Papers by Keyword: KOH

Abstract: The fabrication of high-quality 4H-SiC epitaxial layers for power semiconductor devices involves complex processes including bulk crystal growth, wafer slicing, polishing, and chemical vapor deposition (CVD) epitaxy with precise step-flow control on slightly off-cut Si-face substrates. Despite advances, intrinsic crystallographic defects such as threading dislocations, basal plane dislocations, and stacking faults remain significant challenges, propagating into epitaxial layers and degrading device performance and reliability. This study examines defect types and their impact on 4H-SiC wafers, emphasizing the transition from 150 mm to 200 mm substrates, which introduces increased defect densities and polytype inclusions. Comprehensive defect characterization using advanced microscopy, molten KOH etching, and electrical wafer sorting reveals strong correlations between physical defects—such as micropipes, carrot-like stacking faults, and triangular 3C-SiC inclusions—and device failures, particularly under reliability stress tests like High Temperature Reverse Bias (HTRB). The findings highlight the critical role of substrate quality, epitaxial growth conditions, and defect mapping in improving yield and device robustness. This work underscores the necessity of integrating multi-scale defect inspection and targeted reliability assessments to optimize 4H-SiC power device manufacturing and performance.

Abstract: The solid – state nuclear track detector (SSNTDs) CR-39 can be used to study the different factors for alpha particle. Alpha particle is very dangerous inside the human body so the study its very important. In this article, we investigated the impact of two different etching solutions (NaOH and KOH)) on registrations properties, diameter D, track Diameter growth velocity VD, number of tracks and removal layer thickness of CR-39 nuclear track detector. The two types NaOH and KOH were dissolved in water with varied normality (3,5,7,9,11)N under a temperature of (70±1)°C to create the solution. During the experiment, a source of (α-particles) with a 4MeV energy was used to bombard all detectors (30 Sec). It was found the values of the diameter, number of tracks, removal layer thickness, track Diameter growth velocity VD by using the etching solution (NaOH +water) Solution greater than the values in (KOH + water) solution. the results showed excellent agreement with the outcomes of others who utilized different normalities.

Abstract: This paper reports the temperature and the concentration dependence of anisotropic etching for (100) p-Silicon in an aqueous KOH solution etching rate of wet etching has been experimentally determined with varying concentrations and the temperature of the KOH solution. The texturing process was managed at different etching durations ( 20 min, 40 min, and 60 min). XRD test showed that the lowest value of grain size was 5.0 nm (obtained with the highest porosity percentage of 50% with 4.5% KOH concentration for 60 min). FESEM test showed that the pore diameter increased with increasing etching time. The lowest reflectance value was (2.8 % at 550 nm wavelengths for samples treated with 4.5% KOH concentration for 60 min etching time. The refractive index value was 1.8 for the same black Si sample, also Hall test is introduced.

Abstract: In this study, the α and β modifications of MnO₂ have been successfully synthesized by the hydrothermal method. The obtained materials have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and low-temperature nitrogen adsorption. In addition, the supercapacitor performance of the materials has been pre-tested to assess their suitability for practical applications. The average particle size of the α modification is 12-15 nm, and the β modification is 14-18 nm. The surface areas of the α and β modifications of MnO₂ are 200 m²/g and 70 m²/g, respectively. The average pore sizes are 3.2 nm and 5.3 nm, respectively. The specific capacitance of 40 F/g is observed at 1 mV/s, which has been recorded using cyclic voltammetry and constant current charge-discharge cycling in 30 % aqueous KOH solutions. It has been determined that the specific capacitance of the β - MnO₂/electrolyte system decreases from 40 F/g to 15 F/g with an increase in the scan rate from 1 to 30 mV/s. In addition, the total capacitance of the material was divided into the electric double layer capacitance and the diffusion-controlled redox capacitance due to the Faraday reverse redox reactions. Finally, the pseudocapacitance contribution has been determined to be 90 % of the total specific capacitance.

Abstract: X-ray topography shows that selective KOH etching after CVD growth of n-type epilayers on highly N doped 4H SiC substrates can be used to reliably map pure and mixed Threading Screw Dislocations (TSD). The influence of the mapping grid density and the wafer position in the crystal on the average TSD density are investigated. A reliable mapping of TSD contributed to the development of 100mm SiC wafers with average TSD density down to 200 cm^-2.

Abstract: We have investigated the “straight-line defect,” which has not been classified separately and is quite similar to the carrot defect. We found that the straight-line defect differed structurally from the carrot defect. The presence of a particle on the substrate-epi layer interface seemed to be the cause of the defect; a layer of poly-type (3C-SiC) extended from the particle to the epi-layer surface. The straight-line defect likely resulted from shape change from the 3C-SiC triangular defect. This change in shape from triangular to straight-line defects depended on the C/Si ratio. To investigate the electrical characteristics, we fabricated a Schottky barrier diode (SBD) structure on a silicon carbide (SiC) epi wafer. With application of a high voltage, destruction occurred on both the upstream and the downstream side of the step flow of straight-line defects in the reverse voltage test. This reverse direction characteristic differed from that observed with triangular defects.

Abstract: Rubber-seed shell was selected as the precursor for the preparation of activated carbon by chemical activation with KOH as an activating agent. Impregnation-Activation Method and Carbonization-Impregnation-Activation Method were investigated with different concentration of KOH solution. Rubber-seed shell activated carbons were characterized by using scanning electron microscope, fourier transform infared spectroscopy and nitrogen adsorption isotherms. The results present that the first method which impregnation of precursor in 2%wt. KOH solution with the ratio of 300 g/l for 24 hrs before thermal activation at 700°C for 2 hrs under 2 cm³/min of nitrogen flow, was satisfied to prepare the Rubber-seed shell activated carbon. Products with maximum BET surface area, average pore diameter and volume ratio of micropores to mesopores were equal to 429 m²/g, 2.09 nm and 4.19, respectively.

Abstract: To remove the surface damages induced during mechanical polishing (MP) of 4H-SiC, a variety of wet etching recipes and etching conditions were studied. By evaluating the epilayers grown on these etching-treated wafers, it has been found that triangular defects (TRDs) are the main defects originated from the MP-induced damages in these samples. High temperature molten KCl etching at 1100 °C with KOH additive is very effective to remove the damaged surface while keeping a relatively flat surface. Epilayer grown on the KCl+KOH etched wafer showed a TRD density <0.9 cm^-2.

Abstract: Geopolymer synthesis has two main requirements to fulfil which are the source material that is rich in Silicon (Si) and Aluminum (Al) and alkali activator such as sodium/potassium hydroxide. Sodium hydroxide (NaOH) is widely used for the synthesis of geopolymer compared to potassium hydroxide (KOH) with addition of silicate solution for the purpose of increasing dissolution process. However, the comparison of using different activator in the absence of silicate solution for geopolymer synthesis is not well established. This paper presents an evaluation on compressive strength of fly ash–based geopolymer by using different activator (KOH and NaOH) with respect to different curing conditions (time and temperature) in the absence of sodium silicate. The samples were mixed using mortar mixer and prepared in 50mm x 50mm x 50mm mould for determination of compressive strength. It can be observed that the highest compressive strength up 65.28 MPa was obtained using NaOH. Meanwhile, synthesis using KOH only recorded 28.73 MPa. The compressive strength was better when cured at elevated temperature (60°C) than room temperature (25°C). Further analysis on the microstructure of the highest compressive strength geopolymer samples for both activators was carried out using Field Emission Scanning Microscopy (FESEM) and Raman spectroscopy.

Abstract: BiFeO₃ nanoparticles were successfully synthesized by a hydrothermal method by a mineralizer (KNO₃). Structural characterization was performed by thermal analysis, powder X-ray diffraction (XRD) and scanning electron microscopy (TEM).The results showed that the products were perovskite structure BiFeO₃ powders. Optimal conditions for the synthesis of single-phase BiFeO₃ ceramics were obtained.