III-V Nano-Optoelectronics for On- Chip Optical Interconnects · 2017. 9. 5. · 2 . Motivation...

III-V Nano-Optoelectronics for On-Chip Optical Interconnects

Wai Son (Wilson) Ko Fanglu Lu, Roger Chen, Billy Ng,

Thai Tran, Kun Li, Stephon Ren,

Connie Chang-Hasnain

EECS Department

University of California, Berkeley

Nov 1st, 2012 For Internal E3S Use Only

These Slides May Contain Prepublication Data and/or Confidential Information.

UC Berkeley, Wilson Ko 2 E3S Tele-Seminar – Nov 1st, 2012

Motivation

Integrated silicon photonics Inter- and intra-chip optical interconnects

for better energy efficiency and speed Bio-sensing Lab-on-a-chip

Silicon is an indirect bandgap material! III/V material – 2-3 order of magnitude

higher in absorption and gain Challenges in integrations

Lattice and thermal mismatch High temperature process

For Internal E3S Use Only



Lasers on Silicon

III-V Nanostructures Low growth temperature Small footprint relieves mismatch problems

Fang et al, Optics Express 14 (2006)

Heterogeneous Integration Germanium Laser

Camacho-Aguilera et al, Optics Express 20 (2012) Kunert et al, IPRM, 2011

Ga(NAsP) Laser

Chuang et al, Applied Physics Letters 90 (2007)




Outline

Motivation New III-V growth mode on lattice-mismatched substrates Nanopillar Lasers

InGaAs nanopillar laser on Si InGaAs nanopillar laser on MOSFET InGaAs nanopillar laser on silicon waveguide

Room-temperature optoelectronic devices on Si GaAs APD with very high gain InGaAs LED InGaAs phototransistor

Summary




Outline




Summary




0 60

time (min)

→

~ 4 mm

0.6 mm

GaAs Nanoneedle Growth Catalyst-free metal-organic chemical vapor deposition

(MOCVD) growth (Tg~400°C) Hexagonal needle shape Single crystalline Wurtzite phase Core-shell growth mode

500 nm

HRTEM 3 lattice spacings at tip

M. Moewe et al., APL 93 (2008) R. Chen et al., APL 96 (2010)

LC Chuang et al., APL 93 (2008)




Outline




Summary




Low index contrast and absorption loss by Si Helically-propagating modes naturally supported by nanopillars provide optical feedback High Q factors (~4,300) despite tiny footprints Growth parameters can be controlled

to achieve nanopillar geometry Core-shell growth for suppression of surface velocity

θ small

Helical Modes in Natural Resonator

TM m=5 TE m=4

TE m=5 TM m=6

Si n~3.6

InGaAs

n~3.7 Low index contrast interface

Azimuthal components

Total internal reflection faciliatating

optical feedback 500 nm

Silicon

InGaAs coreGaAs shellGaAs shell

Silicon

Chen et al, Nature Photonics 5, 170–175 (2011)




Imaging Nanopillar Modes Direct confirmation of axial mode propagation Helical modes reflect strongly from InGaAs/Si interface axial standing waves

attributed to helical modes

1 µm

1 µm

1 µm

Si

InGaAs

70°

n=1

n=2

n=3

Experimental results





InGaAs Nanopillar Laser on (111)-Silicon Up to 25 mW peak power (21.7 mW average

power) when pumped by Ti/Sapphire laser Room temperature optically pumped laser with

10 mW peak power

Q~200 β~0.01

T=4K

Pth=22 µJ/cm2 Nth~1x1018 cm-3

1 10 100 1000

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

Peak

Pow

er (W

)

Pump fluence (mJ/cm2)

850 900 950 1000

0

100

200

300

Inte

nsity

(a.u

.)

Wavelength (nm)

1.8 Pth 1.0 Pth 0.8 Pth 0.3 Pth 0.1 Pth

Below threshold

Above threshold

Below threshold

Above threshold

0 50 100 150 200 0

2

4

6

8

10

Peak

Pow

er (m

W)

0

10

20

30

40

50

FWH

M (nm

)

T=293 K

Pump fluence (mJ/cm2)

500 nm





InGaAs Laser on MOSFETs Room temperature operation of naopillar laser

P=0.74Pth

P=1.48Pth

Lu et al, Optics Express, Vol. 20, Issue 11, pp. 12171-12176 (2012)




MOSFET Compatibility No significant changes observed in MOSFET characteristics after nanopillar

growth (1.5 hr @410C) Direct demonstration of CMOS compatibility

Fanglu Lu, et.al., unpublished 2011 For Internal E3S Use Only



Nanopillar Growth on Different Substrates

Si (111) plane can be created on Si(100) or Si (110) substrate, where nanopillars preferentially grow along Si [111] direction nanopillar

(111) plane

(111) plane




Horizontal Nanopillar

Significant amount of light emits from the bottom of nanopillar

End-fire coupling is possible with horizontal nanopillar

SiO2

FDTD Simulation NP Laser intensity

Si (110)

Nanopillar

Si (110)

Light output

Si waveguide

Nanopillar




Growth Result

Silicon waveguide: length~27μm, height~5μm, width~4μm

Nanopillar: diameter~800nm, height~1.8μm Si (110) Si waveguide

SiO2 Nanopillar




Laser Oscillation

Optically-pumped pulsed lasers are achieved at low temperature 4K Emission wavelength at 915nm Side Mode Suppression Ratio ~ 20dB Threshold power density ~ 1.2kW/cm2 Average output power of 8.7μW (peak power ~ 10mW)




Waveguide Coupling Result

Focused ion beam technique is used to create a 45ο inclined facet on the back end, to reflect light upwards

13% of laser emission couples into waveguide

Light output

45ο inclined facet

Silicon (110)

Si waveguide Nanopillar

Vertical Si (111) plane




Outline




Summary




Ohmic Contacts of P-NN and n-NN on Si

No barrier was observed between GaAs-Si interface Excellent Ohmic behavior

Current scales with number of NNs Estimated ~1018 /cm3 from I-V curves

n-NN on n-Si p-NN on p-Si

L. C. Chuang, et.al., Nano Lett. 11, 385-390 (2010)




Avalanche Photodiode with High Gain

p-Shell contacted by top metal n-Core contacted through n-Si Light can only be coupled in

through the uncoated openings

L. C. Chuang, et.al., Nano Lett. 11, 385-390 (2010)

Light




Avalanche Photodiode with High Gain

Light can only be coupled in through the uncoated openings High current gain M >250 at -8 V Linear gain with voltage




Photo Carrier Collection Clear evidence of Si absorption and collection in GaAs NN-APD Exponential decay in off-pad photocurrent limited by the hole

diffusion length in n-type Si. Experimental hole diffusion length (Lp) of ~340 µm in good

agreement with published value.

l=980 nm, 0.26 W/cm2




Internal E-field Enhanced Carrier Collection

E-field enhancement by highly curved, cylindrical shape Reaching breakdown field 4x105 V/cm at low reverse voltages Built-in field in vertical direction to help collect carriers




InGaAs/GaAs/AlGaAs LED Structure on Si Structure begins with n-GaAs nanoneedle core on n-Si In0.3Ga0.7As stops the nanoneedle vertical growth

transforming needles into pillars P-Al0.2Ga0.8As cladding used to passivate GaAs surface

As-grown pillar LEDs




Turn on < 1 V

Room-Temp InGaAs LED on Si All standard fabrication

processes As-grown double

heterostructure diode Excellent LI and IV at room

temperature

I-V curve

L-I curve

Chuang, Chang-Hasnain, et. al., Nano Letters, DOI: 10.1021/nl102988w (2010)

0 1 2 3 4 50

50

100

150

200

P

ower

(a.u

.)

Bias current (mA)

1 µm




Receiver-less Detector Design

Logic circuit needs voltage I → V with trans-impedance amplifier

Photodiode + trans-impedance amplifier = phototransistor Eliminate wire capacitance between photodiode and amp Lower capacitance → higher sensitivity




InGaAs Nanopillar HBT on Silicon Substrate

InGaAs nanopillar HBT monolithically grown on silicon substrate

High optical absorption of III-V material allows small detector

Small detector offers small capacitance and high sensitivity 2.7

µm

1.2 µm 30° Tilt

Si(111)

collector, n-InGaAs, 600 nm base, p-InGaAs, 200 nm

emitter, n-GaAs, 100 nm

VE

VC

emitter base

collector

n-GaAs

p-InGaAs n-InGaAs




InGaAs Nanopillar HBT on Silicon Substrate

Leverage nanopillar on silicon as platform to realize highly sensitive III-V HBT on silicon substrate

Device can be scaled down further to reduce capacitance

n-Si(111)

collector, n-InGaAs base, p-InGaAs

emitter, n-GaAs

VE

VC

Detection area

1 µm

Detection area VE




Summary

Silicon

InGaAs coreGaAs shellInGaAs Core GaAs shell

Silicon

Nanolaser on silicon

Avalanche photodetector

Nanolaser on MOSFET Nanolaser on waveguide

Nanopillar LED

n-Si(111)

collector, n-InGaAs base, p-InGaAs

emitter, n-GaAs

VE

VC

Nanopillar HBT

Thank you

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III-V Nano-Optoelectronics for On- Chip Optical Interconnects · 2017. 9. 5. · 2 . Motivation...

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