Abstract Resonant electro-optic modulators are of interest for encoding electrical signals to the optical domain with an option to perform simultaneous wavelength-division multiplexing while reducing the modulation energy consumption. Here, we demonstrate a compact, high-speed, and energy-efficient resonant modulator exploiting the ultrafast characteristics of graphene and organic materials, enabling efficient electro-optic modulation on the silicon platform. Graphene, with its extraordinary electronic and optical properties, is used as a transparent electrode material that brings the radio frequency field close to the photonic mode with minimal extra losses, while the organic material provides a high linear electro-optic coefficient. This arrangement provides both efficient light modulation in a compact device with an active length of 50 μm and a large modulation bandwidth of ∼35 GHz. High-speed data transmission experiments demonstrate a line rate of 320 Gbit/s, while a rate of 128 Gbit/s is achieved under CMOS-compatible voltages with energy consumption of ∼10.1 femtojoules per bit. The presented technology offers a practical and promising route toward integration of graphene into high-speed communication links.
Abstract This study systematically investigates the temperature-dependent electrical and optical characteristics of AlGaInP-based red micro-light-emitting diodes (micro-LEDs) across a cryogenic range from 80 to 300 K. Experimental results demonstrate that decreasing temperatures lead to an increase in operating bias voltage and an enhancement in external quantum efficiency (EQE). Using a modified ABC model that incorporates carrier transport and leakage effects, the carrier recombination behaviors behind EQE results were analyzed. By fitting the size-dependent Shockley–Read–Hall (SRH) coefficients, the surface recombination velocity (SRV) was extracted, showing a reduction from 1. 53 × 105 cm/s at 300 K to 2. 62 × 104 cm/s at 80 K. Furthermore, an effective trap offset regarding the bulk defect (ΔE = 6. 05 meV) was identified through a theoretical fitting of the temperature-dependent bulk SRH lifetime. These findings provide a comprehensive understanding of the underlying thermal behavior of defects, specifically how bulk and surface SRH recombination evolve at cryogenic temperatures.
Abstract Spatially varying strain provides a route to control exciton transport and localization in two-dimensional semiconductors, but resolving these processes requires correlated spatial, spectral, and temporal measurements. Here, we investigate multilayer GaSe suspended over nanopillar arrays using photoluminescence spectroscopy, Raman mapping, and wavelength-resolved fluorescence lifetime imaging microscopy (FLIM). Raman mapping confirms localized tensile strain around the nanopillars, while FLIM reveals complementary emission patterns: free-exciton emission at 615–625 nm forms annular distributions around the pillars, whereas red-shifted strain-localized emission at 630–670 nm is concentrated toward the highly strained pillar regions. For GaSe on Al2O3-coated nanopillars, the strain-localized emission exhibits biexponential decay with characteristic lifetimes near 1.20 and 1.46 ns, together with an increase in the slow lifetime toward the pillar apex and a slow-to-fast amplitude ratio of 7.68. In contrast, the corresponding red-shifted emission on metallic Cu nanopillars is predominantly single exponential, highlighting the influence of the local interface on exciton recombination. The combined spatial redistribution, strain-correlated spectral redshift, and systematic lifetime evolution support strain-guided exciton funneling in multilayer GaSe. These results establish wavelength-resolved FLIM as an effective approach for mapping strain-dependent exciton dynamics and demonstrate nanopillar-induced strain as a means to engineer exciton localization in layered semiconductors.
Abstract Current neuromorphic vision sensors still struggle to accurately emulate the complex and dynamic photoresponse behaviors of the biological retina, limiting their capability to replicate realistic visual perception characteristics. The integration of two-dimensional (2D) materials with self-rolled-up three-dimensional (3D) microtube architectures has emerged as an effective strategy for constructing neuromorphic vision sensors. Herein, we have systematically demonstrated the functional evolution from a planar WS2 photodetector to a 3D microtube WS2/graphene heterojunction optoelectronic synapse capable of emulating the photoresponse dynamics of the retina. Upon integration of a van der Waals (vdW) heterojunction with graphene and in situ self-rolling into a 3D microtube, the device achieves a pivotal functional evolution: the microtube cavity enhances the light-trapping efficiency, while the curvature-induced strain further modulates the energy band and defect states of materials, triggering the hyperpolarization behavior analogous to that of biological photoreceptors and ON-bipolar cells under optical stimulation. The 3D microtube WS2/graphene heterojunction device delivers a biomimetic composite photoresponse, consisting of an initial current dip corresponding to photoreceptors hyperpolarization, a subsequent current rise mimicking the activation of ON-bipolar cells, a fast decay with undershoot reflecting ON-bipolar cells hyperpolarization, and a prolonged slow recovery process analogous to dark adaptation of rod cells. This work mitigates partial functional mismatches between artificial optoelectronic devices and biological retinal cells and provides a viable route to fabricate neuromorphic vision sensors emulating biological photoresponse characteristics.
Abstract Second-harmonic generation (SHG) is a sensitive optical probe of symmetry breaking because the allowed nonlinear susceptibility components are directly constrained by crystal and magnetic symmetry. In magnetic materials, the onset of spin order commonly activates additional SHG channels or redistributes intensity among polarization geometries, often producing an enhanced nonlinear response. Here we demonstrate the opposite phenomenology in the van der Waals antiferromagnet CrOCl: SHG is strongly quenched across the incommensurate and commensurate magnetic transitions. The suppression occurs broadly across polarization angles, in both co- and cross-polarized detection channels, and in all fitted magnetic-dipole tensor elements. By ruling out structural distortion, classical optical effects, and optical-resonance shifts as dominant origins, we assign the anomalous quench to a bulk magnetic-dipole SHG process whose radiative matrix element is reduced by reconstruction of the Cr d-orbital wave function assisted by spin–orbit coupling. This mechanism can be understood as magnetic-order-induced rotation of orbital pseudospin within the even-parity d manifold, revealing a novel route to nonlinear optical control that is distinct from conventional symmetry activation.
