Helicity-multiplexed metasurfaces based on symmetric spin–orbit interactions (SOIs) have practical limits because they cannot provide central-symmetric holographic imaging. Asymmetric SOIs can effectively address such limitations, with several exciting applications in various fields ranging from asymmetric data inscription in communications to dual side displays in smart mobile devices. Low-loss dielectric materials provide an excellent platform for realizing such exotic phenomena efficiently. In this paper, we demonstrate an asymmetric SOI-dependent transmission-type metasurface in the visible domain using hydrogenated amorphous silicon (a-Si:H) nanoresonators. The proposed design approach is equipped with an additional degree of freedom in designing bi-directional helicity-multiplexed metasurfaces by breaking the conventional limit imposed by the symmetric SOI in half employment of metasurfaces for one circular handedness. Two on-axis, distinct wavefronts are produced with high transmission efficiencies, demonstrating the concept of asymmetric wavefront generation in two antiparallel directions. Additionally, the CMOS compatibility of a-Si:H makes it a cost-effective alternative to gallium nitride (GaN) and titanium dioxide (TiO2) for visible light. The cost-effective fabrication and simplicity of the proposed design technique provide an excellent candidate for high-efficiency, multifunctional, and chip-integrated demonstration of various phenomena.
The MoS2 photodetector on different substrates stacked via van der Waals force has been explored extensively because of its great potential in optoelectronics. Here, we integrate multilayer MoS2 on monocrystalline SiC substrate though direct chemical vapor deposition. The MoS2 film on SiC substrate shows high quality and thermal stability, in which the full width at half-maximum and first-order temperature coefficient for the $E_{2g}^1$ Raman mode are 4.6 cm−1 and −0.01382 cm−1/K, respectively. The fabricated photodetector exhibits excellent performance in the UV and visible regions, including an extremely low dark current of ~1 nA at a bias of 20 V and a low noise equivalent of 10−13–10−15 W/Hz1/2. The maximum responsivity of the MoS2/SiC photodetector is 5.7 A/W with the incident light power of 4.35 μW at 365 nm (UV light). Furthermore, the maximum photoconductive gain, noise equivalent power, and normalized detectivity for the fabricated detector under 365 nm illumination are 79.8, 7.08 × 10−15 W/Hz1/2, and 3.07 × 1010 Jonesat, respectively. We thus demonstrate the possibility for integrating high-performance photodetectors array based on MoS2/SiC via direct chemical vapor growth.
Abstract-Wavelength conversion by difference frequency generation is demonstrated in domain-disordered quasi-phase matched waveguides. The waveguide structure consisted of a GaAs/AlGaAs superlattice core that was periodically intermixed by ion-implantation. For quasi-phase matching periods of 3.0-3.8 µm, degeneracy pump wavelengths were found by secondharmonic generation experiments for fundamental wavelengths between 1520-1620 nm in both type-I and type-II configurations. In the difference frequency generation experiments, output powers up to 8.7 nW were generated for the type-I phase matching interaction, and 1.9 nW for the type-II interaction. The conversion bandwidth was measured to be over 100 nm covering the C, L, and U optical communications bands, which agrees with predictions.
As a representative wide bandgap semiconductor material, gallium nitride (GaN) has attracted increasing attention because of its superior material properties (e.g., high electron mobility, high electron saturation velocity, and critical electric field). Vertical GaN devices have been investigated, are regarded as one of the most promising candidates for power electronics application, and are characterized by the capacity for high voltage, high current, and high breakdown voltage. Among those devices, vertical GaN-based PN junction diode (PND) has been considerably investigated and shows great performance progress on the basis of high epitaxy quality and device structure design. However, its device epitaxy quality requires further improvement. In terms of device electric performance, the electrical field crowding effect at the device edge is an urgent issue, which results in premature breakdown and limits the releasing superiorities of the GaN material, but is currently alleviated by edge termination. This review emphasizes the advances in material epitaxial growth and edge terminal techniques, followed by the exploration of the current GaN developments and potential advantages over silicon carbon (SiC) for materials and devices, the differences between GaN Schottky barrier diodes (SBDs) and PNDs as regards mechanisms and features, and the advantages of vertical devices over their lateral counterparts. Then, the review provides an outlook and reveals the design trend of vertical GaN PND utilized for a power system, including with an inchoate vertical GaN PND.
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