Monolithic III-V Quantum Dot Lasers on
Si for Silicon Photonics
March 23rd 2018, Dresden, Germany
20 μm
Siming Chen (RFREng 、Ph.D.)
Department of Electronic and Electrical Engineering
University College London, UK
2
1. Why III-V QD laser on silicon
2. III-V QD FP lasers monolithically grown on Ge and Ge-on-
Si substrates
3. III-V QD FP lasers monolithically grown on silicon
4. III-V QD DFB laser array monolithically grown on silicon
5. Summary
Outline
Challenge for Data Centre
3
1. Why III-V QD laser on Si?
➢ Global data centre traffic is booming
➢ Traditional copper cabling is stifling
datacentre evolution
➢ Silicon photonics can solve the slow
data transfer problem
Si Photonics = Optical + Electronic
Source: Intel® Silicon Photonics
1. Why III-V QD laser on Si?
Challenge for Si photonics
What is missing in
silicon photonics?
Electrically-pumped
silicon Lasers
Various Waveguides 25G Modulator (NEC) 340G APD (Intel)
8 channel WDM (IBM) -0.8dB Vertical Coupler(Helios)
4
Limitation of group-V lasers- Indirect bandgap
5
1. Why III-V QD laser on Si?
D. Liang and J. Bowers, Nature Photon. 4, 511 (2010)
Two major non-radiative processes:
Auger recombination
Free-carrier absorption
Extremely poor internal
quantum efficiency ƞi,
which is defined as:
and is generally of the
order of 10-6.
Combine III-Vs and silicon
6
1. Why III-V QD laser on Si?
Si substrates
III-V laser
Silicon
• Pure and have low defect density
• Compatible with CMOS
• Low losses Si waveguide
• High thermal conductivity
• SiO2 serve as protective layer and a naturally good optical waveguide cladding
III-V compound semiconductors
• Mainstays in photonics for light emitters
• Dominance holds for near- and mid-infrared wavelengths
• More expensive than silicon
• The integration of III-V photonics components with Si
microelectronics – ideal solution for Si photonics.
• Wafer bonding – The most successful approach so far
• Monolithic growth – ‘holy grail’ for cost-effective, massive
scalable and streamlined fabrication.
Solution
QDs is the better solution!
7
1. Why III-V QD laser on Si?
δ-function peaks centered at the
atomic-like energy levels
•Low threshold current density
•Less sensitive temperature
dependent operation
•Higher speed in comparison to
QW laser
•Single photon devices are
possible to use quantum dot
structure
K. Nishi et al, IEEE J. Sel. Topics Quantum Electronics.
23, 1901007 (2017)
Advantages of QDs- low threshold
8
1. Why III-V QD laser on Si?
1960 1970 1980 1990 2000 2010 2020
101
102
103
104
105
Mi et al.
(Si)
Egawa et al.
(Si)Kazi et al.
(Si, CW)
Lee et al.
(SiGe)
Hayashi et al. Lee et al.
(SiGe, CW)
Tang et al.
(Si)
Lee et al.
(Si)
Liu et al.
(Ge, CW)
Ribbat, Selin
Ribbat,
SelinLiu et al.
Ledentsov et al.
Quantum DotQuantum Well
Alferov et al.Chand et al.
Tsang
Dupuis et al.
Miller et al.
Alferov et al.
T
hre
shh
old
cu
rren
t den
sity
(A
/cm
2)
Year
Alferov et al.
Double Hetero
Structure
Kirstaedter et al.
CW
Jiang Wu et al., J. Phys. D: Appl. Phys. 48, 363001 (2015)
Figure 1. The historical development of heterostructure lasers showing the record threshold current
densities at the time of publication (□ QD laser on GaAs; ■ QD laser on Ge; ○ QD laser on SiGe; ♦QD laser on Si.) CW indicates that the threshold current values were obtained from QD lasers under
continuous operation. The rest were obtained from QD lasers tested in pulse mode.
Advantages of QDs- temperature insensitive
9
1. Why III-V QD laser on Si?
A comparison of typical power–current characteristics of FP lasers. The QD FP laser
(left) provides temperature-insensitive operation with almost constant threshold
current and slope efficiency. The other two panels show characteristics for two
typical conventional quantum well lasers.
M. Sugwara et al., Nature Photonics 3, 30 (2009)
Advantages of QDs- less sensitive to defects
10
1. Why III-V QD laser on Si?
Liu et al., Photonics Research 3, B1-B9 (2015)
Si Si
1. Why III-V QD laser on Si?
1. Any threading dislocations through the QW will become non-radiative
recombination centre; one TD can only one or a very limited number of dots.
2. TDs can be either pinned or propelled away from QDs- the strong strain field of a
QD array prevents the in-plane motion of dislocations.
Advantages of QDs
12
1. Why III-V QD laser on silicon
2. III-V QD FP lasers monolithically grown on Ge and Ge-
on-Si substrates
3. III-V QD FP lasers monolithically grown on silicon
4. III-V QD DFB laser array monolithically grown on silicon
5. Future plan and summary
Outline
1313
Why QD laser on Ge substrate and what is the challenge?
• Very small mismatch between GaAs and Ge (0.08%);
• The fabrication of low-defect (~106/cm2) Ge/Si “virtual substrates” are well
studied and available commercially;
• Ge epilayer will replace Si as p-channel in future CMOS, because Ge has
a four times larger hole mobility compared to Si
• The problem is “self-terminating one-monolayer As” surface does not work
for Ge epi-surface.
G. Brammertz et al., Thin Solid Film 517, 148 (2008)
GaAs/Ge by MOCVD
2. III-V QD lasers monolithically grown on Ge and Ge-on-Si substrates
1414
The first 1.3 µm InAs QD laser on Ge
H. Liu et al., Nature Photonics 5, 416 (2011)
Ge
GaAs
2. III-V QD lasers monolithically grown on Ge and Ge-on-Si substrates
➢ CW mode
➢ Jth = 55.2 A/cm2 (RT)
➢ Pout =28 mW/facet at (RT)
➢ λpeak = 1305 nm
➢ Tmax = 60 oC
Ga prelayer technique
1515
The first 1.3 µm InAs QD laser on Ge/Si
A. Lee et al., Opt. Express 20, 22181 (2012)
2. III-V QD lasers monolithically grown on Ge and Ge-on-Si substrates
• Low CW threshold (16 mA)
• ~180 mW maximum CW output power
• CW lasing up to 119oC
• Over 2700 h of constant current
stress at 30 oC
16
Alan Liu et al., Appl. Phys. Lett. 104, 041104 (2014)
2. III-V QD lasers monolithically grown on Ge and Ge-on-Si substrates
InAs QD laser on Ge/Si - Results from Bowers’s Group
A. Liu et al, IEEE J. Sel. Topics Quantum Electron. 21, 1900708 (2015)
17
1. Why III-V QD laser on silicon
2. III-V QD FP lasers monolithically grown on Ge and Ge-on-
Si substrates
3. III-V QD FP lasers monolithically grown on silicon
4. III-V QD DFB laser array monolithically grown on silicon
5. Summary
Outline
1818
3. III-V QD lasers monolithically grown on silicon
• Native SiOx removal within III-V MBE
- HF etch, difficult to control;
• Polar/non-polar growth => Anti-phase
domains;
• Large lattice mismatch (4.1%) => Threading
dislocations (TDs);
• Large thermal expansion coefficient
mismatch(120%) => Micro-cracks and TDs.
Challenges for direct GaAs growth on Si
APD High density of TDs
Wafer surface after completion of 3 etch stages
Ridge waveguide Deep Trench
Mesa
Crack line on wafer surface
Crack line in etched areas
silicon
GaAs
The first 1.3 μm QD laser on Si
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3. III-V QD lasers monolithically grown on silicon
1050 1100 1150 1200 1250 1300 1350 1400
PL
In
ten
sit
y (
a.u
.)
Wavelength (nm)
GaAs x1/2
380 oC
400 oC
420 oC
0 200 400 600 800 1000 1200
0
10
20
30
20 oC
1250 1275 1300 1325 1350
Inte
nsit
y (
a.u
.)Wavelength (nm)
Ou
tpu
t p
ow
er
(mW
)
Current density (A/cm2)
0 200 400 600 800 1000 1200
0
2
4
6
8
10
12
14
16
Ou
tpu
t p
ow
er
(mW
)
Current density (A/cm2)
20oC
24oC
28oC
34oC
38oC
42oC
➢ Off-cut substrate
➢ Pulse mode
➢ Jth = 725 A/cm2 (RT); Pout =26 mW/facet at (RT)
➢ λpeak = 1300 nm
➢ Tmax = 42 oC ; T0 = 44 K (20-42 oC)
T. Wang et al., Opt. Express 19, 11381-11386 (2011)
Optimization of III-V buffer layer
• Phosphorus-doped Si(100) wafers
with 4º offcut to the [011] plane-
prevent the formation of APBs
• A thin AlAs nucleation layer was
deposited by MEE at a low growth
temperature of 350 ºC- suppress
three-dimensional growth and
provides a good interface for
succeeding III-V material growth.
• InGaAs/GaAs DFLs were grown to
effectively suppress the propagation
of the TDs
• in situ thermal annealing of SLS
was also carried out to further
improve the efficacy of filtering
defects.
• After the last set of SLS, the density
of TD has been reduced to the order
of ~105 cm-2.
20
3.III-V QD lasers monolithically grown on silicon
S. Chen et al., Nature Photon. 10, 307-311 (2016)
High-performance 1.3µm QD laser on Si
21
0 100 200 300 400 500 6000
20
40
60
80
100
Jth = 62.5 A/cm2
105.1 mW @ 650 A/cm2
Room temperature
c.w.
Outp
ut p
ow
er
(mW
)
Current density (A/cm2)
0
1
2
3
4
Voltag
e (
V)
1200 1250 1300 1350 1400 1450
Room temperature
c.w.
Cur
rent
den
sity
(A/c
m2 )
650
450
225
62.5
50
Inte
nsity (
a.u
.)
Wavelength (nm)
0 100 200 300 400 500 600 7000
2
4
6
8
10
12
14
16
18 oC
28 oC
38 oC
48 oC
58 oC
64 oC
70 oC
75 oC
Ou
tpu
t p
ow
er
(mW
)
Current density (A/cm2)
c.w.
➢ Off-cut substrate
➢ CW
➢ Jth = 62.5 A/cm2 (RT)
➢ Pout =105 mW/facet at (RT)
➢ λpeak = 1315 nm
➢ T max = 75 oC (c.w.) 120 oC (pulsed)
➢ Extrapolated lifetime > 100,000 hours
S. Chen et al., Nature Photon. 10, 307-311 (2016)
3. III-V QD lasers monolithically grown on silicon
26 oC
1.3 µm InAs QD laser on on-axis Si (001)
22
3. III-V QD lasers monolithically grown on silicon
S. Chen et al., Optics Express 25, 4632 (2017)
0 200 400 600 800 1000 1200 1400
0
10
20
30
40
50
Ou
tput
Po
wer
(mW
)
Current Density (A/cm2)
0
1
2
3
4
5
6
Vo
lta
ge
(V
)
Room temperature
CW
➢ On-axis Si (001) substrate
➢ CW
➢ Jth = 425 A/cm2 (RT)
➢ Pout =40 mW/facet at (RT)
➢ λpeak = 1292 nm
➢ T max = 36 oC (c.w.) 102 oC (pulsed)
23
1. Why III-V QD laser on silicon
2. III-V QD FP lasers monolithically grown on Ge and Ge-on-
Si substrates
3. III-V QD FP lasers monolithically grown on silicon
4. III-V QD DFB laser array monolithically grown on
silicon
5. Summary
Outline
The first QD DFB array on Si
• Thresholds as low as 12mA.
• SMSRs as high as 50 dB
• Well-aligned channel spacing of 20±0.2
nm for CWDM
• A record wavelength coverage range of
100 nm24
4. III-V QD DFB laser array monolithically grown on silicon
arXiv preprint arXiv:1801.01052
25
1. Why III-V QD laser on silicon
2. III-V QD FP lasers monolithically grown on Ge and Ge-on-
Si substrates
3. III-V QD FP lasers monolithically grown on silicon
4. III-V QD DFB laser array monolithically grown on silicon
5. Summary
Outline
Summary
26
Si (001)
Ge
Ge-on-Si
Si (offcut)
Ge
GaAs
Ge
Si
1.3 µm FP QD laser
QD DFB laser array
Collaboration:
27
Acknowledgement:
Team:
Mengya Liao, Mingchu Tang, Jiang Wu, Alwyn Seeds,
Huiyun Liu
Thanks
28