We report on the strong coupling of surface plasmon polaritons and molecular vibrations in an organic-inorganic plasmonic hybrid structure consisting of a ketone-based polymer deposited on top of a silver layer. Attenuated-total-reflection spectra of the hybrid reveal an anticrossing in the dispersion relation in the vicinity of the carbonyl stretch vibration of the polymer with an energy splitting of the upper and lower polariton branch up to 15 meV. The splitting is found to depend on the molecular layer thickness and saturates for micrometer-thick films. This new hybrid state holds a strong potential for application in chemistry and optoelectronics.
We report on our efforts to cultivate the ternary compound ZnCdO as a semiconductor laser material. Molecular beam epitaxy far from thermal equilibrium allows us to overcome the standard solubility limit and to fabricate alloys with band gaps ranging from 3.4 down to 2.1 eV. Optimized structures containing well-defined quantum wells as active zones are capable of low-threshold lasing under optical pumping up to room temperature. The longest lasing wavelength achieved so far is 510 nm.Green-wavelength laser action of a ZnCdO/ZnO multiple quantum well structure at room temperature.
The use of the free-electron gas in a heavily doped semiconductor (ZnO:Ga) enables the realization of almost arbitrarily shaped surface-plasmon-polariton dispersion curves in planar geometries. In particular, by preparing metal-metal-type interfaces, we demonstrate surface-plasmon polaritons exhibiting finite frequencies in the long-wavelength limit. Moreover, coupling of surface plasmon polaritons at adjacent interfaces allows for the controlled formation of frequency gaps or, alternatively, the opening of otherwise forbidden regions by an appropriate layer design. Our findings reveal a considerable plasmonic potential of this semiconductor-based approach, e.g., for achieving propagation control or phase matching for nonlinear optical processes as well as novel many-particle phenomena.
As a result of growth imperfections, (Zn,Cd)O/ZnO quantum well structures exhibit random laser action. Fabrication of microresonators allows us to study and to compare directly cavity and scattered feedback. Our experimental and theoretical analysis shows that (i) pure random lasing generally requires a larger gain than in the standard Fabry-Perot regime, (ii) the presence of Mie scatterers in the semiconductor-based cavity does not substantially increase the lasing threshold, and (iii) the random feedback creates a subtle modal gain distribution that might be of particular importance for the dynamical properties, both with and without Fabry-Perot cavity.
We report on room temperature laser action of an all monolithic ZnO-based vertical cavity surface emitting laser (VCSEL) under optical pumping. The VCSEL structure consists of a 2λ microcavity containing 8 ZnO/Zn0.92Mg0.08O quantum wells embedded in epitaxially grown Zn0.92Mg0.08O/Zn0.65Mg0.35O distributed Bragg reflectors (DBRs). As a prerequisite, design and growth of high reflectivity DBRs based on ZnO and (Zn,Mg)O for optical devices operating in the ultraviolet and blue-green spectral range are discussed.Semiconductor lasers operating in the ultraviolet (UV) and blue spectral range have become of great technological importance, e.g., for data storage applications. Compared to the commonly employed edge-emitting devices, vertical cavity surface emitting lasers (VCSELs) offer several advantages such as single mode emission, a circular beam profile, and the possibility for integration into two dimensional arrays. VCSELs based on GaN and its alloys reached a promising stage of development [1] and laser devices working in the strong exciton-photon coupling regime, so called polariton lasers, have been demonstrated at room temperature [2]. In principle, with ZnObased alloys, a similar spectral range can be covered as with the (Al,In,Ga)N heterosystem. Room temperature lasing of (Zn,Cd)O/ZnO quantum well (QW) structures was achieved from UV to green wavelengths [3]. In the strong coupling regime, ZnO was predicted to be even superior due to its high oscillator strength and exciton binding energy [4,5]. However, necessary prerequisites to both VCSELs and polariton lasers are microcavities (MCs) with a high quality factor and good optical quality ZnO active layers. So far only hybrid MCs [6-9] consisting of, e.g., an epitaxially grown GaN-based bottom distributed Bragg reflector (DBR), a ZnO active layer, and a top dielectric DBR have been employed.In this letter, we report on the monolithic growth of ZnO and (Zn,Mg)O based DBRs and MCs by radicalsource molecular beam epitaxy (MBE). With a properly chosen DBR ternary alloy composition, it is possible to obtain high reflectivities with a moderate number of mirror pairs in the range from 375 nm to 500 nm. Finally, we demonstrate an UV emitting all-ZnO VCSEL.The samples are grown in a commercial DCA-450 MBE apparatus equipped with standard metal sources and a radical plasma cell for oxygen. A-plane (1120) sapphire wafers are used as substrates. The (Zn,Mg)O DBRs and MCs containing ZnO/(Zn,Mg)O QWs are grown without interruption at T g = 340 • C with an oxygen limited growth rate of 330 nm/h, which was previously determined from oscillations in the specular beam intensity of in situ reflected high-energy electron diffraction (RHEED) [3]. Note that the low T g allows for the growth
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