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Introducing super‐resolution techniques to imaging through scattering media potentially revolutionizes the technical analysis for many exotic applications, such as cell structures behind biological tissues. The main challenge is scattering media's inhomogeneous structures, which scramble the light path and create noise‐like speckle patterns, hindering object's visualization even at a low‐resolution level. Here, a computational method is proposed relying on the object's spatial and temporal fluctuation to visualize nanoscale objects through scattering media non‐invasively. Taking advantage of the optical memory effect and multiple frames, the point spreading function (PSF) of scattering media is estimated. Multiple images of fluctuating objects are obtained by deconvolution; then, the super‐resolution image is achieved by computing the higher‐order cumulants. Non‐linearity of high order cumulant significantly suppresses artifacts in the resulting images and enhances resolution by a factor of N$\sqrt N $, where N is the cumulant order. The proof‐of‐concept demonstrates a resolution of 266 nm at the 6th‐order cumulant with numerical aperture (NA) of 0.42, breaking the diffraction limit by a factor of 2.45. An adaptive approach is also demonstrated for imaging through dynamic scattering media. The non‐invasive super‐resolution speckle fluctuation imaging (NISFFI) presents a nanoscopy technique with straightforward imaging hardware configuration to visualize samples behind scattering media. [ABSTRACT FROM AUTHOR]

The article titled "Non-Invasive Super-Resolution Speckle Fluctuation Imaging" discusses a technique called non-invasive super-resolution speckle fluctuation imaging (NISSFI) that allows for the visualization of objects behind scattering media with sub-diffraction-limit resolution. By analyzing multiple speckle patterns from a fluctuating object within the optical memory effect region, high order cumulants are computed to reconstruct an image with reduced noise and improved resolution. The authors suggest that NISSFI has the potential for various applications, including nanometer-level resolution imaging of biological samples, tissues, bacteria, or viruses under the skin. [Extracted from the article]

Charge transfer plasmons (CTPs) in coupled plasmonic cavities have gained attention for their interesting resonance mechanisms and potential applications in sensing. The authors present the first investigation of the CTP mode in top‐down fabricated tall plasmonic nanostructures with deep nanogaps, whose excitation becomes possible by the interaction of transversal and longitudinal plasmonic modes. Hybridization of dipole and CTP modes at different parts of the plasmonic nanostructures, for both capacitively coupled dimer of sub‐5 nm gap and conductively coupled dimer with junction bridge is extensively studied. Importantly, the authors demonstrate the conditional emergence of a hybrid dimer‐CTP mode based on the cladding refractive index and analyte thickness, which can present an opportunity for highly specific surface sensing applications. The sensing performances of these modes are evaluated, showing a figure‐of‐merit of ≈18.4 and Q≈ 44 for the hybrid dimer‐CTP mode in the visible spectrum. Surface sensing based on alkanethiol adsorption shows surface sensitivity as high as ≈3.2 nm/carbon‐chain for this mode, which is higher than the typical values obtained by LSP structures. [ABSTRACT FROM AUTHOR]

Achieving high transmission of light through a highly conductive structure implemented on a semiconductor remains a challenge in optoelectronics as the transmission is inevitably deteriorated by absorption and Fresnel reflection. There have been numerous efforts to design structures with near-unity transmission, yet they are typically constrained by a trade-off between conductivity and optical transmission. To address this problem, we propose and demonstrate a transmission mechanism enabled by a monolithic GaSb subwavelength grating integrated with Au stripes (metalMHCG). Near-unity transmission of polarized light is achieved by inducing low-quality factor resonance in the air gaps between the semiconductor grating stripes, which eliminates light absorption and reflection by the metal. Our numerical simulation shows 97% transmission of transverse magnetic polarized light and sheet resistance of 2.2 ΩSq−1. The metalMHCG structure was realized via multiple nanopatterning and dry etching, with the largest transmission yet reported of ∼90% at a wavelength of 4.5 µm and above 75% transmission in the wavelength range from 4 to 10 µm and sheet resistance at the level of 26 ΩSq−1. High optical transmission is readily achievable using any high refractive index materials employed in optoelectronics. The design of the metalMHCG is applicable in a wide electromagnetic spectrum from near ultraviolet to infrared. [ABSTRACT FROM AUTHOR]

We report a detailed comparative investigation of resonance behaviors and sensing capability of gold U-shape spilt-ring resonator (U-SRR) and fourfold rotated SRR (U4-SRR) metasurfaces in near- and middle-infrared (IR) range. All the resonant modes of the U4-SRR metasurfaces occur at longer wavelengths compared to the U-SRR metasurfaces with the same U size. Stronger field intensities are observed in all the three resonance modes of the U4-SRR metasurfaces and the intensity in the fundamental magnetic (m0) mode is almost three times of that of U-SRR metasurface under unpolarized incidence. All the three peak resonance wavelengths shift to longer wavelengths and the sensitivity increases with the increase of U size. A sensitivity of 642 nm RIU−1 is obtained in the U4-SRR metasurface for unpolarized incidence. This provides an excellent candidate for high performance sensing in the near- and mid-IR regions without polarization concern. [ABSTRACT FROM AUTHOR]

The nanoscale confinement of plasmonic fields, coupled with their high susceptibility to refractive index changes, makes localized surface plasmons (LSPs) an excellent platform for rapid and label‐free sensing. However, the small spatial overlap of the LSP fields with the adsorbed analyte dictates the sensitivity and figure of merit (FOM) of LSP‐based sensing. The linear dependence of sensitivity on resonance wavelength, coupled with the dependence of FOM on the achievable resonance Q factor, leads to a sensitivity of ≈100–300 nm per RIU and FOM < 5 for gold‐based LSP resonance in the visible range. This presents a dilemma for the realization of a practical sensing platform that requires high sensitivity and high FOM in the visible spectrum. Higher sensitivity and resonance Q factor can be achieved with a larger interaction volume between the plasmonic field and the analyte. This work explores a hybrid mode resulting from an interaction between transverse LSP and longitudinal Fabry–Perot (FP) modes, capable of improving the sensitivity and FOM simultaneously. This hybrid mode is demonstrated in tall v‐shaped split ring resonator structures, fabricated via seedless pulsed gold electrodeposition, with FOM of ≈24 in the visible range. [ABSTRACT FROM AUTHOR]

We report high quality GeSn/GaAs heterostructure photodetectors grown by a modified magnetron sputtering system. A metal-semiconductor-metal photoconductor is fabricated to examine the ability of photodetection for GeSn alloy. Then the GeSn/GaAs heterostructure photodetector is first demonstrated with a detectivity of $1.8\times 10^{9}$ Jones achieved at 1450 nm under an applied reverse voltage bias of −0.1 V, which is comparable to or even better than the GeSn-based photodetectors grown by chemical vapor deposition. The work provides an alternative technique for low cost and large-area fabrication of GeSn based devices. [ABSTRACT FROM AUTHOR]

The collective oscillation of plasmons in metallic nanostructures generates localized surface plasmons (LSP), which are responsive to their surrounding dielectric environment and can be used for low-cost, label-free sensing platforms. However, the inherently short evanescent decay field saturates the optical response within 10–30 nm of the metal surface, hindering multi-layered functionalization strategies typically used for specific binding due to its limited surface proximity. In this work, we propose the use of tall nanostructures to engineer the plasmonic response for biosensing applications. The resonance mode characteristics are investigated, where the emergence of hybrid modes is found to arise from the decoupling of localized plasmon modes at increasing antenna height. Using high aspect ratio plasmonic nanostructures, we demonstrate its viability with up to 4.3 $\times$ higher sensitivity and 18.4 $\times$ higher figure of merit within the visible range. Coupled with a cost-effective fabrication method, the height provides an additional degree of freedom for tailoring the optical spectrum. [ABSTRACT FROM AUTHOR]

Strong plasmon–exciton interactions in monolayer transition‐metal dichalcogenides (TMDs) is emerging as a promising material platform for light emissions, nonlinear optics, and quantum communications, and their realizations require highly localized electric fields parallel to the transition dipole moment of TMD excitons. Here, a systematic study of light–matter interaction in planar dimer nanoantenna of nanoscale gaps coupled with monolayer WS2 is presented, where the effects of the local field enhancement and spatial mode overlap in the plasmon–exciton coupling strength are experimentally investigated. Importantly, anticrossing behaviors in the strong coupling regime with a Rabi splitting of Ω = 118 meV for gold bowtie antennas with 7 nm gaps and Ω = 138 meV for gold dimer arrays with 10 nm gaps are demonstrated. [ABSTRACT FROM AUTHOR]

We report the growth of direct bandgap single-crystalline Ge1−xSnx thin films on unheated substrates by a modified magnetron sputtering system. The Ge1−xSnx thin films were deposited on Si, Ge, and GaAs substrates at room temperature. They were characterized by X-ray diffraction and X-ray photoelectron spectroscopy that revealed the existence of Ge1−xSnx (004) peak and Ge-Sn bonds. Transmission and photoluminescence (PL) measurements confirm the direct bandgap dominated transition, and the bandgap values obtained are in agreement with the results calculated by 8-band k.p method. This article provides a simple and cost-effect way for fabrication direct bandgap GeSn films. [ABSTRACT FROM AUTHOR]

We comprehensively study the characteristics of dark current for a p-i-n heterostructure photodiode. To reduce the dark current, a wide-bandgap layer (AlGaSb) and thin quaternary layers (AlInAsSb) are inserted in the heterostructure for blocking the dark carrier diffusion and limiting type-II transition at interface, respectively. The activation energy derived from measurement results indicates the positive (negative) correlation between the dominant dark current density and voltage bias (temperature). Whatever the voltage bias (temperature), this relationship always exists, indicating the high stability and reliability of our devices. Indeed, the measures taken for reducing dark current are confirmed to be effective as the dark current density for this photodiode is limited to a lower level. For the typical square mesa with 350 μm side length, at the bias of −0.4 V, the dark current density is 1.78 A/cm2 for T=293 K, and reduces to 0.4 A/cm2 for T=77 K, where the room-temperature value is lower than or comparable with that of the state-of-the-art mid-infrared photodetectors. A room-temperature detectivity of 8.3 × 108 cm ⋅ Hz1/2/W with a cut-off wavelength of 4μm is demonstrated. [ABSTRACT FROM AUTHOR]

We extend the previous 30-band k ⋅ p model effectively employed for relaxed Ge1-xSnx alloy to the case of strained Ge1-xSnx alloy. The strain-relevant parameters for the 30-band k ⋅ p model are obtained by using linear interpolation between the values of single crystal of Ge and Sn that are from literatures and optimizations. We specially investigate the dependence of band-gap at L-valley and Γ-valley with different Sn composition under uniaxial and biaxial strain along [100], [110] and [111] directions. The good agreement between our theoretical predictions and experimental data validates the effectiveness of our model. Our 30-band k ⋅ p model and relevant input parameters successfully applied to relaxed and strained Ge1-xSnx alloy offers a powerful tool for the optimization of sophisticated devices made from such alloy. [ABSTRACT FROM AUTHOR]

Half-wave plate (HWP) is one of the key polarization controlling devices in optical systems. The conventional HWPs based on birefringent crystals are inherently bulky and difficult to be monolithically integrated with other optical components. In this work, metasurface-based HWPs with high compactness are demonstrated on a 12-inch silicon complementary metal-oxide-semiconductor platform. Three-dimensional finite difference time domain simulation is used to design the nanostructure and investigate the impact of fabrication process variation on the device performance. In addition, the cross- and co-polarization transmittance (Tcross and Tco) of the HWPs located at different wafer locations are characterized experimentally. The peak Tcross and valley Tco values of 0.69 ± 0.053 and 0.032 ± 0.005 are realized at the wavelength around 1.7 μm, respectively. This corresponds to a polarization conversion efficiency of 95.6% ± 0.8%. [ABSTRACT FROM AUTHOR]

To eliminate spurious solutions in the multiple-band k·p theory, we developed the Fourier transform-based k·p approach through combining the Fourier transform technique with Burt-Foreman operator ordering. The performance is perfect for the six-band k·p calculation, and the spurious solutions in the conduction band met in the eight-band calculation can also be easily screened away in the inborn cut-off step in FTM, i.e., choosing a proper order of Fourier truncation. Truncating high-order terms of Fourier coefficients of the envelope function prevents the occurrence of a wild-spreading spectrum of the Fourier expansion coefficients, which can be taken as the signature of spurious solutions. [ABSTRACT FROM AUTHOR]

This Special Issue is associated with the 10th International Conference on Materials for Advanced Technologies (ICMAT), Symposium C: Semiconductor Photonics held on 23–28 June, 2019 at Marina Bay Sands in Singapore. Organised through the Materials Research Society of Singapore (MRS-S), ICMAT has been held since 2001 and has attracted strong interest amongst the global materials science and engineering research communities. The 10th conference in the ICMAT series attracted over 3,500 delegates with a number of keynote and plenary presentations notably including four Nobel Laureates in Physics and Chemistry. The ICMAT conference consists of a number of topical symposia. Symposium C was organized jointly with Australian MRS and co-chaired by Professors Dao-Hua Zhang (NTU, Singapore), Chennupati Jagadish (ANU, Australia), Stephen J. Sweeney (University of Surrey, UK), Boon S. Ooi (KAUST, Saudi Arabia), Hao Gong (NUS, Singapore) and Weijun Fan (NTU, Singapore). The Symposium focused on recent developments in materials for applications in photonic devices covering systems including III-V and II-VI semiconductors, group IV alloys for silicon compatibility, oxides and perovskites for solar cell and emitter applications, quantum dot based devices and in general a wide variety of organic and inorganic materials spanning applications from the ultra-violet through to the mid-infrared. In total, 20 invited and 53 oral and 19 poster papers were presented over the four days of technical sessions. [ABSTRACT FROM AUTHOR]

We present the design, fabrication, and characterization of middle-wavelength infrared photodetector based on active InAs0.9Sb0.1-based hetero-p-i-n structure grown on GaSb substrate. In this structure, the active absorption layer is sandwiched between thin quaternary p-type and n-type AlInAsSb layers and a heavily doped AlGaSb layer is introduced to reduce dark current. We observed good lattice matching between GaSb substrates and epitaxial layers by high-resolution X-ray diffraction. Photoluminescence (PL) spectrum at 13 K shows a full width at half maximum of ~ 29 meV, demonstrating good quality active absorption layers. The band gap energy of InAs0.9Sb0.1 is derived as ~ 0.322 eV at 0 K by Varshni fitting from PL spectra at different temperatures. A rather flat room-temperature responsivity of ~ 0.8-0.9 AW−1 over a wavelength range of ~ 2.1 µm is demonstrated without antireflection coating. A detectivity of 8.9 × 108 cm Hz1/2 W−1 at 3.5 µm for room-temperature operation is achieved under applied bias of − 0.5 V. [ABSTRACT FROM AUTHOR]

Middle wavelength infrared (MWIR) photodetectors have a wide range of applications, but almost all of them operate at low temperature due to the limit of materials and device structures. The capability of plasmonic structures to localize electromagnetic wave on the deep subwavelength scale provides the possibility for MWIR photodetectors operating at room temperature. Here, we report a high sensitivity room temperature MWIR photodetector which is an InAs0.91Sb0.09-based heterojunction n-i-p photodiode integrated with a Au-based two-dimensional subwavelength hole array (2DSHA). A room temperature detectivity of 0.8 × 1010 cm Hz1/2 W−1 and a response time of 600 ns are achieved. The non-cooling high performance of 2DSHA-InAs0.91Sb0.09 based heterojunction photodetectors will make their applications easier, broader, and economic. [ABSTRACT FROM AUTHOR]

We present a simple thermal treatment with the antimony source for the metal-organic chemical vapor deposition of thin GaSb films on GaAs (111) substrates for the first time. The properties of the as-grown GaSb films are systematically analyzed by scanning electron microscopy, atomic force microscopy, x-ray diffraction, photo-luminescence (PL) and Hall measurement. It is found that the as-grown GaSb films by the proposed method can be as thin as 35 nm and have a very smooth surface with the root mean square roughness as small as 0.777 nm. Meanwhile, the grown GaSb films also have high crystalline quality, of which the full width at half maximum of the rocking-curve is as small as 218 arcsec. Moreover, the good optical quality of the GaSb films has been demonstrated by the low-temperature PL. This work provides a simple and feasible buffer-free strategy for the growth of high-quality GaSb films directly on GaAs substrates and the strategy may also be applicable to the growth on other substrates and the hetero-growth of other materials. [ABSTRACT FROM AUTHOR]

We propose a figure of merit (FoM) to optimize the multilayered metal–dielectric (MD) structure for subwavelength imaging. The proposed FoM accounts both the waveguiding and transmission properties of the multilayered MD structure. We numerically demonstrate that the FoM can be used to find the optimized geometry parameters, as well as the optimized working wavelength. Such a FoM can act as an efficient tool for design and fabrication of the multilayered MD lenses. [ABSTRACT FROM PUBLISHER]

This paper presents the capability of sonicated cold development process for sub-40-nm pitch metal dots patterning with potentially ∼100 times shorter writing time, where lift-off pattern transfer of ∼10-nm-sized metal dots at pitch as short as ∼34 nm from 110-nm-thick positive-tone resist is demonstrated with good repeatability. Strategies to achieve sub-30-nm pitch are also discussed based on overlay nanofabrication approaches, which we believe could pave the way toward cost-effective 1 Tbit/in ^2 bit-patterned-media patterning. [ABSTRACT FROM PUBLISHER]

A 3-D, fully vectorial optical numerical model is used to design a high contrast grating for use as the top mirror of a 980-nm arsenide-based vertical-cavity surface-emitting laser. We study the parameters of two high contrast gratings made from GaAs/AlOx and Si/SiO x, respectively. Parameters providing high degrees of reflectivity, high levels of polarization discrimination, and fine tuning of the reflectivity of the high contrast grating are determined. The results demonstrate that both configurations if carefully designed by advanced numerical models can offer better performance in comparison to conventional distributed Bragg reflectors. [ABSTRACT FROM PUBLISHER]

Split ring resonator (SRR) metamaterials working in the visible spectrum have great potential applications, but their fabrication is challenging due to the stringent requirements in the feature size and critical dimension. This paper reports fabrication and systematic characterization of silver SRRs with sub‐100‐nm sizes that can have magnetic resonance entering into the visible frequency spectrum. SRR size as small as ∼60 nm and fundamental magnetic resonance (LC‐resonance) as short as ∼604 nm have been successfully demonstrated, which to the best of our knowledge represent the smallest fabricated SRR and the shortest LC‐resonance based on SRR geometry. The resonance wavelengths of the LC and plasmon modes of the sub‐100‐nm SRRs are found to linearly decrease with SRR size. Excellent agreement between LC‐model and experimental data is obtained when the capacitance of the sub‐100‐nm SRRs is interpreted as capacitance between two spheres instead of between two parallel plates. [ABSTRACT FROM AUTHOR]

We show the increase of the photoluminescence intensity ratio (PLR) and the emission rate enhancement of perovskite cesium lead bromide (CsPbBr3) and formamidinium lead bromide (FAPbBr3) nanocrystals (NCs) in the presence of single and double gold layer cavities, which we refer to as Metal-Emitter (ME) and Metal-Emitter-Metal (MEM) nanostructures. Up to 1.9-fold PLRs and up to 5.4-fold emission rate enhancements were obtained for FAPbBr3 NCs confined by double gold layers, which are attributed to plasmonic confinement from the gold layers. The experimentally obtained values are validated by analytical calculations and electromagnetic simulations. Such an effective method of manipulation of the spontaneous emission by simple plasmonic nanostructures can be utilized in sensing and detection applications. [ABSTRACT FROM AUTHOR]

Surface effects in atomically flat colloidal CdSe nanoplatelets (NLPs) are significantly and increasingly important with their thickness being reduced to subnanometer level, generating strong surface related deep trap photoluminescence emission alongside the bandedge emission. Herein, colloidal synthesis of highly luminescent two‐monolayer (2ML) CdSe NPLs and a systematic investigation of carrier dynamics in these NPLs exhibiting broad photoluminescence emission covering the visible region with quantum yields reaching 90% in solution and 85% in a polymer matrix is shown. The astonishingly efficient Stokes‐shifted broadband photoluminescence (PL) emission with a lifetime of ≈100 ns and the extremely short PL lifetime of around 0.16 ns at the bandedge signify the participation of radiative midgap surface centers in the recombination process associated with the underpassivated Se sites. Also, a proof‐of‐concept hybrid LED employing 2ML CdSe NPLs is developed as color converters, which exhibits luminous efficacy reaching 300 lm Wopt−1. The intrinsic absorption of the 2ML CdSe NPLs (≈2.15 × 106 cm−1) reported in this study is significantly larger than that of CdSe quantum dots (≈2.8 × 105 cm−1) at their first exciton signifying the presence of giant oscillator strength and hence making them favorable candidates for next‐generation light‐emitting and light‐harvesting applications. [ABSTRACT FROM AUTHOR]

Strong plasmonic resonance in the visible spectrum requires high aspect ratio metallic resonators with deep subwavelength dimensions, which find applications as part of a cost‐effective and practical optics‐based sensing platform. Electrodeposition is a highly suitable method for fabricating such structures as it allows deposition of metals with much larger thickness and better morphology than that achieved by physical deposition. Herein are presented an in‐depth study of pulsed electrodeposition of a gold film directly onto a transparent substrate without a seed layer and the development of a reliable and efficient fabrication method for high aspect ratio metallic nanostructures with sub‐10 nm features. Based on this approach, a low‐cost fabrication of sub‐100 nm metallic nanostructures is demonstrated with a very high deposition rate (up to 7 nm per pulse), yet with good surface morphology. Specifically, high aspect ratio rotationally symmetric plasmonic nanostructures suitable for a practical sensing platform are realized, exhibiting strong resonances in the visible spectrum with Q factors as high as 10 under unpolarized excitation. Pulsed electrodeposition is used to grow gold films directly onto indium tin oxide‐coated glass using various pulse parameters, and the results are compared using spectroscopy and electron microscopy. A suitable set of pulse parameters is then used to vertically grow gold nanostructures through a template, showing superior spectral characteristics to their planar conventionally deposited counterparts. [ABSTRACT FROM AUTHOR]