Efficient Multiterminal Spectrum Splitting via a Nanowire Array Solar Cell

Nanowire-based solar cells opened a new avenue for increasing conversion efficiency and rationalizing material use by growing different III-V materials on silicon substrates. Here, we propose a multiterminal nanowire solar cell design with a theoretical conversion efficiency of 48.3% utilizing an efficient lateral spectrum splitting between three different III-V material nanowire arrays grown on a flat silicon substrate. This allows choosing an ideal material combination to achieve the proper spectrum splitting as well as fabrication feasibility. The high efficiency is possible due to an enhanced absorption cross-section of standing nanowires and optimization of the geometric parameters. Furthermore, we propose a multiterminal contacting scheme that can be fabricated with a technology close to standard CMOS. As an alternative we also consider a single power source with a module level voltage matching. These new concepts open avenues for next-generation solar cells for terrestrial and space applications

Mie Scattering for Photonic Devices

Mie scattering is increasingly exploited to manipulate electromagnetic fields to achieve strong resonant enhancement, to obtain perfect absorption of radiation, and to generate polarization or wavelength selectivity and/or sensitivity. In fact, a multitude of photonic applications are arising that benefit from Mie scattering and have already led to the formation of novel image and hologram schemes or to the design of efficient and compact photodetectors and light sources. Here, the Mie scattering theory for spherical scatterers is reviewed, the basics of the field-decomposition onto the Mie modes are shown, and dielectric and metallic particles are compared. Recent applications for light spectrum control, detection, non-linear effects enhancement, and emission are reviewed. How a periodic arrangement of Mie-scatterers can be utilized to create a strong (in the order of 10 to 100) absorption enhancement in otherwise weakly absorbing layers is also demonstrated. The enhancement dependence on the diameter-to-wavelength ratio of the scatterer is analyzed, and how the influence of different Mie-modes can be distinguished in the periodic array by looking at the field components normal to the scatterer surface is discussed.ISSN:1863-8880ISSN:1863-889

Design of CMOS-compatible metal–insulator–metal metasurfaces via extended equivalent-circuit analysis

Photonic metasurfaces compatible with large-scale production such as CMOS are of importance because they promise cointegration of electronics with photonics for detection, communication and sensing. The main challenges on the way of designing such metasurfaces are: (1) large variety of possible geometrical shapes of metasurface elements that makes finding the most appropriate shape difficult; (2) poor compatibility of available electronic layer stacks with photonics. In this paper we show how to address both of these challenges utilizing extended equivalent-circuit analysis. In a first step we classify the behavior of different metasurfaces using the equivalent circuit. We discover that metasurfaces that use inverted-dipole resonator type exhibit higher tolerance to dielectric spacer thickness, higher angular stability and have similar resonance quality-factor as other types. In the second step we utilize the equivalent-circuit scheme to efficiently optimize the parameters of inverted-dipole based metasurfaces for a layer stack such as given in a CMOS process. Finally, as an example we demonstrate how an inverted-cross structure can be adapted to a commercial 110 nm CMOS process with Al metal layers. We measured peak absorption above 90% at center wavelength around 4 µm with quality factor of approximately 5 and angular stability larger than 60°.ISSN:2045-232

Compact Mid-Infrared Gas Sensing Enabled by an All-Metamaterial Design

The miniaturization of mid-infrared optical gas sensors has great potential to make the “fingerprint region” between 2 and 10 μm accessible to a variety of cost-sensitive applications ranging from medical technology to atmospheric sensing. Here we demonstrate a gas sensor concept that achieves a 30-fold reduction in absorption volume compared to conventional gas sensors by using plasmonic metamaterials as on-chip optical filters. Integrating metamaterials into both the emitter and the detector cascades their individual filter functions, yielding a narrowband spectral response tailored to the absorption band of interest, here CO2. Simultaneously, the metamaterials’ angle-independence is maintained, enabling an optically efficient, millimeter-scale cavity. With a CO2 sensitivity of 22.4 ± 0.5 ppm·Hz–0.5, the electrically driven prototype already performs at par with much larger commercial devices while consuming 80% less energy per measurement. The all-metamaterial sensing concept offers a path toward more compact and energy-efficient mid-infrared gas sensors without trade-offs in sensitivity or robustness.ISSN:1530-6984ISSN:1530-699

On-Chip Narrowband Thermal Emitter for Mid-IR Optical Gas Sensing

Efficient light sources compatible to complementary metal oxide semiconductor (CMOS) technology are key components for low-cost, compact mid-infrared gas sensing systems. In this work we present an on-chip narrowband thermal light source for the mid-infrared wavelength range by combining microelectromechanical system (MEMS) heaters with metamaterial perfect emitter structures. Exhibiting a resonance quality factor of 15.7 at the center wavelength of 3.96 μm and an emissivity of 0.99, the demonstrated emitter is a spectrally narrow and efficient light source. We show temperature-stable (resonance wavelength shift 0.04 nm/°C) and angular-independent emission characteristics up to angles of 50° and provide an equivalent circuit model illustrating the structure’s resonance behavior. Owing to its spectrally tailored, nondispersive emission, additional filter elements in a free-space optical gas sensing setup become obsolete. In a proof-of-concept demonstration of such a filter-free gas sensing system with CO₂ concentrations in the range of 0–50000 ppm, we observe a 5-fold increase in relative sensitivity compared to the use of a conventional blackbody emitter. Our light source is fully compatible with standard CMOS processes and tunable in emission wavelength through the mid-infrared wavelength band. It paves the way for a new class of highly integrated, low-cost optical gas sensors

Highly Responsive Mid-Infrared Metamaterial Enhanced Heterostructure Photodetector Formed out of Sintered PbSe/PbS Colloidal Quantum Dots

Efficient and simple-to-fabricate light detectors in the mid infrared (MIR) spectral range are of great importance for various applications in existing and emerging technologies. Here, we demonstrate compact and efficient photodetectors operating at room temperature in a wavelength range of 2710–4250 nm with responsivities as high as 375 and 4 A/W. Key to the high performance is the combination of a sintered colloidal quantum dot (CQD) lead selenide (PbSe) and lead sulfide (PbS) heterojunction photoconductor with a metallic metasurface perfect absorber. The combination of this photoconductor stack with the metallic metasurface perfect absorber provides an overall ∼20-fold increase of the responsivity compared against reference sintered PbSe photoconductors. More precisely, the introduction of a PbSe/PbS heterojunction increases the responsivity by a factor of ∼2 and the metallic metasurface enhances the responsivity by an order of magnitude. The metasurface not only enhances the light–matter interaction but also acts as an electrode to the detector. Furthermore, fabrication of our devices relies on simple and inexpensive methods. This is in contrast to most of the currently available (state-of-the-art) MIR photodetectors that rely on rather expensive as well as nontrivial fabrication technologies that often require cooling for efficient operation.ISSN:1944-8244ISSN:1944-825