GaAs nanostructures on SiStefano Sanguinetti

LNESS and Dipartimento di Scienza dei MaterialiUniversità di Milano Bicocca, Milano, Italy

Progress in photonicsOctober 16th

FirenzeOUTLINE

1. Droplet Epitaxy GaAs/AlGaAs QNs on Ge/Si susbtrates

• Single Photon Emitters

2. Site controlled Metal NPs on Si

• embedded metal NP

• Droplet epitaxy controlled QWires

3. 3D GaAs integration on Si

• 3D GaAs /Si

Silicon

Germanium

GaAsAlGaAs

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Firenze

Droplet Epitaxy Nanostructures on Ge/Si susbtrates

Silicon

Germanium

GaAsAlGaAs

MONOLITHIC INTEGRATION STACK

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FirenzeGe Thin Epilayer

i. THIN (< 2µm) RELAXED Ge LAYERii. LOW TD DENSITY (≈ 1 X 10 7 cm-2)iii. LOW SURFACE ROUGHNESS (≈ 1 nm RMS)

4.0µm (f)

Ge

1. Fast growth of a thin (1-3 µm) Ge epilayer by LEPECVD at 500 °C

2. Thermal annealing cicles (600 °C - 700 °C)

Si substrate

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GaAs

Germanium VirtualSubstrate

Si (100) 6° offcut toward [110]

Thin Ge layerGrown by LEPECVD

Low thermal budget growth of III-As:

Droplet Epitaxy + Migration Enhanced Epitaxy

DE QD on Si at LTB

AlGaAs

GaAs

Ge

Si

1.

Al,Ga, In

2.

N, P, As, Sb

Droplet size, density and distribution control by1.Flux2.Coverage3.Substrate Temperature

Nanostructure morphologycontrol by:1.Flux2.Substrate Temperature

Group III reservoir

deposition (droplets)

III-V crystallization under group V

flux

DE – an MBE two steps process for QN

AdvantagesAdvantages1. Strain independence2. Shape control3. Independent size and density control4. Large Variety of Substrates (including Si)5. Nucleation site position control

6

AlGaA

s

AlGaA

s

GaAs

20 years development

500 nm500 nm

ON Si AND GeON Si AND Ge

MoleculeQUANTUM DOT:QUANTUM DOT:

Circular Exagonal Elongated

Triangular

Arrow

(311) A(311) A (100)(100)(100)(100) (100)(100) (111)A(111)A (111)A(111)A

SingleSingle Multiple ConcentricMultiple ConcentricQUANTUM RING:QUANTUM RING:

Ring-DiskRing-DiskDOT-DiskDOT-Disk

Dot-RingDot-RingDot-DRingDot-DRing

COUPLED NANO-COUPLED NANO-STRUCTURESSTRUCTURES

100nm

Flux

Temperature

0.1 ML/s

300 °C

Ga droplets

Ga molecular beam

8

Metallic Droplet Assembly Step

Progress in photonicsOctober 16th

Firenze

10/25/2015

1.688 1.696 1.704 1.712 1.720

Energy (eV)

10 K

30 K

50 K

70 K

90 K

110 K

130 K

150 KIntensity (arb. units)

APL 100 (23), 231112 (2012)1.6720 1.6724 1.6728

Inte

nsity

(arb

. uni

ts)

Energy (eV)

FWHM=80 eV

Single Photon Emitter on Si

APL 98, 103104 (2011) APL 100,231112 (2012)

2 um X 2um

n = 2.5 108 cm-2

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-40 -20 0 20 40

0.25

0.50

0.75

1.00

1.25

1.69 1.70

g(2) ()

Time (ns)

g(2)(0)=0.16

Inte

nsity

(arb

. uni

ts)

Energy (eV)

HBT Measurement at 15 K

-40 -20 0 20 400.0

0.5

1.0

1.5

nT [ns]

gT(2)[0] = 0.17 =0.1

START

STOP

50%BEAMSPLITTER

CORRELATOR

PHOTONSOURCE

DETECTOR 2(STOP)

DETECTOR 1(START)

HISTOGRAM:START-STOPDELAY

Channel

Cou

nts

START

STOP

50%BEAMSPLITTER

CORRELATOR

PHOTONSOURCE

DETECTOR 2(STOP)

DETECTOR 1(START)

HISTOGRAM:START-STOPDELAY

Channel

Cou

nts

DE-QDs on Ge/SiDE-QDs on GaAson Si

on GaAs

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START

STOP

50%BEAMSPLITTER

CORRELATOR

PHOTONSOURCE

DETECTOR 2(STOP)

DETECTOR 1(START)

HISTOGRAM:START-STOPDELAY

Channel

Cou

nts

START

STOP

50%BEAMSPLITTER

CORRELATOR

PHOTONSOURCE

DETECTOR 2(STOP)

DETECTOR 1(START)

HISTOGRAM:START-STOPDELAY

Channel

Cou

nts

HBT interferometer:second ordercorrelation function

0≤g 2(τ=0 )<1

HBT at 80 K

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Site controlled Metal NPs on Si

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ΔG: work of formation of the droplet embryo at constant temperature and pressure

droplet nucleation site control - 1

Surface curvature

Surface tension

Pits, Steps, etc.

Chemical composition, Strain

Droplet Position Control

ΔG modulation over the substrate surface

ΔG = γA + (γint-γsub)Aint – Δμ i

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Firenzedroplet nucleation site control

Use of DE to deposit Ga droplets withcontrolled size and density and to grow

GaAs islands on Si (111) surface…

Si

Si

Si

GaAs

ΔG modulation via substrate chemical composition patterning

…and finally to deposit group III atoms whichcreate droplets on top of GaAs only due surface tension modulation introduced on Si by the GaAs nanoislands

SiIn

Si GaAs

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Firenzedroplet nucleation site control

On AlGaAs

On Si

ΔG modulation via surface curvature (pits)

M. Bollani et al. Nanotechnology, 25, 205301 (2014)

E. Sala, J. Vac. Sci. Technol. B 32, 061206 (2014)

J. Wu et al. Adv. Funct. Mater., 24, 530 (2014)

Self-assembled

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FirenzeTEM and KMC

AsTEM

KMC

M. Bollani et al.Nanotechnology, 25 (2014) 205301

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FirenzeTarget 1: NW Density and Size Control

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FirenzeNanopatterning via Surface Tension

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Firenze

1.3 1.4 1.5 1.6 1.7107

108

109

0.01 0.1 1 106

107

108

109

Dens

ity (c

m-2)

1000/T (K-1)

Flux (ML s-1)

0.0 0.5 1.0 1.50

5

10

15

Coun

ts

Normalized Droplet Volume

Droplet and Size Density Control Si(111)

S. Bietti et al. J. Phys. D. Appl. Phys., 47, 394002 (2014)C. Somaschini et al. Nano Lett. 13, 3607 (2013)

Progress in photonicsOctober 16th

FirenzeDroplet and Size Density Control Si(111)

C. Somaschini et al. Nano Lett. 13, 3607 (2013)

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Firenze

C. Somaschini et al. Nano Lett. 13, 3607 (2013)

NW Density (ρ) and Diameter (δ) control

ρ = 4 107/cm2 δ = 120 nm

ρ = 3 108/cm2 δ = 40 nm

On oxidised Si substrates

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Johanson and Dick, CrystEngComm 13, 7175 K. Dick et al Nano Lett. 12, 3200 (2012)

Sharp interfaces between different semiconductors with different band

structures can form a tunnel barrier for different applications, such as single

electron transistors, resonant tunneling diodes, and memory components.

Target 2: NW sharp Axial Heterostructures

Au Catalyzed MOVPE growth

Self Catalyzed MBE growth

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10/25/2015

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FirenzeAnalysis: TEM

Energy Dispersive X-ray Spectroscopy

In Ga As Resolution: 7-8 nm

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High resolution STEM-HAADF

Analysis: TEM

InterfaceThickness<1.5 nmD. Scarpellini et al. Nano Lett.,15,3677 (2015)

High Resolution TEM

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3D GaAs integration on Si

Si

GaAs

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aeas

as

MDsTDs

TDs – threading dislocations MDs – misfit dislocations

<sub

Dislocations, wafer bowing and cracks

Lattice mismatch Thermal mismatchWafer Bowing

Layer Cracking

Integration of mismatched layers

Anti Phase Domains

ae

Stress during cooling/heating

Progress in photonicsOctober 16th

Firenze3D Aspect Ratio Trapping: Ge/Si case

Aspect Ratio Trapping (ART)J. Z. Li et al., APL 91, 021114 (2007)

C. V Falub et al. Science 335 (2012) 1330

PATT

ERN

ED

cracks

UN

PATT

ERN

ED

Ge/Si by LEPECVD

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1. Rate 0.5 ML/s, 2. V/III ratio = 50 (BEP ratio) 3. Growth T = 580°C4. Substrate 6° off toward [110] 5. Flux beam 30° off the vertical

2 μm

Si

GaAs

25μm

UNIFORMITY

VERTICAL GROWTH

3D GaAs MBE deposition on Si pillars

Growthparameters:

APL 103 (26), 262106 (2013)

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FirenzeDefect Analisys

APD domains

APL 103 (26), 262106 (2013)

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FirenzePL at 15 K - Spectrum

4 µm thick GaAs/Si pillars1.2 1.3 1.4 1.5

E2 I

nten

sity

(arb

. uni

ts)

Energy (eV)

E1

1.46 1.48 1.50 1.52 Inte

nsity

(arb

. uni

ts)

Energy (eV)

1.46 1.48 1.50 1.52 1.54 Int

ensit

y (a

rb. u

nits

)

Energy (eV) 1.45 1.50 Inte

nsity

(arb

. uni

ts)

Energy (eV)

APL 103 (26), 262106 (2013)

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Firenze

32

PL at 15 K - Intensity

Inte

nsity

(arb

. uni

ts)

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1.40 1.45 1.50 1.55 1.60

GaAs bulk GaAs/Si pillar

Inte

nsity

(arb

. uni

ts)

Energy (eV)

PL at Room Temperature

334 µm thick GaAs/Si pillars

Progress in photonicsOctober 16th

FirenzeSUMMARY

-40 -20 0 20 40

0.25

0.50

0.75

1.00

1.25

1.69 1.70

g(2) ()

Time (ns)

g(2)(0)=0.16

Inte

nsity

(arb

. uni

ts)

Energy (eV)

Droplet Epitaxy for •integration of GaAs QN based photonic devices on Si• GaAs/Si NW control

3D growth for monolithic integration of GaAs on Si(001)

COLLABORATIONS

Somaschini, ClaudioSalvalaglio, MarcoMarzegalli, AnnaMontalenti, FrancescoBonera, EmilianoMiglio, Leo

Frigeri, CesareGrillo, Vincenzo

CNR-IMEMCNR-S3-Nano

(Italy)

Univ. Milano Bicocca (Italy)

Gurioli, MassimoVinattieri, AnnaBiccari, FrancescoSarti, FrancescoAbbarchi, Marco

Univ. Firenze & LENS (Italy)

Isella, GiovanniFrigerio, JacopoPolitecnico di Milano (Italy)

Geelhar, LutzTrampert, AchimPaul Drude Instituet (Dermany)

University of Michigan (USA) Millunchick, JoannaSmereka, Peter

Sergio BiettiPost-Doc

David ScarpelliniPost-Doc

Alexey FedorovResearcher

III-V MBE group at LNESS

Luca EspositoPhD student

Andrea BallabioPhD student

Stefano Sanguinetti

Thank You for Your Attention.

We acknowledge support from:

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