Silicon n-Channel Metal Oxide Semiconductor Field Effect Transistor Fabrication And Its Effect On Output Characteristics

n-channel metal oxide semiconductor field effect transistor (n-MOSFET) fabrication requires specialized and expensive technologies such as ion implantation, chemical vapor deposition (CVD) and hazardous gases such as silane (SiH4), HCl and hydrogen. Low cost emulsion photomask with 35 μm channel length is used in this work. Fabrikasi transistor semikonduktor logam oksida kesan medan saluran n-silikon, “nchannel metal oxide semiconductor field effect transistor (n-MOSFET)” memerlukan teknologi khusus dan berkos tinggi seperti penanam ion, endapan wap kimia dan gas-gas berbahaya seperti silane, asid hidroklorik dan hidrogen. Topeng foto berkos rendah dengan lebar saluran 35 μm digunakan di dalam projek ini

Optoelectronic properties of nano-structured silicon carbide prepared by anodic electrochemical etching

Ph. D. ThesisSilicon carbide (SiC) nanostructures are appealing as non-toxic, water-stable and oxidation resistant nanomaterials. Owing to these unique properties, 3-dimensionally confined SiC nanostructures, namely SiC quantum dots (QDs) have found applications in bioimaging of living cells. Photoluminescence (PL) investigations however revealed that across the polytypes: 3C-, 4H- and 6H-SiC, excitation wavelength dependent PL is observed for larger sizes but deviate for sizes smaller than approximately 3 nm, thus exhibiting a dual-feature in the PL spectra. Additionally, nanostructures of varying polytypes and bandgaps exhibit strikingly similar PL emission centred at approximately 450 nm. At this wavelength, 3C-SiC emission is above bulk bandgap as expected of quantum size effects, but for 4H-SiC and 6H-SiC the emissions are below bandgap. 4H-SiC is a suitable polytype to study these effects. In this thesis, the hypotheses that mixed phases of polytypes or surface related defects obscuring the quantum confinement of 4H-SiC based nanostructure were investigated. Density functional theory (DFT) calculations within the Ab initio Modelling Programme (AIMPRO) were performed on OH-, F- and H-terminated 4H-SiC QDs with diameters in the range of 10 to 20 A° . The chosen surface terminations relate to the HF/ethanol electrolyte used in preparation of SiC QDs and the choice of size coincide with where deviation was observed in experiments. It was found that the absorption onset energies deviated from quantum confinement with -OH and -F terminations, but conform to the prediction when terminated with -H. The weak size-dependent absorption onsets for -OH and -F is due to surface states arising from lone pair orbitals that are spatially localised to the quantum dot surface where these terminations reside. On the other hand -H termination show strong size-dependent absorption onsets due to delocalisation of the electron wavefunction towards the quantum dot core assisting quantum confinement. It is predicted that the surface related states dominate up to sizes 25 and 27 °A for -F and -OH terminations respectively. As a result, the recombination mechanism would involve the interplay between quantum confinement and surface states affecting the resultant energy gap and the resulting PL. The PL would exhibit a dual-feature: excitation-wavelength independence for small sizes and excitationwavelength dependence for diameters larger than 3 nm as observed in the experiments. Mesoporous 4H-SiC was fabricated by anodic electrochemical etching in ethanoic HF electrolyte. The porous SiC suspended in ethanol exhibited three PL bands, those at wavelengths of 303 nm and 345 nm were rarely reported, above bulk bandgap and indicative of quantum confinement. The usually observed emission at 455 nm was below bulk bandgap. Dual-feature and below bandgap PL observed for wavelengths around 450 nm indicate that mesoporous 4H-SiC exhibited optical properties dictated by both quantum confinement (red-shifting with longer excitation wavelengths) and surface states (below bandgap). X-ray photoelectron spectroscopy provided evidence of -F, C=O and -COOH surface terminations that may contribute to these surface states. Raman scattering data exhibited a red-shift of 12.2 cm1 and broadening in the lower frequency side of the longitudinal optical (LO) mode peak indicative of carrier depletion, surface phonons or phonon confinement as dimensions were reduced. The following ultrasonication process produced dimensions ranging from 16.9 5.5 down to 2.9 1.0 nm. The data from high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) showed lattice spacing of 0.267 nm and peaks corresponding to the 4H-SiC polytype. No evidence of polytypic transformation from 4H-SiC to 3C-SiC resulting from ultrasonication was found in this work. Instead high crystallinity of 4H-SiC lattice was retained which suggested that the obscured quantum confinement may arise from surface effects rather than mixed polytypes. Thermal oxidation and subsequent HF dip of mesoporous 4H-SiC resulting in pore wall thinning and surface removal was undertaken. Cross sectional SEM analysis showed reductions in average pore wall thickness to (20.5 2.8) nm, (18.2 2.9) nm, (17.0 1.8) nm and (15.9 1.4) nm for 1, 3, 6 and 9 hours of oxidation respectively. Following ultrasonication, the PL and PL excitation (PLE) characterisation showed absorption/emission band centred at 290/325 nm which were above bandgap. The below bandgap emission centred at 455 nm was removed and is a significant finding. Surface removal by thermal oxidation and HF dip resulted in suppressed below bandgap PL but retained the above bandgap PL. The evidence strongly indicate that the dual-feature PL and below bandgap emission in 4H-SiC seen in experiments are surface related rather than due to polytypic transformation during ultrasonicationUniversiti Sains Malaysia, Ministry of Higher Education (MOHE

VIS-NIR spectral and particles distribution of Au, Ag, Cu, Al and Ni nanoparticles synthesized in distilled water using laser ablation

In this research, gold (Au), silver (Ag), copper (Cu), aluminium (Al) and nickel (Ni) nanoparticles have been prepared by laser ablation in distilled water using Q-switched Nd: YAG. Comparative analysis between 1064 nm and 532 nm laser wavelength in term of absorption spectra and particle size distribution is performed. The synthesized nanoparticles were characterized by visible (VIS) and near infrared (NIR) spectrometer and transmission electron microscopy (TEM). The effect of laser pulse energy and laser wavelength on the size distribution and absorbance spectrum of metal nanoparticles was studied. The absorption peak intensities of the nanoparticles increase at higher laser pulse energy. It is discovered that for all metals, 532 nm laser produced nanoparticles with higher absorption peak intensities than 1064 nm. The work also shows that there is no noticeable difference in the size of the nanoparticles produced at 532 and 1064 nm for the Ni and Cu metals. However, a considerable size difference can be seen for Au, Ag, and Al at the two laser wavelengths. Smaller Ag nanoparticles were produced by 1064 nm laser while smaller Au and Al nanoparticles were produced by 532 nm laser

Characterization Of SiO2/SiC Interface Of Phosphorous-Doped MOS Capacitors By Conductance Measurements

Interface states of MOS structures capacitors incorporated with low levels of phosphorous have been investigated by conductance and C-ψs method. The frequency response of interface states was observed by the conductance method up to 10 MHz. The correlation between the frequency response of interface states and interface state density determined by C-ψs method was studied. It was found that fast states in phosphorous incorporated samples reduced significantly at high frequency (>5 MHz) while sample annealed with nitrogen remained high up to 10 MHz. The interface state density, Dit of phosphorous incorporated sample near conduction band is lower compared to nitridated sample. These results indicate phosphorous passivation effectively reduces Dit at the SiO2/SiC interfaces and can be correlated to high channel mobility

Surface-state dependent optical properties of OH-, F-, and H-terminated 4H-SiC quantum dots

Density functional calculations are performed for OH-, F- and H-terminated 4H-SiC 10–20 Å diameter clusters to investigate the effect of surface species upon the optical absorption properties. H-termination results in a pronounced size-dependent quantum-confinement in the absorption, whereas F- and OH-terminations exhibit much reduced size dependent absorption due to surface states. Our findings are in good agreement with recent experimental studies, and are able to explain the little explored dual-feature photoluminescence spectra of SiC quantum dots. We propose that along with controlling the size, suitable surface termination is the key for optimizing optical properties of 4H-SiC quantum structures, such as might be exploited in optoelectronics, photovoltaics and biological applications

Pore Wall Thinning of Mesoporous 4H-SiC by Sacrificial Oxidation

Pore wall thinning of mesoporous 4H‐SiC by sacrificial oxidation is performed. The dimensions within the as‐etched porous SiC are reduced during dry oxidation at 1100 °C by consuming SiC and removing the grown SiO2 in the subsequent hydrofluoric acid (HF) dip step. The process reduces the average pore wall thickness from 27 nm to approximately 16 nm and reduces the thickness standard deviation from ±5 to ±1.4 nm for the investigated 9 h oxidation interval. The new pore wall thinning method will enable controlled nanoscale size reduction capability for mesoporous 4H‐SiC derived nanostructures

Performance Improvement of Graded Bandgap Solar Cell via Optimization of Energy Levels Alignment in Si Quantum Dot, TiO₂ Nanoparticles, and Porous Si

Charge carriers’ generation from zinc includes silicon quantum dots (ZnSiQDs) layer sandwiched in-between porous silicon (PSi) and titania nanoparticles (TiO2NPs) layer-based solar cell is an efficient way to improve the cell’s performance. In this view, ZnSiQDs layer with various QDs sizes have been inserted, separating the PSi and TiO2NPs layers to achieve some graded bandgap quantum dot solar cells (GBQDSCs). In this process, ZnSiQDs of mean diameter 1.22 nm is first prepared via the top-down method. Next, ZnSiQDs have been re-grown using the bottom-up approach to get various mean diameters of 2.1, 2.7 and 7.4 nm. TiO2NPs of mean diameter in the range of 3.2 to 33.94 nm have been achieved via thermal annealing. The influence of different ZnSiQDs sizes on the designed GBGQDSCs performance has been determined. The proposed cell attains a short circuit current of 40 mA/cm2 and an efficiency of 4.9%. It has been shown that the cell performance enhances by optimizing the energy levels alignment in the PSi, ZnSiQDs, TiO2NPs layers

Mesoporous TiO2 implanted ZnO QDs for the photodegradation of tetracycline: material design, structural characterization and photodegradation mechanism

A sol-gel method was used to prepare a mesoporous TiO2 implanted with a ZnO quantum dot photocatalyst (TZQ) for the photodegradation of tetracycline (TC) under fluorescent light irradia�tion. Scanning electron microscopy (SEM) shows the presence of cavities on the photocatalyst surface due to the use of starch as a synthetic template, where the nitrogen sorption results indicate that TZQ contains mesopores with reduced size (ca. 4.3 nm) versus the pore size of the parent meso-TiO2 (ca. 7.5 nm). The addition of ZnO quantum dots (QDs) resulted in spherically-shaped binary composite particles in layers onto the surface of TiO2. The coexistence of the ZnO QDs and TiO2 phase was observed using high resolution-transmission electron microscopy (HR-TEM). The photodegradation of TC was carried out in a homemade reactor equipped with two fluorescent lights (24 W each) and within 90 min of irradiation, 94.6% of TC (40 mg L−1) was photodegraded using 250 mg L−1 of TZQ at pH 9. The major reactive oxygen species identified from the scavenging tests were O2 •− followed by HO•. The deconvolution of the photoluminescence spectrum of TZQ indicates the presence of a strong quantum confinement effect (QCE) of the ZnO QDs, a defect related to Ti-species and oxygen. The analysis of the intermediates detected by LC-time-of-flight/mass spectrometry (LC/TOF-MS) suggest two photodegradation pathways. The pathways were validated using the Fukui function approach and the Wheland localisation approach. This simple and efficient photocatalytic technology is anticipated to benefit small-scale animal husbandries and aquaculture operators that have limited access to sustainable water treatment technolog

Photovoltaic Performance of Spherical TiO₂ Nanoparticles Derived from Titanium Hydroxide Ti(OH)₄: Role of Annealing Varying Temperature

High-quality titanium dioxide (TiO2 or titania) nanoparticles (TiO2NPs) with tailored morphologies are desirable for efficient photovoltaic applications. In this view, some thin films containing spherical TiO2NPs were prepared on indium tin oxide (ITO) and silicon (Si) substrates from titanium hydroxide Ti(OH)4 using the unified sol-gel, spray and spin coating method followed by thermal annealing at different temperatures (in the range of 200–650 °C). Samples were characterized using various analytical tools to determine the influence of annealing temperatures on their structures, morphologies, and optical and photovoltaic characteristics. A field-emission scanning electron microscope (FESEM) and energy-filtered transmission electron microscopy (EFTEM) images of the annealed films displayed the existence of spherical TiO2NPs of average size in the range of 3.2 to 33.94 nm. XRD analysis of the films showed their amorphous nature with anatase and rutile phase. Optical UV-Vis spectral analysis of the annealed films exhibited a decrease in the bandgap energy from 3.84 to 3.24 eV with the corresponding increase of annealing temperature from 200 to 650 °C. The optimum films obtained at 500 and 600 °C were utilized as electron transport layers to fabricate the metal-insulator-semiconductor solar cells. The cells’ power conversion efficiency assembled with the spherical TiO2NPs-enclosed thin films annealed at 500 and 600 °C were 1.02 and 0.28%, respectively. Furthermore, it was shown that the overall properties and photovoltaic performance of the TiO2NPs-based thin films could be improved via thermal annealing

Enhancement of Temperature Fluorescence Brightness of Zn@Si Core-Shell Quantum Dots Produced via a Unified Strategy

Despite many dedicated efforts, the fabrication of high-quality ZnO-incorporated Zinc@Silicon (Zn@Si) core–shell quantum dots (ZnSiQDs) with customized properties remains challenging. In this study, we report a new record for the brightness enhancement of ZnSiQDs prepared via a unified top-down and bottom-up strategy. The top-down approach was used to produce ZnSiQDs with uniform sizes and shapes, followed by the bottom-up method for their re-growth. The influence of various NH4OH contents (15 to 25 µL) on the morphology and optical characteristics of ZnSiQDs was investigated. The ZnSiQDs were obtained from the electrochemically etched porous Si (PSi) with Zn inclusion (ZnPSi), followed by the electropolishing and sonication in acetone. EFTEM micrographs of the samples prepared without and with NH4OH revealed the existence of spherical ZnSiQDs with a mean diameter of 1.22 to 7.4 nm, respectively. The emission spectra of the ZnSiQDs (excited by 365 nm) exhibited bright blue, green, orange-yellow, and red luminescence, indicating the uniform morphology related to the strong quantum confinement ZnSiQDs. In addition, the absorption and emission of the ZnSiQDs prepared with NH4OH were enhanced by 198.8% and 132.6%, respectively. The bandgap of the ZnSiQDs conditioned without and with NH4OH was approximately 3.6 and 2.3 eV, respectively