Resonant medium: Up to four (Zn,Cd)Se quantum wells. Luminescence selection is possible with a variation of the Cd-content or the well width.

The front side of the structure is covered with high reflection (R > 0.95) distributed Bragg-Mirrors of ZnSe and YF3. The microcavity is completed with backside Bragg-Mirrors after substrate wet etching.

A standing wave is manifested in the cavity: quantum wells or quantum dots are placed near its antinodes which guarantees an effective coupling efficiency between excitonic and photonic mode.

The structure is particularly suited for investigation of the strong and weak coupling regime in semiconductor microcavites.

A ZnSe multi quantum well microcavity structureA ZnSe multi quantum well microcavity structure

0 nm

100 nm

200 nm

6 x

8 x

ZnS /4-layerYF /4-layer3

optical sizeat = 538 nm

real layerth ickness

/4 ZnS layer /4 YF layer3

ZnSe-Cavity

(Zn,Cd)Se-QW s

1/2

The most important structural parameters of the microcavities are quantum well length L, cadmium content x and the cavity size d.

Further interesting parameters for the optimization of our structures are the alloy scattering in the (Zn,Cd)Se wells as well as the strain status of the microcavity.

61 62 63 64 65 66 67 6810-7

10-6

1x10-5

1x10-4

10-3

10-2

10-1

100

101

Inte

nsit

y

2 (deg)

(004)-Reflex /2-scan

(Zn,Cd)Se

GaAs

ZnSe

81 nm ZnSe

5.8 nmZn Cd Se

quantum wells0.65 0.35

81 nm ZnSe

12.5 nmZnSe spacer

GaAs

rel. sim ulation error ~ 2 %

82 nm ZnSe

7 nmZn Cd Se

quantum wells0.65 0.35

82 nm ZnSe

14 nmZnSe spacer

GaAs

Growth process parameters Ex-situ X-ray diffraction data

Structural characterisation of ZnSe/(Zn,Cd)Se QWsStructural characterisation of ZnSe/(Zn,Cd)Se QWs

300 K reflection measurements of a typical microcavity300 K reflection measurements of a typical microcavity

2,20 2,24 2,28 2,32 2,36 2,40 2,44

Q = 210

300 K

= 41 meV

MQW emission

Lc=200.5 nm

Lc=201.9 nm

Lc=203.3 nm

Lc=205.5 nm

refle

ctiv

ity (

arb

. un

its)

photon energy (eV)

The dots depict the experimental data, the curves represent Lorentzian fits. The respective cavity length values, which are also indicated in the figure, were calculated from the shift of the photonic mode (cavity mode), which is caused by the layer thickness gradient.

In dependence on the cavity length, the photonic mode shifts to higher energies. At Lc = 200.5 nm

the photonic mode approaches the luminescence energy and a splitting of the reflectivity spectrum into two peaks at 2.290 eV and 2.331 eV is observed. The energy difference between both peaks is = 41 meV.

The figure below shows the room temperature reflectivity spectra of the microcavity obtained at different sample positions.

2.20 2.25 2.30 2.35 2.40 2.45 2.50

min

= 44 meV

330 K

320 K

310 K

300 K

290 K

280 K

270 K

no

rmal

ized

Pl i

nte

nsi

ty (

a.u

.)

photon energy (eV)

260 270 280 290 300 310 320 330 3402.22

2.24

2.26

2.28

2.30

2.32

2.34

2.36

2.38

ph

oto

n e

ner

gy

(eV

)

temperature (K)

calculated dispersion experimental data

Temperature dependent photoluminescenceTemperature dependent photoluminescence

The picture to the left shows photoluminescence spectra of a complete microcavity structure at temperatures between 270 - 330 K. The variation of the temperature leads to a shift of the quantum well luminescence energy according to the bandgap shift. Therefore the excitonic mode approaches the photonic mode at a constant cavity length of Lc = 200.5 nm. It is evident

from Fig. 4 that the luminescence peaks show a clear anticrossing behaviour.

The curves below are a fit of the experimental data using a model of the polariton dispersion. In our calculation we used Ex = 2.627 – 1.1

· 10-3 T (eV) for the temperature dependence of our quantum well

luminescence and Ep =

2.298 eV as the constant cavity mode energy, yielding Rabi = 45 meV.

This value is in good agreement to the experimental data of the reflection measurements and confirms in addition the existence of the strong coupling regime.