A hybrid silicon evanescent laser fabricated with a silicon

waveguide and Ⅲ-Ⅴ offset quantum wells

Hyundai Park, Alexander W. Fang, Satoshi Kodama, and John E. Bowers

Min Hyeong KIMHigh-Speed Circuits and Systems Laboratory

E.E. Engineering at YONSEI UNIVERITY2011. 4. 13.

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[ Contents ]

1. Abstract2. Introduction

- Several laser structures3. Device structure

I. Lasing gain material II. Waveguides III. Bonding technologyIV. Additional layer

4. Fabrication process5. Experimental results6. Conclusion & Summary

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1. Abstract

A laser can be utilized on a silicon waveguide bonded to a multiple quantum wells(MQW).

This structure allows the optical waveguide defined by CMOS technology to get an optical gain provided by Ⅲ-Ⅴ materials.

It has a 1538nm laser, pulsed threshold of 30mW, and an output power of 1.4mW.

How to implement this structure?How to operate??Which principles???

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2. IntroductionIt is challenge to build light-emitting devices on VLSI CMOS technology. Because Si has an indirect bandgap(E_g).How to overcome this challenges?1. Raman laser2. Using porous silicon or nanocrystalline-Si3. SiGe quantum cascade structures4. Er doped silica5. Etc….In this paper, we report the first demonstration of silicon evanescently** coupled laser structure.

** Evanescent waveAn evanescent wave is a nearfield standing wave with an intensity that exhibits exponential decay with distance from the boundary at which the wave was formed.

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3. Device structure

Silica

Si substrate

InP Cladding

MQW gain material

Si

MQW laser+

SL barrier+

Bonding technology+

SOI waveguide

Light-emitting Process :Current or Laser Pumping >> MQW lasing >> wave evanescent to SOI waveguide >> output guiding

3.6%

42.8%QW

Si

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3. Device structureⅠ. Lasing gain material – MQW(mutiple quantum wells)

Ⅱ. Waveguides – SOI structure(last topic)

• A quantum well laser is a laser diode in which the active region of the device is so narrow that quantum confinement occurs.

• The wavelength of the light is determined by the width of the active region.

• Much shorter wavelengths can be obtained.

• Low threshold current.• The greater efficiency.

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* 28

out C I

I

E E E

hEm d

Ⅰ

Ⅱ

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3. Device structureⅢ. Bonding technology – Plasma-Assisted Low Temperature Wafer Bonding

Ⅲ

• Two samples are bonded together via oxygen plasma assisted wafer bonding

• Low temperature annealing(~250℃) preserves the optical gain of MQW.

• High temperature annealing makes (1) a surface non-uniformities and (2) gain reduction.

Hydrophilic surface bonding : 125℃Hydrophobic surface bonding : 400℃Are better choices.

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3. Device structure Ⅳ

Ⅳ. Additional layer – SL(Superlattice) barrier

SL interpositio

n

Doped SL

Non-intentionally doped SL

• Defect-blocking layer : It prevents the deep propagation of defects by fusing process.

• Luminescent properties are improved.

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3. Device structure _ detailed design

• InP cladding layer• MQW absorber (500nm)• MQW laser structure• MQW absorber (50nm)• InP cladding layer (110nm spacer)• SL barrier (7.5nm)• Si waveguide (W=1.3u, H=0.97u,

L=0.78u)• Silica layer (500nm)• Si substrate

For operating 1538nm wavelength

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4. Fabrication process1. Form SiO2 layer on Si substrate _ thermal oxidation for 2

hours at 1050℃2. Form Si rib waveguides _ using inductively coupled

plasma etching3. Hetero-bond InP(already completed)/Si _ Plasma-Assisted

Low Temperature Wafer Bonding4. Dice the device for mirroring 5. Polish and HR coat**(High-reflection coatings) for

mirroring

** HR coating

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5. Experimental results[Experimental Conditions]

• 980nm laser diode pumping• Through the top InP cladding

layer• Recorded on an IR camera

through a polarizing beam splitter

Laser diode Pumping

[Results Pictures]

Calculated TE mode profile TE near field image

3.6%

42.8%QW

Si

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5. Experimental results

• A laser output almost occurs in the optical mode(Si waveguide)

• Slab mode(MQW) do not support lasing output

• The pumping threshold increase from 30mW to 50mW between 12℃~20 ℃.

• Quantum efficiency at 12℃ : about 3.2%

Cavity length 600umTemperature 12℃Pump power=1.4* thresholdGroup index=C/Vg=3.85

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6. Conclusion & Summary

• We can make the optically pumped Si evanescent laser consisting of MQW as active region bonded to Si waveguide as a passive device. (conclusion!)

• For operating at 1538nm, pump threshold is 30mW and slope efficiency is 3.2%. (conclusion!)

• On bonding process, use Plasma-Assisted Low Temperature Wafer Bonding to maintain the optical gain of gain material.

• By using SL(Superlattice) barrier, we can block the defects propagation from fusing(bonding) process.