Cover Picture: Phys. Status Solidi C 7–8/2014

In their Invited Article on pp. 1267–1272, Klein et al. report on the realization of monolithic, i.e. fully epitaxial ZnSe‐based microcavities with 1 λ ‐ to 3 λ ‐cavities for the investigation of strong coupling phenomena. The lattice matched distributed Bragg reflectors consist of quaternary ZnMgSSe layers as the high‐index material and a MgS/ZnCdSe superlattice as the low‐index material. This microcavity design allows for the use of high‐quality ZnSe quantum wells. Strong coupling was achieved with a vacuum Rabi splitting of 19 meV for the 1 λ ‐cavity (at 70 K) and of 40 meV for the 3 λ ‐cavity (at 7 K). Effectively the Rabi splitting can be chosen by the sample design. Q ‐factors up to 6500 are found, exceeding state‐of‐the‐art optical quality in II–VI microcavities. Microstructures such as micropillars, waveguides, ring resonators, and molecule chains were fabricated using focused ion‐beam etching. Discrete optical modes in micropillars were observed for both cavity lengths confirming three‐dimensional optical confinement and low sidewall damage, even for small pillar radii. In summary, such microcavities offer new perspectives for the investigation of exciton‐polariton fluids: stability at elevated temperature, large Rabi splitting, comparable with optical phonon frequency, together with full control over in‐plane confinement.