Surface lattice resonances for beaming and outcoupling green μ LEDs emission

Light-Emitting Diodes (LEDs) exhibit a typical Lambertian emission, raising the need for secondary optics to tailor their emission depending on specific applications. Here, we introduce plasmonic metasurfaces to InGaN green emitting quantum wells for LEDs to control their far-field emission directionality and enhance the collection efficiency. The proposed mechanism is based on surface lattice resonances (SLRs) and relies on the near-field coupling between the InGaN multiple quantum wells (MQWs) and periodic arrays of aluminum (Al) nanodisks. Fourier microscopy measurements reveal that the angular photoluminescence emission pattern depends on the lattice constant of the metasurfaces. We demonstrate that integrating Al metasurfaces in LED wafers can enhance the collected outcoupled light intensity by a factor of 5 compared to the same sample without metasurfaces. We have also performed numerical calculations of the far-field emission based on the reciprocity principle and obtained a very good agreement with the experimental data. The proposed approach controls the emission directionality without the need for secondary optics and it does not require post-etching of the GaN, which makes it a potential candidate to control and enhance the generated light from micro-LEDs.</p

Room Temperature Exciton-Polariton Condensation in Silicon Metasurfaces Emerging from Bound States in the Continuum

We show the first experimental demonstration of room-temperature exciton-polariton (EP) condensation from a bound state in the continuum (BIC). This demonstration is achieved by strongly coupling stable excitons in an organic perylene dye with the extremely long-lived BIC in a dielectric metasurface of silicon nanoparticles. The long lifetime of the BIC, mainly due to the suppression of radiation leakage, allows for EP thermalization to the ground state before decaying. This property results in a condensation threshold of less than 5 \mu J cm^{-2}, one order of magnitude lower that the lasing threshold reported in similar systems in the weak coupling limit

Collective Mie Exciton-Polaritons in an Atomically Thin Semiconductor

Optically induced Mie resonances in dielectric nanoantennas feature low dissipative losses and large resonant enhancement of both electric and magnetic fields. They offer an alternative platform to plasmonic resonances to study light-matter interactions from the weak to the strong coupling regimes. Here, we experimentally demonstrate the strong coupling of bright excitons in monolayer WS$_2$ with Mie surface lattice resonances (Mie-SLRs). We resolve both electric and magnetic Mie-SLRs of a Si nanoparticle array in angular dispersion measurements. At the zero detuning condition, the dispersion of electric Mie-SLRs (e-SLRs) exhibits a clear anti-crossing and a Rabi-splitting of 32 meV between the upper and lower polariton bands. The magnetic Mie-SLRs (m-SLRs) nearly cross the energy band of excitons. These results suggest that the field of m-SLRs is dominated by out-of-plane components that do not efficiently couple with the in-plane excitonic dipoles of the monolayer WS$_2$. In contrast, e-SLRs in dielectric nanoparticle arrays with relatively high quality factors (Q $\sim$ 120) facilitate the formation of collective Mie exciton-polaritons, and may allow the development of novel polaritonic devices which can tailor the optoelectronic properties of atomically thin two-dimensional semiconductors.Comment: 27 pages, 7 figure

Light-Matter Coupling Strength Controlled by the Orientation of Organic Crystals in Plasmonic Cavities

Strong light–matter coupling is a powerful mechanism to engineer materials properties and a platform to study polariton physics. Excitons in organic crystals are interesting candidates for the investigation of light–matter coupling due to the large magnitude and well-defined orientation of their transition dipole moments. We demonstrate the coupling of excitons in tetracene crystals to optical modes in open cavities formed by anisotropic arrays of plasmonic nanoparticles and investigate the coupling strength as a function of the alignment of the exciton dipole moment to the cavity field. The anisotropy of the cavity and the crystal provides a practical method to tune the light–matter coupling strength from weak to the onset of the strong coupling regime, by rotating the crystal with respect to the plasmonic array. The possibility to control the coupling within a single excitonic material, paves the way to study the effects of the coupling strength on polariton physics, such as exciton-polariton dynamics, transport, or condensation

Effective Negative Diffusion of Singlet Excitons in Organic Semiconductors

Using diffraction-limited ultrafast imaging techniques, we investigate the propagation of singlet and triplet excitons in single-crystal tetracene. Instead of an expected broadening, the distribution of singlet excitons narrows on a nanosecond time scale after photoexcitation. This narrowing results in an effective negative diffusion in which singlet excitons migrate toward the high-density region, eventually leading to a singlet exciton distribution that is smaller than the laser excitation spot. Modeling the excited-state dynamics demonstrates that the origin of the anomalous diffusion is rooted in nonlinear triplet-triplet annihilation (TTA). We anticipate that this is a general phenomenon that can be used to study exciton diffusion and nonlinear TTA rates in semiconductors relevant for organic optoelectronics

Light beaming and outcoupling enhancement from quantum wells with Al metasurfaces

The emission pattern of Light-Emitting Diodes (LEDs) is Lambertian, which requires secondary optics to improve directionality. In addition, Gallium Nitride (GaN) based LEDs and micro-LEDs (µLEDs) have low outcoupling efficiency due to the high refractive index difference between air and GaN. Here, we experimentally investigate the impact of introducing a simple design of aluminum (Al) nanoparticles arrays (metasurfaces) to control the far-field emission of InGaN green emitting quantum wells (MQWs). This tailoring of emission originates from the near-field coupling between the InGaN MQWs and the resonant nanoparticles. Fourier microscopy measurements reveal that the period of the Al array controls the angular photoluminescence (PL) emission pattern. Furthermore, we obtain a five-fold enhancement of the collected outcoupled light intensity by implementing Al metasurfaces to the InGaN MQWs.</p

Light beaming and outcoupling enhancement from quantum wells with Al metasurfaces

The emission pattern of Light-Emitting Diodes (LEDs) is Lambertian, which requires secondary optics to improve directionality. In addition, Gallium Nitride (GaN) based LEDs and micro-LEDs (µLEDs) have low outcoupling efficiency due to the high refractive index difference between air and GaN. Here, we experimentally investigate the impact of introducing a simple design of aluminum (Al) nanoparticles arrays (metasurfaces) to control the far-field emission of InGaN green emitting quantum wells (MQWs). This tailoring of emission originates from the near-field coupling between the InGaN MQWs and the resonant nanoparticles. Fourier microscopy measurements reveal that the period of the Al array controls the angular photoluminescence (PL) emission pattern. Furthermore, we obtain a five-fold enhancement of the collected outcoupled light intensity by implementing Al metasurfaces to the InGaN MQWs.</p

Effective Negative Diffusion of Singlet Excitons in Organic Semiconductors

Using diffraction-limited ultrafast imaging techniques, we investigate the propagation of singlet and triplet excitons in single-crystal tetracene. Instead of an expected broadening, the distribution of singlet excitons narrows on a nanosecond time scale after photoexcitation. This narrowing results in an effective negative diffusion in which singlet excitons migrate toward the high-density region, eventually leading to a singlet exciton distribution that is smaller than the laser excitation spot. Modeling the excited-state dynamics demonstrates that the origin of the anomalous diffusion is rooted in nonlinear triplet–triplet annihilation (TTA). We anticipate that this is a general phenomenon that can be used to study exciton diffusion and nonlinear TTA rates in semiconductors relevant for organic optoelectronics