Electronic and Computer Engineering Department
Hong Kong University of Science and Technology,
Clear Water Bay, Hong Kong
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III-V on Si: Toward a heterogeneous world
Opportunities– III-V logic with advanced CMOS– Hybrid integrated circuits with on-chip interconnect
Challenges– Material: III-V on Si– Device: III-V logic device technology and integrated light
sources
*IEDM 2013, p.699
*Nature Materials 6, 810 - 812 (2007)
P-channel
1/8/2017
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III-V/Silicon Photonic On-Chip WDM Network
Epitaxially grown Quantum Dot laser and Epitaxially grown III-V-on-Si photodetector
Source: Andrew Poon, HKUST1/8/2017
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Silicon as growth substrates for III-V Devies
• Low cost manufacturing: high quality Si wafers up to 12-inch (300mm) commercially available
• Silicon technologies are the most advanced and cost effective
• Integration of high performance III-V devices with Si logics and memory circuits, Si photonics, lighting drivers……
• No need for brittle and expensive InP substrates
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Microdisk lasers on silicon
1/8/2017
* III-V on silicon
+ Quantum Dots
+ Whispering Gallery
Mode (WGM) Resonant
cavity
• High quality factor
• Small footprint
• Low threshold /power
• In-plane/waveguide
coupling
Silicon
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What are the choices?
Wafer Bonding
– Sample size
difference
– Alignment
– Yield
– Volume
manufacturing
Direct growth
– Material issues
– Process integration
1/8/2017
*Takagi Takenaka Group
HKUST @ 2008
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Challenges: Heteroepitaxy of III-V on Si
High-density defects– 4-8% lattice mismatch (dislocations & stress)– Thermal expansion coefficient mismatch (stress)– Polar on non-polar (APD)
Buffer thickness: cost, process throughput
Poor thermal conductivity of ternary alloy buffer
200 nm
Source: IEEE spectrum
Threading dislocations
Stacking faultsAnti-phase domains
1/8/2017
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Review: Defect Engineering Approaches
Combined with thermal annealing
NucleationTwo-step growth
Compositional graded buffer Interlayer/superlattices
* J. Crys. Growth 324, 103 (2011) *Appl. Phys. Lett.73, 2917 (1998)
* J. Mater. Res., 6 (1991) 376
1/8/2017
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Blanket epitaxy: InP/GaAs/Si Direct growth of InP on planar Si : high defect density
Ge, superlattices, graded compositions commonly used
Our approach: GaAs as intermediate buffer between Si and InP
Source: SEMATECH
1/8/2017
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MOCVD Systems @ HKUST for III-As/P/Sb Alloy growth
AIX200/4 Reactor on single 4 in substrate
CCS 6x2" or single 4” /6”
As/P based materials
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Blanket epitaxy @ HKUST: InP/GaAs/Si
HT-InP buffer
HT-GaAs buffer
Exact Si (001) substrate
Two-step growth method
– Surface/Kinetic limited regime at low temperature (LT)
• Full coverage/better stress release
– Mass transport limited regime at high temperature (HT)
• Improved crystalline quality
H2 Annealing
LT-GaAs
HT-GaAs
LT-InP
HT-InP
InGaAsLT-InP
LT-GaAs
1/8/2017
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High-electron mobility transistors
Our planar buffer since 2008
In0.52Al0.48As
In0.53Ga0.47As channel
In0.52Al0.48As
InP/GaAs/Si compliant substrate
Conventional HEMT
Inverted HEMT (iHEMT)
In0.52Al0.48As
In0.53Ga0.47As channel
In0.52Al0.48As
InP/GaAs/Si compliant substrate
Delta-doping
Delta-doping
*Appl. Phys. Lett., 58 (1991), p.71
1/8/2017 Q. Li et al, IEEE, TED, 60-12, p. 4112, 2013.
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Defect Trapping in Nano-patterns
Trapping most of the threading dislocations
1/8/2017
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GaAs-on-V-grooved (001) Si
50 nm
GaAs
Si
SiO2
Antiphase-domain-free, low density
defect, smooth morphology...
Start with exact (001) Si substrateV-grooved Si (111) surfaces
*Q. Li et al.,Appl. Phys. Letts.106 (7), 072105, 2015
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Cross-sectional TEM comparison with offcut Si
• Defects generated at the GaAs/Si hetero-interface were trapped by the V-grooved structure on GoVS template
• A larger amount of stacking faults (SFs) and threading dislocations were observed in the GaAsbuffer in the offcut Si template.
GaAs on V-groove
patterned on-axis (001) Si
GaAs on planar offcut
(001) Si
Dislocation lines punching through the active region will create non-radiative
recombination centers
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GaAs on V-groove patterned on-axis (001) Si
GaAs on planar offuct (001) Si
Cross-sectional TEM comparison
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Typical plan-view TEM comparison
• A three-fold reduction of threading dislocation using V-grooved Si• V-grooved Si: 2.8x108/cm2
• Offcut Si: 8.3 x 108/cm2
GaAs on V-groove
patterned on-axis (001) SiGaAs on planar offcut (001) Si
400 nm
The TDD was determined by counting numbers of dislocations in a given area
based on an average number of 30 plane-view TEM images for accuracy
400 nm
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181/8/2017
Growth template: GaAs-on-V-grooved Si (GoVS)
V-grooved nano-patterned (001) Si substrate
• No Ge. No offcut.
• Aspect ratio trapping combined with epitaxial lateral overgrowth
*Q. Li et al.,Appl. Phys. Letts.106 (7), 072105, 2015
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InAs QD on (001) Si GaAs thin films grown on exact (001) Si substrate by MOCVD
• No Ge, No offcut
5x quantum dot microdisk active region was regrown by MBE
QD Diameter of ∼21 nm and height of ∼6 nm
@UCSB
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• 5x InAs quantum dot layers– 500°C, 0.11 ML/s, 2.75 ML, V/III 35
– 8 nm In0.15Ga0.85As QW
• Dot density ~5x1010 cm-2 per layer
• Uniform wavelength across sample
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MBE Growth of Quantum Dots @ UCSB
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TEM comparison: QD on GoVS and Offcut Si
• A three-fold reduction of threading dislocation using V-grooved Si
• V-grooved Si: 2.8x108/cm2 Offcut Si: 8.3 x 108/cm2
QD grown GaAs on
V-groove patterned
on-axis (001) Si
QD grown on GaAs on
planar offuct (001) Si
*TDD was determined by counting numbers of dislocations in a given area
based on an average number of 30 plane-view TEM images for accuracy
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• 1.3 µm room temperature emission
• strong peak intensity
• FWHM of 29 meV
Photoluminescence comparison at 300K
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Micro-fabricated WGM cavities
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1.3 μm RT lasing on (001) silicon RT CW lasing from a 4 μm disk
Q~5000, Xc~1.3 μm
*Y Wan, et al., Optics Letters 41 (7), 1664-1667, 2016
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1.3 μm RT lasing on (001) silicon
1050 1100 1150 1200 1250 1300 1350 1400
10 K
200 K
300 K
Inte
nsit
y (
a.u
.)
Wavelength (nm)
CW lasing from 4 μm diameter microdisks up to RT
At RT, single mode lasing at 1.3 μm
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1/8/2017
Temperature characteristics of 4 μm MDL on (001) silicon
*Y Wan, et al., Appl. Phys. Lett., 109, 011104, 2016
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1/8/2017
300K laser Spectra below (8 mW) and above (495mW) threshold
*Y Wan, et al., Appl. Phys. Lett., 109, 011104, 2016
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1/8/2017
10K laser Spectra below (8 mW) and above (495mW) threshold
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Comparison of 10K characteristics for different substrates
1/8/2017
Q Li, et al., Optics Express 24 (18), p. 21038, 2016
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1/8/2017
Comparison of 300K characteristics for different substrates
Q Li, et al., Optics Express 24 (18), p. 21038, 2016
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Subwavelength microlasers on Si
Y Wan, et al Applied Physics Letters 108 (22), 221101 (2016)
Dense integration
Low power consumption
Single mode (well- separated cavity modes)
High surface recombination
Limited gain medium
nmRneff
13246.3)5.0(2
]2.1[
2
22
m
m
Free Spectral Range
Pros Cons
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Ultra-low threshold down to 35 μWLasing characteristics at 10K
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Lasing characteristics at 10K lasing mode :TE1,5 by FDTD simulation
The spontaneous emission factor (β) was extracted to be 0.3 by fitting the
experimental data to a semiconductor cavity-QED model
Y. Wan, et. al Applied Physics Letters 108 (22), 221101 (2016)
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Benchmarking with subwavelength MDL on GaAs
Average lasing
threshold, μW
Threshold
range, μW
Si 50 35-67
GaAs 33 24-50
Table. Lasing statistics summary
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Typical GoVS 100mm compliant substrate
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p- (001) Si with nano-pattern
~2.2 µm GaAs
15 × {5nm GaAs/5nm Al0.3Ga0.7As}
1100 nm GaAs
600 nm UID-GaAs
300 nm GaAs
3 cycles of thermal cycle annealing
0
2500
5000
7500
10000
32 .825 32 .850 32 .875 32 .900 32 .925 32 .950 32 .975
Fi tted P eak A rea: 390 .667Fi tted P eak He igh t: 11280 .7Fi tted P eak FW HM: 0 .031Fi tted P eak Cen te r: 32 .900 B ac kground : 3 .9681
Inte
ns
ity
(c
ps
)
Om ega (deg)
3552 T CA -perpend ic u lar-115 a rc s ec .x00*
P ears on V II Curve
XRD rocking curveFWHM = 112 arcsecTDD = 4 x 107 /cm2
(Ayers ‘ Model)
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Challenges
8% lattice mismatch leads to high density of defects
Polarity difference and generation of APBs
Methods to integrate InP NW on Si
*Li et al. Appl. Phys. Lett, 108, 021902 (2016).
Thick GaAs buffer
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LT-InP at 370 oC,
V/III ratio >2000
*Merckling et al. J. Appl. Phys, 115, 023710 (2014).
*Wang et al. Nat. photonics, 9(12), 837–842 (2015)
500-nm-wide
CMP bulk InP
Planar InP nanowires on (001) Si
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Growing InP NWs on Si
800 nm pitch, 300 nm openings with 150 nm SiO2
Diamond pocket formed by KOH wet etching
LT-GaAs buffer and three-step InP growth procedure
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LT-GaAs nucleation
Large indium diffusion coefficient and low TBP decomposition rate
Complete coverage of LT-GaAs on initial Si enclosure
LT-GaAs aligned along Si surface and formation of stacking faults
38*Y Han, et al., Appl. Phys. Lett., 108, 242105, 2016
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Morphology evolution
Coalescence of InP islands
Rhombic nanowire formation
(111) plane InP contacts
with SiO2
Surface fluctuation
Dents
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XRD characterization
XRD (-rocking curve)
FWHM (arcsec) 659
Both Si and InP peaks can be clearly identified
“Defect necking effect” leads to more defective region at the bottom
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Defect trapping
Defects confined within the diamond pocket
Stacking faults formed along (111) surface to release strain
Dislocations traveling upwards observed 41
15 nm
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InGaAs quantum well (QW-1)
10 nm flat InGaAs quantum well flush with the diamond pocket
Uniform thickness across the opening
Dislocations penetrate QW and terminate at (111) InP surface
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Quasi-quantum wire (QWR-1)
Crescent quasi-quantum wire formation at higher position
(111) facet size increases and (001) facet size decreases
Growth rate difference between (001) and (111)
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Quasi-quantum wire (QWR-2)
Further elevating position leads to the reduction of lateral size
Quantum confinement from both vertical and lateral direction
No (111) plane InGaAs observed
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Room temperature PL measurement
1200 1400 1600 1800
P
L In
tensity
Wavelength (nm)
QWR-2
QWR-1
QW
10 100
In
teg
rate
d P
L in
ten
sity
Laser power (mW)
QW-1
QWR-1
QWR-2
Broad PL spectrum due to thickness and composition
inhomogeneity
PL enhancement from QW to QWR samples, due to less
defect intrusion45
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“Uncertainty principle” and Detective work
• Consistency of growth system
• Correlation/optimization of a few M x N matrices (m, n variable parameters)
Device layer design parameters => Device characteristics (models and simulation)
Intended device structure => grown device structure
Growth parameters => Material characteristics
Material Characteristics => Device characteristics
Fabrication process => Device characteristics
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1/8/2017
Lau group at HKUST
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HKUST
Where we are in Hong Kong
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1/8/2017
AcknowledgementsSupported in part by Grants (Nos. 614813 and 16212115) from the Research Grants Council of Hong Kong, a DARPA MTO EPHI grant, and the U.S. Department of Energy NNSA Contract DE-AC04-94AL85000.
HKUST Campus @ Clear Water Bay