ACS Photonics最新文献

The development of silicon-compatible, high-performance infrared photodetectors is crucial for advancing thermal imaging, security, and communication systems. While germanium is a promising near-infrared material, its behavior in nanostructured forms with silicon heterojunctions reveals complex photophysics. This work demonstrates a germanium nanowire photodetector grown on a silicon-on-insulator (SOI) platform that exhibits a striking, tunable coexistence of both positive photoconductivity (PPC) and negative photoconductivity (NPC). We show that the dominant photoresponse can be switched by the wavelength of incident light: NPC dominates at visible wavelengths (e.g., 532 nm), while PPC prevails in the near-infrared (e.g., 1310 nm). Through systematic experiments and FDTD and TCAD simulations, we elucidate that this phenomenon arises from the interplay of light absorption in the different layers of the heterostructure. At short wavelengths, strong absorption in the underlying Si layer forward-biases the heterojunction, injecting carriers that quench the Ge channel conductance (NPC). At long wavelengths, absorption is confined to the Ge layer, resulting in conventional PPC. Negative photoconductivity was consistently observed over the temperature range from 78 to 298 K. Notably, the maximum responsivity of the nanowire increased from −56.7 A/W at room temperature to −1421.5 A/W at 78 K. This is attributed to the suppression of surface recombination velocity, increasing the minority carrier lifetime by 2 orders of magnitude. The −3 dB bandwidth is 2.9 kHz under 532 nm light and 3.9 kHz under 1310 nm light. The minimum noise equivalent power is determined to be 5.3 × 10^–14 W/Hz^0.5, corresponding to a specific detectivity of 4.0 × 10⁹ Jones at room temperature. Furthermore, we demonstrate that the crossover wavelength is intensity-dependent and that the photocurrent follows an established logarithmic model for nanowire photoconductors. This work provides a controllable model system for studying NPC and presents a novel device architecture with tunable, multifunctional photoresponse for advanced optoelectronic applications.

Deep-red perovskite lasers hold great promise for biomedical and optoelectronic applications, yet their performance is hindered by Auger recombination at high carrier densities. This study demonstrates that molecular dipole-moment engineering effectively suppresses Auger recombination in CsPb(I_xBr_1–x)₃ perovskite films. By introducing a passivation molecule with a strong electron-withdrawing group and a large dipole moment, the surface electron cloud is redistributed. This not only passivates defects but also reduces the exciton binding energy and enhances lattice rigidity, thereby weakening both defect-assisted and Auger recombination. Transient absorption spectroscopy confirms an extended Auger lifetime and improved optical gain. As a result, the optimized film achieves low-threshold amplified spontaneous emission at 3.4 μJ cm^–2 in the deep-red region. This work highlights dipole-moment manipulation as a potent strategy for developing high-performance, low-threshold perovskite lasers.

We present the development of InGaN/AlGaN nanowire light-emitting diodes (LEDs) as superior candidates for extreme thermal environments, demonstrating exceptional performance even at 1000 °C. Through a combination of advanced simulations and experimental validation, our study reveals that nanowire LEDs effectively mitigate thermal stress and enhance heat dissipation compared with traditional thin-film LEDs. This is attributed to their high surface-to-volume ratio and reduced defect density. Remarkably, these nanowire LEDs exhibit virtually zero efficiency droop up to 500 °C and minimal droop between 600 °C and 1000 °C, while maintaining stable peak wavelength emission (∼525 nm), outperforming thin-film counterparts. The improved thermal management is due to efficient phonon transport and strain relaxation inherent to nanowire structures. These findings highlight InGaN/AlGaN nanowire LEDs as a transformative solution for high-temperature applications such as space exploration, industrial processes, and advanced sensing, offering unparalleled reliability in harsh conditions.

Optical logic operations are considered as important components of optical computing, overcoming the inherent limitations of traditional electronic systems in transmission bandwidth and power, thus enabling applications in high-speed signal processing, parallel computing, and all-optical communication systems. The traditional optical logic gates implemented by methods such as semiconductor optical amplifiers, highly nonlinear optical fibers and micronano waveguides suffer from instability, difficulty in miniaturization, and the precise control of the input optical signals. Recently, diffractive neural networks have emerged as a new framework for implementing optical logic operations because of their high parallelism, low energy consumption and antinoise ability. In this study, we demonstrate three-dimensional (3D) microscale optical logic operation structures by the two-photon polymerization printed diffractive neural network. Specifically, the diffractive neural network featuring a volume size of 100 × 100 × 50 μm³ and neural size of 2 μm can execute the seven optical logic operations at the visible wavelengths with an accuracy of 100%. Furthermore, the logic operation neural network can be readily printed on commercially available CMOS chips, enabling ultracompact and miniaturized integrated devices. This study provides a feasible path for scaling optical logic components into practical optical computing systems by leveraging the existing CMOS-compatible platform.

We present a novel experimental approach to investigate power-dependent nonlinearities in metasurfaces. By monitoring a spectrally distinct, nonpump resonance during SHG excitation, our method enables in situ observation of resonance evolution without interference from the intense pump. This technique allows direct correlation of nonlinear emission with real-time resonance changes, clearly distinguishing between reversible resonance shifts and irreversible structural damage. Combined with numerical simulations incorporating measured refractive index variations, we reveal how resonance detuning governs nonlinear saturation dynamics. Our approach provides a general strategy for probing dynamic nonlinear processes in high-quality metasurfaces and offers actionable insights for designing robust, power-tolerant nonlinear photonic devices, advancing the development of ultracompact SHG sources and integrated nonlinear nanophotonic technologies.

Conventional Purcell theory emphasizes high quality factors (Q) for spontaneous emission (SE) enhancement in cavities but overlooks collective Bloch mode effects in nonlocal periodic nanostructures like photonic crystal slabs. We introduce a unified temporal coupled-mode framework to evaluate Purcell and photoluminescence factors through momentum-space integration, revealing anomalous SE enhancement mediated by bound states in the continuum (BICs) in non-Hermitian systems. In nonlocal dielectric metasurfaces with comparable effective mode volumes, this yields substantial SE enhancement in low-Q regimes, defying the traditional high-Q paradigm and is inversely correlated with system Q, while emission rates are stably twice the photoluminescence, eliminating critical coupling requirements. Unique spectral profiles, contradicting Lorentzian/Fano-like assumptions, arise from collective mode interactions. Full-wave simulations confirm these challenges to conventional wisdom, with BICs outperforming high-Q designs across broad numerical apertures. This establishes a novel paradigm leveraging non-Hermiticity and topological protection for robust, bright emitters, redefining nanophotonic applications in lasers and light-emitting diodes.

Optical phased arrays (OPAs) have become essential components in light detection and ranging (LiDAR) systems and free-space optical communication (FSO), where OPAs with optimized power output and aperture size are crucial for enhancing the detection range and improving signal transmission reliability. While current methods focus on utilizing high-power-tolerant waveguide materials (e.g., SiN) to boost OPA output power and increasing the number of grating antennas to enlarge the output aperture, several factors─such as on-chip tree-like beam-splitting structures, on-chip losses, and the limitations of the effective photolithographic area─restrict the achievable output power and aperture size. We demonstrate the coherent beam synthesis of multiple OPAs using off-chip phase-locked loop compensation, which results in a 319% enhancement in peak power in the far-field main lobe while achieving a 62% reduction in fwhm of the main lobe compared to that of a single OPA. Moreover, our method enables precise beam steering without the need for tedious recalibration. The demonstrated technique shows excellent scalability for modular expansion, offering a promising framework for next-generation OPA applications in long-range sensing and reliable optical communication systems.

Topological three-dimensional (3D) Dirac semimetals are promising for advanced optoelectronics due to their nontrivial band topology and ultrahigh carrier mobility. Their intrinsic centrosymmetry, however, should forbid second-order nonlinear optical processes, severely limiting their nonlinear photonics potential. Contrary to this expectation, we observe pronounced coherent terahertz (THz) emission arising from second-order nonlinear effects in both pristine 3D Dirac semimetal Cd₃As₂ thin films and its noncentrosymmetric alloy counterpart. This highly efficient, broadband THz radiation can be controlled by varying the pump polarization and incident angle, with the resulting transient photocurrents aligning with symmetry analysis. Crucially, we demonstrate two effective strategies to activate these nonlinear photocurrents: (i) using oblique excitation to create an asymmetric carrier distribution in momentum space, and (ii) deliberately breaking inversion symmetry via alloy engineering. Both strategies are generalizable approaches for unlocking second-order transient photocurrents in centrosymmetric Dirac semimetals through symmetry breaking. These findings establish new approaches for controlling nonlinear responses in 3D topological materials, advancing their application in next-generation, on-chip THz photonic devices.

Selective control over exciton (X⁰) and trion (X^–) emissions in colloidal quantum wells is key to realizing state-selective and tunable light sources in excitonic photonic systems. In CdSe nanoplatelets (NPLs), surface charging or chemical doping induces a continuous and irreversible shift from X⁰ to X^– emission, without enabling selective control over individual excitonic states. Here, we demonstrate deterministic enhancement of X⁰ and X^– emission by coupling NPLs to a two-dimensional dielectric metasurface resonator (MSR) that supports high-Q, polarization-split guided-mode resonances. Using temperature as a tuning parameter to shift the NPL band gap, we achieve spectral alignment with the MSR mode and observe Purcell-enhanced emission with up to 4.2 and 3× integrated intensity enhancement for X^– and X⁰, respectively, along with line width narrowing up to 2.5 meV. The anisotropic MSR further enables polarization-selective emission control, establishing temperature and polarization as independent knobs for scalable, tunable quantum light sources. In this context, “selective” denotes control over both the excitonic state (X⁰ vs X^–) and emission polarization, achieved, respectively, by tuning the detuning parameter (ΔE) with temperature and by setting the analyzer orientation.

Precise signal identification in solar-blind deep-ultraviolet (DUV) detection critically relies on high-performance devices with exceptional spectral selectivity. A novel strategy is proposed to significantly enhance DUV photodetector performance by integrating plasmonic nanohole engineering with ultrashort-period AlN/GaN superlattices for ultranarrow-band detection. Simulations indicate that Al-filled nanoholes with a diameter of 230 nm and a sidewall angle of 60° can yield up to a 31-fold enhancement of the localized electric field at the Al-nanohole sidewall interfaces compared to nanohole structures without Al. Accordingly, metal–semiconductor–metal (MSM) photodetectors incorporating Al-filled hexagonal nanohole arrays within the AlN/GaN superlattice absorption layers were fabricated. The designed three-dimensional architecture, which provides an increased interaction area and effective optical path length, achieves a remarkable peak responsivity of 42.6 mA/W at 238 nm under a 15 V bias. This represents a 4.5-fold improvement over planar reference devices. Furthermore, the devices exhibit ultranarrow spectral selectivity with a full-width at half-maximum (fwhm) of only 19 nm, attributed to the precise spectral alignment between the localized surface plasmon resonance (LSPR) and the superlattice absorption profile. This novel combination of plasmonics and nanohole superlattices offers a promising avenue for high-performance DUV photodetectors in applications requiring highly selective spectral operation.