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II-VI semiconductor microcavities

• microcavity physics

• polariton stimulation

• prospects

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z

QW ~ 10 nm optical cavity ~ 1 µm

Semiconductor microcavity

Confinement along z for both cavity modes and QW excitons

2D light-matter interaction

mirror

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cavity mode exciton

kz1, k// kz2, k//

Rabi

Selection rule : conservation of in-plane wavevector k//

exciton (k//) cavity mode (same k//)

2D light-matter interaction

cav X

cav ,, X < Rabi strong coupling regime : polaritons

> weak coupling regime : Purcell effect

UP

LP

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Polariton in-plane dispersion

Cavity mode confined along z : k1z ~ 8.106 m-1 >> k//

photon dispersion >> exciton dispersion

photon mass ~ 10-4 exciton mass

Polariton = photon * exciton

polariton DOS ~ 10-4 exciton DOS

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• finite lifetime 1 ps (mirror reflectivity)

high radiative recombination rate

• k//

k// = ( / c) sin

direct injection / probe of polariton population

• LP = trap in k space with small DOS

macroscopic state occupancy can be achieved for densities well below the exciton screening limit

bosonic final state stimulation Bose condensation

z

k//

Polariton features

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II-VI VS III-V

• Lattice mismatch

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GaAs CdTe ZnSe

• Oscillator strength (x 1013 cm-2 ) 0.6 2.3

Rabi splitting ~ 6 meV 4 QWs one QW

• Exciton binding energy (meV) 10 25 40

screening density (x 1011 cm-2 ) < 1 5 > 10

II-VI microcavities well suited for polariton condensation

II-VI VS III-V

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Probe of polariton population

PL measured at different angles to the microcavity normal

24 QWs

T = 4K

+ 5 meV

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II-VI VS III-V Probe of polariton population

N PL

Bottleneck effect

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Polariton stimulation

Non-resonant quasi-cw excitation

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Polariton stimulation

polariton-polariton scattering P2 !

Bosonic final state stimulation

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Polariton stimulation

Suppression of bottleneck effect

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Polariton stimulation

New polariton dispersion above stimulation threshold

Evidence of macroscopic coherence ?

(Ciuti, PRB 2001)

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Resonant excitation : parametric gain

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Parametric gain : II-VI VS III-V

M. Saba et al., Nature 2001

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Parametric gain : II-VI VS III-V

M. Saba et al., Nature 2001

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Prospects

Polariton stimulation under non-resonant excitation conditions at RT ?

• Larger exciton binding energy, e.g. in ZnSe, GaN, organic microcavities

• Deeper trap / scattering efficiency ?

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Microcavity activities in Grenoble

Polariton stimulation Single photon solid source

(2D microcavity + QW) (0D microcavity + QD)

Régis André Régis André

Robert Romestain Robert Romestain

Le Si Dang Le Si Dang

Maxime Richard (PhD) Jean-Michel Gérard

Kuntheak Kheng

Henri Mariette

Yvan Robin (PhD)

Sebastian Moehl (PhD)