259 research outputs found
Investigation of silicon nanowires photodetector
No full textSilicon nanowires (SiNWs) research has intensified over the past decade with the advancement in nanowires fabrication technology. The objectives of this study are to (i) develop a fabrication process to obtain top-down SiNWs with cross-sectional dimensions of 10 nm or less, (ii) characterize the physical structures of the SiNWs, (iii) form SiNWs p+-n+ and p+-p-n+ diodes along the nanowires and (iv) characterize the SiNWs diodes under dark and illuminated conditions to gain an understanding of the nanoscale junction devices.
The diodes fabricated consist of multiple SiNWs of 1 μm long connected in parallel, as well as larger dimension bulk diodes that are served as control diodes. Three different batches of diodes were fabricated. Batch 0 samples demonstrated the successful fabrication of SiNWs p+-p-n+ diodes. The subsequent fabrication was to examine the formation of the nanowires and to improve the electrical characteristics of the SiNWs diodes. The silicon fin width and oxidation time were reduced in batch 1 samples fabrication. Silicon oxide was deposited on the SiNWs as passivation, to replace the thermal oxide that was removed for the purpose of inspection. The last round of fabrication was to reduce the high leakage current observed in batch 1 diodes. The batch 2 samples have either deposited or thermal oxides as passivation for the SiNWs. The dopant activation time was reduced from 20 s to 5 s in batch 2 samples.Master of Engineerin
Optical properties of anisotropic photonic crystals
No full textA photonic crystal can be simply viewed as a lattice with a motif attached to each lattice point. If the re-orientation of the motif causes changes in the optical properties of the photonic crystal then the corresponding photonic crystal is an anisotropic photonic crystal. Anisotropic photonic crystals can be classified as materially and geometrically anisotropic photonic crystals. The study so far in the field of anisotropic photonic crystal was concentrated mainly in optimizing and tuning the photonic bandgaps. This thesis aims to provide a unified understanding of anisotropic photonic crystals using proper symmetrical tools. Apart from this, the thesis also examines the properties of anisotropic photonic crystals that remain unexplored. Basic equations and operators that describe light propagation in one, two, and three dimensional anisotropic photonic crystals are formulated. The decoupling of the two independent polarizations of light in the case of a materially anisotropic photonic crystal is analyzed in detail. The symmetrical properties of the defined operator are investigated in detail using group theory, and novel concepts such as orientational group and fundamental zone of orientation are introduced. We have revealed a standard solution method based on plane wave expansion technique in order to solve the basic equations. In addition, a powerful approximation technique that leads to analytical equations to the evolution of the states in a two-dimensional photonic crystal is proposed. Equal frequency surface of the anisotropic crystal is analyzed. We propose one-plane-wave and two-plane-waves approximation techniques for calculating equal frequency surfaces in the photonic crystals with a small spatial modulation. When the modulation is large, it is found that the equal frequency surfaces can be defined using a set of negative principal refractive indices. The properties of such anisotropic negative index states were analyzed in detail, and the tuning of negative principal refractive indices and the phenomena of accidental isotropy in the anisotropic states are reported. Equal frequency surfaces are also used in predicting conduction properties of light in the anisotropic photonic crystals. Controllable conduction devices such as tunable superprism and polarization splitters are proposed, based on two-dimensional anisotropic photonic crystals, with electrically re-orientable motif. We have shown both switching action and continuous tunability in these devices. Apart from the conduction properties, bandgap engineering in materially anisotropic one- and two-dimensional photonic crystals is also investigated. In particular, we have shown how polarization dependent partial and full bandgaps are being created in a materially anisotropic square lattice photonic crystal. With the use of anisotropic materials and the flexibility of arranging the principal axes, the requirement on filling ratio, refractive index and anisotropy to achieve the largest bandgap is greatly alleviated.DOCTOR OF PHILOSOPHY (EEE
Nano gold template formed by using duv lithography process
No full textNanowires have been greatly researched in recent years as many see its potential in the future applications. There are many ways in fabricating nanowires and one of which is via vapor liquid solid (VSL) method. This technique makes use of metallic catalyst to aid its growth into nanowire. The catalyst plays a very important role as it would directly characterize the nanowire that would be formed.
Among all catalyst for the used for the growth of nanowire, gold (Au) has been widely used as it is very active and applicable for different types of catalytic reactions. Furthermore, several researches have reported that most of the semiconductor nanowires have been successfully grown with the use of gold nanoparticles.
There are currently many methodologies to form catalyst. Dewetting thin film deposited on substrate is a common and neat technique which many are using. Thin film is deposited onto the substrate formed by annealing. However, despite its advantages, easy and neat method, it usually produces nanoparticles of with size of broad distribution and the nanoparticles are not orderly formed.
In this project, a nano template of circular Au pad of different dimension is created using Deep UV lithography process. The template is then annealed using furnace so to allow the Au film to dewet into small particles. The process conditions such as annealing temperature, thickness of the film, pad dimension and annealing time are varied in aim to obtain the optimized conditions for the growth of the nano gold template.Bachelor of Engineerin
Electrical Characterization of CMP-Less Via-Last TSV under Reliability Stress Conditions
No full textGrowth and characterization of amorphous Si based multilayer structures
No full textSilicon is a widely available material with very good electrical, thermal and mechanical properties suitable for the manufacture of electronic devices and has contributed to the big success of microelectronics. The trend in Si microelectronics towards faster and smaller devices has resulted in many issues such as heat dissipation, crosstalk and RC delay in metal interconnects. To address these issues while achieving faster inter-component communication and keeping the costs low, Si microphotonics which focuses on the development of Si based phtonics devices has been actively pursued. Todate almost all Si based optoelectronic components, such as waveguides, detectors and modulators have been realized except for an efficient light source. Many attempts have been made to obtain visible light emission from Si utilizing amorphous Si (a-Si) and/or Si nanostructures. These include porous Si, Si nanocrystals embedded in a dielectric matrix. Another approach to based low dimensional Si based materials to achieve light emission, is to utilize multilayer structures. These structures have the advantages of reproducibility and thickness controllability, which makes them leading competitors in this field. In this work we have fabricated a-SiNx:H/SiO2 multilayer quantum well structures consisting of 20 alternating layers of a-SiNx:H and SiO2 using the plasma enhanced chemical vapor deposition (PECVD) technique. a-SiNx:H has been chosen as it is an efficient light emitting material and its bandgap can be tuned in a wide energy range. This property will give rise to greater flexibility in controlling and optimizing the emission characteristics. With the prospect of optimizing the N content in our a-SiNx:H material for its light emission we have started with studying single layer a-SiNx:H material. They have been grown by varying the Si source gas (SiH4) and N source gas (NH3) flow ratio in the range of 1.05 to 3.16. Their optical properties, including the bandgap, Urbach energy and complex refractive indices were obtained by a detailed study of their spectroscopic ellipsometry data. The optimum gas flow ratio for efficient light emission was found to be 1.58. The multilayers consist of 20 alternating layers of a-SiNx:H material as the well and SiO2 as the barrier layers. The growth condition for a-SiNx:H well layer was chosen to be the same as the sample with gas flow ratio of 1.58, since it was found to be the optimum condition for PL efficiency. The SiO2 barrier layer were grown using N2O and SiH4 as O and Si source gases. To study the effect of well layer thickness, two different multilayer structures with fixed barrier layers of 10 nm and well layer thicknesses of 3 and 6 nm were fabricated. The complex refractive index of the a-SiNx:H well layers and SiO2 barrier layers were determined from SE data fitted to a model utilizing Tauc-Lorentz and Cauchy dispersions to describe the well and barrier materials respectively. The layer thicknesses obtained from SE results are in good agreement with the ones measured from TEM graphs. To achieve a high efficiency EL, we have used a structure where electric current is injected laterally and parallel to the multilayer structure. In this way, the current mainly flows only through the well layers and not the barrier layers, and hence the injection process is expected to be more efficient. In total, 20 layers of alternate a-SiNx:H well and SiO2 barrier layers with respective thicknesses of 6 nm and 5 nm were grown. N2O and SiH4 were used as the source gases for SiO2 barrier layer deposition. A post annealing process at 1000oC for one hour in N2 ambient was performed to enhance the PL intensity. To make the contacts for lateral injection of current, we have etched away the multilayer using reactive ion etching and deposited heavily doped n and p type poly Si on each side of the multilayer structure forming interdigitated contacts. For comparison, a similar multilayer structure has been grown for the fabrication of devices with electric field applied vertically. Heavily n-doped Si substrate and a 100 nm thick layer of heavily doped p-type poly Si were used as the bottom and top electrodes respectively. The current-voltage relation of the laterally injected PIN structure indicates good rectifying characteristics of the device. A significant improvement of more than nine orders of magnitude has been observed in the laterally injected device as compared to the vertical one. This can be attributed to the absence of highly resistive barrier layers in the current path. We have observed orange color EL from the device under forward bias condition, a result of radiative recombination of electron hole pairs injected from the n and p poly Si.DOCTOR OF PHILOSOPHY (EEE
- …
