Transcript Presentation

A hybrid silicon evanescent laser
a silicon waveguide
Ⅲ-Ⅴ offset quantum wells
Hyundai Park, Alexander W. Fang, Satoshi Kodama, and John E. Bowers
Min Hyeong KIM
High-Speed Circuits and Systems Laboratory
E.E. Engineering at YONSEI UNIVERITY
2011. 4. 13.
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[ Contents ]
1. Abstract
2. Introduction
- Several laser structures
3. Device structure
I.
Lasing gain material
II.
Waveguides
III. Bonding technology
IV. Additional layer
4. Fabrication process
5. Experimental results
6. 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. Introduction
It 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.
2.
3.
4.
5.
Raman laser
Using porous silicon or nanocrystalline-Si
SiGe quantum cascade structures
Er doped silica
Etc….
In this paper, we report the first demonstration of silicon
evanescently** coupled laser structure.
** Evanescent wave
An 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
MQW laser
+
SL barrier
+
Bonding technology
InP Cladding
MQW gain
material
Si
Silica
+
SOI waveguide
Si substrate
Light-emitting Process :
Current or Laser Pumping >> MQW lasing
QW  3.6%
 Si  42.8%
>> wave evanescent to SOI waveguide >> output guiding
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3. Device structure
Ⅰ
Ⅱ
Ⅰ. Lasing gain material
– MQW(mutiple quantum wells)
Eout  EC  EI
• 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.
h2
EI 
8m*d 2
Ⅱ. Waveguides – SOI structure(last topic)
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3. Device structure
Ⅲ. Bonding technology
Ⅲ
– Plasma-Assisted Low Temperature Wafer Bonding
•
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 nonuniformities 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
•
Defect-blocking layer : It prevents the deep
propagation of defects by fusing process.
•
Luminescent properties are improved.
Non-intentionally doped SL
Doped SL
SL
interposition
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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 process
1. Form SiO2 layer on Si substrate _ thermal oxidation for 2 hours
at 1050℃
2. Form Si rib waveguides _ using inductively coupled plasma
etching
3. Hetero-bond InP(already completed)/Si _ Plasma-Assisted Low
Temperature Wafer Bonding
4. 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]
QW  3.6%
 Si  42.8%
Calculated TE mode profile
TE near field image
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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 600um
Temperature 12℃
Pump power=1.4* threshold
Group 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.
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