Search Results (12)

Fiber Bragg gratings (FBGs) have gained substantial research interest due to their exceptional sensing capabilities. Traditionally, FBG fabrication has required the use of pre-hydrogenated fibers and high-cost laser systems such as excimer lasers at 193 nm or femtosecond lasers. In this study, we present the first instance of FBG inscription in hydrogen-loaded, standard single-mode silica optical fibers using a more affordable 266 nm solid-state pulsed laser combined with a scanning phase mask lithography technique. We systematically explored the effects of pulse energy and scanning speed on the quality and spectral characteristics of the gratings, achieving reflectivities as high as 99.81%. Additionally, we tracked the spectral evolution during the FBG inscription process, demonstrating uniform growth of the core mode. We also investigated the stability of the core mode during a 24-h thermal annealing process up to 150 °C. The sensitivity was 10.7 pm/°C in the range of 0 to 130 °C. Furthermore, strain measurement was conducted based on the FBG annealed at 100 °C, showing a sensitivity of 0.943 pm/µε in the range of 0 to 1667 µε. Full article

Blue laser annealing can be used to obtain a high-mobility thin-film transistor (TFT) through a laser annealing (i.e., LTPS: low-temperature Poly-Si) process. However, the laser annealing process’s low productivity (as well as high cost) is an issue because the high output power of blue lasers still needs to be addressed. Therefore, productivity can be improved if blue laser energy is efficiently supplied during the laser annealing process using a continuous wave laser instead of a conventional pulsed excimer laser. We developed a blue laser light source (440 ± 10 nm) using the wavelength beam combining (WBC) method, which can achieve a laser power density of 73.7 kW/cm². In this semiconductor laser, when the power was increased s by 2.9 times, the laser scanning speed was increased by 5.0 times, achieving twice the productivity of conventional lasers. After laser annealing, the size of the crystal grains varied between 2 and 15 μm, resulting in a crystallization rate of 100% by Raman scattering rsult and low resistivity of 0.04 Ωcm. This increase in production capacity is not an arithmetic increase with increased power but a geometric production progression. Full article

We applied excimer laser annealing (ELA) on indium-zinc oxide (IZO) and IZO/indium-gallium-zinc oxide (IGZO) heterojunction thin-film transistors (TFTs) to improve their electrical characteristics. The IZO and IZO/IGZO heterojunction thin films were prepared by the physical vapor deposition method without any other annealing process. The crystalline state and composition of the as-deposited film and the excimer-laser-annealed films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. In order to further enhance the electrical performance of TFT, we constructed a dual-heterojunction TFT structure. The results showed that the field-effect mobility could be improved to 9.8 cm²/V·s. Surprisingly, the device also possessed good optical stability. The electron accumulation at the a-IZO/HfO, HfO/a-IGZO, and a-IGZO/gate insulator (GI) interfaces confirmed the a-IGZO-channel conduction. The dual-heterojunction TFT with IZO/HfO/a-IGZO-assisted ELA provides a guideline for overcoming the trade-off between high mobility (μ) and positive V_Th control for stable enhancement mode operation with increased I_D. Full article

A method for enhancing the photoluminescence of silicon nanocrystals in a silicon oxide matrix by fabrication of periodic surface structures through laser irradiation is demonstrated. ArF excimer lasers are used to produce periodic line structures by material ablation. Photoluminescence, Raman, and transmission electron microscope measurements consistently show the formation of crystalline silicon after high-temperature annealing. A 2.6-fold enhancement of photoluminescence signal is measured for a periodic line structure with 600 nm period. The influence of a surface structure on the photoluminescence from the silicon oxide layer is discussed in terms of a simple model describing the main effect. Full article

We propose an ambipolar chitosan synaptic transistor that effectively responds to binary neuroplasticity. We fabricated the synaptic transistors by applying a chitosan electric double layer (EDL) to the gate insulator of the excimer laser annealed polycrystalline silicon (poly-Si) thin-film transistor (TFT) with Ni-silicide (NiSi) Schottky-barrier source/drain (S/D) junction. The undoped poly-Si channel and the NiSi S/D contact allowed conduction by electrons and holes, resulting in artificial synaptic behavior in both p-type and n-type regions. A slow polarization reaction by the mobile ions such as anions (CH₃COO⁻ and OH⁻) and cations (H⁺) in the chitosan EDL induced hysteresis window in the transfer characteristics of the ambipolar TFTs. We demonstrated the excitatory post-synaptic current modulations and stable conductance modulation through repetitive potentiation and depression pulse. We expect the proposed ambipolar chitosan synaptic transistor that responds effectively to both positive and negative stimulation signals to provide more complex information process versatility for bio-inspired neuromorphic computing systems. Full article

In this study, the efficient fabrication of nickel silicide (NiSi_x) Schottky barrier thin-film transistors (SB-TFTs) via microwave annealing (MWA) technology is proposed, and complementary metal-oxide-semiconductor (CMOS) inverters are implemented in a simplified process using ambipolar transistor properties. To validate the efficacy of the NiSi_x formation process by MWA, NiSi_x is also prepared via the conventional rapid thermal annealing (RTA) process. The Rs of the MWA NiSi_x decreases with increasing microwave power, and becomes saturated at 600 W, thus showing lower resistance than the 500 °C RTA NiSi_x. Further, SB-diodes formed on n-type and p-type bulk silicon are found to have optimal rectification characteristics at 600 W microwave power, and exhibit superior characteristics to the RTA SB-diodes. Evaluation of the electrical properties of NiSi_x SB-TFTs on excimer-laser-annealed (ELA) poly-Si substrates indicates that the MWA NiSi_x junction exhibits better ambipolar operation and transistor performance, along with improved stability. Furthermore, CMOS inverters, constructed using the ambipolar SB-TFTs, exhibit better voltage transfer characteristics, voltage gains, and dynamic inverting behavior by incorporating the MWA NiSi_x source-and-drain (S/D) junctions. Therefore, MWA is an effective process for silicide formation, and ambipolar SB-TFTs using MWA NiSi_x junctions provide a promising future for CMOS technology. Full article

Finding a low-cost and effective method at low temperatures for producing reduced graphene oxide (rGO) has been the focus of many efforts in the research community for almost two decades. Overall, rGO is a promising candidate for use in supercapacitors, batteries, biosensors, photovoltaic devices, corrosion inhibitors, and optical devices. Herein, we report the formation of rGO from two electrically insulating polymers, polytetrafluoroethylene (PTFE) and meta-polybenzimidazole fiber (m-PBI), using an excimer pulsed laser annealing (PLA) method. The results from X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, Raman spectroscopy, and Fourier-transform infrared spectroscopy confirm the successful generation of rGO with the formation of a multilayered structure. We investigated the mechanisms for the transformation of PTFE and PBI into rGO. The PTFE transition occurs by both a photochemical mechanism and a photothermal mechanism. The transition of PBI is dominated by a photo-oxidation mechanism and stepwise thermal degradation. After degradation and degassing procedures, both the polymers leave behind free molten carbon with some oxygen and hydrogen content. The free molten carbon undergoes an undercooling process with a regrowth velocity (<4 m·s⁻¹) that is necessary for the formation of rGO structures. This approach has the potential for use in creating future selective polymer-written electronics. Full article

The effect of KrF excimer laser irradiation on the optical and electrical properties of epitaxial wafers with a p-GaN surface were investigated at different laser energy densities and pulse numbers. The laser-irradiated samples were annealed in oxygen. The laser irradiation-induced changes in optical and electrical properties of GaN epitaxial wafers were examined using PL, I–V, XPS, SIMS, and Hall effect measurements. Experimental results show that under an appropriate laser-irradiated condition, optical and electrical properties of the samples were improved to different degrees. The samples which were annealed after laser irradiation have better electrical properties such as the hole concentration and sheet resistance than those without annealing. We hypothesize that the pulsed KrF excimer laser irradiation dissociates the Mg–H complexes and annealing treatment allows the hydrogen to diffuse out more completely under the oxygen atmosphere at a proper temperature, by which the crystalline symmetry of GaN is improved. Under appropriate laser conditions and O₂-activated annealing, the light output of the laser-irradiated GaN-based LED sample is about 1.44 times that of a conventional LED at 20 mA. It is found that the wall-plug efficiency is 10% higher at 20 mA and the reverse leakage current is 80% lower at 5 V. Full article

We present a method for the simulation of the kinetic evolution in the sub µs timescale for composite materials containing regions occupied by alloys, compounds, and mixtures belonging to the Ni-Si-C ternary system. Pulsed laser irradiation (pulses of the order of 100 ns) promotes this evolution. The simulation approach is formulated in the framework of the phase-field theory and it consists of a system of coupled non-linear partial differential equations (PDEs), which considers as variables the following fields: the laser electro-magnetic field, the temperature, the phase-field and the material (Ni, Si, C, C clusters and Ni-silicides) densities. The model integrates a large set of materials and reaction parameters which could also self-consistently depend on the model variables. A parameter calibration is also proposed, specifically suited for the wavelength of a widely used class of excimer lasers (λ = 308 nm). The model is implemented on a proprietary laser annealing technology computer-aided design (TCAD) tool based on the finite element method (FEM). This integration allows, in principle, numerical solutions in systems of any dimension. Here we discuss the complex simulation trend in the one-dimensional case, considering as a starting state, thin films on 4H-SiC substrates, i.e., a configuration reproducing a technologically relevant case study. Simulations as a function of the laser energy density show an articulated scenario, also induced by the variables’ dependency of the materials’ parameters, for the non-melting, partial-melting and full-melting process conditions. The simulation results are validated by post-process experimental analyses of the microstructure and composition of the irradiated samples. Full article

The crystallization of hydrogenated amorphous silicon (a-Si:H) is essential for improving solar cell efficiency. In this study, we analyzed the crystallization of a-Si:H via excimer laser annealing (ELA) and compared this process with conventional thermal annealing. ELA prevents thermal damage to the substrate while maintaining the melting point temperature. Here, we used xenon monochloride (XeCl), krypton fluoride (KrF), and deep ultra-violet (UV) lasers with wavelengths of 308, 248, and 266 nm, respectively. Laser energy densities and shot counts were varied during ELA for a-Si:H films between 20 and 80 nm thick. All the samples were subjected to forming gas annealing to eliminate the dangling bonds in the film. The ELA samples were compared with samples subjected to thermal annealing performed at 850–950 °C for a-Si:H films of the same thickness. The crystallinity obtained via deep UV laser annealing was similar to that obtained using conventional thermal annealing. The optimal passivation property was achieved when crystallizing a 20 nm thick a-Si:H layer using the XeCl excimer laser at an energy density of 430 mJ/cm². Thus, deep UV laser annealing exhibits potential for the crystallization of a-Si:H films for TOPCon cell fabrication, as compared to conventional thermal annealing. Full article

The effect of laser irradiation with different numbers of laser shots on the microstructure, the surface, and the hardness of gun metal alloy was studied by a KrF pulsed excimer laser system, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and Vickers hardness test. The influence of 100–500 laser shots was irradiated on the surface hardness profile and on the microstructure of gunmetal alloy. XRD results showed the maximum 2θ shift, the maximum full width of half maximum FWHM, the maximum dislocation density, and the minimum crystallite size for the sample irradiated with 300 laser shots. The hardness was measured in three different regions at the laser irradiated spot, and it was found that maximum hardness was present at the heat affected zone for all samples. The hardness value of the un-irradiated sample of gun metal was 180, and the value increased up to 237 by raising the number of laser shots up to 300. The peak value of surface hardness of the laser treated sample was 32% higher than the un-irradiated sample. The Raman shift of the un-exposed sample was 605 cm⁻¹ and shifted to a higher value of wave number at 635 cm⁻¹ at 300 laser shots. The hardness value was decreased by further increasing the number of laser shots up to 500. The samples irradiated with 400 and 500 laser shots exhibited smaller hardness and dislocation defect density, which was assigned to possible annealing caused by irradiation. Full article

We investigated the characteristics of excimer laser-annealed polycrystalline silicon–germanium (poly-Si_1−xGe_x) thin film and thin-film transistor (TFT). The Ge concentration was increased from 0% to 12.3% using a SiH₄ and GeH₄ gas mixture, and a Si_1−xGe_x thin film was crystallized using different excimer laser densities. We found that the optimum energy density to obtain maximum grain size depends on the Ge content in the poly-Si_1−xGe_x thin film; we also confirmed that the grain size of the poly-Si_1−xGe_x thin film is more sensitive to energy density than the poly-Si thin film. The maximum grain size of the poly-Si_1−xGe_x film was 387.3 nm for a Ge content of 5.1% at the energy density of 420 mJ/cm². Poly-Si_1−xGe_x TFT with different Ge concentrations was fabricated, and their structural characteristics were analyzed using Raman spectroscopy and atomic force microscopy. The results showed that, as the Ge concentration increased, the electrical characteristics, such as on current and sub-threshold swing, were deteriorated. The electrical characteristics were simulated by varying the density of states in the poly-Si_1−xGe_x. From this density of states (DOS), the defect state distribution connected with Ge concentration could be identified and used as the basic starting point for further analyses of the poly-Si_1−xGe_x TFTs. Full article