Due to the small concentration of impurities normally present in semiconductors these impurity concentrations cannot' be measured by ordinary chemical analysis. Electrical methods are the common way by which semiconductor impurity concentrations are measured. The specific problem investigated was to determine the concentration Nd of donors and the concentration Na of acceptors at various points in a crystal of silicon. A description of the crystal structure and the energy band scheme of silicon is given. The density of states in the conduction and valence bands is calculated. The population of the conduction and valence bands by electrons and holes as a function of impurity concentration and temperature is derived. A method is given from which the values of Nd and Na may be found from Hall constant measurements at liquid nitrogen and room temperatures. The experimental apparatus used includes a magnet, cryostat, sample holder, and Hall measuring circuit. The results obtained from the measurements are in agreement with those expected from the available knowledge of the method of crystal growth. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The method of fabrication, the theory and the properties of evaporated silicon thin-film transistors are discussed. The device consists of a p-type silicon film (0.5 to 2µ thick) on a sapphire substrate, with aluminum source-drain electrodes evaporated onto the silicon and followed by a silicon oxide, SiOx , insulating layer and an aluminum gate. The device operates by field-effect conductivity modulation of an n-type inversion layer at the surface of the p-type film. The silicon films were evaporated by electron beam heating in a typical vacuum of 7 x 10⁻⁷ mm Hg at a rate of 200-600 Å/min. The films exhibited single crystal diffraction patterns when deposited at a substrate temperature in the range 1050°C to 1100°C. They were found to be high resistivity ( > 400 Ω -cm) p-type and the hole mobility was of the order of 20-30 cm² /volt-sec. The minority carrier lifetime, was 1-2 µsec and the optical absorption edge of the films was found to be broader than the absorption edge of single crystal silicon at all substrate temperatures. The low carrier mobility and minority carrier lifetime as well as the broadening of the optical absorption edge are attributed to the presence of a large number of crystallographic defects in the films. The effective surface state density at the Si/ evaporated SiOx interface was estimated by the MOS technique and was found to be of the same order of magnitude (3 - 4 x 10¹¹ cm⁻² ) as that at the Si/thermally grown SiO₂ interface. The silicon surface potential in the MOS structure was found to be particularly susceptible to water vapour and contamination by sodium. The silicon thin-film transistors fabricated have typical effective mobilities of 5-10 cm² /volt-sec with transconductances as high as 100 µmho and gain-bandwidth products up to 1 MHz. Surface trapping was found to affect the behavior of the devices at low gate voltages. The characterization of the traps by a method which involves measurements of the source-drain conductance, its temperature dependence and its transient response is discussed. The effect of surface scattering on the mobility at high gate voltages is also considered. The device characteristics were stable in vacuum but drifted when exposed to the atmosphere. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

No description available.

In this research, we design and characterize thermally tuned hybrid tellurium ox- ide coated silicon (TeO2-Si) microdisk resonators for the development of tunable on chip lasers. Several heater designs are proposed that are compatible with stan- dard silicon photonics foundry processes and the requirement to deposit TeO2 onto the fabricated chips in post-processing. The devices are designed using simulation software packages such as Lumerical MODE and HEAT to simulate the mode profiles and thermo-optic coefficients of the microdisk resonators and the heating profiles of the various heater designs. The devices are laid out using the Luceda IPKISS Photonics Design Platform and fabricated at the AMF silicon photonics foundry. TeO2 is then deposited onto the fabricated chips at McMaster University in a single post-processing step via reactive radio frequency magnetron sputter- ing. Passive optical transmission measurements are performed to characterize the intrinsic Q-factors, loss and FSR of the microdisks. This is followed by resonance tuning measurements to characterize the tuning efficiencies of each of the heater designs presented in this thesis. The performances of each of the heater designs are then discussed and compared. / Thesis / Master of Applied Science (MASc)

by Cheung Wing-yiu. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves [170-185]). / ACKNOWLEDGMENT --- p.I / abstract --- p.II / contents --- p.IV / figure captions --- p.C-1 / table captions --- p.C-10 / photo captions --- p.C-11 / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Novel Silicon-Based Materials Structures - Background and Perspectives --- p.2 / Chapter 1.2 --- Light Emission from Porous Silicon --- p.3 / Chapter 1.2.1 --- Quantum size effect --- p.7 / Chapter 1.2.2 --- Chemical luminescence model --- p.9 / Chapter 1.3 --- Germanium Silicon Alloy --- p.11 / Chapter 1.3.1 --- Formation of germanium silicon alloy by ion implantation --- p.16 / Chapter 1.4 --- Scope of this Work --- p.19 / Chapter CHAPTER 2 --- EXPERIMENTAL METHODS --- p.20 / Chapter 2.1 --- Preparation of Porous Silicon Layers --- p.20 / Chapter 2.1.1 --- Anodization --- p.21 / Chapter 2.1.2 --- Post - anodization treatments --- p.25 / Chapter 2.2 --- Preparation of Germanium Silicon Alloy --- p.27 / Chapter 2.2.1 --- Ion implantation --- p.27 / Chapter 2.2.2 --- Thermal treatment --- p.27 / Chapter 2.3 --- Characterization Methods --- p.28 / Chapter 2.3.1 --- Microscopy studies --- p.28 / Chapter 2.3.2 --- Structural studies --- p.30 / Chapter 2.3.3 --- Compositional studies --- p.31 / Chapter 2.3.4 --- Electron spin resonance --- p.32 / Chapter 2.3.5 --- Optical methods --- p.36 / Chapter 2.3.6 --- Electrical measurements --- p.38 / Chapter 2.3.6.1 --- Spreading resistance profiling --- p.38 / Chapter 2.3.6.2 --- Other electrical measurements --- p.40 / Chapter CHAPTER 3 --- POROUS SILICON - RESULTS --- p.41 / Chapter 3.1 --- General observation of on the Appearance of Samples --- p.41 / Chapter 3.2 --- Formation Current Voltage Characteristics --- p.41 / Chapter 3.3 --- Surface Morphology --- p.52 / Chapter 3.4 --- Electron Spin Resonance --- p.56 / Chapter 3.5 --- Composition Characteristics --- p.68 / Chapter 3.6 --- Optical Characteristics --- p.72 / Chapter 3.6.1 --- Infra-red transmittance studies --- p.72 / Chapter 3.6.2 --- Photoluminescence --- p.74 / Chapter 3.7 --- Electrical Properties --- p.82 / Chapter CHAPTER 4 --- POROUS SILICON - DISCUSSION --- p.84 / Chapter 4.1 --- Formation Properties --- p.84 / Chapter 4.2 --- Structural Properties --- p.87 / Chapter 4.3 --- Paramagnetic Centres in Porous Silicon --- p.88 / Chapter 4.4 --- Compositional Properties --- p.93 / Chapter 4.5 --- Photoluminescence --- p.95 / Chapter 4.6 --- Electrical Properties --- p.105 / Chapter 4.7 --- Summary --- p.106 / Chapter CHAPTER 5 --- GERMANIUM SILICON ALLOY - RESULTS --- p.108 / Chapter 5.1 --- Structural Characteristics --- p.108 / Chapter 5.1.1 --- Defect structure --- p.109 / Chapter 5.1.2 --- Crystal structure --- p.115 / Chapter 5.2 --- Optical Characteristics --- p.127 / Chapter 5.3 --- Electrical characteristics --- p.129 / Chapter 5.3.1 --- Spreading resistance profiling --- p.129 / Chapter 5.3.2 --- Other electrical measurements --- p.138 / Chapter CHAPTER 6 --- GERMANIUM SILICON ALLOY - DISCUSSION --- p.142 / Chapter 6.1 --- Structure Analysis --- p.142 / Chapter 6.2 --- Optical Properties --- p.146 / Chapter 6.3 --- Electrical Properties --- p.147 / Chapter 6.4 --- Summary --- p.150 / Chapter CHAPTER 7 --- CONCLUSIONS --- p.152 / Chapter 7.1 --- Porous Silicon --- p.152 / Chapter 7.2 --- Germanium Silicon Alloys --- p.154 / Chapter CHAPTER 8 --- FURTHER WORK --- p.156 / Chapter 8.1 --- Porous Silicon --- p.156 / Chapter 8.2 --- Germanium Silicon Alloys --- p.156 / APPENDIX / Chapter I --- SPECTRA OF GERMANIUM SILICON ALLOY --- p.A1 / Chapter 1.1 --- Rutherford Backscattering Spectra --- p.A2 / Chapter 1.2 --- Spreading Resistance Depth Profile --- p.A8 / Chapter II --- PUBLICATIONS --- p.A14 / BIBLIOGRAPHY --- p.A15

Silicon nanocrystals embedded in silicon nitride have received attention as promising materials for optoelectronic applications. More specifically, band gap engineering of novel materials based on silicon nanocrystals has been proposed for possible application in an all-silicon tandem solar cell within the field of `third generation' photovoltaics. Such an application would require nanocrystals to exhibit quantum confinement whereby the optical and electrical properties of a film could be tuned by controlling the size of these `quantum dots'. This thesis investigates the correlation between the structural and optical properties of silicon nanocrystals grown in silicon nitride multilayer structures via solid phase crystallisation, as part of an experimental investigation into quantum confinement. A study of the relevant processing parameters for the solid phase crystallization of silicon nanocrystals in amorphous silicon nitride is presented and the effectiveness of the multilayer approach for controlling nanocrystal size is demonstrated. Structural characterisation using transmission electron microscopy and glancing incidence x-ray diffraction is complemented with a new application of Fourier transform infrared spectroscopy for the detection of silicon nanocrystals. A case study on the effects of annealing temperature on the photoluminescence from silicon nitride multilayers is presented. While a clear correlation between the structural, molecular and optical properties is demonstrated, evidence of quantum confinement remains ambiguous. The investigation into the limits of parameter space for the formation of silicon nanocrystals in silicon nitride multilayers also leads to the formation of a novel Si-Si3N4 nanocomposite material. A comprehensive study of the photoluminescence from silicon nanocrystals embedded in nitride is presented in the context of homogeneous and multilayer nitride films. Size dependent PL and absorption is demonstrated for silicon nitride multilayers with silicon-rich silicon nitride layer thicknesses varying from 1 to 4.5 nm, indicating the formation of quantum wells. These same structures are annealed to form arrays of silicon nanocrystals. Although the PL and absorption spectra suggest quantum effects, inherent ambiguities remain. The findings in this thesis provide greater insight into the nature of confinement and indicate the need for further research if the successful implementation of these structures into an all silicon tandem cell is to be achieved.

An 89 mm-diameter vertical tubular-flow reactor was used to study the kinetics of nano-sized silicon nitride powder synthesis via the animonolysis of SiO vapor at temperatures ranging from 1300°C to 1400°C. The SiO generation rate was controlled by adjusting the mass of SiO particles initially charged in the SiO generator, when the flow rate of carrier gas argon was maintained unchanged. The molar feed ratio of NH₃/SiO at the feeder outlets was maintained in large excess of the stoichiometric ratio ranging from about 100 to 1200 mol NH₃/mol SiO. The SiO-NH₃ reaction yielded two different morphologies of silicon nitride products at different locations in the reactor: nano-sized powder with an averaged particle size of about 17 nm and whiskers with a variety of shapes and diameters of a few micrometers. Nano-sized powder was the dominant product in the system and its mass fraction over the total product varied from 83% to 100%, depending on operating conditions. The contact pattern between SiO vapor and NH₃ inside the reacting zone was one of the most important parameters that affected Si₃N₄ formation kinetics. When a small single tube was employed for feeding NH₃ (flow condition J), a highest efficiency of SiO vapor utilization was achieved at a high level of SiO conversion. The SiO conversion increased from 72% to 91% with an increase in the residence time from 0.17 s to 0.69 s, indicating that the SiO-NH₃ reaction was not instantaneous but was relatively fast. When the molar feed rate of NH₃ was 2-3 orders of magnitude greater than that of SiO vapor, the rate of nano-sized powder synthesis was independent of NH₃ concentration and of first order with respect to the SiO concentration. A pseudo-first order rate expression was proposed, and the apparent activation energy was determined to be 180 kJ/mol. The gas flow in the reactor simulated with a computational fluid dynamic program revealed that whisker formed where the stagnation of gas flow formed. A power law rate expression for whisker formation was proposed based on measured rates of whisker formation and simulation-predicted reactant-gas concentrations. / Graduation date: 2004

Graduation date: 1996

The self-interstitial defect is commonly regarded as important in regulating diffusion in silicon. A review of the literature reveals that the scientific bases for invoking the self-interstitial defect are weak, while an alternate defect, the vacancy cluster, has been largely ignored. One argument which has been used to establish dominance of the self-interstitial defect over vacancies is based upon attempts to model gold diffusion. Possible behavior of vacancies are considered, and the past analysis is found to be inconclusive. Another argument which has been presented as evidence for presence of silicon self-interstitials is based on observations of type "A" swirl defects. These defects are amenable to interpretation in terms of solidification theory, without need to invoke the interstitial point defect. Two experiments were designed to demonstrate influence of heat treatments upon gold diffusion in electronic grade silicon crystal when the heat treatment was performed prior to gold deposition. Results are interpreted in terms of Ostwald ripening of vacancy clusters retained in the crystal from high temperature processing. / Graduation date: 1996

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 161-165).