hybrid iii-v on silicon lasers -...

Hybrid III-V on Silicon Lasers T. Ferrotti, A. Descos, D. Bordel, H. Duprez, S. Menezo,

and B. Ben Bakir CEA, LETI, Minatec Campus, IIIV Lab, Grenoble, France

STMicroelectronics, Crolles, France

A laser on silicon?

Silicon (Ge, Si-nc+Er…) is a poor light emitter Monolithic integration: No efficient integrated laser sources achievable in the short-medium term Electrically pumped Ge on silicon lasers : promising results, but still require

developments

• III-V materials exhibit excellent laser properties: Direct growth of III-V materials has been studied for decades, but no

convincing results up to now Flip-chip bonding of lasers is a mature but rather expensive technology. Less

flexibility in the laser design

Heterogeneous integration by direct bonding: offers the best compromise between performances/ functionality/ manufacturability

CONFIDENTIAL 8-10 October 2013 | 2

Heterogeneous integration Growth of the III-V wafers

III-V die or wafer bonding on processed SOI

InP substrate removal

Processing of SOI wafers (modulators, detectors, passive waveguides, etc.)

Metallization of lasers, modulators and detectors

Processing of III-V dies/wafer

200mm fab

200mm fab

Back-end: 100mm fab

Heterostructure 3µm- thick


Processing of SOI wafers Growth of the III-V wafers

III-V die or wafer bonding on processed SOI

InP substrate removal

Processing of SOI wafers (modulators, detectors, passive waveguides, etc.)

Metallization of lasers, modulators and detectors

Processing of III-V dies/wafer

200mm fab

200mm fab

Back-end: 100mm fab


Processing of SOI wafers

Waveguide DBR Fiber-coupler

200mm SOI wafer: 500nm-Si / 2µm-BOX Typical thickness of silicon waveguides for efficient coupling with III-V waveguides Laser cavity (DBRs): hard mask/litho/partial etching (10nm) Waveguide-to-fiber couplers: hard mask/litho/partial etching (125nm) Waveguides and tapers: hard mask/litho/partial etching (250nm) Mesas: hard mask/litho/full etching (500nm) SiO2 encapsulation and planarization CMP (100nm)

Resist deposition

193nm DUV litho / hard mask etching

Resist stripping /Si RIE etching

SiO2 encapsulation (PECVD)

CMP


Growth of III-V wafers for hybrid integration

Growth of active layer in a reverse order compared to classical InP devices

Example of a 6 QW MBE grown wafer

Strained MQW InGaAsP/InP for 1.31 and 1.55 µm operation


Molecular bonding

O2 O2

1- Processed SOI substrate

2- PECVD silica deposition

3- CMP planarization

4- Surface Cleaning

1- Surface cleaning

2- PECVD silica deposition

3- O2 plasma activation

Thin layer 10 nm

(roughness < 0.5 nm RMS)

Low temperature bonding

Anneal and Substrate removing

Laser processing

III-V heterostructure SOI substrate


Bonded III-V wafers/dies on SOI Wafer to wafer bonding Die to wafer bonding

2’’

2’’ InP wafer(100nm thick SiO2 spacing layer)

Heterostructure of 3µm-thick Bonding yield > 90%


Bonding of III-V dies on SOI wafer

SiO2 BOX Si waveguide

InP

Active region (InGaAsP)

2’’ InP wafer(100nm thick SiO2 spacing layer)

SiO2 spacing layer: 100nm 250nm

500nm


III-V back-end process (100mm fab) Top view

Cross-sectionnal view


Single-mode DBR laser Gain III-V active waveguide Si-circuit supports all optical functions


Single-mode DBR laser: cavity design Structural parameters of the DBRs:

Width=10µm, Etching depth=10 nm, Period=237nm, Duty cycle=50%

κ=83cm -1

Front mirror: L=100µm R=46.4%, 3dB-BW ≈ 4nm

Back mirror: L=300µm R=97.3%, 3dB-BW ≈ 2.6nm

1,540 1,542 1,544 1,546 1,548 1,550 1,552 1,5540,0

0,2

0,4

0,6

0,8

1,0

R=46.4% @ 1547nm

R=97.3% @ 1547nm

Refle

ctiv

ity

Wavelength (µm)

Period : 237nmDBR length :

10µm 100µm 300µm 500µm

SEM micrograph


Wafer scale optical and electrical testing Courtesy of Ph. Grosse


Experimental results

0 20 40 60 80 100 120 140 160 180 2000,00,51,01,52,02,53,03,54,04,55,05,5

0,0 0,8 1,7 2,5 3,3 4,2 5,0 5,8 6,7 7,5 8,3

0,001,753,505,257,008,7510,5012,2514,0015,7517,5019,25

Si-w

aveg

uide

pow

er (m

W)

J(kA/cm²)

Fibe

r cou

pled

opt

ical p

ower

(mW

)

Current (mA)

10°C 20°C 30°C 40°C 50°C 60°C 65°C

20 40 60 80 100 120 140 1600

1

2

3

4

Fibe

r cou

pled

powe

r (m

W)

Current (mA)

1545

1546

1547

1548

1549

Wav

eleng

th (n

m)

-80-70-60-50-40-30-20-100

A.U.(dB)

CW operation (>60°C) @ λ ~ 1.55µm

Ith: 17-60mA (0.8-2.5 kA.cm-2) for T: 10 to 60°C

Rs= 7.5 Ω Lasing turn-on voltage : 1 V P-Si-waveguide > 14 mW (20°C) P-fiber > 4 mW (20°C) SMSR > 40 dB


DBR Laser-array

1520 1540 1560 1580 1600-80

-70

-60

-50

-40

-30

-20

-10

0

10 d

B/di

v

Wavelength (nm)

235 237 239 241

DBR period (nm):

4 DBR laser-array SMSR > 40dB ∆λ ∼ 12nm


Tunable hybrid DBR laser

Same architecture with heaters placed on the top of the DBRs

Resistive NiCr heater

+ Resistive heater


Tunable hybrid DBR laser Preliminary results (measurements not performed on the best design)

Tunability over 20nm can be achieved

Next step: SG-DBR (Vernier effect) to extend tunability range and to reduce heating power budget


DBR laser: Direct modulation Modulation Bandwidth ~7GHz (RT)

Eye diagram: 7Gb/s and 12.5Gb/s ER> 4.5 dB (17mW RF Power)

Eye diagram for 5Gb/s modulation Small signal modulation response

170mA@12,5Gbps

150mA@7Gbps

0 2 4 6 8 10 12 14-30

-25

-20

-15

-10

-5

0

5

10

EO R

espo

nse (

dB)

Frequency (GHz)

80mA 100mA 125mA 131mA 150mA7,22GHz@-3dB


Perspectives

Exploration of new designs/concepts DFB, SG-DBR Slow-wave structures Photonic crystals, double-racetrack….

Slow wave structure or Photonic crystals

Adiabatic mode transformer

Fiber-coupler

SOA

Fiber-coupler

Si

InP III-V waveguide region


Perspectives Improve performances

Improve output power level, external efficiency (cavity design, current confinement)

Reduce threshold current and Extend the operating T° range up to 80°C Increase wavelength tunability using optimized design

Development of a fully 200mm/300mm process

Integration with other optical and electrical functions, packaging (Si modulators, Ge photodetectors, 3 metallization levels…)

Integrated transceivers on CMOS


Thank you for your attention


APPENDIXES


Hybrid DBR lasers: the best design

0 20 40 60 80 100 120 140 160 180 200 2200

2

4

6

8

10

12

Fibe

r Opt

ical P

ower

(mW

)

Current (mA)

Optical power Tension

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

Threshold = 12mA

Max. fiber coupled power= 11,3mW

SMSR = 51dB

1530 1532 1534 1536 1538 1540 -80

-70

-60

-50

-40

-30

-20

-10

0

Puis

sanc

e op

tique

(dB

m)

Longueur d'onde (nm)

51dB


DESIGN


Adiabatic transition III-V Si

Active region (MQW=InAsP)

W-Si: Tuning parameter

Mode transformation:

IN OUT

SiO2 GAP = 100nm (+-20nm) 250nm 500nm

Wsi Silicon rib waveguide

n-doped layer (n-contact)

n/p++/p doped epilayers stack (p-contact) n graded

p graded TJ

III-V heterostructure:


Adiabatic transition III-V Si W=6µm OUT


IN W=0.5µm

Passive Si -

W-Si

W=0.80µm W=0.9µm W=1.10µm

Power transfer ensured by the supermode A

Adiabaticity criterion

( ) ( )( )

( ) ( ) ( )( )0

0

1 20tan arcsin 2

Si

zz

W z f z

zz z z

γ

δγ κ ε

κ

=

= = −

δ: mismatch of propagation constants between the individual uncoupled waveguide modes

z0: phase matching point (δ=0) κz0: coupling strength between waveguides at

the phase matching point ε: fraction of power scattered in the unwanted

supermode (odd mode)

Universal criterion for designing adiabatic mode transformers Criterion relates ε The shortest possible length of an adiabatic mode transformer Taper shape:

X. Sun, H.-C. Liu, and A. Yariv, Opt. Lett., 34, 280-282 (2009).


γ(z)-shaped adiabatic taper ε∼2%, Lcmin=100µm Taper length >80µm:

η>94%

Robust design: Lc=100µm: ∆WSi = ±50nm η>90%

Win= 430 nm

Wout=1930 nm

~100nm x 100nm

Taper length=100µm


hybrid iii-v on silicon lasers -...

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