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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.

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]

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%.

infrared photodetectors have been used extensively in biomedicine, surveillance, communication and astronomy. however, state of the art technology based on Ⅲ-Ⅴ and Ⅱ-Ⅵ compounds still lacks excellent performance for high-temperature operation. surface plasmon polaritons (spps) have demonstrated their capability in improving the light detection from visible to infrared wave range due to their light confinement in subwavelength scale. advanced fabrication techniques such as electron-beam lithography (ebl) and focused ion-beam (fib), and commercially available numerical design tool like finite-difference time-domain (fdtd) have enabled rapid development of surface plasmon (sp) enhanced photodetectors. in this review article, the basic mechanisms behind the sp-enhanced photodetection, the different type of plasmonic nanostructures utilized for enhancement, and the reported sp-enhanced infrared photodetectors will be discussed.

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]

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 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]

Metallic nanostructures have a variety of interesting properties and applications, especially as substrates for LSPR-based refractometric sensors for biological and chemical species. A common method for metal deposition is electron beam evaporation. However, this is limited to structures with heights on the order of tens of nanometers. Growth of tall structures for such sensors provides greater surface area for binding and increased interaction volume. Methods for creating taller structures are limited, with the most common method being electrodeposition. This is typically done on a nonconductive substrate by using a seed a layer of the metal to be grown, optionally with a thin adhesion layer using a metal such as chromium. In this work, we propose elimination of the need for a seed layer and its subsequent removal by directly electrodepositing onto a transparent conductive substrate suitable for plasmonic applications. [ABSTRACT FROM AUTHOR]

We report high quality InAsSb films grown on GaSb substrates using metal-organic chemical vapor deposition (MOCVD) technique through interface engineering. This work shows that the interface quality of the hetero-epitaxial InAsSb layer strongly depends on the V/III ratio during the growth and it plays a crucial role in the surface morphology, composition, and electrical and optical properties of InAsSb films. Furthermore, by properly engineering the interface conditions, high optical quality InAsSb films which show obvious mid-infrared emissions even at room temperature have been obtained. Therefore, this work provides a simple and feasible method for the growth of high quality InAsSb film which can be used for room temperature mid-infrared optoelectronics. [ABSTRACT FROM AUTHOR]

We developed a theoretical model based on 8-band k.p method to calculate the temperature-dependent band structure of Ge x Sn 1-x /Ge quantum well. The E-k dispersion relation is calculated using two different sets of Luttinger-Kohn’s Hamiltonian effective mass parameters. The spontaneous emission rate spectra including and excluding the contribution of indirect L subbands are compared. Instead of the expected direct band-gap energy transition, we observe indirect band-gap energy transitions which are verified by having abnormal temperature-dependent spontaneous emission rate even for large Sn fraction up to 24%. This phenomenon can be explained by the effect of quantum restriction and build-in compressive strain through our model which are the main obstacles for realizing direct band-gap GeSn/Ge quantum well. [ABSTRACT FROM AUTHOR]

Ge x Sn 1-x is one of the most promising materials in optoelectronics for its direct band-gap nature. In this paper, we report high-quality Ge and Sn thin films deposited on Si (001) substrates by magnetron sputtering. We found that the growth power and chamber pressure affect the quality of the Ge and Sn thin films significantly but in different ways. By optimizing the deposition conditions, high quality Ge and Sn films are achieved. A clear peak of Ge (004) phase in the x-ray diffraction (XRD) pattern which indicates a high-quality Ge lattice formed is observed, and post-treatment like rapid thermal annealing does not significantly affect the quality of the thin films. [ABSTRACT FROM AUTHOR]