Advances in Silicon Photonics

Francesco Priolo Center for MAterials and Technologies for Information,

communication and Solar energy (MATIS, CNR-IMM)

&

Scuola Superiore di Catania, University of Catania, Italy

www.matis.imm.cnr.it www.ssc.unict.it

La Legge di Moore

Silicon Photonics Motivation

Interconnect bottleneck

Courtesy of LUXTERA

Outline

• Photonic crystal nanocavities

• Erbium Silicates

• Silicon Quantum Dots

• Silicon Nanowires

SOI photonic crystal nanocavity light emitting devices

Lasing (III-V)

Science 305, 1444 (2004)

Photonic crystal cavities

Ultrahigh Q

cavities Nature 425, 944 (2003)

Nat. Phot. 1, 49 (2007)

We want to use PhC high Q cavities for

achieving an efficient light emission in Si

Nat. Phot. 5, 297 (2011)

Smart-cut and PL emission from SOI

The smart-cut process leads to the

formation of some H2-related defect,

showing a high PL intensity.

SOI = Silicon-On-Insulator

1300 1350 1400 1450 1500 1550 1600

0.1

1

10 Cz Si

SOI membrane

PL

in

ten

sity

(a.u

.)

wavelength (nm)

T=300 K

PL emission from patterned SOI

The smart-cut process leads to the formation of

some H2-related defect, showing a high PL

intensity.

Max enhancement ≈ 300

FP ≈ 12

1300 1350 1400 1450 1500 1550 16000.1

1

10

100

1000

PhC cavity

SOI membrane

PL

in

ten

sity

(a.u

.)

wavelength (nm)

T=300 K

Effect of Plasma Treatments

Nanobubbles, extended defects

and platelets [(100) and {111}]. The plasma induces the formation

of defects just below the surface.

TEM analyses

50 nm

TEM analyses

100 nm

The defects concentration

increases at the holes sidewalls.

Why do not try to

electrically excite

the defects??

Tunable PL Emission in PhC cavities

220

nm

1.9

μm 10 μm

p+ p+ 1 1019 B/cm3

p from ~1 1015 to 1 1018 B/cm3

Devices features

p p+

1 μm

• triangular lattice

• a = 400 nm and a = 800 nm

• ff varied between 0 and 75%

2

3

2

a

rff

A very high EL intensity is

recorded! Even higher than

PL (at the saturation)!

Laser-like Light Emitting Device

Remarks:

Room temperature

Telecom wavelengths

Potentially tunable between 1100 and 1600 nm

Peak width: 0.5 nm

Output power: 400 W/cm2 800 W/nm/cm2

Source Pumping W/nm/cm2 T

Porous Si 690 nm Electrical 9 300 K ~100 nm

Raman Laser 1686 nm Optical ~1011 300 K <0.001 nm

Si nc (gain) 800 nm Electrical 0.02 300 K ~100 nm

Ge-Si Laser 1600 nm Optical a.u. 300 K 0.5 nm

III-V PhC Laser 1170 nm Electrical 63 <150 K 0.95 nm

2 μm

1019

B/cm3

1019

P/cm3

Erbium Silicates

100

50

10

5

1

.7 .8 .9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

.5

.1

Silica optical fiber

Wavelength ( m)

Lo

ss (

dB

/km

)

0.9 m1.5 dB/km

1.3 m0.6 dB/km

1.55 m0.2 dB/km

OPTICAL AMPLIFIERS FOR MICROPHOTONICS

Low solubility in silica-based hosts

[Er] ≈ 1020 cm-3

A. Polman et al., J. Appl. Phys. 70, 3778 (1991)

Er:SiO2 • All Er ions are optically excitable M. Miritello et al., Adv. Mater. 19, 1582 (2007)

• Theoretical optical gain K. Suh et al., Appl. Phys. Lett. 89, 223102 (2007)

• Electroluminescent devices Y. Yin et al., J. Phys.: Condens. Matter 21, 012204 (2009)

Laser

Optical fiber

Mirrors Modulators

Photodetector

Electronics

Er compounds

Modify the solar spectrum

Egap(Si) Egap(Ge)

Overcome carriers thermalization

Downconverter

Rare Earths in Photovoltaics

Group IV semiconductor solar cells

Absorption of photons with hn < EG

Upconverter

Dipole-dipole interactions Strongly depends on the high Er content

Cross-relaxation

0

5

10

15

en

erg

y (

10

3 c

m-1)

4I

9/24I

11/2

4I

15/2

4I

13/2

High Er content

Up-conversion

0

5

10

15

en

erg

y (

10

3 c

m-1)

4I

9/24I

11/2

4I

15/2

4I

13/2

High Er content High external pumping

Er-Er Interactions

It is possible to change the Er content between

1020 and 1022 cm-3

RE and Er in solid hosts:

Same chemical properties Similar ionic radius Same compounds with similar structural features

Si O RE

Er-based compounds

Er as a constituent inside an OXIDE or SILICATE crystalline structure

Er inside a RE compounds

Er content ≈ 1022 cm-3

Mixed RE and Er All Er

RE

RE= Y

• Er oxide (Er2O3) • Er silicate (Er2SiO5, Er2Si2O7)

• Y-Er silicate (Y2-xErxSi2O7)

Optical Properties

0 3 6 9 12 15

1

2

3

40.0 0.4 0.8 1.2 1.6 2.0

exc = 488 nm

x

NEr

(cm-3)

/0

x1021

PL

NErτ Normalized =

σ

σ0

Low pumping flux

No upconversion!

Linear regime

σNErτ ф τ rad

PL ∝

0 3 6 9 12 15

1

2

3

40.0 0.4 0.8 1.2 1.6 2.0

exc = 488 nm

x

NEr

(cm-3)

/0

x1021

Optical properties

PL

NErτ Normalized = σ

σ0

0.0

0.5

1.0

1.5

2.0

2.54F

7/2

4S

3/2

4I

9/2

4I

11/2

4I

15/2

4I

13/2En

erg

y (

eV)

Pump

488 nm 1.54 μm

Low NEr (x<0.65)

1 excitation per photon

Optical Properties

0 3 6 9 12 15

1

2

3

40.0 0.4 0.8 1.2 1.6 2.0

exc = 488 nm

x

NEr

(cm-3)

/0

x1021

Increase of the 4I13/2

excitation cross section 0.0

0.5

1.0

1.5

2.0

2.54F

7/2

4S

3/2

4I

9/2

4I

11/2

4I

15/2

4I

13/2En

erg

y (

eV)

Medium NEr (0.65≤x<2)

2 excitations per photon

Pump

488 nm 1.54 μm 1.54 μm

PL

NErτ Normalized = σ

σ0

OPTICAL PROPERTIES

0 3 6 9 12 15

1

2

3

40.0 0.4 0.8 1.2 1.6 2.0

exc = 488 nm

x

NEr

(cm-3)

/0

x1021

Maximum excitation efficiency ≈ 300%

for Er disilicate 0.0

0.5

1.0

1.5

2.0

2.54F

7/2

4S

3/2

4I

9/2

4I

11/2

4I

15/2

4I

13/2En

erg

y (

eV)

High NEr (x=2)

3 excitations per photon

4I

15/2

4I

13/2

4I

15/2

4I

13/2

Pump

488 nm

1.54 μm 1.54 μm

1.54 μm

PL

NErτ Normalized = σ

σ0

sYb(lexc=980 nm)= 2.0x10-20 cm2

sEr(lexc=980 nm)= 2.0x10-21 cm2

Very high excitation cross section

Insert gradually Er in Yb2-xErxSi2O7 Strong coupling Yb-Er

Very large absorption band

750 800 850 900 950 10000.0

0.2

0.3

0.5

0.7

0.8

1.0

1000 1100 1200 1500

0.00

0.25

0.50

0.75

1.00

Yb= 19 at.%x 0.25

No

rmali

zed

PL

In

ten

sity

at

10

25

nm

Excitation wavelength (nm)

P

L I

nte

nsi

ty (

a.u

.)Wavelength (nm)

exc= 920 nm

Er-Yb based compounds

PL EMISSION AT 1.5 m

t(4I15/2) is not influenced

by [Yb] presence

Maximum PL(1.5 mm) is reached for [Yb]= 17.2 at.% [Er]= 1.8 at.%

Yb Er

0 2 4 6 8 10 12 14 16 18 20 22

1

2

3

4

5

6

7

8

9

10

11

0

1

2

3

4

5

PL

PL

at

1.5

m

(a.u

.)

NYb

(at.%)

exc=980 nm

_(Yb-Er)2Si

2O

7

_(Y-Er)2Si

2O

7

at

1.5

m

(m

s)

1E17 1E18 1E19 1E20 1E21 1E22 1E230.01

0.1

1

10

100

1000

10000

1E-3

0.01

0.1

1

10

100 Yb-Er

Y-Er

exc= 980 nm

PL

In

ten

sity

@ 1

.5 m

(a.u

.)

flux (cm-2s

-1)

N1/N

Er (

%)

PL EMISSION AS A FUNCTION OF FLUX

Very high percentage of excited Er ions

is obtained in Yb-Er disilicate

[Yb]= 17.2 at.% [Er]= 1.8 at.% [Yb]= 0 at.% [Er]= 1.8 at.%

Yb= 2.0x10-20 cm2

Cup = (6 ± 1)×10-16 cm3/s

Yb= 2.0x10-21 cm2

Cup = (6 ± 1)×10-16 cm3/s

Integration of photonic crystals with Er-based RE compounds

RE or Er

O Si

RE-Er)2Si2O7 It is possible to vary Er content

between 1020 and 1022 cm-3 RE-Er)2Si2O7, RE=Y or Yb

on top of L3 cavity

c-Si

SiO2

Si

RE-Er)2Si2O7

a

1500 1520 1540 1560 15800

3

6

9

12

15 Y-Er disilicate

on SOI

PL

in

ten

sity

(a.u

.)

Wavelength (nm)

lattice constant, a

416 nm

422 nm

423 nm

424 nm

425 nm

429 nm

x 100

Er coupling with cavity modes

10-4

10-3

10-2

10-1

100

101

102

103

10-1

100

101

102

Em

itte

d p

ow

er

(pW

)

Pump power (mW)

1020

1021

1022

1023

1024

1025

1026

10-4

10-3

10-2

10-1

100

Ex

cit

ed

Er

fracti

on

Photon flux (cm-2s

-1)

(Y-Er)2Si2O7

(Yb-Er)2Si2O7

0.8×1021 Er/cm3

High excited Er fraction

Silicon Quantum Dots

Samples preparation PE-CVD

N2O+SiH4

RF magnetron sputtering

Co-sputtering from 3 different targets

Amorphous Si nanoclusters

Si nanocrystals

Targets: SiO2 Er2O3 Si

• SiOx

• SiOx + Er ions

0 10 20 30 40 50

SiOx

T = 1250 °C

Energy (eV)

Co

un

ts (

a.u

.)

Si

SiO2

Electron energy loss spectra

20 nm

Dark field TEM

20 nm

Energy filtered TEM

Formation of Si Nanoclusters

5 nm 10 nm 10 nm

1100 C 1150 C 1250 C 10 nm

10 nm

10 nm

As-deposited 900 C 1000 C

Nanocrystals luminescence

600 700 800 900 1000110012000,0

0,2

0,4

0,6

0,8

1,0

1,2

Si nc radius

1250 °C 1 h

35 at. Si

37 at. Si

39 at. Si

42 at. Si

44 at. Si

PL Inte

nsity (

a.u

.)

Wavelength (nm)

Silicon nanocrystal MOSLED device

x

100 nm

Metallization

Poly-Si

SiO x

Si substrate

Erbium in Si Nanostructures

1400 1500 1600 17000,0

0,5

1,0

1,5

2,0

2,5

3,0

x 5

Er doped Si nanoclusters

Er doped SiO2

PL

In

ten

sity (

a.u

.)

Wavelength (nm)

RT PL

10 mW

400 500 600 700 800 900 1000

10-13

10-12

10-11

10-10

1.54 m (Er + Si nc)

1.54 m (Er in SiO2)

0.90 m (Si nc)

I PL

E/

(a

rb.

un

its)

Excitation Wavelength (nm)

4I11/2 - 4I15/2

4I9/2 - 4I15/2

2H11/2 - 4I15/2

4F7/2 - 4I15/2

1000 1200 1400 16000,00

0,02

0,04

0,06

0,08

E

L I

nte

nsity (

a.u

.)

Wavelength (nm)

0 200 400 600 800 1000

10-1

100

Electroluminescence

Photoluminescence

Time ( s)

Norm

aliz

ed I

nte

nsity

Er doped Si nanoclusters device

Electrically-Driven Er and Si Nanocluster Optical Amplifier

photon

Si nc

Er3+

1.54 mm

Stimulated emission Er3+

Silicon nanowires light emitting devices

Metallic catalyst

V L

(111) Substrate

S

• Gibbs Thompson Effect in VLS

• Gold Diffusion

• Doping

Vapor Liquid Solid drawbacks

Koren E. et al. , Nano Letters 10, 1163 (2010)

Den Hertog M. et al., Nano Letters 8, 1544 (2008)

Critical radius!

Dubrovskii V. et al.., PRB 78, 235301 (2008)

Si

Si RT

Si

HF + H2O2 + H2O Si RT

2-3 nm-thick Au layer

Si KI etch

100 nm

Si Au

30nm

0.0

0.1

0.2

thAu = 3 nm

(dSi = 6 ± 1 nm)

thAu = 2 nm

(dSi = 9 ± 2 nm)

thAg = 10 nm

(dSi = 12 ± 3 nm)

Diameter of uncovered Si regions (nm)

0.0

0.1

0.2

Rel

ativ

e fr

equ

ency

0 5 10 15 20

0.0

0.1

Si Au

30nm

10 nm

505 510 515 520 525

thAu

= 3 nm

dNW

= 5 1 nm

thAu

= 2 nm

dNW

= 7 2 nm

thAg

=10 nm

dNW

= 9 2 nm

bulk Si

No

rmali

zed

in

ten

sity

(a.u

.)

Raman shift (cm-1)

Si plasmon SiO2 plasmon

d = 4 nm d = 7 nm

ηq ext > 0.5%

600 650 700 750 800 850 9000.0

0.2

0.4

0.6

0.8

1.0

dNW

= 5 1 nm

dNW

= 7 2 nm

dNW

= 9 2 nm

PL

in

ten

sity

(a.u

.)

Wavelength (nm)

0 50 100 150 200

0.1

1

No

rmali

zed

PL

in

ten

sity

time ( s)

640 nm = 17 s

690 nm = 25 s

750 nm = 38 s

Fractal geometry &

Blackbody behavior

Coherent Enhanced Raman Backscattering

Si/Ge Nanowires

Si NWs LED AZO

Si NWs

400 600 800 1000 12000

50

100

150

200

2 V

3 V

4 V

5 V

6 V

EL

in

ten

sity

(a.

u.)

Wavelength (nm)

Room temperature

Conclusions

0 3 6 9 12 15

1

2

3

40.0 0.4 0.8 1.2 1.6 2.0

exc = 488 nm

x

NEr

(cm-3)

/0

x1021