Integrated Si-Based
Photonics
James S. Harris
Stanford University
Peking University Summer School
Beijing, China
July 19, 2013
Demands for Optics at
Shorter Distances
Internet, Wide Area Local Area
Network (WAN)
Network (LAN)
On-card
Rack-to-Rack
Inter-chip
STANFORD
Card-to-Card
Intra-chip
Distance
Multi-km
10 - 2000m
30+m
1m
# of Lines
1
1-10
~100
~100 - 1000
Use of
Optics
Since 1980s to early Since late
Present
1990s
1990s
Distance 0.1 - 0.3m
10 - 100mm
<10mm
Present ++
# of Lines
~1000
~10,000
~100,000
Use of
Optics
2010 - 2015
Probably after
2015
Sometime in the
future
Adapted fromtechnology
IBM Research
Can evolution of telecom
address Inter/Intra chip applications?
Peking University Summer School, July 19, 2013
JSH 2
Architecture change
STANFORD
• Multiple cores on a chip are already available
– Trend: increase # of cores NOT speed or complexity
• Parallel architectures  increased bandwidth
• Nanophotonic communication is a credible solution
D. Fattal & M. Fiorentino HP Labs
Peking University Summer School, July 19, 2013
JSH 3
Communications Challenge
Intel Microprocessor, 2005
Peking University Summer School, July 19, 2013
STANFORD
Broadway, New York City, 1887
JSH 4
On-chip Interconnects
STANFORD
100
Gate Delay
FO = 4
Relative Delay
Local
10
ITRS Roadmap 2005
Global W
Repeaters
Global WO
Repeaters
Global
interconnects
RC limited
1
CMOS device
Local connects
100
250
190
130
90
66
45 32
Process Technology Node (nm)
What is required to solve this challenge?
LOW COST, LOW POWER, INTEGRATED, CMOS
COMPATIBLE, OPTICAL TRANSCEIVERS
Peking University Summer School, July 19, 2013
JSH 5
Interconnect Performance
STANFORD
Energy/bit
Latency
Wmin for Cu CNT from ITRS
for optics = 0.6µm
Cdet=Cmod=10fF
- Electrical interconnects
power dissipated by wire and
repeaters
latency by wire and repeaters
- Optical interconnect (1 Channel)
power dissipated by end devices
latency by end devices
• Cu, CNT: small wire width → Energy per bit decreases as wire pitch is scaling (CV2).
Latency increases as wire pitch scales down
• Optics favorable for longer wires
Koo, Kapur and Saraswat, IEEE Trans. Electron Dev., Sept. 2009
Peking University Summer School, July 19, 2013
JSH 6
Photonic Integrated Circuit-1993
STANFORD
Soref, Proc. IEEE,
1687 (1993)
Waveguide architecture with butt coupled fibers III-V edge emitting
lasers, modulators, detectors and high-speed electronics (HBT or HEMT)
All off-chip and Mostly III-V devices
Peking University Summer School, July 19, 2013
JSH 7
Silicon-Compatible Photonics:
A Materials Challenge
STANFORD
Integrate the required photonic devices on silicon
Intel
http://www.research.ibm.com/photonics/images/soi_phwire.jpg
Y.-H. Kuo, et.al., Nature 437 (2005)
http://www.bit-tech.net/news/2007/09/18/intel_has_worlds_fastest_sige_photo_detector/1
Can a new material be engineered to suit our needs?
Peking University Summer School, July 19, 2013
JSH 8
Band Structures of GaAs, Si & Ge
STANFORD
E
[111]
[100]
GaAs
E
Global Minima
at zone center
k
Local Minima
at zone center
[100]
[111]
Si
k
E
[100] k
[111]
Ge
Poor
Efficient
Efficient
Emission &
Emission &
Absorption
Absorption
Absorption
Silicon Based
Germanium
Peking University Summer School, July 19, 2013
JSH 9
Unique Multiple Band Ge/SiGe QW
STANFORD
Deep direct band gap,  QW
Ec,
e-
Ec,L
Ev,lh
Ev,hh
Relaxed
Si1-yGey
buffer
Strained
Si1-xGex
barrier
Strained
Ge
QW
Peking University Summer School, July 19, 2013
<1ps tunneling
>100 GHz modulation
Lower, shallow indirect
band L minima
Direct band gap
transition
h+
∆EC, direct = 0.4 eV
∆EV = 0.1 eV for heavy hole
Strain causes valence
band splitting
JSH 10
Quantum-Confined Stark Effect
STANFORD
l
l
Electro-absorption and electro-optic modulation by tuning
electron-hole coupling in quantum wells
More pronounced for excitons (bound electron-hole pairs)
Ec
Ev
No E-field
E-field
1. Red shift of absorption edge
2. Smaller wave function overlap – lower α
3. Change of n through Kramers-Kronig relationship
Peking University Summer School, July 19, 2013
JSH 11
SiGe and GE QW Growth on Si
l
Graded SiGe buffer is widely used
l
l
l
Direct growth of SMOOTH, THIN buffer
l
l
Si
Graded buffer
Low surface roughness
Post anneal reduces dislocation density
Buffer thickness is critical for single
mode waveguide devices on SOI
High Dislocation Density
400nm
10µm
l
Graded SiGe
Low defect density
Thick buffer layer
Large surface roughness-Critical for QWs
Ge or SiGe
Si
Single-Tgrowth
direct growth
Peking University Summer School, July 19, 2013
400nm
Ge or SiGe
l
STANFORD
High-T
Ge or SiGe
Anneal
Low-T SiGe
Si
Two-Tgrowth
direct growth
JSH 12
SiGe Surface Morphology
STANFORD
QWs require surface roughness ≤ 0.2nm
2-Temp-step Ge-on-Si by MBE
l
As-grown roughness
RMS ~ 0.2nm
Peking University Summer School, July 19, 2013
Single-Temp-step SiGe-on-Si by CVD
l
l
As-grown roughness
RMS ~ 2.5nm
Annealed roughness
RMS ~ 0.228nm
JSH 13
Strain-balanced Structure
STANFORD
growth direction
n+ SiGe cap layer
Undoped SiGe buffer layer
Ge/SiGe MQWs
Compressive
Tensile
Undoped SiGe buffer layer
Strain force ε
p+ Relaxed SiGe buffer layer
Silicon Substrate
Average Si concentration
in Ge/SiGe QWs equals
that of SiGe buffer
Y.-H. Kuo, et al, Nature 437, 1334 (2005)
Peking University Summer School, July 19, 2013
JSH 14
Ge/SiGe Modulator on Si
STANFORD
Ge 10nm/
Si0.15Ge0.85 16nm
Y.-H. Kuo, et al,
Nature 437, 1334
(2005)
Materials, Processes and Temperature are
all CMOS-compatible
Peking University Summer School, July 19, 2013
JSH 15
Strong QCSE in Ge/SiGe QWs
STANFORD
Y.-H. Kuo, et al, Nature
437, 1334 (2005)
Peking University Summer School, July 19, 2013
JSH 16
Fabrication Process
STANFORD
Peking University Summer School, July 19, 2013
JSH 17
Small Signal Modulation
STANFORD
Bias: 2.5V Device top view size: 6µm *6 µm
Response limited by contact resistance
Peking University Summer School, July 19, 2013
JSH 18
Integrated Waveguide
Modulator, Detector and Laser
STANFORD
Ge Quantum Well(s)
N-SiGe
P-SiGe
P-Si
Waveguide
modulator
SiO2
Source, Modulator and Detector have identical QWs
Function determined by bias polarity
Light source
Modulator
Photodetector
SiGeSn cap layer
GeSn QWs
SiGeSn buffer layer
Si waveguide
SiO2
Si substrate
Peking University Summer School, July 19, 2013
JSH 19
Outline
STANFORD
l
l
Introduction
Ge/SiGe QCSE Electroabsorption Modulator
l
l
l
l
Strained Ge and GeSn Emitters
l
l
l
SiGe Growth and Characterization
Device Fabrication and Measurement
Optical Characterization
Growth & Characterization of Tensile Strained Ge
Growth & Characterization of GeSn
Summary
Peking University Summer School, July 19, 2013
JSH 20
Si Based Laser
Ge direct band gap engineering
STANFORD

GeSn material
- Sn is semi-metal
- Reported direct bandgap for SnxGe1-x
is between 10% and 20% Sn
- Lattice relaxed or compressive
strained layer

Strain
- Theoretically,1.8% tensile
strained Ge is direct bandgap
- Thin layer of Ge
- Potential buffer layer (larger
lattice constant)
Relaxed GeSn, GaAsSb, InGaAs
M. Bauer et al., APL, 81, 2992 (2002)
He and Atwater, PRL, 97(10), 1937 (1997)
M.V. Fischetti et al., JAP. 80(4) 2234 (1996)
Peking University Summer School, July 19, 2013
JSH 21
Ge Laser
STANFORD
Si-Ge Laser Structure
Si-Ge Laser Spectrum
Camacho-Aguilera-MIT OptExp 20 11317 (2012)
Good News—Ge can be made to lase
Bad News—Insanely high threshold current
Peking University Summer School, July 19, 2013
JSH 22
Role of Heterostructures and
Dimensionality on Lasers
STANFORD
Impact of epitaxy,
improved materials
Zh. Alferov, IEEE
JSTQE, 6 832 (2000)
Nobel Lecture
FOUR orders of magnitude decrease in threshold current density
as a result of heterojunctions and energy band engineering
Peking University Summer School, July 19, 2013
JSH 23
Highly Strained Ge Nano-bridge
STANFORD
Nano-bridge Structure
Calculated Gain & Loss
Süess-PSI Nature Photon 10 1038 (2013)
Free carrier absorption increases with carrier densities
and creates high laser threshold current
More sophisticated band engineering & QWs are essential
Peking University Summer School, July 19, 2013
JSH 24
The Potential of Ge/GeSn:
Direct Bandgap
STANFORD
Advantages of Ge:
• Si-compatible material
• Low effective mass in Γ
(0.038m0)
• Nearly direct-bandgap
and band engineer-able
Large effective mass (0.22m0)
Γ
Eg = 0.8eV
Inefficient optical transitions
L
Eg = 0.664eV
Simplified Ge Bandstructure
Peking University Summer School, July 19, 2013
JSH 25
The Potential of Ge/GeSn:
Direct Bandgap
STANFORD
Advantages of Ge:
The Biaxaial Tensile-Strain Effect
• Si-compatible material
~1.5%Large
Strain
Required
effective mass (0.22m0)
• Low effective mass in Γ
(0.038m0)
Γ
Inefficient optical transitions
• Nearly direct-bandgap
and band engineer-able
L
Eg = 0.8eV
Eg = 0.664eV
Y. Huo, et al., APL (2011)
Simplified Ge Bandstructure
Peking University Summer School, July 19, 2013
JSH 26
The Potential of Ge/GeSn:
Direct Bandgap
STANFORD
The Sn-Alloying Effect
~6-8% Sn Required
Γ
L
R. Chen, et al., Applied Physics Letters 99 (2011)
Simplified Ge Bandstructure
Peking University Summer School, July 19, 2013
JSH 27
Tensile strained Ge (TEM)
STANFORD
In0.3Ga0.7As 10nm
tensile strained Ge 10nm
In0.3Ga0.7As 300nm
In0.15Ga0.85As 200nm
GaAs substrate


100 nm
InGaAs buffer layers:
Defects are terminated at
interface
Ge layer:
2.46% in-plane tensile strain
Peking University Summer School, July 19, 2013
Ge
10 nm
JSH 28
Measured Strain & PL
in Ge/InGaAs
STANFORD
Strain (Raman)
Normalized intensity
(a.u.)
1
Photoluminescence
1
Straine
d Ge
0.8
0.8
InGaAs
0.4
Intensity (a.u.)
0.6
Bulk
Ge
0.2
0
260
270
280
0.34%
0.92%
1.81%
2.33%
290
300
310
0.6
0.4
320
0.2
Raman shift (cm-1)
Normalized intensity (a.u.)
1
0.8
0.6
In0.1Ga0.9A
s
In0.2Ga0.8A
s
In0.3Ga0.7A
s
In0.4Ga0.6A
s
0
1300
0.4
0.2
0
260
280
300
raman shift (cm-1)
320
Peking University Summer School, July 19, 2013
1350
1400
1450 1500
 (nm)
1550
1600
Indium
concentration
Ge Raman
shift (cm-1)
Strain
(Raman)
10%
1.05
0.26%
20%
3.63
0.91%
30%
7.13
1.78%
40%
9.60
2.35%
JSH 29
Photoluminescence Ge/In0.4Ga0.6As
STANFORD
1
20K
30K
40K
50K
75K
100K
150K
200K
300K
Intensity (a.u.)
0.8
0.6
0.4
0.2
40% InGaAs
Strained Ge
40% InGaAs
27% InGaAs
13% InGaAs
GaAs
0
1200 1400 1600 1800 2000 2200
 (nm)
Strained Ge/In0.4Ga0.6As is a Type II Heterojunction
Peking University Summer School, July 19, 2013
JSH 30
The Issue for GeSn:
Solid-Solubility
STANFORD
3.5% Sn Attempted
SGTE Alloy Database,
http://www.crct.polymtl.ca/fact/phase_diagram
.php?file=Ge-Sn.jpg.
Increasing Sn
400oC
Sn
HighTemperature 
Segregation
>4.5%
High-Strain  Precipitation
Y. Shimura, et. al. Jpn. J. Appl. Phys. 48 (2009)
Peking University Summer School, July 19, 2013
JSH 31
MBE Ideal for Investigative Tool
STANFORD
GeSn and SiGeSn
Challenges:
1. Low solid-solubility (1%) of Sn in Ge
– MBE can decouple source and
substrate growth temperatures
2. Challenges in finding precursors that
decompose at low temperature
– Very high-purity (99.999% or better)
solid sources available for evaporation
3. Lattice constant changes greatly with
Sn or Si alloying, adversely affecting the
bandstructure and film quality
III-V Chamber
(InGaAs/GaAs
)
Group IV
Chamber
(GeSiSn, GeSn)
Peking University Summer School, July 19, 2013
Group IV
Stack
Strain Control
with III-V
JSH 32
Want High-Quality, DirectBandgap GeSn
STANFORD
Goal: Explore basic material properties and unravel
competing strain and composition bandgap effects
to provide basis for quantum well device design
Our Method: MBE Growth on
GaAs/lattice relaxed InGaAs
• Ability to control strain
with Indium composition
• GaAs/InGaAs & GeSn
optically distinguishable
• Higher Ge strain and
higher Sn incorporation
using low-temperature
MBE growth (200oC)
Peking University Summer School, July 19, 2013
GeSn
InGaAs
Anneal
InGaAs
GaAs
JSH 33
TEM of 7% GeSn Layers
STANFORD
7 X greater than
equilibrium solubility
Ge0.07Sn0.93
10% InGaAs Buffer
strained Ge or GeSn
5 nm
InxGa1-xAs 200nm
GaAs substrate
GaAs Substrate
High quality Ge93%Sn7% epi layer:
• No defects
• No precipitation (phase segregation)
Peking University Summer School, July 19, 2013
H. Lin, et al., Thin Solid
Films 520 (2012)
JSH 34
Surface Quality Maintained
w/High Sn Fraction
Increasing Sn percentage
4.5% Sn, 100oC
7.0% Sn, 200oC
STANFORD
8.8% Sn, 100oC
RMS = 0.529nm
RMS = 0.403nm
RMS = 0.626nm
4.5% and 7.0% Samples grown on In0.10Ga0.90As,
~50nm GeSn
8.8% Sn Sample grown on In0.25Ga0.75As
Surface RMS roughness changes only slightly with
H. Lin, et al., Thin Solid
increasing
Sn
%.
Peking University Summer School, July 19, 2013
JSH 35
Films 520 (2012)
Great Material Quality
Possible with MBE
STANFORD
GeSn with 10.5% Sn, low-T growth
GeSn Film
InGaAs
Buffer
RMS=0.519nm
Peking University Summer School, July 19, 2013
H. Lin, et al., Thin Solid Films 520 (2012)
JSH 36
Where Does GeSn Become
Direct Bandgap?
STANFORD
R. Chen, et al., APL
99 (2011)
Bowing = 2.1 eV, ~7% Sn
H. Lin, et al., APL 100
(2012)
Bowing = 2.4 eV, ~6.5% Sn
Peking University Summer School, July 19, 2013
J. Mathews, et al., APL 97 (2010)
Consensus: It’s a lot less than
people thought! Experimental
data suggests it’s around 5.5-7%
Sn – very achievable!!
JSH 37
SiGeSn/GeSn/SiGeSn Quantum Well
STANFORD
SiGeSn
50nm
InGaAs
buffer
GeSn/Si
GeSn
InGaAs buffer
STEM-EDX
Intensity for Si
(a.u.)
SiGeSn
30nm
GeSn 30nm
Intensity for Ga and Ge (a.u.)
Glue
Ge
Si
Ga
Position (arb. unit)
GaAs
substrate
Peking University Summer School, July 19, 2013
JSH 38
Strain and Compositional Analysis
STANFORD
• Composition and Strain measured by SIMS
and XRD-RSM
– SiGeSn: Si = 5.58%; Sn = 9.16% Eg = 0.785 eV
– GeSn: Sn = 7.91%; strain = 0.3% Compressive
• Previous studies1,2 decoupled Sn
composition and strain effects
– Eg = 0.548 eV calculated
for Ge0.92Sn0.08
1) H. Lin, et al., Appl. Phys. Lett. 100 141908 (2012)
2) H. Lin, et al., Appl. Phys. Lett. 100 102109 (2012)
Peking University Summer School, July 19, 2013
Direct
Indirect
In-plane tensile strain
JSH 39
GeSn Low-Temperature
Photoluminescence
STANFORD
T=20K
T=294K
Peking University Summer School, July 19, 2013
JSH 40
Lattice-Matched Options for
GeSn QWs
STANFORD
Direct Bandgap
Energy (eV)
Unstrained Quantum Wells possible with the addition of Si
Peking University Summer School, July 19, 2013
JSH 41
The Stage Is Set – What About
Lasers?
STANFORD
Mirror
Mirror
Gain Region
Photon Emission > Photon
Absorption
Onset of lasing when optical gain ≥ loss
Require low-threshold lasers
LOW LOSS
Optical Losses:
• Minimize mirror losses -> Ge difficult to cleave, high-Q resonators
• Free carrier absorption µ n, p -> Minimize doping to reach threshold
• Optical scattering and mode confinement: Good design and fabrication
Carrier Recombination and Threshold Current:
• Reduce SRH recombination µ n, p -> Maintain high material quality,
reduce doping
• Auger recombination µ n 2 p -> Minimize doping to reach threshold
With competing L-Valley occupation, n-type
doping of 2-5 x 1018 cm-3 is optimum
Peking University Summer School, July 19, 2013
JSH 42
Challenges for a GeSn Laser
STANFORD
High Carrier Concentration Produces Free Carrier Absorption
Effect of FCA on Laser threshold:
• Large internal losses increase threshold since required carrier
concentration at threshold is an exponential function of αi
• Even worse for threshold current,
(Ideal case),
(Auger Recombination dominant)
Peking University Summer School, July 19, 2013
JSH 43
Gain Spectra for GeSn QWs
STANFORD
Gain Spectrum for p=n=2.4e19 cm-3 Gain Spectrum for 8% Sn (GeSn)
Increasing Sn
Increasing
Carrier
Concentration
Pure Ge
Addition of Sn greatly increases the net material gain for fixed carrier
concentration!! MUCH LOWER threshold current lasers!
Only need carrier density of ~5e18 cm-3 for 1000 cm-1 of gain for 8% Sn
Peking University Summer School, July 19, 2013
JSH 44
High-Quality Material is Paramount
STANFORD
Relative Laser Threshold vs. Carrier Lifetimes
in Just Direct-Bandgap GeSn (ΔEc = 0)
Relative
Threshold,
log10
Due to Density of States, ~98% of carriers still in the L-valley
• Non-radiative lifetimes critical for both valleys
• Need high-quality material to reduce defect states
• Moderate n-type doping
Peking University Summer School, July 19, 2013
JSH 45
The Benefits of Direct-Gap Materials
ΔEc
GeSn Photoluminescence
STANFORD
Γ
L
R. Chen, et al., Applied Physics Letters 99 (2011)
Increase in PL with Sn because more carriers occupy
the direct Γ-valley! Sn alloying results in increased
optical efficiency
Peking University Summer School, July 19, 2013
JSH 46
carrier concentration (cm -3)
Carrier Confinement (for Ge/SiGe)
Energy (eV)
1
0.5
0
-0.5
-1
450
500
Y (um)
550
STANFORD
20
10
10
10
450
500
550
Bias = 0.76V
Simulation:
•10nm Ge QW in Si0.2Ge0.8 pn junction
Carrier concentration:
•1.5E19 in QW and <1E18 in barrier
•Carriers are confined in QW (15 – 50 X)
•Calculated net gain of 200cm-1
Experiment:
•Ge 14nm*3QW
•200nm Ge grown on SiGe
buffer
PL signal:
•Stronger PL from QWs
•Carrier confinement in QWs
Xiaochi Chen et al. “Room Temperature Photoluminescence from Ge/SiGe
Quantum Well Structure in Microdisk Resonator” [2012]
Peking University Summer School, July 19, 2013
JSH 47
Can Lase, but not easy with Q=100
STANFORD
100nm Ge
20nm GeSn (8%)
90nm Ge
15% of TE mode experiences GeSn Gain and FCA
75% of TE mode experiences Ge FCA (no band-to-band absorption)
~30x higher carrier density in GeSn
QW than in Ge barriers due to
heterostructure
Choose low resonator loss to
hit threshold, Q of 500 ->
~100cm-1
Peking University Summer School, July 19, 2013
JSH 48
GeSn Photoluminescence
8.00E-07
STANFORD
5% GeSn
Mostly Relaxed
7.00E-07
6.00E-07
5.00E-07
3% GeSn
Compressive
1% GeSn
Compressive
4.00E-07
3.00E-07
0% GeSn
Relaxed
2.00E-07
1.00E-07
0.00E+00
1400
1600
1800
Peking University Summer School, July 19, 2013
2000
2200
2400
JSH 49
Microdisk Ge QW Photoluminescence
STANFORD
PL intensity (a.u.)
8000
10 mW
20 mW
30 mW
40 mW
60 mW
6000
4000
2000
0
1350
1400
1450
1500
Wavelength (nm)
•Amplified spontaneous emission
pumped by 900nm pulsed laser
1550
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Peking University Summer School, July 19, 2013
• Two small peaks on each fringe
 TE / TM or higher order
mode
 Ridge waveguide profile,
thick disk
•PL intensity is super linear,
estimated gain of 1500 cm-1
JSH 50
Summary of Initial MBE GeSn Studies
STANFORD
• Strain-free layers of high-Sn% GeSn alloys
– Low-growth temperatures using MBE
– Lattice-matched growth using InGaAs buffers
• Increased photoluminescence for higherSn samples
–
–
–
–
Large increase in integrated PL
Shrinking ΔEc energy with increased Sn
Bandgap mapped out for strain/Sn combinations
Only ~7% Sn necessary for direct-bandgap!
• GeSn is favorable for lasers!
– Low density of states in Γ-valley reduces current to
reach transparency optical gain at low carrier
concentrations
– Low carrier concentrations means reduced free-carrier
absorption and Auger recombination, results in lowthreshold lasers
Peking University Summer School, July 19, 2013
JSH 51
Summary
STANFORD
● Strong quantum confined Stark effect and absorption
shift observed in Ge/SiGe quantum well device
● Modulation demonstrated at 30 GHz & 100 GHz possible
● Waveguide modulator can be integrated into SiGe
waveguides, eliminating alignment and coupling losses
● Both tensile strain and GeSn alloy will be required to
achieve direct bandgap Ge and stimulated emission
● Photonic crystal or optical disks will be required to
achieve high-Q cavities
● Strained Ge and GeSn/SiGeSn are all CMOS compatible
Peking University Summer School, July 19, 2013
JSH 52
Acknowledgements
STANFORD
STUDENTS, POSTDOCS and COLLABORATORS
Yu-Hsuan Kuo
Shen Ren
Theodore I. Kamins
Yiwen Rong
Jonathan E. Roth
Marco Fiorentino
Yijie Huo
Elizabeth Edwards
Michael R.T. Tan
Hai Lin
Rebecca Schaevitz Jae-Hoon Kim
Yangsi Ge
Onur Fidaner
Lars Thylen
Yong Kyu Lee
Selcuk Yerci
Guillaume Huyet
Tomasz Ochalski
Yiyang Gon
Seongjae Cho
Ed Fei
Suyog Gupta
Edris Mohammed
Robert Chen
Jelena Vuckovic
Krishna Saraswat
Colleen Shang
Ian Young
Mark Brongersma
SUPPORT
DARPA
Intel
SRC-IFC
Thank You
Peking University Summer School, July 19, 2013
JSH 53