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
