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Metal Hybrid Cavities

Final Report Summary - HYMECAV (Metal Hybrid Cavities)

During the past few decades, the plasmonic properties of metallic nanostructures have received considerable interest in both fundamental and applied fields. Modern plasmonics are based on the physics of surface plasmons – the states of an electromagnetic field localized at the interface between a metal and dielectric – which are analogues of waveguide mode. Due to their ability to manipulate light at the nanoscale, these nanostructures are of great importance in many applications such as biosensing, surface-enhanced Raman scattering, and photonic circuits. Tamm plasmona are a novel type of localized mode of the electromagnetic field. Tamm plasmons (TP) are localized at the interface of a specially designed Bragg reflector and a metal and are the analogues to Fabry-Perot cavity modes.
Tamm plasmons are very feasible to make: they can be obtained by depositing the metal film on top of Bragg reflector (which can contain some active media). The TP provides a very simple way of laterally localizing light in the semiconductor structures (microcavity) and are readily fabricated by basic photolithography without the need of etching through micrometer-scale thick multilayer structures. Coupling of an exciton in a quantum dot to such a photonic dot induced by the TP was successfully used as a source of single photons for example, now used in quantum cryptography (see figure 3). Despite metallic mirrors being the most commonly used type of light reflectors in normal life, metallic optical components have not found wide use in optoelectronics, despite the obvious advantages of the metals. They are cheap and can be conveniently deposited and flexibly structured. The main obstacle preventing the application of metallic mirrors in optoelectronics is the optical loss and heating of the metal due to optical absorption which leads to a catastrophic degradation of the mirrors and surrounding materials and a reduced transmittance. However, application of metals is particularly necessary for prospective organic light emitting diodes or lasers, where high charge carrier densities need to be injected into organic transport layers. In photovoltaics, lighting and display technology, organic semiconductors are attractive active materials due to their technological feasibility and a broad range of attractive optical properties and low cost, additive device fabrication. Many organic materials exhibit very large oscillator strengths in their electronic transitions, providing the potential for large optical gain.
Moreover, they exhibit large exciton binding energies, orders of magnitude larger than for inorganic emiconductor materials giving rise to stable excitons at room temperature. This in turn allows exciton coherences at room temperature. As an example, polariton lasing was reported recently in a single crystal organic microcavity at room temperature. In this project we aimed to combine structures based on Tamm plasmons with organic materials to achieve new optical phenomena from effectively combining the physics of metal layers with organic thin films. Organic and metallic layers are embedded into a microcavity and confined by distributed Bragg reflectors (DBRs), leading to the formation of Tamm modes interacting with organic emitter materials. A major goal was to achieve optimization of semiconductor Tamm plasmon based lasers that could lead to room temperature operation.