Cornelius Grossmann 1

ULTRAFAST CONTROL OF POLARITON STIMULATED SCATTERING IN SEMICONDUCTOR MICROCAVITIES

Cornelius Grossmann

G. Christmann, C. Coulson and J.J. BaumbergNanophotonics Centre, Cavendish Laboratory, University of Cambridge

N. T. Pelekanos, Z. Hatzopoulos, S. I. Tsinzos and P. G. SavvidisDepartment of Materials Science and Technology, University of Crete

PLMCN10, Cuernavaca, Mexico15th april 2010

Cornelius Grossmann 2

Strong coupling regime

Mirror MirrorActiveregion

C. Weisbuch et al., PRL 69 3314 (1992)

|excited,0> |ground,1>

h

Lower polariton

Upper polariton

Strong-coupling regime:reabsorption time < cavity lifetime

semiconductor microcavity

Exciton

Cavity

UPB

LPB

Energy

Momentum

coupling between a electronic transition and a Fabry-Perot mode

Cornelius Grossmann 3

Parametric scattering processparametric conversion:• probe stimulation at ks= 0• energy and momentum conservation!

Savvidis et. al., PRL 84 1547 (2000)

• coherent χ(3) process in semiconductor microcavities• χ(3)-nonlinearity: exciton-exciton interaction• probe gain highly dependent on pump-LPB resonance

2kp= ks+ki

2E(kp)= E(ks)+E(ki)

PumpEP, kP

EI, kI

ES, kS

Signal

Idler

χ(3)

Cornelius Grossmann 4

Under external bias

Polariton light emitting diode

D. Tsintzos et al., Nature 453 372 (2008)

Quantum confined Stark effect

conductionband

valence band

GaAs InGaAs GaAsGrowth axis

F

Applied bias

consequences

change of energy of excitonic transition separation of electron and hole wavefunctions

Cornelius Grossmann 5

Electrically pumped polariton devices

Optical bistability in GaAs-based Polariton LED

Bajoni et. al., PRL 101 266402 (2008)

Electroluminescence up to RT

Tsintzos et. al., APL 94 071109 (2009)Khalifa et. al., APL 92 061107 (2008)Bajoni et. al., PRB 77 113303 (2008)

Cornelius Grossmann 6

Motivation for the bias

The parametric scattering process is due to exciton-exciton interaction through χ(3)

-+

-+

- +

- +

The excitons are alignedTailoring of the exciton-exciton interaction

Consequences on the parametric amplification in microcavities?

Growth axis

F

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Experimental setup

fs mode-locked Ti:Sa laser system• pump spectrally filtered and broadband probe pulse• pump at the magic-angle• probe at k||= 0 • recording of

pump reflected spectrum incident probe reflected probe

• in parallel: electrical measurements

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Voltage scan: Stark effect

Ref

lect

ivity

(arb

. uni

ts)

1.4161.4121.4081.404Energy (eV)

2.5V

-2.4V

T=7.5 K LP

X

UP

C

1

1.416

1.414

1.412

1.410

1.408

1.406

1.404

1.402

1.400

Ener

gy (e

V)

210-1

Bias (V)

Stark tuning of the excitonsRabi splitting of 6 meV

Refle

ction

spec

tra

Cornelius Grossmann 9

Voltage scan: pump-probe

50

40

30

20

10

0

Gain

1.4161.4121.4081.404

Energy (eV)

Ipum

p

2.5V

-1.5V

c)

a)b)

LP(kp)

LP

UP

10

8

6

4

2

0

Peak

gain

210-1

Bias (V)

1.416

1.414

1.412

1.410

1.408

1.406

1.404

Energy

(eV)

210-1

Bias (V)

2 effects: • gain-loss at negative bias, dispersion-less

50

40

30

20

10

0

Gai

n

1.4161.4121.4081.404

Energy (eV)Ipum

p

2.5V

-1.5V

c)

a)b)

LP(kp)

LP

UP

10

8

6

4

2

0

Peak

gai

n

210-1

Bias (V)

1.416

1.414

1.412

1.410

1.408

1.406

1.404

Ener

gy (e

V)

210-1

Bias (V)

50

40

30

20

10

0

Gai

n

1.4161.4121.4081.404

Energy (eV)

Ipump

2.5V

-1.5V

c)

a)b)

LP(kp)

LP

UP

10

8

6

4

2

0

Peak

gai

n

210-1

Bias (V)

1.416

1.414

1.412

1.410

1.408

1.406

1.404

Ener

gy (e

V)

210-1

Bias (V)

500

0

Cur

rent

(A

)-2 0 2

Bias (V)

Cur

rent

(μA)

Bias (V)

pump onpump off

gain-loss at negative bias:detuning of pump and LPB

• gain dip at positive bias

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Negative bias: gain loss

• unbiased

• biased

Stark-tuning of excitons:pump out of resonance with LPB inefficient carrier injection

resonance of pump and LPB:efficient parametric amplification efficient carrier injection

Growth axis

No screening of external electric field!

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sharp gain dip

-20

-15

-10

-5

0

Current (

A)

1.00.80.60.4Bias (V)

x6

c)

a) b)

1.1 V

0.4 V

80

60

40

20

0

Gain

1.4121.4111.4101.4091.4081.407

Energy (eV)

40

30

20

10

0

Peak

gain

1.00.80.60.4Bias (V)

-20

-15

-10

-5

0

Current (

A)

1.00.80.60.4Bias (V)

x6

c)

a) b)

1.1 V

0.4 V

80

60

40

20

0

Gain

1.4121.4111.4101.4091.4081.407

Energy (eV)

40

30

20

10

0

Peak gain

1.00.80.60.4Bias (V)

100 mV

> 90%

sharp dip

additionalphotocurrentat this bias

50

40

30

20

10

0

Gai

n

1.4161.4121.4081.404

Energy (eV)

Ipump

2.5V

-1.5V

c)

a)b)

LP(kp)

LP

UP

10

8

6

4

2

0

Peak

gai

n

210-1

Bias (V)

1.416

1.414

1.412

1.410

1.408

1.406

1.404

Ener

gy (e

V)

210-1

Bias (V)

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Tunneling

-1.20

-1.16

-1.12

-1.08Ener

gy (e

V)

40200Position (nm)

0.40

0.36

0.32

0.28LP

LQW RQW

τc

τe

τtτLO

τΩ

τo

700fs8ps

20ps

2 competing processes• Rabi-oscillations: redistribution of e-/h-pairs over QWs • carrier tunneling: separation of e-/h-pairs

• LO-phonon induced tunneling 100 fs• carrier escape 180 ns, 230 fs• extra e- population creates extra scattering• OPO gain sensitive to broadening

C. Ciuti et al. PRB 62 R4825 (2000)

0.6

0.51.00.5

Bias (V)

LQW RQW

ωLO

Ee (eV)

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Summary & outlook

electrical control of the parametric gain sharp and dramatic gain modulation

Stark tuning with “small” electrical fields: ultrafast response expected Potential realization of Thz modulators?

Cornelius Grossmann 14

Support and funding

• Pavlos G. Savvidis et. al.: Polariton LED sample• Gabriel Christmann, Chris Coulson and Jeremy Baumberg: spectroscopy & simulation

Funding: • UK EPSRC EP/C511786/1, EP/F011393 • EU Clermont 4