Sha Shiong Ng

Indium gallium nitride (InGaN) has attracted considerable attention for ultraviolet (UV) optoelectronic applications due to its tunable bandgap and compatibility with GaN-based device platforms. However, the optoelectronic performance of InGaN is strongly influenced by lattice strain, indium distribution, surface morphology, and carrier transport properties. In this work, the UV photoresponse of an Mg-doped InGaN/GaN heterostructure subjected to postgrowth annealing at 600 °C is systematically investigated. Structural properties, including lattice parameters, strain state, degree of relaxation, and indium composition, are examined using high-resolution X-ray diffraction reciprocal-space mapping (HRXRD RSM). The results indicate that the Mg-doped InGaN epilayer is partially relaxed on the GaN layer and exhibits phase separation. The indium composition determined from HRXRD RSM ranges from 4.12% to 8.77%. Atomic force microscopy analysis reveals a step-terrace surface morphology. Optical absorption measurements obtained from ultraviolet–visible spectroscopy show a sharp absorption edge at ∼380–382 nm, corresponding to a bandgap of ∼3.25 eV, indicating suitability for UV photodetection. Hall effect measurements reveal a carrier concentration of ∼1018 cm–3 and a mobility of ∼188 cm2 V–1 s–1. The fabricated photodetector exhibits a responsivity of 0.024 A W–1 and a rise/fall response time of 0.70 s at a bias of 6 V, demonstrating the potential of Mg-doped InGaN for UV photodetector applications.

Dynamic tuning of optical absorption remains a significant challenge for conventional plasmonic nanostructures because their optical properties are largely fixed after fabrication. Here, a physics-driven numerical investigation of a porous indium oxide (In ₂ O ₃ ) film fabricated on an anodic aluminum oxide substrate and functionalized with a dielectric DNA layer is presented as a dynamically tunable optical platform. Introduction of the DNA layer enhances three characteristic absorptance modes from 0.16 to 0.43, 0.20 to 0.50, and 0.21 to 0.35, respectively, owing to dielectric-environment-induced modulation of optical impedance matching and electromagnetic energy coupling. Under infrared pump-light excitation, photons with energies exceeding the deep-donor ionization threshold generate free carriers through photoionization of localized defect states, thereby modifying the complex refractive index of In ₂ O ₃ . As the pump-light intensity increases, the absorptance of the three modes further rises to 0.56, 0.55, and 0.44, respectively. Analysis of electromagnetic power-flow distributions reveals that absorptance enhancement is governed by the formation and confinement of characteristic localized energy-flow topologies, including bottleneck-type, vortex-type, and convergent flows, together with their spatial overlap with regions of non-zero optical loss. These findings establish a direct physical link between defect-mediated carrier dynamics, localized electromagnetic energy flow, and optical absorption in porous semiconductor structures, providing new insight into dynamically tunable optical materials and design guidelines for reconfigurable semiconductor-based photonic and sensing platforms.

With the advent of 6G mobile communication, the demand for ultra-high bandwidth wireless communication has increased rapidly, drawing significant attention to visible light communication (VLC) as a promising emerging technology. GaN-based laser diodes (LDs) are regarded as high-speed light sources for VLC owing to their high modulation bandwidth and high optical power density. Apart from the active region design, the LD’s structure also plays a crucial role in determining their dynamic properties, which have yet to be thoroughly studied in III-nitride LDs. In this work, we systematically investigate InGaN/GaN laser diodes with three ridge waveguide configurations: a conventional single-ridge structure, a dual-ridge large-mesa structure, and a dual-ridge small-mesa structure. The threshold current, small-signal modulation bandwidth of devices with different structures are comparatively analyzed. Experimental results reveal that the double-ridge small mesa laser diode achieves a modulation bandwidth of −3 dB at 6.02 GHz. These results provide valuable insights into the structural optimization of GaN-based high-speed laser diodes and offer practical guidance for the development of high-performance, energy-efficient VLC transmitters.

ZnMgO thin films (0%–3% Mg) were deposited via ultrasonic spray pyrolysis and characterized from 40 to 320 K. Three conduction regimes were identified: Mott variable‐range hopping (VRH), nearest‐neighbor hopping (NNH), and thermally activated conduction. At 0% Mg, VRH dominates; at 1–2% Mg, VRH and NNH coexist; and at 3% Mg, NNH prevails. Key parameters include a density of states near the Fermi level of 5.7 × 10 ¹⁹ cm ⁻³ eV ⁻¹ (0% Mg) and 3.9 × 10 ¹⁸ cm ⁻³ eV ⁻¹ (1% Mg), localization lengths of 11.0 nm (0% Mg) and 23.4 nm (1% Mg), hopping energies of 3.1 meV (VRH, 0% Mg) and 4.8 meV (VRH, 1% Mg), and NNH activation energies from 5.5 meV (1% Mg) to 9.9 meV (3% Mg). High‐temperature activation energy increases from 26.9 to 70.2 meV. Optical measurements show bandgap widening from 3.264 to 3.308 eV, aligning with transport trends. These results advance ZnMgO conduction understanding for optoelectronic and sensing applications.

Silver nanoparticles (AgNPs) were synthesized using pulsed laser ablation in liquid (PLAL) and integrated onto bulk gallium nitride (GaN) to enhance deep-ultraviolet (DUV) photodetector (PD) performance. Structural and optical characterizations confirmed the formation of crystalline AgNPs with an average size of 8 nm. These nanoparticles exhibited a surface plasmon resonance (SPR) peak at 405 nm, which red-shifted to 415 nm upon deposition onto bulk GaN, a change attributed to nanoparticle-substrate coupling. Field-emission scanning electron microscopy and atomic force microscopy analyses revealed uniformly distributed AgNPs and increased surface roughness from 0.146 nm to 39.5 nm, thereby facilitating stronger light–matter interaction. The AgNPs/bulk GaN metal–semiconductor–metal (MSM) DUV PD exhibited a tenfold enhancement in photocurrent. At 6 V bias under 280 nm illumination, its responsivity increased from 81.9 to 829 mA/W and its external quantum efficiency rose from 36.6% to 370%, significantly outperforming the bare bulk GaN device. These results confirm that plasmonic coupling between AgNPs and bulk GaN effectively amplifies photoresponse, establishing a promising strategy for high-performance DUV PDs.