Shoou-Jinn Chang

This work demonstrates the scalable fabrication of a two-dimensional (2D) SnS ₂ -based metal–semiconductor–metal (MSM) structured gas sensor and systematically investigates its layer-dependent sensing behaviors toward various gas species. Few-layer Sn S 2 films were synthesized and comprehensively characterized using X-ray diffraction (XRD) and Raman spectroscopy to confirm their high crystallinity, predominant phase purity, c -axis preferred orientation, and characteristic lattice vibrations. X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (TEM) were further utilized to validate the chemical bonding states—including trace surface-oxygen/residual-oxide contributions—and precise layer-number configurations, respectively. The MSM devices were evaluated for their gas-sensing capabilities under varying thermal conditions at a fixed concentration of 5 Parts per Million (ppm). The experimental results reveal that the sensor response, operating temperature, sensitivity, and selectivity profile are strongly dictated by the precise number of SnS ₂ layers. Specifically, the bi-layer SnS ₂ sensor yields the highest absolute sensitivity at the 50 °C operating temperature, while the tri-layer configuration exhibits the most robust performance when restricted to room-temperature (25 °C) operation. Outstanding sensitivity and specific selectivity toward NO ₂ were achieved, highlighting the immense potential of layer-controlled 2D SnS ₂ frameworks for advanced, high-performance environmental monitoring applications.

Green-emitting KZn1−0.12−xPO4:Tb3+0.12,Ce3+x (x = 0.007, 0.01 and 0.03) phosphors were synthesized by conventional solid-state reaction and sintered between 900 and 1200 °C, and the combined influence of sintering temperature and Ce3+ concentration on their structure and luminescence was systematically investigated. X-ray diffraction confirms that all samples crystallize as single-phase hexagonal α-KZnPO4 (space group P63) without detectable secondary phases, while scanning electron microscopy reveals progressive grain coarsening from ~2–3 μm at 900 °C to >10 μm at 1200 °C. Re-examining the Shannon ionic radii suggested that Tb3+ and Ce3+ may preferentially occupy the nine-coordinated K+ channel sites rather than the tetrahedral Zn2+ sites, with possible charge compensation through cation vacancies. Under 380 nm near-ultraviolet (NUV) excitation, which is relevant to commercial NUV chips, the phosphors emit the characteristic Tb3+ 5D4→7FJ lines dominated by saturated green emission at 547 nm; the possible spectral overlap between the Ce3+ 5d emission and the Tb3+ excitation manifolds together with the strong green emission under 380 nm excitation suggests a possible Ce3+→Tb3+ energy-transfer pathway. The tested Ce3+ series has its maximum intensity at x = 0.01, beyond which concentration-related quenching may occur. The Dexter analysis (slope ≈ −2, θ ≈ 6) suggests an electric dipole–dipole interaction but does not establish the operative quenching mechanism. The CIE 1931 coordinates remain tightly clustered near (0.29, 0.70) across processing conditions. These results identify KZnPO4:Tb3+,Ce3+ as a promising NUV-excitable green phosphor for further evaluation in white light-emitting diodes (WLEDs).

To address contact-limited transport commonly encountered in two-dimensional semiconductors, this study fabricated few-layer two-dimensional molybdenum disulfide (MoS₂) films on sapphire substrates via controllable oxide-to-sulfide conversion. Combined sputtering deposition of molybdenum trioxide and precise chemical-vapor sulfidation afforded high-quality, high-uniformity, and thickness-tunable MoS₂. The resulting films exhibit distinct differences in the frequencies of the Raman modes, consistent elemental ratios, and uniform interlayer spacing of ~0.65 nm. The MoS₂-based devices exhibit robust photodetection with microampere-scale photocurrents. Bilayer MoS₂ exhibited negative photoconductivity under ambient atmosphere, which is hypothesized to be linked to environment-induced surface doping and molecular adsorption rather than permanent structural traps. Contact engineering via mild thermal annealing of Ni electrodes significantly enhanced the photocurrent by improving effective interfacial carrier injection. These findings underscore the oxide sulfidation strategy as a scalable approach for engineering the layer-dependent behavior of transition metal dichalcogenides for optoelectronic applications.

This work presents a comprehensive TCAD investigation of p-GaN etching-depth variation in enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs), calibrated with experimental ICP etching conditions. Three representative scenarios were examined: nominal etch depth, residual p-GaN (under-etch), and over-etch into the AlGaN barrier. In the residual regime, the remaining p-GaN forms a p–i–n-like junction with the underlying heterostructure, altering the electrostatic distribution and partially depleting the two-dimensional electron gas (2DEG). As the residual thickness increases, both the threshold voltage ( V _th ) and ON resistance ( R _ON ) exhibit a rapid increase followed by saturation, reflecting the strong sensitivity of channel electrostatics to small residual variations. In contrast, over-etching into the AlGaN barrier reduces the effective barrier thickness and weakens carrier confinement, thereby reducing 2DEG density. This leads to a simultaneous increase in V _th and R _ON due to reduced channel conductivity and altered voltage distribution. A ±0.2 V V _th tolerance was adopted to define a quantitative process window of approximately –0.8 to +1.2 nm relative to the nominal etch depth, within which stable E-mode operation is maintained. These results clarify the electrostatic origins of etch-depth-induced V _th and R _ON variations and provide a predictive guideline for process optimization in p-GaN gate HEMT fabrication.

This study presents the fabrication and integration of vertically stacked dual-color Micro-LEDs using laser eutectic bonding with Au–Sn alloy. A blue flip-chip and a green vertical-array Micro-LED were individually processed, including epitaxial etching, transparent electrode formation, and passivation. A nanosecond-pulsed 1064 nm fiber laser was employed to induce localized eutectic bonding at 233 °C, forming robust Au₅Sn intermetallic compounds at the interface. SEM-EDX analysis confirmed the presence of eutectic and Au₅Sn phases, validating the metallurgical integrity of the joint. Electrical characterization revealed minimal threshold voltage shift post-bonding, indicating preserved device performance. The bonding process demonstrated precise alignment, thermal stability, and mechanical reliability, enabling scalable integration of stacked Micro-LEDs for advanced display applications.

This study investigated the switching characteristics of HfSnO ₂ as the insulating layer in Resistive Random Access Memory (RRAM) compared with those of Conductive–Bridge Random Access Memory (CBRAM) (Ag/HfSnO ₂ /Pt) and Oxide–based Random Access Memory (OxRAM) (Al/HfSnO ₂ /Pt). CBRAM exhibited superior performance in terms of (set Voltage) Vset, resistance uniformity and endurance. Increasing the HfSnO ₂ thickness increased Vset but decreased endurance; a 40[ ]nm layer achieved a Vset of 0.4[ ]V with over 1000 cycles, whereas a 20[ ]nm layer reduced Vset to 0.35[ ]V but endured only 306 cycles. Setting the sputtering pressure to 5[ ]mTorr decreased Vset to 0.369[ ]V with an endurance exceeding 1000 cycles, whereas increasing the O ₂ ratio to 30% decreased Vset to 0.33[ ]V with similar endurance. To further enhance performance, we used a two–layer HfSnO ₂ structure, achieving a Vset of 0.259[ ]V with an endurance surpassing 1000 cycles. This study demonstrated that optimizing the HfSnO ₂ thickness, sputtering conditions and multilayer structures significantly improves HfSnO ₂ –based RRAM performance.

The V-pits have been widely reported as a special structure in GaN wurtzite materials, which can improve hole injection efficiency and screen non-radiative recombination centers. Therefore, it is of great importance to utilize the characteristics of V-pits and study its growth mechanism for improving the opto-electronic performance and luminous efficiency of GaN-based micro light-emitting diodes (μ-LEDs). In this work, we have fabricated green AlGaN quantum barrier (QB) μ-LEDs to introduce V-pits engineering and investigated the opto-electrical performance and intrinsic mechanisms. The results of low-temperature EL and SEM measurements indicated that the introduction of Aluminum in QBs leads to better hole injection efficiency due to increasing the V-pits area ratio and more uniform carrier distribution within QWs. The CL and EDX results show that AlGaN QB can form higher potential barrier height between side-wall MQWs and c-plane MQWs, thereby enhancing the V-pits screening effect. The EL characteristics indicate that there is a better EQE, lower forward voltage and better efficiency-droop ratio in AlGaN QB μ-LEDs. Thermal resistance, junction temperature and aging tests indicate that AlGaN QB μ-LEDs have better thermal stability and lifespan. These results provide a reference for improving the quantum efficiency and opto-electronic performance of GaN-based green μ-LEDs by V-pits engineering.

This study aimed to enhance the performance of Resistive Random Access Memory (RRAM) cells with a switching layer of MgNiO. We investigated the Mg_xNi[ ]O material and utilized it as the oxide layer in the RRAM structure. In the experiment, Ni was employed as the upper electrode, and the oxide layer was stacked in an attempt to improve the RRAM characteristics. The I–V characteristics were then analyzed to examine the switching behavior of the RRAM. After stacking Mg[ ]Ni[ ]O beneath Mg[ ]Ni[ ]O, a slight increase in the HRS/LRS order was observed, while the stability of the element showed significant improvement. The heterojunction memory exhibited the ability to switch between HRS/LRS states more than 2,500 times, as demonstrated in the I–V sweep. Moreover, no significant changes were observed in the I–V curve between the first and the 2,500th cycles.

This study investigated the crystal structure, surface morphology, and sensing properties of Zn-doped indium oxide (IZO). IZO thin films were deposited onto a four-finger structure using RF sputtering with varying oxygen ratios to enhance sensing performance. SEM analysis revealed a petal-like structure with a preferential growth orientation along the (222) direction. In contrast, X-ray photoelectron spectroscopy analysis demonstrated surface O_L, O_V. In this study, the NO₂ detection range was 100–5000 ppb. When exposed to 1000 ppb of NO₂, the sensor exhibited a response of 9.39 (ΔR/Rair) with a response time of 22 s and a recovery time of 23 s. Compared to other gases, including H₂S, CO, H₂, and NH₃, the sensor demonstrated excellent selectivity, which can be attributed to the petal-like structure and the presence of OV and Oads. These characteristics make the sensor highly promising for applications requiring high sensitivity and selectivity in NO₂ detection.