1) The document discusses erbium-containing rare earth compounds such as yttrium-erbium oxide (Y-Eroxide) and yttrium-erbium silicates for applications in silicon optical communications. 2) Thin films of Y-Eroxide were synthesized with varying erbium content using co-sputtering. Higher erbium content led to increased phonon energy and decreased visible and infrared photoluminescence emission. 3) Films with around 3.3% erbium content showed optimal 1.54 μm emission due to reduced erbium-erbium interactions compared to higher concentration films.

1. UNIVERSITA’ DEGLI STUDI DI CATANIA
Dottorato di Ricerca in Scienza dei Materiali
XXI Ciclo
Tutor: Prof. F. Priolo
Supervisor: Dott. M. Miritello
Coordinatore: Prof. A. Terrasi
Roberto Lo Savio
Erbium-rich thin film materials
for optical communications in silicon

2. Outline
 Importance of optical communications in silicon
 Er-containing rare earth compounds
• Yttrium-Erbium oxide
• Yttrium-Erbium silicates
 Influence of Er content on the structural and optical properties
 Optical amplification at 1.54 μm
 Conclusions

3. Communication technology
Optical data transmission
across very long distances
Development of communication systems
(World Wide Web)
OPTICAL FIBERS NETWORKS
Wireline technology improves by
following an exponential trend
Billion
Thousand
Million
Bitspersecond

4. Optical interconnections
 DATA SPEED
 DATA FLOW
 POWER DISPERSION
 SIGNAL LOSSES
OPTICAL COPPER
High
High
Low
Low
Low
Low
High
High
Move this limit
towards lower distances
PHOTONS
BETTER THAN
ELECTRONS

5. Si-based microphotonics
Integration of photonic
components on Si-chip
ACTIVE COMPONENTS
Optical planar amplifiers
×
Building block research
 Size reduction
 Si-compatible materials
 ULSI Integration

6. Optical amplification in silicon
L. Pavesi et al., Nature 408, 440 (2000)
Quantum confinement in Si
H.-S. Han et al., Appl. Phys. Lett. 81, 3720 (2002)
Erbium in Si-based materials
Raman amplified emission in bulk Si
H. Rong et al., Nature 433, 725 (2005)
Photonic crystal on bulk Si
S. G. Cloutier et al., Nat. Mater. 4, 887 (2005)

7. Why erbium?
4I13/2
4I15/2
Widely used in large-scale amplifiers
(≈ tens of meters long)
1.54 μm photon emission
and amplification
Population inversion between
4I13/2 and 4I15/2 states
 Fast depopulation of pumped energy level
 Slow depopulation of 4I13/2 level
Er3+ in solid host
RE in solid hosts → RE3+, [Xe]-4fN
4f electrons shielded by outer shells 5s24p6
Atomic-like levels

8. Er-doped materials for optical amplifcation
HOST FOR ERBIUM DOPING
 IR transparency
 Ability to dissolve high Er contents
• silicon oxide
• silicon oxide containing Si nanoclusters
• aluminum oxide
• […]
Reduce the sizes of
Er-doped amplifiers?
Increase Er content
Er concentration
optically suitable
1017 ÷ 1020 at/cm3
 Increase solubility
 Avoid Er-Er interactions ?

9. Limits of Er-Er interactions
Up-conversion
Population of higher-energy levels
at expenses of the lower-energy ones
0
5
10
15
energy(10
3
cm
-1
)
4
I9/24
I11/2
4
I15/2
4
I13/2
High Er3+ concentration
in the excited states
 High Er content
 High pumping powera,b) energy migration;
c) 1.54 μm photon emission;
d) non-radiative energy dissipation.
0
1 1
8 Er Er q ErR C N N
    
Increase of 1.54 μm decay rate
E. Snoeks et al., Opt. Mater. 5, 159 (1996)
c)
-OH
a
a
b
c
b d
Concentration quenching

10. Erbium-containing rare earths compounds
a
b
c
x
y
z
Er2O3
a
b
c
x
y
z
Y2O3
 lattice mismatch < 1 %
 Same bcc lattice
 Similar lattice parameters
RE oxides (RE2O3)
RE silicates (RE2O3 + SiO2)
 Same phase diagram
 Same stoichiometric composition (RE2SiO5 and RE2Si2O7)
 Same crystalline structures with similar lattice parameters
RE in solid hosts:
 Same trivalent state RE3+
 Similar ionic radius
r(Y3+) = 0.89 Å
r(Er3+) = 0.88 Å
Varying Er content in
mixed Y-Er compounds
La → [Xe]-5d16s2
Y → [Kr]-5d16s2
Same chemical
properties

11. Thin films synthesis
Y2O3
SiO2
Er2O3
CONFOCAL CO-SPUTTERING
UHV magnetron sputtering
Er2O3
c-Si
RFRFRF
 ULSI compatible
 Planar thin films
Careful control of films composition
 rotating
 heated (400 °C)

12.  Y-Eroxide
 Y-Er silicate

13. Y-Er oxide for optical applications
Up-converter material
for visible phosphors
Low phonon energy host
J. A. Capobianco et al.,
J. Phys. Chem. B 106, 1181
(2002)
1.54 μm
emission
J. Hoang et al., J. Appl. Phys. 101, 123116 (2007)
 Er ions are substitutional in Y sites
Low-concentration regime (< 10 at.%)
Y-O-Y or Er-O-Y bonds → dEr-Er ≈ 10 Å
High-concentration regime (> 10 at.%)
Er-O-Y or Er-O-Er bonds → dEr-Er ≈ 5 Å
EXAFS Analysis
J. Hoang et al., J. Appl. Phys. 101, 123116 (2007)

14. 1.5 1.6 1.7 1.8 1.9 2.0
0
10
20
30
40
50
60
ErY
P(Er2
O3
)
0 W
15 W
25 W
40 W
70 W
100 W
150 W
NormalizedYield(a.u.)
Energy (MeV)
Y-Eroxide films composition
RBS spectra Th = 120 ± 10 nm (ellipsometry)
 Total [Y]+[Er] is constant
 Ratio [Y]+[Er] / [O] = 2/3
THIN FILMS DEPOSITION
 Co-sputtering from Y2O3, and Er2O3 targets
 P(Y2O3) = 500 W, constant
P(Er2O3)
(W)
[Er]
(at/cm3)
[Er]
(at.%)
Y2-xErxO3
x
15 1.2×1020 0.2 0.01
25 7.7×1020 1.1 0.06
40 2.45×1021 3.3 0.17
70 5.41×1021 8.2 0.41
100 7.68×1021 11.4 0.57
150 1.030×1022 14.3 0.72
200
P(Y2O3) = 0 W
2.944×1022 40.0 2.00

15. Crystalline structure
 Same diffraction spectra
 Slight 2θ peaks shift for different [Er]
20 30 40 50 60
0
200
400
600
800
Y1.99
Er0.01
O3
, [Er] = 0.2 at.%
Y1.43
Er0.57
O3
, [Er] = 14.3 at.%
Intensity(cps)
2 (degree)
(622)
(541)
(440)
(431)
(422)
(222)
(211)
0.0 0.5 1.0 1.5 2.0
10.50
10.55
10.60
10.65
10.70
Er2
O3
Latticeparameter(Å)
xY2
O3
Lattice parameter decreases
by increasing the Er content
a(Y2O3)
XRD spectra
a(Er2O3)
No evidence of phase separation

16. 0
5
10
15
20
1535 nm
4
F9/2
4
S3/2
488 nm
4
F7/2
4
I11/2
4
I15/2
4
I13/2
energy(10
3
cm
-1
)
560 nm
660 nm
980 nm
600 800 1000 1200 1400 1600
0.000
0.005
0.010
0.015
0.020
0.025
PLIntensity(a.u.)
Wavelength (nm)
4
I13/2
4
I11/2
4
S3/2
4
F9/2
exc
= 488 nm
Pexc
= 10 mW
PL emission of Y1.95Er0.05O3, [Er] = 1.1 at.%
RT PL spectra
 Low phonon energy (Rn,n-1 ≈ Rn0)
LESS-PROBABLE
NON-RADIATIVE DECAYS
980 nm

17. 10
19
10
20
10
21
10
22
10
23
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
2.0
exc
= 488 nm
exc
= 980 nm
IntegratedPLintensityat0.56m(a.u.)
Photon flux (cm
-2
sec
-1
)
1.0
4
S3/2
4
I15/2
Up-conversion in Y1.95Er0.05O3, [Er] = 1.1 at.%
 λexc = 488 nm, n = 1 → direct absorption
 λexc = 980 nm, n = 2 → up-conversion
0 100 200 300 400 500
0.01
0.1
1 
exc
= 980 nm

exc
= 1.0 10
22
cm
-2
s
-1

exc
= 488 nm

exc
= 7.5 10
22
cm
-2
s
-1NormalizedPLintensityat0.56m
Time (s)
fast
slow
slow
n
PL excI P
n → number of involved photons
0
5
10
15
20
(4)
(3)
(2)
(1)
980 nm
energy(10
3
cm
-1
)
4
F7/2
4
S3/2
4
F9/2
4
I9/2
4
I11/2
4
I15/2
4
I13/2
560 nm
(1)
UP-CONVERSION

18. Optical properties for different Er contents
600 800 1000 1200 1400 1600
0
10
20
30
40
50
60
70
80
4
I13/2
4
I11/2
x = 0.05, [Er] = 1.1 at.% ( 1.6)
x = 0.17, [Er] = 3.3 at.%
x = 0.57, [Er] = 11.4 at.% ( 4.2)
PLIntensity(a.u.)
Wavelength (nm)
4
S3/2
4
F9/2

exc
= 488 nm
Pexc
= 10 mW
Visible and near-IR emission decrease
by increasing the Er content
Phononic decay rates increase
at expenses of radiative ones
PHONON ENERGY
INCREASE IN Y2-xErxO3
BY INCREASING x

19. 0.0 0.2 0.4 0.6 0.8
0
20
40
60
80
0 4 8 12 16
[Er] (at.%)
PL
PLIntensity(a.u.)
x
0
2
4
6
8

Lifetime(ms)
Pexc
= 10 mW

exc
= 488 nm
Influence of Er content on 1.54 μm PL emission
 Maximum IPL for [Er] = 3.3 at.%
PL
RAD
I N





20. 0 2 4 6 8 10 12 14 16
0
1
2
3
4
5
R=
-1
(10
4
s
-1
)
[Er] (at.%)
Concentration quenching of 1.54 μm PL decay
Extrapolated τ0 = 8 ± 2 ms
Calculated τradiative = 7.75 ms
M. J. Weber, Phys. Rev. 171, 283 (1968)
0
1 1
8 Er Er q ErR C N N
    
Low-concentration regime → dEr-Er ≈ 10 Å
High-concentration regime → dEr-Er ≈ 5 Å
Slope increase by a factor of 64
 
 
66
6 6
1 10
64
5


 
    
 
Er Er
Er Er
d high
C
d d low
1.54 μm rate increase is explained
by the Er-Er dipole interaction
0 2 4 6 8
0.00
0.05
0.10
0.15
0.20
0.25
R=
-1
(10
4
s
-1
)
[Er] (at.%)

21. Optical applications of Y2-xErxO3
0.0 4.0x10
21
8.0x10
21
1.2x10
22
0.00
0.02
0.04
0.06
0.08
0.10
0.12 Y1.95
Er0.05
O3
, [Er] = 1.1 at.%
Y1.43
Er0.57
O3
, [Er] = 11.4 at.%
IPL
(visible)/IPL
(1.54m)
Photon flux (cm
-2
s
-1
)
exc
= 980 nm
 Y1.95Er0.05O3, [Er] = 1.1 at.% ↔ Lower phonon energy → Up-converted VIS emission
 Y1.43Er0.57O3, [Er] = 11.4 at.% ↔ Higher phonon energy → Emitter at 1.54 μm
0
5
10
15
20
4
F9/2
4
S3/2
4
F7/2
4
I11/2
4
I15/2
4
I13/2
energy(10
3
cm
-1
)
560 nm
660 nm
980 nm
Up-conversion
0
5
10
15
20
1535 nm
4
F9/2
4
S3/2
4
F7/2
4
I11/2
4
I15/2
4
I13/2
energy(10
3
cm
-1
)
980 nm
Down-conversion

22.  Y-Er oxide
 Y-Er silicate

23. mixing two oxides: SiO2 and RE2O3
RE2O3 + SiO2  RE2SiO5
RE2O3 + 2SiO2  RE2Si2O7
RE silicates
RE2SiO5
≈1100 °C ≈1400 °C
amorphous A B
RE2Si2O7 amorphous
≈1450 °C≈1000 °C ≈1200 °C
y α
≈1300 °C
β γ
POLYMORPHISM
Varying Er content in
mixed Y-Er silicate

24. Er silicate for optical applications
Er2SiO5 +
1250 °C, 30 min
structures not suitable for
planar active devices:
thin films required
X. X. Wang et al., J. Cryst. Growth. 289, 178 (2006)
Poor stability under
high temperature
thermal treatments
H. Isshiki et al., Appl. Phys. Lett. 85, 4343 (2004)
Er-Si-O islands
J.H. Shin et al., Nano Lett. 5, 2432 (2005)
Si / Er2Si2O7 nanowires
Non-resonant Er excitation through Si-NW

25. Y-Er silicate for optical applications
[Er] = 1.5 at.%
Cup= 1.710-18 cm3/s,
LOW UP-CONVERSION
K. Suh et al., Appl. Phys. Lett. 92, 121910 (2008)
A-Y2-xErxSiO5 nanoaggregates
THIN FILMS
?

26.  Influence of Y-Er silicate composition
on the structural and optical properties
 Optimization of Er content in Y-Er silicate
Y-Er silicate thin films

27.  Influence of Y-Er silicate composition
on the structural and optical properties
 Optimization of Er content in Y-Er silicate
Y-Er silicate thin films

28. 0.6 0.8 1.0 1.6 1.8
0
20
40
60
80
100
ErSi
Er2
SiO5
intermediate
Er2
Si2
O7
NormalizedYield(a.u.)
Energy (MeV)
O
Films composition
[Er] ≈ 1 – 2 × 1022 cm-3
Thickness = 150 – 160 nm
THIN FILMS DEPOSITION
 Co-sputtering from SiO2, and Er2O3 targets
 P(Er2O3) = 200 W, constant; P(SiO2) = 150 – 350 W
Three different atomic compositions
 stoichiometric (mono-, di-silicate)
 non-stoichiometric (intermediate)
Post-deposition annealing
RTA 1200 °C, 30 s
O2 (reactive)

29. Thermal stability
Er2SiO5 Er2Si2O7intermediate
1.6 1.7 1.8 1.9
0
20
40
60
80
100
Er Er
NormalizedYield(a.u.)
Energy (MeV)
1.6 1.7 1.8 1.9
as deposited
1200 °C, 30 s, O2
Energy (MeV)
1.6 1.7 1.8 1.9
Er
Energy (MeV)
no compositional change
formation of
interfacial Er2Si2O7
evolution in
Er2Si2O7 composition
Er2SiO5 + SiO2  Er2Si2O7
R. Lo Savio et al., Appl. Phys. Lett. 93, 021919 (2008)
Stoichiometric films are chemically
stable after reactive annealing

30. 20 30 40 50 60
0
100
200
300
400
500
A-Er2
SiO5
Intensity(cps)
2 (degree)
JCPDS 70-2379
20 30 40 50 60
0
200
400
600
800
1000
1200
1400
Intensity(cps)
2 (degree)
-Tm2
Si2
O7
JCPDS 31-1391
y-Y2
Si2
O7
JCPDS 74-1994
Film crystallization
Er2SiO5
Er2Si2O7
Er2Si1.6O5
Same crystalline structure
mixture y-Er2Si2O7 + α-Er2Si2O7
Composition
evolution
in Er2Si2O7
1200 °C, 30 s, O2 annealing

31. 0
2
4
6
8
10
12
14
16
0
40
80
120
160
200
240
280
Er2
Si2
O7
non
stoichiometric
1200 °C, 30 s, O2
IPL
IntegratedPLIntensity(a.u.)
Er2
SiO5
Pexc
= 1 mW

exc
= 488 nm

PLlifetimeat1.5m(s)
Influence of stoichiometry
 Higher PL signals
 Longer lifetimes
y and α phases of Er2Si2O7
Er2SiO5
Defects cannot be recoveredwith
the same annealing conditions
R. Lo Savio et al., Appl. Phys. Lett. 93, 021919 (2008)
1450 1500 1550 1600 1650
0
500
1000
1500
2000
2500
PLintensity(a.u.)
Wavelength (nm)

32. 1500 1520 1540 1560 1580 1600
0
2000
4000
6000
PLIntensity(a.u.)
Wavelength (nm)
T = 12 K
10
PL from y + α mixture due
mainly to Er ions in the α phase
Optical and structural properties correlation
y-Er2Si2O7
y-Er2Si2O7 +
α-Er2Si2O7
Maximum efficiency
associated to Er in
α-RE2Si2O7 structure
High resolution PL spectra
Pure y-Er2Si2O7
Annealing 1200 °C, 30 s, N2
of Er2Si2O7 film

33.  Influence of Y-Er silicate composition
on the structural and optical properties
 Optimization of Er content in Y-Er disilicate
Yttrium-Erbium disilicate thin films

34. 0.6 0.7 0.8 0.9 1.0 1.1 1.6 1.7 1.8 1.9
0
10
20
30
40
50
ErYSi
x = 0.03, [Er] = 0.3 at.%
x = 0.20, [Er] = 1.8 at.%
x = 0.46, [Er] = 4.2 at.%
x = 0.69, [Er] = 6.3 at.%
x = 1.33, [Er] = 12.1 at.%
NormalizedYield(a.u.)
Energy (MeV)
O
Y-Erdisilicate films composition
THIN FILMS DEPOSITION
 Co-sputtering from SiO2, Y2O3, and Er2O3 targets
 P(SiO2) = 300 W, constant
 Total [Y]+[Er] is constant
 Disilicate-like composition
RTA 1200 °C, 30 s, O2
[Er]
(at/cm3)
[Er]
(at.%)
Y2-xErxSi2O7
x
2×1020
0.3 0.03
1.2×1021
1.8 0.20
2.9×1021
4.2 0.46
5.0×1021
6.3 0.69
8.7×1021
12.1 1.33
1.5×1022 18.0 2.00

35. 15 20 25 30 35 40 45 50 55 60
0
200
400
600
800
1000
 phase
Intensity(cps)
2 (degree)
x = 0.03
x = 1.33
x = 2
 phase
y phase
Y2-xErxSi2O7 crystallization
 Different relative intensities
 Slight shift of peaks position
 Mixture of y, α, β phases
 High-T phases increase by reducing
Er content
RE2Si2O7 amorphous y α β γ

36. Influence of Er content on 1.54 μm emission
 PL associated to Er ions in α phase
 Maximum IPL for Er2Si2O7
0.0 0.5 1.0 1.5 2.0
0
2
4
6
8
10
12
14
0
2
4
6
PL Intensity
PLIntensity(a.u.)
x
Pexc
= 10 mW

exc
= 488 nm

det
= 1.54 m
Lifetime
Lifetime(ms)
0.0 0.5 1.0 1.5 2.0
0.0
0.2
0.4
0.6
0.8
PLIntensity/(a.u.)
x
Pexc
= 10 mW

exc
= 488 nm

det
= 1.54 m
 Higher “emitting power” for
lower-Er containing films

37. Up-conversion in α-Y2-xErxSi2O7
Higher influence of up-conversion
for higher Er content
900 1000 1100 1400 1500 1600 1700
0
2
4
6
8
10
12
14
x = 0.03 - [Er] = 0.3 at.%
x = 0.69 - [Er] = 6.3 at.%
x = 2.00 - [Er] = 18.0 at.%
4
I11/2

4
I15/2
PLIntensity(a.u.)
Wavelength (nm)
Pexc
= 200 mW

exc
= 488 nm
4
I13/2

4
I15/2
PL signal related to
up-conversion phenomena
0
5
10
15
energy(10
3
cm
-1
)
4
I9/24
I11/2
4
I15/2
4
I13/2
1.54 m
0.98 m

38. Up-conversion coefficient in α-Y2-xErxSi2O7 (i)
0 200 400 600
0.1
1
Pump power
0.1 mW
1 mW
10 mW
100 mW
600 mW
NormalizedPLIntensityat1.54m
Time (s)
Er2
Si2
O7
M. Miritello et al., Mater. Sci. Eng. B 146, 29 (2008)
 τ1 = 230 μs;
 N1(0)Cup for different
pump power
 
 
 
      1
1 1
t
1 1 1 up 1 1 up 1
N t I t 1
N 0 I 0 1 N 0 C e N 0 C
 
   
21 1
1 up 1
1
dN N
(N N ) 2C N
dt
    

Rate equation for the
4I13/2 level (φ = 0)

39. 0 100 200 300 400 500 600
0.0
0.5
1.0
1.5
2.0

det
= 1.54 m
Er2
Si2
O7
Y1.31
Er0.69
Si2
O7
Y1.97
Er0.03
Si2
O7
PLIntensity(a.u.)
Power (mW)
Up-conversion coefficient in α-Y2-xErxSi2O7 (ii)
Rate equation for the 4I13/2 level
 
 1 up 1 1 1
PL 1
up 1
1 2 8C N (1 )
I N
4C
        
  

21 1
1 up 1
1
dN N
(N N ) 2C N 0
dt
     

M. Miritello et al., Adv. Mater. 19, 1582 (2007)

40. α-Y1.31Er0.69Si2O7, [Er] = 6.3 at.%
 Cup = (4 ± 2) × 10-17 cm3/s
α-Y1.97Er0.03Si2O7 , [Er] = 0.3 at.%
 Cup = (1.0 ± 0.2) × 10-18 cm3/s
α-Er2Si2O7, [Er] = 18.0 at.%
 Cup = (9 ± 2) × 10-17 cm3/s
Up-conversion coefficient in α-Y2-xErxSi2O7 (ii)
Er-doped hosts ([Er] ≈ 1020 cm-3)
SiO2 → Cup = 2 × 10-17 cm3/s
Al2O3 → Cup = 4 × 10-18 cm3/s
0 100 200 300 400 500 600
0.0
0.5
1.0
1.5
2.0

det
= 1.54 m
Er2
Si2
O7
Y1.31
Er0.69
Si2
O7
Y1.97
Er0.03
Si2
O7
PLIntensity(a.u.)
Power (mW)
M. Miritello et al., Adv. Mater. 19, 1582 (2007)

41. 1 10 100 1000
0.01
0.1
1
10
100
Er2
Si2
O7
Y1.31
Er0.69
Si2
O7
Y1.97
Er0.03
Si2
O7
Erionsinthe
4
I13/2
state(%)
Power (mW)
Optical amplification in α-Y2-xErxSi2O7
Population inversion
threshold
Y1.31Er0.69Si2O7 and Er2Si2O7
Higher pump powers required
Y1.97Er0.03Si2O7
Suitable for optical
amplification at
low pump powers

42. Conclusions
0.0 4.0x10
21
8.0x10
21
1.2x10
22
0.00
0.02
0.04
0.06
0.08
0.10
0.12 Y1.95
Er0.05
O3
, [Er] = 1.1 at.%
Y1.43
Er0.57
O3
, [Er] = 11.4 at.%
IPL
(visible)/IPL
(1.54m)
Photon flux (cm
-2
s
-1
)
exc
= 980 nm
Two distinct regimes:
 low Er content → good up-converter
 high Er content → good down-converter
Y-Er OXIDE THIN FILMS
1 10 100 1000
0.01
0.1
1
10
100
Y1.97
Er0.03
Si2
O7
Y1.31
Er0.69
Si2
O7
Er2
Si2
O7
Erionsinthe
4
I13/2
state(%) Power (mW)
1500 1520 1540 1560 1580 1600
0
2000
4000
6000
8000
PLIntensity(a.u.)
Wavelength (nm)
T = 12 K
10
 RE2Si2O7 is the
most stable composition
 α-RE2Si2O7 is the most efficient
structure for 1.54 μm emission
 Population inversion at low
pump powers in α-Y1.97Er0.03Si2O7
Y-Er SILICATE THIN FILMS