nanophotonics with silicon nanocrystals -...
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NanoScience Laboratory
Nanophotonicswith silicon nanocrystals
Lorenzo Pavesi
NanoScience Laboratory
Material of choice for microelectronics:
• Advanced fabrication capabilities • Mass production• Cheap
Introduction – Silicon photonics
Courtesy of Intel.
Solarpowerninja.com
CMOS compatibility
http://www.galleries.com/Rock_crystal
Silicon photonicsIntegrated “On-chip” optical elements
SiSiO2
• Semiconductor• Band-gap:1.12 eV
• Refractive index:3.4
• Transparent in IR
• Insulator• Band-gap:
8.9 eV• Refractive index:
1.46 • Transparent in
visible and IR
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Luxtera single-chip 100-Gbps transceiver targets multiple applications
• The new transceiver chip, which measures 5x6 mm, offers 4x28-Gbps transmission over single mode fiber.
• The device features waveguide, waveguide structures, modulators, couplers, and photodetectors integrated at the wafer level. The photodetectors are germanium, but applied to the wafer using the same CMOS processes as the other devices. A single CW laser powers all four channels; it attaches to the CMOS wafer via a hybrid integration process.
November 8, 2011
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Projected integration density
Silicon photonic NOC
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Silicon Nanocrystalsa material to widen the scope of silicon
photonics
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Silicon quantum dots
50 nm
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Micro-disk resonatorsWhispering-gallery mode (WGM) resonators:
Light recirculation by total internal reflection.
• Free-standing geometry(Silicon-rich oxide film [SRO] on silicon pedestal)
• Far field detection based on radiative loss of optical resonator
SRO film thickness:200 nm
µ-disk diameter:7 µm
4 µm diameter
|E|2
Si pedestal
SEM imageMicroscope image
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Active microdisks
Low dimensional Si (Si nanoclusters)
2
Whispering gallery mode microdisk-cavity:
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Q factors > 3000
Optics Express 16, 13218 (2008)
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~200 - upper limit on cavity Q
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
Photoluminescence: excitation by optical pumping
Electroluminescence: excitation by electrical injection
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Injection into a dielectric
• The only way is to use the tunneling effect
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Injection rate engineering
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nc-Si/SiO2 Multilayer LED
• Confined growth of nanocrystals• Better oxide quality• Control over the oxide thickness
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-6 -4 -2 0 2 4 610
-13
10-11
10-9
10-7
10-5
(2 nm SiO2 / 3 nm SRO)
(2 nm SiO2 / 4 nm SRO)
| Gat
e cu
rren
t | (
A)
Gate voltage (V)
Reverse biasForward bias
EL data
points
Low onset of EL voltages, < 3.2 V
J. Appl. Phys. 106, 033104 (2009)
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20
Si-NC LEDon a CMOS wafer
CMOS LED
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21
Si-NC LEDon a CMOS wafer
CMOS LED
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Graded gap active layer
Large nanocrystals: Easy injectionSmall nanocrystals: high emission
Injection rate engineering
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10-3
10-2
10-1 1
0.00
0.05
0.10
0.15
0.20 (2 nm SiO2 / 3 nm SRO)
Optimized
(2 nm SiO2 / 4 nm SRO)
Po
we
r p
lug
-in
eff
icie
ncy
(%
)
Current density (mA / cm2)
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Optical gain
JAP 96, 5747
expON PL
QZ Q SiZ nc P Si nc
O
gI
JI
T d dI
IT I0
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How we measured gain
JAP 96, 5747
I0IT
expON PL
QZ Q SiZ nc P Si nc
O
gI
JI
T d dI
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Summary on optical properties of Si-nc
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N4
N3
N2
N1
fast
spontaneous
fast
stimulated
Auger
pump
4 levels system model
1
4
2
3
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Model for the 4 levels
Si=O bond formed
at the interface of
the Si-nc with the
matrix
A. Filonov, S. Ossicini, PRB 65 195317 (2002)
Ground state
Excited state
oxygen
oxygen
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Silicon nanocrystal nonlinearity
Silica
Bulk Silicon
GaAs
Si-ncs
n2= (1.54x10-16) cm2/W
n2= (1.59x10-13) cm2/W
n2= (4.5x10-14) cm2/W
n2= (2 ÷ 8x10-13) cm2/W
n=n0+n2I
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All optical switching
l = n d
A. Martinez et al. Nanoletters (2010)
NanoScience LaboratoryA. Martinez et al. Nanoletters (2010)
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Active microdisk for optical switching
The top of the waveguide is free
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Active microdisk for optical switching
Silicon nanocrystals
silicon
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Optical bistability
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Use of solar spectrum in crystalline silicon cells
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Use of nanocrystals: tandem cells
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Use of nanocrystals: downshifter layer
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The structure of the device
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No. Active layerPeriod of multi-layer
Layer thickness
Q1 SRO/SiO2 5 2 nm +1 nm
Q2 SRO/SiO2 5 3 nm + 1 nm
Q3 SRO 20 nm
Q5 -Si/SiO2 5 3 nm + 1 nm
Q7 SRN/SiO2 5 3 nm + 1 nm
Q8 SRO/Si3N4 5 3 nm + 1 nm
Q9 SRN/Si3N4 5 3 nm + 1 nm
The structure of the device
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-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.41E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
ICu
rre
nt (A
)I
Voltage (V)
SRO/SiO2
SRO
a-Si/SiO2
I-V curves measured in dark
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Photoresponsivity
400 500 600 700 800
10-5
10-4
10-3
Q1(SRO/SiO2=2nm/1nm)
Q2(SRO/SiO2=3nm/1nm)
Q3(SRO)
Q5(-Si/SiO2=3nm/1nm)
Q7(SRN/SiO2=3nm/1nm)
Ph
oto
resp
on
siv
ity (
A/W
)
Wavelength (nm)
Q5
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a-Si/SiO2 shows the best PV effect
0.00 0.05 0.10 0.15 0.200
1
2
3
4
5
6
7
Cu
rre
nt
(A
)
Voltage (V)
3.4 A
120 mV
FF: 30.2
Isc
: 6 ± 1 A
Voc
: 220 ± 1 mV
Pmax
: 40.8 W/cm2
Rserial = 23.6 kΩ
Rshunt = 51.2 kΩ
Rserial = 6.41 kΩ
Rshunt = 54.1 kΩ
Lambert W function
Conversion efficiency 0.41 %
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Si-nc as down-shifter layer
Silicon nanocrystals
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Si-nc as down-shifter layer
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400 500 600 7000.0
0.2
0.4
0.6
0.8
1.0
Op
tica
l fu
nctio
n
Wavelength (nm)
TSRO
RSRO
ASRO
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400 500 600 7000.0
0.2
0.4
0.6
0.8
1.0
Op
tica
l fu
nctio
n
Wavelength (nm)
TSRO
RSRO
ASRO
0.0
0.1
0.2
0.3
Ph
oto
resp
on
siv
ity (
A/W
)
PRARC
(b) PDS-2
PRARC calculated photoresponsivity with a passive layer
ARCPR
ARC
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400 500 600 7000.0
0.2
0.4
0.6
0.8
1.0
Op
tica
l fu
nctio
n
Wavelength (nm)
TSRO
RSRO
ASRO
0.0
0.1
0.2
0.3
Ph
oto
resp
on
siv
ity (
A/W
)
PR
PRARC
(b) PDS-2
PR measured photoresponsivityPRARC calculated photoresponsivity with a passive layer
PL+ARCPR
ARCPR
ARC
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A maximum enhancement of the internal quantum efficiency of 14%
400 500 600 7000.0
0.2
0.4
0.6
0.8
1.0
Op
tica
l fu
nctio
n
Wavelength (nm)
TSRO
RSRO
ASRO
0.0
0.1
0.2
0.3
Ph
oto
resp
on
siv
ity (
A/W
)
Inte
rnal q
ua
ntu
m e
ffic
iency e
nh
an
ce
me
nt
PR
PRARC
INT
(b) PDS-2
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Modeling of Si-QD solar cells
Laboratory reference
LaboratoryDS layer
CommercialReference
CommercialDS layer
16.50 % 17.56 % 14.20 % 15.11 %
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Si-nc as imaging agents
Preparation:
1. Sonication of poroussilicon
2. Photoinduced hydrosilylation reaction between undecylenic acid and hydrogen passivated Si-nc surface
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Si-nc as bioimaging agent
COOH
COOH
CO
OH
Hydrophilic alkyl-capped Si-nc
High quantum yieldQY ~ 30 %
TEM image
Luminescent clear suspensionin different solvents (water, ethanol).
No change in PL lineshapein different solvents.
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Si-nc as bioimaging agent
1. Si-nc-COOH can be storedin ethanol for long periods
of time.
2. In water Si-nc-COOH slowlyoxidized and dissolve.
Biodegradability is achieved.
Si-nc-COOH without physical coating:
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Si-nc-COOH with physical coating:
Biodegradability is mantained.
Si-nc as bioimaging agent
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DCA was not added
Bio imaging
• DCA (sodium deoxycholate monohydrate ) shows similiarbehaviour as SDS
• DCA less toxic than SDS
Fluorescence images of SKOV-3 cells incubated with Si-nc-COOH+DCA for 30 min.
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Silicon quantum dots
• Light emission
• Optical gain
• Nonlinear optical effects
• Photoresponse
• Biocompatibility
• Interface properties
• Sensitization action
• …
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Si-nc as Er3+ sensitizer
Si-nc
Er3+
Sensitization:
Si-nc upon excitation (optical or electrical)transfers its energy to nearby Er3+ ions.
• Increase in effective excitationcross-section for up to 5 ordersof magnitudes(≈ 10-21 → ≈ 10-16 cm2)
• Broadband excitation
4I13/2 - 4I15/2 Er3+ radiative transitions falls in the third telecom window (maximum transparency
of silica fibers).
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Si-NCs:Er LEDs
• SiOx: LPCVD ~ 50 nm, Si excess: 9-16 at. %;
• SiOx anneal: 900°C, 1 h;
• Er implantation: 20 keV, 1x1015/cm2;
• Er post-implantation anneal: 800°C, 6 h
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Si-NCs:Er LEDs - Results
External
Quantum
Efficiency
0.55 % in DC
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Si-NCs:Er LEDs - Results
External
Quantum
Efficiency
0.55 % in DC
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Conclusions
• Silicon nanocrystals are a viable platform to improve-enable-widen the scope of silicon photonics
• A lot of new physics can be found in an already mature research field such as Silicon Photonics
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Acknowledgments
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Acknowledgments