Monolithic III-V Quantum Dot Lasers on Si for Silicon ... Chen.pdf · • ~180 mW maximum CW output...

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

[email protected]

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


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


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


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


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


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


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


Liu et al., Photonics Research 3, B1-B9 (2015)

Si 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


2. III-V QD FP lasers monolithically grown on Ge and Ge-

on-Si substrates



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


➢ 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)


• 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)


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



Si substrates



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

19


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

)


20oC

24oC

28oC

34oC

38oC

42oC

➢ Off-cut substrate

➢ Pulse mode

➢ Jth = 725 A/cm2 (RT); Pout =26 mW/facet at (RT)


➢ 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

)


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

)


c.w.

➢ Off-cut substrate

➢ CW

➢ Jth = 62.5 A/cm2 (RT)



➢ T max = 75 oC (c.w.) 120 oC (pulsed)

➢ Extrapolated lifetime > 100,000 hours

S. Chen et al., Nature Photon. 10, 307-311 (2016)


26 oC

1.3 µm InAs QD laser on on-axis Si (001)

22


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)



➢ T max = 36 oC (c.w.) 102 oC (pulsed)

23



Si substrates


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


arXiv preprint arXiv:1801.01052

25



Si substrates



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

Monolithic III-V Quantum Dot Lasers on Si for Silicon ... Chen.pdf · • ~180 mW maximum CW output...

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