nanophotonics with silicon nanocrystals -...

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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

NanoScience Laboratory10/3522/11/2012

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