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1. Ultra-thin plasmonic detectors

   https://doi.org/10.1364/OPTICA.438039  

   Nordin, Leland; Petluru, Priyanka; Kamboj, Abhilasha; Muhowski, Aaron_J; Wasserman, Daniel (December 2021, Optica)

   Plasmonic materials, and their ability to enable strong concentration of optical fields, have offered a tantalizing foundation for the demonstration of sub-diffraction-limit photonic devices. However, practical and scalable plasmonic optoelectronics for real world applications remain elusive. In this work, we present an infrared photodetector leveraging a device architecture consisting of a “designer” epitaxial plasmonic metal integrated with a quantum-engineered detector structure, all in a mature III-V semiconductor material system. Incident light is coupled into surface plasmon-polariton modes at the detector/designer metal interface, and the strong confinement of these modes allows for a sub-diffractive ( $\sim <\#comment/>{\mathrm{\lambda <\#comment/>}}_0/33$) detector absorber layer thickness, effectively decoupling the detector’s absorption efficiency and dark current. We demonstrate high-performance detectors operating at non-cryogenic temperatures ( $T=195\mathrm{K}$), without sacrificing external quantum efficiency, and superior to well-established and commercially available detectors. This work provides a practical and scalable plasmonic optoelectronic device architecture with real world mid-infrared applications. 

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2. Adiabatic frequency shifting in epsilon-near-zero materials: the role of group velocity

   https://doi.org/10.1364/OPTICA.374788  

   Khurgin, Jacob_B; Clerici, Matteo; Bruno, Vincenzo; Caspani, Lucia; DeVault, Clayton; Kim, Jongbum; Shaltout, Amr; Boltasseva, Alexandra; Shalaev, Vladimir_M; Ferrera, Marcello; et al (March 2020, Optica)

   The conversion of a photon’s frequency has long been a key application area of nonlinear optics. It has been discussed how a slow temporal variation of a material’s refractive index can lead to the adiabatic frequency shift (AFS) of a pulse spectrum. Such a rigid spectral change has relevant technological implications, for example, in ultrafast signal processing. Here, we investigate the AFS process in epsilon-near-zero (ENZ) materials and show that the frequency shift can be achieved in a shorter length if operating in the vicinity of $\mathrm{R}\mathrm{e}\left\{{\mathrm{\epsilon <\#comment/>}}_r\right\}=0$. We also predict that, if the refractive index is induced by an intense optical pulse, the frequency shift is more efficient for a pump at the ENZ wavelength. Remarkably, we show that these effects are a consequence of the slow propagation speed of pulses at the ENZ wavelength. Our theoretical predictions are validated by experiments obtained for the AFS of optical pulses incident upon aluminum zinc oxide thin films at ENZ. Our results indicate that transparent metal oxides operating near the ENZ point are good candidates for future frequency conversion schemes. 

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3. Heavy ion irradiation induced failure of gallium nitride high electron mobility transistors: effects of in-situ biasing

   https://doi.org/10.1088/1361-6463/accfa7  

   Rasel, Md Abu Jafar; Schoell, Ryan; Al-Mamun, Nahid Sultan; Hattar, Khalid; Harris, C. Thomas; Haque, Aman; Wolfe, Douglas E.; Ren, Fan; Pearton, Stephen J. (May 2023, Journal of Physics D: Applied Physics)

   Abstract While radiation is known to degrade AlGaN/GaN high-electron-mobility transistors (HEMTs), the question remains on the extent of damage governed by the presence of an electrical field in the device. In this study, we induced displacement damage in HEMTs in both ON and OFF states by irradiating with 2.8 MeV Au⁴⁺ion to fluence levels ranging from $1.72\times {10}^{10}$to $3.745\times {10}^{13}$ions cm⁻², or 0.001–2 displacement per atom (dpa). Electrical measurement is donein situ, and high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray (EDX), geometrical phase analysis (GPA), and micro-Raman are performed on the highest fluence of Au⁴⁺irradiated devices. The selected heavy ion irradiation causes cascade damage in the passivation, AlGaN, and GaN layers and at all associated interfaces. After just 0.1 dpa, the current density in the ON-mode device deteriorates by two orders of magnitude, whereas the OFF-mode device totally ceases to operate. Moreover, six orders of magnitude increase in leakage current and loss of gate control over the 2-dimensional electron gas channel are observed. GPA and Raman analysis reveal strain relaxation after a 2 dpa damage level in devices. Significant defects and intermixing of atoms near AlGaN/GaN interfaces and GaN layer are found from HRTEM and EDX analyses, which can substantially alter device characteristics and result in complete failure. 

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4. Phase segregation in inorganic mixed-halide perovskites: from phenomena to mechanisms

   https://doi.org/10.1364/PRJ.402411  

   Wang, Yutao; Quintana, Xavier; Kim, Jiyun; Guan, Xinwei; Hu, Long; Lin, Chun-Ho; Jones, Brendon Tyler; Chen, Weijian; Wen, Xiaoming; Gao, Hanwei; et al (October 2020, Photonics Research)

   Halide perovskites, such as methylammonium lead halide perovskites ( ${\mathrm{MAPbX}}_3$, $\mathrm{X}=\mathrm{I}$, Br, and Cl), are emerging as promising candidates for a wide range of optoelectronic applications, including solar cells, light-emitting diodes, and photodetectors, due to their superior optoelectronic properties. All-inorganic lead halide perovskites ${\mathrm{CsPbX}}_3$are attracting a lot of attention because replacing the organic cations with ${\mathrm{Cs}}^{+}$enhances the stability, and its halide-mixing derivatives offer broad bandgap tunability covering nearly the entire visible spectrum. However, there is evidence suggesting that the optical properties of mixed-halide perovskites are influenced by phase segregation under external stimuli, especially illumination, which may negatively impact the performance of optoelectronic devices. It is reported that the mixed-halide perovskites in forms of thin films and nanocrystals are segregated into a low-bandgap I-rich phase and a high-bandgap Br-rich phase. Herein, we present a critical review on the synthesis and basic properties of all-inorganic perovskites, phase-segregation phenomena, plausible mechanisms, and methods to mitigate phase segregation, providing insights on advancing mixed-halide perovskite optoelectronics with reliable performance. 

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5. Guided-mode resonances in flexible 2D terahertz photonic crystals

   https://doi.org/10.1364/OPTICA.388761  

   Kyaw, Chan; Yahiaoui, Riad; Chase, Zizwe_A; Tran, Viet; Baydin, Andrey; Tay, Fuyang; Kono, Junichiro; Manjappa, Manukumara; Singh, Ranjan; Abeysinghe, Don_C; et al (May 2020, Optica)

   In terahertz (THz) photonics, there is an ongoing effort to develop thin, compact devices such as dielectric photonic crystal (PhC) slabs with desirable light–matter interactions. However, previous works in THz PhC slabs have been limited to rigid substrates with thicknesses $\sim <\#comment/>100\mathrm{s}$of micrometers. Dielectric PhC slabs have been shown to possess in-plane modes that are excited by external radiation to produce sharp guided-mode resonances with minimal absorption for applications in sensors, optics, and lasers. Here we confirm the existence of guided resonances in a membrane-type THz PhC slab with subwavelength ( ${\mathrm{\lambda <\#comment/>}}_0/6-<\#comment/>{\mathrm{\lambda <\#comment/>}}_0/12$) thicknesses of flexible dielectric polyimide films. The transmittance of the guided resonances was measured for different structural parameters of the unit cell. Furthermore, we exploited the flexibility of the samples to modulate the guided modes for a bend angle of $\mathrm{\theta <\#comment/>}\ge <\#comment/>5^{\circ <\#comment/>}$, confirmed experimentally by the suppression of these modes. The mechanical flexibility of the device allows for an additional degree of freedom in system design for high-speed communications, soft wearable photonics, and implantable medical devices. 

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