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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]

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]

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 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 the effect of interface quality on the performance of InAsSb based hetero n-i -p middle wavelength infrared (MWIR) photodiodes. By adopting heavily doping wide bandgap p- and n-type layers and inserting a thin layer between the two doped layers and the absorbing InAsSb region, the interface quality can be improved. We also employed proper fabrication processes in device fabrication to improve surface quality. It is found that the improved interface and surface quality can reduce the noise current and enhance detection performance. A detectivity of ∼1.5 × 10 9 cmHz 1/2 W −1 can be achieved at room temperature, and it can be increased to ∼4.0 × 10 9 cmHz 1/2 W −1 at 250 K. [ABSTRACT FROM AUTHOR]

A passive scanning imaging system that can operate at multiband spectra covering infrared, THz, and MMW regions has been developed. A high-quality optical system, which consists of a scanning swing planar mirror and a concave mirror, is used to be compatible in different frequency ranges. An elliptical aperture is opened at the center of the swing mirror to allow the focused light to pass through. Four types of detectors that contain two homemade bolometric detectors are used to distinguish images that range from infrared to millimeter waves. Our results demonstrate that the reflection-type imaging system performs well and exhibits compatibility to operate at different frequencies. [ABSTRACT FROM AUTHOR]

The development of wide-band microwave absorbing materials based on carbonaceous fillers remains a great challenge. In this study, carbon nanotubes (CNT) assembled coronal hollow clusters with efficient microwave absorbing performance have been obtained through successive hydrothermal and calcination process. Microstructural analysis reveals the distinct features of multiple assembly structures in the fabricated materials. The electromagnetic responses of Ni/CNT assembled clusters were examined across a frequency range of 2–18 GHz. Results demonstrate that the microwave frequency dispersion of electromagnetic parameters and reflection loss of Ni/CNT clusters are strongly influenced by weight loading. Multi-absorbing peaks with reflection loss better than − 40 dB could be achieved, while the equivalent absorbing band for RL < −10 dB covers 3.2–18 GHz, which account for 92.5% of the whole evaluated frequency range, and 62.5% for condition of RL < −20 dB. Furthermore, intrinsic attenuation beyond thickness derived semi-wavelength resonant absorption makes a major contribution to this superior performance. The underlying mechanism of dielectric response was investigated through Cole-Cole analysis and finite element simulation. 'Micro-dipoles' relaxation and hopping relaxation originated from defects within CNT and barrier between CNT, while the high magnetic dissipation capability of Ni nanoparticles make a major contribution to overall absorbing performance. All these are beneficial to regulation and optimization of microwave absorption performance of novel Ni/ CNT functionalized multistage architecture. [Display omitted] • Ni/CNT clusters were prepared through a sample solvothermal method; • Carbon nanotubes were assembled in situ into coronal hollow spherical multilayer carbon nanotube clusters; • The absorption efficiency of CNT is improved by anisotropic strong dielectric loss and multi-layer structure. • The microwave absorption of the new Ni/ CNT functionalized multistage structure greatly improves the performance. [ABSTRACT FROM AUTHOR]

Ringent hollow carbons synthesised by CDs through controllable reaction temperatures show great absorbing values and absorbing bands as well as relative compression ratios of radar cross section. Finite element simulation demonstrats that unique structure of ringent hollow carbons can lower normal reflected wave and promote energy attenuation which provides a new direction for the structural design of absorbers. [Display omitted] • A high-yield of carbon quantum dots derived ringent hollow carbon spheres (RHCs) for efficient microwave absorber has been proposed. • Outstanding microwave absorbing performance with optimal reflection loss of −67 dB as well as superior absorbing bandwidth (covering C, X and Ku band) could be achieved. • A relative compression ratio of 56.7 % of of RHCs loaded coating could be achieved due to ringent hollow structure and intrinsic nanosheets attenuation. Carbon nanomaterials have steadily grown into a class of composite absorbers with remarkable properties due to their unique structure, low density, high specific surface area, strong electrical conductivity, and substantial dielectric losses. In this paper, a facile strategy with low-cost, high-efficiency, and scalable strategy for carbon dots-derived ringent hollow carbon (RHC) for superior microwave absorption is proposed. Controllable structures ranging from amorphous carbon to ringent hollow carbon are well performed through simple heat-treated temperature. In addition, an optimal absorption value of −67 dB and a superior absorption band width covering the C, X, and Ku bands, as well as a relative compression ratio of 56.7 percent in the case of perpendicular incidence, have been achieved. Further, finite element simulations have demonstrated that the unique structure of partially ringent hollow carbon is considered as an effective way to lower normal reflected wave and promote energy attenuation. New applications of carbon dots-derived RHC as superior microwave absorbers are opening up, and the scalable strategy may pave a solid foundation for rapid applications. [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 prepare undoped Mn 1.5 Co 1 Ni 0.5 O 4 and Cu and Sc co-doped Mn 1.5 Co 1 Ni 0.25 Cu x Sc 0.25−x O 4 (x = 0.05, 0.1, 0.15) films on Al 2 O 3 substrate by chemical solution deposition method. The crystallinity, surface morphologies, electrical transport property, optical property, and 1/ f noise property of these films are characterized. It shows that the Mn 1.5 Co 1 Ni 0.25 Cu 0.15 Sc 0.1 O 4 film possesses excellent electrical transport, optical and 1/ f noise properties compared with the other films. The absolute temperature coefficient of resistance and characteristic temperature of the Mn 1.5 Co 1 Ni 0.25 Cu 0.15 Sc 0.1 O 4 film are higher than that of Mn 1.5 Co 1 Ni 0.5 O 4 film, while its resistivity of 250 Ω·cm at 295 K is half of that Mn 1.5 Co 1 Ni 0.5 O 4 film. The transmittance and reflectance spectra of the films are measured and analyzed in the range of 0.55–2.0 µm, all the films show similar absorption structures in the measured spectrum. The 1/ f noise of the co-doped Mn 1.5 Co 1 Ni 0.5 O 4 films decreases significantly. The (γ/n)0.5/| TCR | value of the Mn 1.5 Co 1 Ni 0.25 Cu 0.15 Sc 0.1 O 4 reaches 2.3 × 10−12 cm1.5 K/% at 295 K, which is two orders lower than that of Mn 1.5 Co 1 Ni 0.5 O 4 film. Our results discover a thermosensitive material with excellent performance, which is expected to be applied to high performance uncooled infrared detectors. • We did a complete and systematic study for the Cu and Sc co-dopants effects on the electrical transport, optical, and low-frequency noise properties of Mn 1.5 Co 1 Ni 0.5 O 4 (MCN) thin films. • Mn 1.5 Co 1 Ni 0.25 Cu 0.15 Sc 0.1 O 4 thin film was found to be excellent electrical transport, optical and low-frequency noise performance, and we investigated and discussed the mechanisms of enhanced performance of the Cu and Sc co-doped MCN films. • The optical and low-frequency noise properties of Cu and Sc Co-doped MCN films were studied for the first time. • This study provides an insight to understand the effects of Cu and Sc co-dopants on Mn 1.5 Co 1 Ni 0.5 O 4 thin films, which has great significance for preparing high-performance uncooled infrared detectors based on MCN films. [ABSTRACT FROM AUTHOR]