Guo-En Chang

Biosensing platforms based on localised surface plasmon resonance (LSPR) have become prominent due to their capability for label-free and real-time detection of biomolecular interactions. This paper proposes a slab waveguide-enhanced scattering-based nanoplasmonic sensing approach that utilizes the strong light–matter interaction of gold nanoparticles (AuNPs) to achieve refractive index (RI) sensing and biomolecule detection. Unlike conventional transmission or spectral-shift-based methods, the proposed system relies on monitoring variations in the scattered light intensity, providing a high-contrast and simplified detection mechanism. The sensing principle is governed by plasmonic scattering, where the intensity of scattered light increases with the surrounding RI owing to enhanced local electromagnetic field confinement. Experimental results demonstrate a clear and linear response of the normalized scattered intensity to RI variations, confirming a reliable sensing performance. A waveguide-integrated AuNP plasmonic sensor based on light scattering detection is demonstrated for RI sensing. The platform achieves high sensitivity (1.60 RIU ⁻¹ ) and resolution (6.21 × 10 ⁻⁵ RIU), outperforming absorption-based detection. Enhanced evanescent coupling and LSPR significantly improve the signal response, enabling accurate, reliable, and high-resolution optical sensing in compact configurations. Furthermore, biosensing experiments using immunoglobulin G reveal a concentration-dependent signal with a limit of detection of 3.26 ng ml ⁻¹ (21.7 pM) and excellent linearity ( R ² = 0.99), enabling accurate quantitative detection. The obtained results underscore the suitability of slab waveguide-enhanced scattering-based nanoplasmonic sensing platforms for enabling compact, cost-efficient, and high-performance solutions across biomedical diagnostics, environmental analysis, and point-of-care testing.

GeSn alloys are promising for Si-based mid-infrared (MIR) lasers owing to their direct bandgap. This study compares the performance of optically pumped ridge waveguide GeSn MIR lasers fabricated without (Device A: Si/Ge/GeSn ~10%) and with (Device B: Si/Ge/GeSn 5%/GeSn ~10.41%) a GeSn buffer. At 77 K, Device A exhibited a lower threshold (454.77 kW/cm ² ) and higher maximum operating temperature (110 K) than Device B (470.21 kW/cm ² , 100 K). Overall, optical confinement, carrier transport, and thermal effects critically influence performance beyond defect reduction. This study provides design insights for GeSn lasers, facilitating the development of efficient, integrated Si-photonics MIR light sources.

We report on a low-cost, and highly sensitive waveguide-coupled metallic photonic crystal (WGMPC) optical sensor for real-time refractive index (RI) sensing applications. The proposed sensor endows enhanced light–matter interaction within a compact two-dimensional structure. The metallic photonic crystal structures are fabricated using a scalable nanoimprint-based process on a TiO ₂ waveguide platform, ensuring high reproducibility and compatibility with large-area manufacturing. Finite-element simulations confirm strong electromagnetic field confinement at the metal–dielectric interface, indicating efficient plasmonic excitation and improved sensing performance. Experimental RI sensing, conducted using sucrose solutions, demonstrates a clear and linear intensity response over a broad RI range, along with good stability and reversibility. The sensor achieves a normalized sensitivity of 0.8051 ± 0.002579 RIU ⁻¹ and an RI resolution of 1.18 × 10 ⁻⁴ RIU, highlighting its capability to detect small RI variations. These results validate the effectiveness of the proposed WGMPC platform as a low-cost and reliable optical sensing solution. Owing to its real-time response, reasonable sensitivity, and scalable fabrication, the sensor shows strong potential for point-of-care clinical and biosensing applications.

Heavy n-type doping is essential for GeSn-based optoelectronic and plasmonic devices, yet remains challenging due to the low thermal stability of GeSn alloys and the resulting dopant deactivation, strain relaxation, and Sn redistribution during post-growth processing. Here, we investigate phosphorus ion implantation combined with millisecond flash lamp annealing (FLA) as a non-equilibrium doping approach for Ge0.95Sn0.05 layers grown on Ge virtual substrates. Compared with previous ex-situ doping studies, the implantation process was redesigned using reduced implantation fluences, room-temperature implantation, an amorphous Si capping layer, and FLA without substrate preheating to improve dopant activation and minimize implantation-induced damage. Raman spectroscopy identifies a narrow recrystallization window between 71 and 84 J/cm2, while Rutherford backscattering spectrometry demonstrates nearly complete recovery of the crystalline quality after annealing, with a Sn lattice-site occupancy exceeding 95%. No measurable Sn redistribution is observed after implantation and annealing within the sensitivity limits of Rutherford backscattering spectrometry and X-ray diffraction. Hall-effect measurements reveal active electron concentrations of up to 5.0 × 10^19 cm-3 and electron mobilities of around 200 cm2 V-1 s-1. These results represent a 10% improvement in maximum carrier concentration and a ninefold increase in dopant activation efficiency compared to previously reported ex-situ doping approaches, reaching approximately 54%. These results establish an optimized processing route for highly activated n-type GeSn that suppresses Sn redistribution.

Semiconductor devices have traditionally relied on lattice‐matched heterojunctions formed via epitaxy. However, expanding device functionalities increasingly demands integration across extreme lattice mismatches. Here, a lattice‐mismatched, single‐crystalline GaAs/GeSn‐multi‐quantum well (MQW)/Ge n‐i‐p heterojunction photodiode is realized through advanced “semiconductor grafting” technology. This method enables simultaneous engineering of band alignment and optical field distribution. Comprehensive STEM characterization reveals an atomically clean GaAs/GeSn‐MQW interface with no observable interdiffusion. The resulting photodiode exhibits outstanding performance: a record‐low dark current density of 1.22 × 10 ⁻⁷ A/cm ² , extended spectral response from ∼0.5 to 2 µm, and high photo responsivities of 0.85 A/W and 0.40 A/W at 520 nm (VIS) and 1570 nm (NIR), respectively. Compared to epitaxial reference device, this represents a reduction in dark current by over five orders of magnitude, and responsivity enhancements of ∼7× in the VIS and ∼3× in the NIR ranges. This work establishes a new strategy for constructing lattice‐mismatched optoelectronic heterojunctions. Beyond the GaAs/GeSn‐MQW/Ge system, the approach offers a broadly applicable platform for high‐performance device integration free from conventional strict lattice‐matching requirement.

We present an investigation on the effect of low‐thermal‐budget microwave annealing (MWA) on the structural and light‐emitting properties of compressively strained GeSn films deposited on a Ge‐buffered (001) Si substrate. After post‐growth annealing at MWA powers below 1050 W, the Sn content and strain in the GeSn films remained nearly unchanged, whereas the material quality improved, thereby enhancing light‐emitting efficiency. Annealing GeSn films at an MWA power of 1650 W induced strain relaxation and then reduced light‐emitting efficiency caused by the generation of misfit dislocations. Annealing GeSn films at MWA powers above 2100 W resulted in significant bidirectional thermal diffusion of Sn atoms, leading to the formation of substantial Sn clusters within the GeSn film, the emergence of β‐Sn droplets on the film surface, and Sn diffusion into the Ge buffer layer; this resulted in reduced Sn content in the GeSn film and light‐emitting efficiency. Results obtained on optically pumped GeSn lasers, fabricated using the as‐grown and annealed GeSn samples, indicated the significantly improved lasing threshold and maximum lasing temperature via MWA of GeSn films. These results indicate that MWA is a promising low‐thermal‐budget approach for improving the material quality and light‐emitting efficiency, thereby enhancing the performance of GeSn‐based lasers intended for use in silicon photonics.

Group-IV GeSn alloys have gained significant attention as an attractive material system for silicon photonics. Thermal annealing provides an efficient route to improve the crystalline quality and overall performance of GeSn layers. Here, we present a comparative study on the effects of rapid thermal annealing (RTA) and microwave annealing (MWA) on GeSn samples grown on Si via Ge buffer layers containing ∼6.3% Sn under a compressive strain of 0.793%. Structural analysis reveals that RTA at ∼380 °C yields a modest strain relaxation of ∼20% and enhanced crystallinity. However, RTA at higher temperatures results in defect generation and a decrease in photoluminescence (PL) emission intensity. In contrast, MWA at a moderate power of ∼900 W achieves a higher strain relaxation of ∼27–28% while preserving both material quality and PL emission. This advantage is attributed to the more localized energy delivery and reduced thermal budget of MWA, which mitigates Sn diffusion and maintains alloy integrity. In addition, theoretical analysis of the strain-dependent band structure and spontaneous emission in GeSn further confirms that increased strain relaxation enhances the direct-gap character and radiative recombination. These findings demonstrate that MWA offers a more robust and scalable post-growth annealing route for optimizing GeSn layers while balancing strain engineering, optical performance, and material stability, thereby advancing the development of high-performance, complementary metal oxide semiconductor-compatible GeSn-based photonic devices.

GeSn has emerged as a promising alternative in Si photonics due to its narrow and tunable bandgap. In this study, GeSn waveguide photodetectors (WGPDs) based on a lateral p–i–n homojunction architecture are demonstrated. Incorporating 10.82% Sn effectively reduces the bandgap, extending the photodetection range to 2745 nm and covering the entire short‐wave infrared (SWIR) region. A lateral p–i–n homojunction diode with good optical confinement and long photon‐absorbing length is developed to significantly enhance the optical responsivity. The close proximity of the direct (Γ _c ) and indirect ( L _c ) conduction bands allows excitation of electrons from Γ _c to L _c , increasing electron lifetime. As a result, the carrier collection efficiency improves with higher bias. This momentum‐space separation mechanism enables device operation at a low electric field of ≈2.5 kV cm ⁻¹ . These findings suggest that the fabricated GeSn WGPDs are strong candidates for full‐range SWIR detection applications.