A hybrid silicon evanescent laser

stingymilitaryElectronics - Devices

Nov 27, 2013 (3 years and 8 months ago)

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A hybrid silicon evanescent laser
a silicon waveguide

-
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.

1

[ Contents ]

1.
Abstract

2.
Introduction

-

S
everal 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

2

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???

3

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.
Raman laser

2.
Using porous silicon or
nanocrystalline
-
Si

3.
SiGe

quantum cascade structures

4.
Er

doped silica

5.
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.

4

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
 
 
5

3. Device structure



Ⅰ. Lasing
gain
material





MQW(
mutiple

quantum wells)


. 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
.


M
uch
shorter wavelengths can be
obtained.


Low threshold current.


The greater efficiency.

2
* 2
8
out C I
I
E E E
h
E
m d
 





6

3. Device structure




. Bonding technology





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 non
-
uniformities and (2) gain reduction.

Hydrophilic surface bonding : 125


Hydrophobic
surface bonding :
400


Are better choices.

7

3. Device structure





Ⅳ. Additional layer





SL(
Superlattice
)
barrier

SL
interposition

Doped SL

Non
-
intentionally doped SL


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


L
uminescent properties are improved.

8

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

9

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

10

5. Experimental results



[Experimental
C
onditions]


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
 
 
11

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

12

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.

13