Mid-term Strategic ConferenceGranada, Spain, Nov. 13-14, 2019

CUSPIDOR: CMOS Compatible Single PhotonSources based on SiGe Quantum Dots

Thomas Fromherz

This project has received funding from the European Union’sHorizon 2020 research and innovation programme

under grant agreement No 731473.

Introduction

Integrated quantum optics at telecom wavelengths

I SOI integrated optic extremelymature

I can compact quantum opticalsources be added to establish SOIintegrated quantum optics in thetelecom wave length region ?

I currently: elaborate buildingblocks based on spontaneous4-wave mixing, externally pumped

I SiGe quantum dots as quantumoptical sources ?

Intel Silicon Photonics 100 Gb/s optical transceiver

Inset: Device A1 and B1

Laser input

SPDs RF CMOS electronic logic

N SiliconPhCW’s

IntegratedAWG’s

Fibre delay Low-loss PLZTNx2 switch

Sub-Poissonianheralded singlephoton output

Noiseport

NX

2 O

PTIC

AL S

WIT

CH

n0 ng n0

I P S

SFWM

M.J. Collins et al., Integrated spatial multiplexing ofheralded single-photon sources, Nat. Com. 4: 2582(2013)

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Main objectives

O1: A room-temperature electrically driven, optical matrix-element enhanced,silicon- germanium quantum dot based deterministic single photon source(SPS) with a generation rate of 50 MHz, with a second-order correlationfunction, g (2)(0) < 0.05 at cryogenic temperatures (∼ 10K) andg (2)(0) < 0.2 at room temperature, unprecedented for these type ofquantum dots;

O2: A single photon source based on the unconventional photon blockade(UPB), with a generation rate of 10 MHz and g (2)(0) < 0.05 at cryogenictemperatures (∼ 10K) and g (2)(0) < 0.2 at room temperature.

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Consortium

Johannes Kepler University Linz Austria T. Fromherz

Universita degli Studi di Pavia Italy D. Gerace

Cork Institute of Technology Ireland L. O’Faolain

Masaryk University Brno CzechRepublic

P. Klenovsky

Tyndall National Institute Ireland F. Murphy

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Role of partnersJohannes Kepler University Linz, Austria

I site controlled epitaxial growth ofSiGe based nanostructures

I defect engineered SiGe quantumdots (DEQDs)

I SOI integrated nano photonics

I project coordination

a

1 µm

b

c

1 µm

x

y x

y

z

Ge QD

airholeSi capping layer

pit

Ge wetting layer

mode M2

DEQD LED

2µm

µ-disc laser

4

Role of partnersUniversita degli Studi di Pavia, Italy

I quantum photonics theory

I photonic nanostructuressimulations

I quantum optical spectroscopyand characterization in thetelecom band.

2μm

Energy (meV)793 800 806 812 817 822

0

0.5

1

RS

Int

ensi

ty (

arb.

)

M1

M2 M3 M4M5

M6

M1 M2 M3

M4 M5 M6

|E |y2

a',r'

a,r

Frequency comb

Unconventional photon blockade, pulsed excitation

UPB, photonic moleculeThe “bichromatic” cavity

Marco Clementi - University of Pavia 8/20

a’/a= 0.857

a’/a= 0.96

Alpeggiani et al., Appl. Phys. Lett. 107 (2015)

FDTD|E|2

Model|cn|2

Gaussian mode envelope(fundamental mode)

Simbula et al., APL Photonics 2 (2017)

Bichromatic cavity

FS

R ( m

ΓΓ

-FSR-FSR

Selective tuning of comb-modesSolutions

Marco Clementi - University of Pavia 16/20

Increase linewidth(introduce losses)

Selective tuning of the resonant modes

Portalupi et al., Opt. Express 18 (2010)Chen et al., Opt. Express 19 (2011)

Laser inducedlocal oxidation

5

Role of partnersCork Institute of Technology, Ireland

I doping of p-i-n structures

I nano-structuring of state-of-artphotonic devices

I integrated nano-optical systems

6

Role of partnersMasaryk University Brno, Czech Republic

I interfaceing mircoscopic andmesoscopic simulation methods

I mesoscopic energy level simulations inSiGe DEQDs including strain

I multi-particle effects

Simulated SiGe QD structure

3/17

Simulated SiGe QD had a shape of pyramid with base length of 20 nm and height of 2.5 nm. The whole structure is situated in Si; g.s. means ground state in the figure below. The electrons in the dot were considered to have a constant mixture of pure Γ Ge character and that for intersticial being mixed between Γ and X or L bands (this was provided by DFT).

QD

electron g.s.

hole g.s.

Simulated SiGe QD structure

3/17

Simulated SiGe QD had a shape of pyramid with base length of 20 nm and height of 2.5 nm. The whole structure is situated in Si; g.s. means ground state in the figure below. The electrons in the dot were considered to have a constant mixture of pure Γ Ge character and that for intersticial being mixed between Γ and X or L bands (this was provided by DFT).

QD

electron g.s.

hole g.s.

7

Role of partnersTyndall National Institute, Ireland

I ab initio electronicstructure calculationsof the implanted Gedefect levels

I simulations ofimplanted Si, Sn, Sbdefects

I develop interface formesoscopick · p−simulations

I transport simulationssingle DEQD pin diode

8

Main progress

I fabrication of bichromaticcavities with comb-likespectrum, Q >1M and recordfinesse (Si only)

I permanent tuning of modes inbicromatic photonic crystalcavities with ultra high Q

2μm

Energy (meV)793 800 806 812 817 822

0

0.5

1

RS

Int

ensi

ty (

arb.

)

M1

M2 M3 M4M5

M6

M1 M2 M3

M4 M5 M6

|E |y2

a',r'

a,r

Frequency comb

Quality factors

Marco Clementi - University of Pavia 21/20

Highest Q factor:Q ≈ 1.1 × 106 (fabrication limited)

Average Q is reduced by far-field optimization toQ ≈ 2 × 105 (load limited)

1560.855 1560.860 1560.8650

1

2

Bichromatic cavityN=48, a=410nm, R=100nm, r'=59nm, ff=0nm

Experimental points Fano fit

RS

sign

al (a

.u.)

Wavelength (nm)

Mode n. 1λ=1560.861 nmQ=1.1x106

Solutions

Marco Clementi - University of Pavia 16/20

Increase linewidth(introduce losses)

Selective tuning of the resonant modes

Portalupi et al., Opt. Express 18 (2010)Chen et al., Opt. Express 19 (2011)

FS

R ( m

ΓΓ

-FSR-FSR

Selective tuning of comb-modesSolutions

Marco Clementi - University of Pavia 16/20

Increase linewidth(introduce losses)

Selective tuning of the resonant modes

Portalupi et al., Opt. Express 18 (2010)Chen et al., Opt. Express 19 (2011)

Laser inducedlocal oxidation

9

Main progress

I site controlled growth of Geimplanted SiGe DEQDs

I nucleation sites in registry withbichromatic PhC design

I realistic DFT modelling of Gesplit-[110] interstitial, tracing backincrease of optical oscillatorstrength observed in experiments

I multi-scale modeling: k · p bandstructure parameters for Gesplit-[110] bands from DFTsimulations

15000 10000 5000 0 5000 10000 15000

10000

7500

5000

2500

0

2500

5000

7500

10000

10

Key challenges

I achieving ultra large Q-factors in Ge containing PhC cavities. New route:growth of a single QD per cavity on a 2D wetting layer

I demonstrate single photon emission of DEQDs

I reduce spectral drift resulting in large linewidths of SiGe QDs

I combine large Q factor cavities with contacts for pin diodes

I achieve efficient current injection into single DEQDs embedded in a pindiode

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Dissemination and valorization

List of papers and conference contributions can be found on CUSPIDORhomepage http://www.cuspidor-quantera.eu

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