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1. Epitaxial Growth and Characterization of AlInN-Based Core-Shell Nanowire Light Emitting Diodes Operating in the Ultraviolet Spectrum

   https://doi.org/10.1038/s41598-020-59442-0  

   Velpula, Ravi Teja ; Jain, Barsha ; Philip, Moab Rajan ; Nguyen, Hoang Duy ; Wang, Renjie ; Nguyen, Hieu Pham ( December 2020 , Scientific Reports)

   null (Ed.)

   Abstract We report the demonstration of the first axial AlInN ultraviolet core-shell nanowire light-emitting diodes with highly stable emission in the ultraviolet wavelength range. During epitaxial growth of the AlInN layer, an AlInN shell is spontaneously formed, resulting in reduced nonradiative recombination on the nanowire surface. The AlInN nanowires exhibit a high internal quantum efficiency of ~52% at room temperature for emission at 295 nm. The peak emission wavelength can be varied from 290 nm to 355 nm by changing the growth conditions. Moreover, significantly strong transverse magnetic (TM) polarized emission is recorded, which is ~4 times stronger than the transverse electric (TE) polarized light at 295 nm. This study provides an alternative approach for the fabrication of new types of high-performance ultraviolet light emitters. 

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2. Large‐Area Heteroepitaxial Nanostructuring of Molecular Semiconductor Films for Enhanced Optoelectronic Response in Flexible Electronics

   https://doi.org/10.1002/adfm.202113085  

   Park, Kwang‐Won ; Vijayan, Raaghesh ; Andrew, Trisha L. ( February 2022 , Advanced Functional Materials)

   Organized nano‐ and microstructures of molecular semiconductors display interesting optical and photonic properties, and enhanced charge carrier mobilities, as compared to disordered thin films. However, known directed‐growth and self‐organization strategies cannot create structured molecular heterojunctions and cannot be practically incorporated into existing device fabrication routines to create large‐area optoelectronic devices. Here, an ultrathin (<2 nm) seed layer of the compound coronene creates 1D nanostructures of an electron‐transporting molecule (IFD) is shown, which possesses an intrinsic proclivity to form disordered thin films in the absence of the seed layer. It is revealed that nanostructured IFD films exhibit enhanced light absorption and emission, and greater electron mobilities, as compared to amorphous counterparts. This seed layer strategy creates uniform IFD nanowires over large areas of up to 18 mm²at low processing temperatures. Notably, the coronene seed layer creates IFD nanowires when applied over either oxide surfaces or predeposited organic layers, meaning that this structuring approach can be integrated into diode manufacturing routines to realize large‐area flexible optoelectronic devices. Flexible organic light‐emitting diodes and fullerene‐free organic solar cells containing IFD nanowires in the photoactive layer to demonstrate that molecular nanostructures can lead to robust, large‐area device arrays on flexible substrates being fabricated.

    

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3. Shallow-etched thin-film lithium niobate waveguides for highly-efficient second-harmonic generation

   https://doi.org/10.1364/OE.395545  

   Zhao, Jie ; Rüsing, Michael ; Javid, Usman A. ; Ling, Jingwei ; Li, Mingxiao ; Lin, Qiang ; Mookherjea, Shayan ( June 2020 , Optics Express)

   High-fidelity periodic poling over long lengths is required for robust, quasi-phase-matched second-harmonic generation using the fundamental, quasi-TE polarized waveguide modes in a thin-film lithium niobate (TFLN) waveguide. Here, a shallow-etched ridge waveguide is fabricated in x-cut magnesium oxide doped TFLN and is poled accurately over 5 mm. The high fidelity of the poling is demonstrated over long lengths using a non-destructive technique of confocal scanning second-harmonic microscopy. We report a second-harmonic conversion efficiency of up to 939 %.W⁻¹(length-normalized conversion efficiency 3757 %.W⁻¹.cm⁻²), measured at telecommunications wavelengths. The device demonstrates a narrow spectral linewidth (1 nm) and can be tuned precisely with a tuning characteristic of 0.1 nm/°C, over at least 40 °C without measurable loss of efficiency.

    

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4. Mode-evolution-based ultra-broadband polarization beam splitter using adiabatically tapered extreme skin-depth waveguide

   https://doi.org/10.1364/OL.434110  

   Mia, Md Borhan ; Ahmed, Syed Z. ; Jaidye, Nafiz ; Ahmed, Ishtiaque ; Kim, Sangsik ( September 2021 , Optics Letters)

   We present an ultra-broadband silicon photonic polarization beam splitter (PBS) using adiabatically tapered extreme skin-depth (eskid) waveguides. Highly anisotropic metamaterial claddings of the eskid waveguides suppress the crosstalk of transverse-electric (TE) mode, while the large birefringence of the eskid waveguide efficiently cross-couples the transverse-magnetic (TM) mode. Two eskid waveguides are adiabatically tapered to smoothly translate TM mode to the coupled port via mode evolution while keeping the TE mode in the through port. The tapered cross-section of the eskid PBS was designed numerically, achieving a large bandwidth at 1400–1650 nm with extinction ratios$><\#comment/>20\mathrm{d}\mathrm{B}$. We experimentally demonstrated the tapered-eskid PBS and confirmed its broad bandwidth at 1490–1640 nm, limited by laser bandwidth. With its mode evolution, the tapered-eskid PBS is tolerant to fabrication imperfections and should be crucial for controlling polarizations in photonic circuits.

    

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5. Highly Sensitive, Affordable, and Adaptable Refractive Index Sensing with Silicon‐Based Dielectric Metasurfaces

   https://doi.org/10.1002/admt.201800567  

   Ollanik, Adam J. ; Oguntoye, Isaac O. ; Hartfield, George Z. ; Escarra, Matthew D. ( December 2018 , Advanced Materials Technologies)

   A sensing platform is presented that uses dielectric Huygens source metasurfaces to measure refractive index changes in a microfluidic channel with experimentally measured sensitivity of 323 nm RIU⁻¹, a figure of merit (FOM) of 5.4, and a response of 8.2 (820%) change in transmittance per refractive index unit (T/RIU). Changes in the refractive index of liquids flown through the channel are measured by single‐wavelength transmittance measurement, requiring only a simple light source and photodetector, significantly reducing device expense in comparison to state‐of‐the‐art refractive index sensing technologies. A technoeconomic analysis predicts a device costing ≈$2400 that is capable of detecting refractive index changes of the order of 2*10⁻⁸. The metasurfaces utilized are low profile, scalable, and use materials and fabrication processes compatible with CMOS and other technologies making them suitable for device integration. The Huygens metasurface system, characterized by spectrally overlapping electric and magnetic dipole modes, offers a high degree of customizability. Interplay between the two resonances may be controlled via metasurface geometry, leading to tunability of device sensitivity and measurement range. Ultrahigh sensitivity of 350 nm RIU⁻¹with FOM of 219, corresponding to single‐wavelength sensitivity of 360 RIU⁻¹, is demonstrated computationally through use of antisymmetric resonances of a Huygens metasurface illuminated at small incidence angles.

    

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