Hybrid mode for absorption enhancement in the Ga2O3 nanocavity photodetector with grating electrodes.

Gallium oxide (G a 2 O 3) photodetectors have drawn increased interest for their widespread applications ranging from military to civil. Due to the inherent oxygen vacancy defects, they seriously suffer from trade-offs that make them incompetent for high-responsivity, quick-response detection. Herein, a G a 2 O 3 nanocavity photodetector assisted with grating electrodes is designed to break the constraint. The proposed structure supports both the plasmonic mode and the Fabry-Perot (F-P) mode. Numerical calculations show that the absorption of 99.8% is realized for ultra-thin G a 2 O 3 (30 nm), corresponding to a responsivity of 12.35 A/W. Benefiting from optical mechanisms, the external quantum efficiency (EQE) reaches 6040%, which is 466 times higher than that of bare G a 2 O 3 film. Furthermore, the proposed photodetector achieves a polarization-dependent dichroism ratio of 9.1, enabling polarization photodetection. The grating electrodes also effectively reduce the transit time of the photo-generated carriers. Our work provides a sophisticated platform for developing high-performance G a 2 O 3 photodetectors with the advantages of simplified fabrication processes and multidimensional detection.

High-enhancement photoluminescence of monolayer MoS2 in hybrid plasmonic systems.

Monolayer molybdenum disulfide (M o S 2) has a weak light-matter interaction due to ultrathin thickness, which limits its potential application in lasing action. In this study, we propose a hybrid structure consisting of a nanocavity and Au nanoparticles to enhance the photon emission efficiency of monolayer M o S 2. Numerical simulations show that photoluminescence (PL) emission is significantly enhanced by introducing localized surface plasmon resonance (LSPR) to the proposed structure. Furthermore, an exciton energy band system is proposed to elucidate the physical mechanism of the PL process. By optimizing the spacer thickness, a high Purcell enhancement factor of 95 can be achieved. The results provided by this work pave the way to improve the PL efficiency of two-dimensional (2D) material, which constitutes a significant step towards the development of nanodevices such as nanolasers and sensors.

Electro-Optical Modulation in High Q Metasurface Enhanced with Liquid Crystal Integration.

Electro-optical tuning metasurfaces are particularly attractive since they open up routes for dynamic reconfiguration. The electro-optic (EO) modulation strength essentially depends on the sensitivity to the EO-induced refractive index changes. In this paper, lithium niobate (LiNbO3) metasurfaces integrated with liquid crystals (LCs) are theoretically investigated. Cylinder arrays are proposed to support quasi-bound states in the continuum (quasi-BICs). The quasi-BIC resonances can significantly enhance the lifetime of photons and the local field, contributing to the EO-refractive index changes. By integrating metasurfaces with LCs, the combined influence of the LC reorientation and the Pockels electro-optic effect of LiNbO3 is leveraged to tune the transmitted wavelength and phase spectrum around the quasi-BIC wavelength, resulting in an outstanding tuning sensitivity up to Δλ/ΔV ≈ 0.6 nm/V and relieving the need of high voltage. Furthermore, the proposed structure can alleviate the negative influence of sidewall tilt on device performance. The results presented in this work can foster wide application and prospects for the implementation of tunable displays, light detection and ranging (LiDAR), and spatial light modulators (SLMs).

High-Q resonance in GeSn-based bound states in the continuum microcavity.

In recent years, the investigations of lasers based on group IV material have been limited by the low quality (Q) factor of the resonant modes. With the improvement of the optical bound states in the continuum (BICs) in various dielectric systems, we propose a novel design that takes advantages of both the direct bandgap dielectric material GeSn and the BIC phenomenon. In addition to the demonstration of the unprecedented high-Q factors (i.e., ∼1010) that improve the emission process, the vertical symmetry broken structure can emit light at the wavelength of 1870 nm with higher luminous intensity (i.e., ∼24). The modulation effect of the material and geometric parameters on the Q value and the luminous intensity of the structure are also demonstrated. Our investigations provide useful guidelines for potential applications such as on-chip light sources in group IV photonics and optical communications.

Effects of Post Annealing on Electrical Performance of Polycrystalline Ga2O3 Photodetector on Sapphire.

Effects of post annealing on the physical and electrical properties of solar-blind polycrystalline gallium oxide (Ga2O3) ultraviolet photodetectors on the sapphire substrate are investigated. The grain size of poly-Ga2O3 becomes larger with the post annealing temperature (PAT) increasing from 800 °C to 1000 °C, but it gets smaller with further raising PAT to 1100 °C. A blue shift is observed at the absorption edge of the transmittance spectra of Ga2O3 on sapphire as increasing PAT, due to the incorporation of Al from the sapphire substrate into Ga2O3 to form (AlxGa1-x)2O3. The high-resolution X-ray diffraction and transmittance spectra measurement indicate that the substitutional Al composition and bandgap of (AlxGa1-x)2O3 annealed at 1100 °C can be above 0.30 and 5.10 eV, respectively. The Rmax of the sample annealed at 1000 °C increases about 500% compared to the as-deposited device, and the sample annealed at 1000 °C has short rise time and decay time of 0.148 s and 0.067 s, respectively. This work may pave a way for the fabrication of poly-Ga2O3 ultraviolet photodetector and find a method to improve responsivity and speed of response.

Multiple-layer black phosphorus phototransistor with Si microdisk resonator based on whispering gallery modes.

In this study, we investigate the whispering gallery modes (WGMs) of a 14-layer black phosphorous (BP) phototransistor based on a silicon microdisk. The transmission characteristics of the waveguide-coupled microdisk resonator with and without BP are analyzed to determine the resonance wavelength. The effect of BP on the electric field distributions of the WGMs of the Si microdisk resonator is simulated by using the finite-element method. In addition, the enhanced optical absorption of the BP-covered Si microdisk resonator is further analyzed by the coupled mode theory. Contrastingly, the device also functions as a phototransistor with a peak responsivity of 328.1 A/W and high field-effect mobility of nearly 466.6 cm2 V-1 s-1. Our proposed device paves the path for the exploitation of BP optoelectronics devices with the assistance of optical microresonators in the near-infrared range (NIR).

Localized plasmon resonances for black phosphorus bowtie nanoantennas at terahertz frequencies.

In this work, a periodic bowtie structure based on black phosphorus (BP) is theoretically proposed and characterized. It is demonstrated that localized surface plasmons can be excited in the BP nanoantennas at terahertz (THz) frequencies. Numerical investigations, using the numerical method finite-difference time-domain (FDTD), have been utilized to analyze the the dimensions' impact on absorption spectra. Furthermore, the electric field distribution is plotted and discussed to explain the resonance wavelength tuning by different geometrical sizes of the structure. Results reveal that the optimized BP bow-tie structure can be allowed for the realization of two-dimensional nanophotonics at terahertz frequencies.

Simulation investigation of strained black phosphorus photodetector for middle infrared range.

In this paper, we design the uniaxially and biaxially strained black phosphorus (BP) photodetectors. Different strains applied in the zigzag or armchair direction can effectively tune the direct band gap of 5-layer of BP. The optical field intensity is modeled to determine the absorption for the BP layer. The strain effect on the band structure of BP is investigated using first-principles method based on density functional theory. The cut-off wavelength of strained 5-layer of BP pin photodetector is extended to middle infrared range with a high responsivity of 66.29 A/W, which means that the strained black phosphorus photodetector provides a new approach for the middle-infrared range optoelectronic devices.

Engineering rainbow trapping and releasing in ultrathin THz plasmonic graded metallic grating strip with thermo-optic material.

In this paper, we propose an ultrathin THz plasmonic metallic strip based on graded grating structure with thermo-optic material, which exhibits a strong engineering of trapping and releasing electromagnetic waves in terahertz regimes. The dispersion properties of the ultrathin spoof slow-wave plasmonic graded grating waveguide are characterized using the finite element method, and the propagation characteristics of the grating structures are thoroughly analyzed by the dispersion curves, electric field magnitude distribution, and electric field vertical distribution. The gradient grating waveguide is demonstrated to be an ideal slow-wave system for trapping and releasing surface plasmon polaritons (SPPs) waves through tuning the refractive index of the thermo-optic material. The reflected location for the SPPs waves on the graded corrugated metal strip at 1.1 THz at different temperatures are compared. It is proved that such ultrathin gradient grating waveguide provides an excellent performance for trapping and releasing surface waves at THz, which permits applications for future optical communications.