Strong exciton-photon coupling in ZnO based resonators

Abstract

The authors report on the fabrication of high quality all-oxide Bragg reflectors (BRs) and ZnO based resonators. The resonator consists of a bulk half-wavelength ZnO microcavity embedded between two BRs, each made of 10.5 layer pairs of yttria stabilized zirconia and Al2O3. Scanning transmission electron microscopy and atomic force microscopy, yield smooth interfaces and low surface roughness for the BR as well as the resonator. For the BR with 10.5 layer pairs the authors obtain reflectivities up to 99.2% within the Bragg stop band. The exciton-polariton dispersion was determined by both, polarization- and angle-resolved photoluminescence (PL) and reflectivity (R) measurements. The detuning between the uncoupled exciton mode and photon mode was changed by shifting the exciton mode energy in the temperature range of 10–290 K. Thereby we observed that a strong exciton-photon coupling regime up to room temperature is present in our resonators with maximum values of the Rabi splitting of about 68 meV (PL, T=10 K) and 76 meV (R,T=10 K).

Two‐dimensional confined photonic wire resonators – strong light–matter coupling

“…In order to investigate the material DFs, the structure properties, and the growth rate, we have grown amorphous and single‐ or microcrystalline single layers and layer stacks with different layer sequences and pair numbers on planar Si, GaAs, InP, and Al 2 O 3 substrates 20, 24–27. For the a‐SiO x and a‐Si layers we have found that the higher the deposition temperature T g is, the lower is the surface roughness (8 and 3 nm rms on a $2.2 \times 2.2\,{\rm \mu m}^2 $ area for $T_{\rm g} = 90\,^\circ {\rm C}$ respective 120 °C) 26.…”

“…For the a‐SiO x and a‐Si layers we have found that the higher the deposition temperature T g is, the lower is the surface roughness (8 and 3 nm rms on a $2.2 \times 2.2\,{\rm \mu m}^2 $ area for $T_{\rm g} = 90\,^\circ {\rm C}$ respective 120 °C) 26. The Al 2 O 3 layers grown at $T_{\rm g} = 735\,^\circ {\rm C}$ have been found to be microcrystalline or amorphous, regardless of the substrate material and the position within a layer stack, and reveal surface roughness values of up to $R_{\rm a} = 0.3\,{\rm nm}$ 20, 28, whereas those grown at $T_{\rm g} = 150\,^\circ {\rm C}$ are amorphous and very smooth with $R_{\rm a} = 0.15\,{\rm nm}$ . For the high‐temperature ($T_{\rm g} = 735\,^\circ {\rm C}$ ) ZrO 2 layers we have obtained slightly rougher surfaces with $R_{\rm a} = 0.25 - 0.80\,{\rm nm}$ .…”

“…In contrast, for the high‐temperature ($T_{\rm g} = 650\,^\circ {\rm C}$ ) YSZ layers we have found a single cubic phase only. With an optimized oxygen partial pressure of $p({\rm O}_2 ) = 0.002\,{\rm mbar}$ we have obtained smooth layers with $R_{\rm a} = 2\,{\rm nm}$ and a full width at half maximum of the (111) reflex in the omega scan of 2° 20. For the low‐temperature ($T_{\rm g} = 150\,^\circ {\rm C}$ ) amorphous YSZ layers we have obtained very smooth surfaces with $R_{\rm a} = 0.1\,{\rm nm}$ .…”

“… (online color at: http://www.pss-b.com/) Room temperature refractive indices and absorption coefficient of the materials used for the BRs 20, 24–28 and for the ZnO active medium 41 determined from planar thin films. For the uniaxial materials Al 2 O 3 and ZnO, spectra for the polarization perpendicular to the optical axis are shown only.…”

“…This makes ZnO based resonators attractive for BEC of exciton–polaritons 15, 16. Recently, exciton–polaritons have been observed in ZnO based planar FP resonators 14, 17–20 and in ZnO nanowire whispering‐gallery mode resonators 21. Values of V up to 55 meV have been reported.…”