LT) can be achieved for weakly absorbed photons with energies close to the absorption edge of silicon. [ 15 ] These properties of b-Si are particularly useful for photovoltaic applications.The limiting effi ciency of a solar cell is given by the detailed balance of absorption and radiative recombination [ 16 ] and by nonradiative processes like Auger-and impurity recombination. [17][18][19] b-Si can help to approach those limits in two ways. On the one hand b-Si improves the coupling of light into the solar cell and the absorption of near band edge photons. This in turn increases the short circuit current and on a logarithmic scale also the open circuit voltage. On the other hand, due to excellent light-trapping properties b-Si might also allow reducing the solar cell thickness substantially below 100 µm while sustaining a high light absorption. This reduces nonradiative bulk recombination losses that scale linearly with the solar cell thickness [ 17,18 ] and hence, increases the open-circuit voltage. Of course, reducing the solar cell thickness also increases the cost effi ciency. Decreasing the amount of required silicon feedstock is a major industry concern as can be seen by the growing interest in kerf-free crystalline silicon solar cell technologies. [20][21][22] Unfortunately, besides bulk effects, surface recombination imposes a very critical limit to the solar This article presents an overview of the fabrication methods of black silicon, their resulting morphologies, and a quantitative comparison of their optoelectronic properties. To perform this quantitative comparison, different groups working on black silicon solar cells have cooperated for this study. The optical absorption and the minority carrier lifetime are used as benchmark parameters. The differences in the fabrication processes plasma etching, chemical etching, or laser processing are discussed and compared with numerical models. Guidelines to optimize the relevant physical parameters, such as the correlation length, optimal height of the nanostructures, and the surface defect densities for optoelectronic applications are given.

Light-emitting sources and devices permeate every aspect of our lives and are used in lighting, communications, transportation, computing, and medicine. Advances in multifunctional and “smart lighting” would require revolutionary concepts in the control of emission spectra and directionality. Such control might be possible with new schemes and regimes of light–matter interaction paired with developments in light-emitting materials. Here we show that all-dielectric metasurfaces made from III–V semiconductors with embedded emitters have the potential to provide revolutionary lighting concepts and devices, with new functionality that goes far beyond what is available in existing technologies. Specifically, we use Mie-resonant metasurfaces made from semiconductor heterostructures containing epitaxial quantum dots. By controlling the symmetry of the resonant modes, their overlap with the emission spectra, and other structural parameters, we can enhance the brightness by 2 orders of magnitude, as well as reduce its far-field divergence significantly.

We study light emission from square arrays of Mie-resonant silicon nanoantennas situated on a fluorescent glass substrate. When the spectral positions of the silicon nanoantennas' resonances overlap with the intrinsic emission from the glass, the emission is selectively enhanced for certain spectral and spatial frequencies detemined by the design of the nanoantenna array. We measure the emission spectra of the coupled system for a systematic variation of the nanoantenna geometry, showing that the spectral maximum of the emission coincides with the antenna resonance positions observed in linear-optical transmittance spectra. Furthermore, we study the directionality of the emission by back focal plane imaging and numerical calculations based on the Fourier modal method and the reciprocity principle. We observe that the nanoantenna array induces a reshaping of the resonantly enhanced emission in the air half-space into a narrow lobe directed out of the substrate plane. This reshaping is explained by coherent scattering of the emitted light in the nanoantenna array. Our results demonstrate that combining emission enhancement by magnetic dipolar Mie-type resonances of silicon nanoantennas with diffractive coupling in the periodic arrangement allows for the creation of flat light sources with tailored spectral and directional emission properties.

Black Silicon nanostructures are fabricated by Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) in a gas mixture of SF6 and O2 at non-cryogenic temperatures. The structure evolution and the dependency of final structure geometry on the main processing parameters gas composition and working pressure are investigated and explained comprehensively. The optical properties of the produced Black Silicon structures, a distinct antireflection and light trapping effect, are resolved by optical spectroscopy and conclusively illustrated by optical simulations of accurate models of the real nanostructures. By that the structure sidewall roughness is found to be critical for an elevated reflectance of Black Silicon resulting from non-optimized etching processes. By analysis of a multitude of structures fabricated under different conditions, approximate limits for the range of feasible nanostructure geometries are derived. Finally, the technological applicability of Black Silicon fabrication by ICP-RIE is discussed

We report on second harmonic generation in a photonic crystal L3 cavity drilled in a thin self-suspended lithium niobate membrane. The cavity, resonant for the pump beam in the telecom wavelength range, exhibits a quality factor of around 500. Second harmonic generation has been measured with a low power continuous laser. A conversion efficiency of 6.4×10-9 has been estimated with an input coupled power of 53 µW