This thesis investigates the defects, charge states and spin properties of phosphorus doped silicon, and is motivated by a number of proposals for quantum information processing (QIP) that involve using the spin or charge of individual donors in silicon as qubits. The implantation of phosphorus into silicon is investigated; specifically the ability to remove damage and activate the implanted donors. The impact of implantation on the transport properties of silicon MOSFETs at cryogenic temperatures is used to investigate the damage. Implanting phosphorus into the MOSFET channel leads to reduced electron mobility. The defect density increases linearly with implant density (??ndefect = 0.08 ?? 0.01nimplant). Silicon implantation does not show this effect, suggesting that the additional defects are ionised P donors in the channel. Implant activation for low density donors was complete for an implant density of 2 x 1012 cm2. Similar studies were undertaken on devices with a variety of dielectrics. Thermally grown SiO2 was found to have the lowest defect density of those studied, although Al2O3 deposited via atomic layer deposition was found to have properties that may be useful for the fabrication of devices with low thermal processing budgets. The as-grown defect density of the thermal silicon dioxide was found to be 2.1 ?? 0.3 x 1011 cm2. Ion implantation of nanoscale devices allowed the spin properties of a small number of phosphorus donors in silicon to be probed via electrically detected magnetic resonance. This allowed the detection of the spin resonance of as few as 100 spins. This represents an improvement in number detection of 4 orders of magnitude over previous EDMR studies of donors in silicon. EDMR was used to investigate the properties of P donors in isotopically purified 28Si . The material had a background doping level too high to detect small numbers of spins, however, the narrow linewidth of the phosphorus resonance confirm that the isotopic purity is greater than 0.999. A proof-of-principle demonstration of pulsed EDMR of ion-implanted donors in silicon is presented. The spin dependent transient that results from manipulating the donor spins via pulsed ESR is sensitive to as few as 104 donors, and is a required component for observation of spin Rabi oscillations by this technique.

Zinc Oxide (ZnO)is a wide band gap semiconductor which has attracted great attention because of its wide applicability. In order to obtain semiconductor devices with stable and reproducible properties further study of deep level defects is essential. DLTS (Deep level Transient Spectroscopy) is a direct and straightforward techniqueto determine the energy level of the deep level defects. Other information such as activation energy and capture cross section of the defect can also be obtained through this method. In our study ZnO single crystal samples were implanted by oxygen with the energy of 150keV. After the pretreatment of hydrogen peroxide, Schottky contacts were fabricated with Au film deposited by thermal evaporation. Deep level defects were studied by deep level transient spectroscopy (DLTS). Single peak spectra were observed in the as-implanted sample and samples anneal at 350oC, 650oC and 750oC with the corresponding activation energy decreasing with the annealing temperature from ~0.29eV as found in theas-implanted sample. Three peaks were identified in the DLTS spectra of the 900oC sample, with the activation energies of 0.11eV, 0.16eV and 0.37eV respectively.After analysis in detail we found some peaks in the DLTS spectra were the combination of two other peaks, dominated in different temperature range. The thermal evolutions of the deep levels up to the temperature of 1200oC were also investigated. / published_or_final_version / Physics / Master / Master of Philosophy

Plasma Source Ion Implantation (PSII) is the process of implanting high energy ions [10-50 keV] into metallic targets, by pulsing them negatively whilst immersed in a background plasma. PSII achieves surface hardening, and increased wear and corrosion resistance. Numerous papers have been published describing numerical simulations and models of the PSII process, most of which have been limited to one dimension. This thesis presents the results of work carried out III the Plasma Processing Laboratory at the University of Natal, Durban, during 1994-1995. In particular, measurements of two-dimensional plasma sheath effects due to spherical and complex shaped targets are compared with a particle-in-cell simulation code. The simulation results are used to define a relationship between the plasma potential of the sheath edge and the saturation currents. Thus allowing for the saturation currents to be used to trace sheath evolution. These results are compared with the experimental measurements from the spherical target. Results from the rectangular and complex saw-tooth targets show a lack of sheath conformality. The ion saturation currents were susceptible to electron swamping, which occured in localised regions associated with target structure. It is thought that secondary electrons ejected from the target are focused and accelerated by the high target potential into these regions, where they swamp the ion current. / Thesis (M.Sc.)-University of Natal, Durban, 1996.

The primary focus of this thesis is to study the effect of doping on magnetic properties in amorphous Fe100−xZrx alloys. Samples with compositions of x = 7,11.6 and 12 at.% were implanted with different concentrations of H. Moreover, the samples with a composition of x = 7 at.% were also implanted with He, B, C and N. Magnetic measurements were performed, using SQUID magnetometry and MOKE, in order to compare the as-grown and the implanted films. The Curie temperature (Tc) increases and the coercivity (Hc) decreases, with increasing dopant volume. We also found that Hc increases with temperature for B and C doped samples. Magnetization curves at low temperature validate the presence of non-collinear spin configurations in the as-grown films, which is suppressed after doping, resulting in films with tunable soft magnetic properties. We have also studied the effect of interlayer mixing and finite size effects on FeZr in Fe92Zr8/AlZr multilayer films, and found an anomalous increase of Tc with decreasing thickness. Strain induced changes in the magnetization of an amorphous Co95Zr5 film at the orthorhombic phase transition of the BaTiO3 substrate, was also studied. The results show that structural modifications of the substrate increases the stress and hence changes the magnetic anisotropy in the amorphous Co95Zr5 layer. Finally, the magnetization reversal of Co and CoX heterostructures, with X being Cr, Fe, Ni, Pd, Pt and Ru, has been studied. For this purpose a synthetic antiferromagnet structure, FM/NM/FM, was used, where FM is a ferromagnetic Co or CoX layer and NM is a nonmagnetic Ru spacer layer. The FM layers are coupled antiferromagnetically across the NM layer. For a range of FM layer thicknesses, the exchange stiffness parameter Aex and the interlayer coupling (JRKKY ) of the Co or CoX layers were obtained. This is done by fitting M(H) curves, measured by SQUID magnetometry, to a micromagnetic model. The alloying in CoX resulted in a decreasing Aex and also a reduced MS. The experimental results are in a good agreement with DFT calculations.

This thesis investigates the defects, charge states and spin properties of phosphorus doped silicon, and is motivated by a number of proposals for quantum information processing (QIP) that involve using the spin or charge of individual donors in silicon as qubits. The implantation of phosphorus into silicon is investigated; specifically the ability to remove damage and activate the implanted donors. The impact of implantation on the transport properties of silicon MOSFETs at cryogenic temperatures is used to investigate the damage. Implanting phosphorus into the MOSFET channel leads to reduced electron mobility. The defect density increases linearly with implant density (??ndefect = 0.08 ?? 0.01nimplant). Silicon implantation does not show this effect, suggesting that the additional defects are ionised P donors in the channel. Implant activation for low density donors was complete for an implant density of 2 x 1012 cm2. Similar studies were undertaken on devices with a variety of dielectrics. Thermally grown SiO2 was found to have the lowest defect density of those studied, although Al2O3 deposited via atomic layer deposition was found to have properties that may be useful for the fabrication of devices with low thermal processing budgets. The as-grown defect density of the thermal silicon dioxide was found to be 2.1 ?? 0.3 x 1011 cm2. Ion implantation of nanoscale devices allowed the spin properties of a small number of phosphorus donors in silicon to be probed via electrically detected magnetic resonance. This allowed the detection of the spin resonance of as few as 100 spins. This represents an improvement in number detection of 4 orders of magnitude over previous EDMR studies of donors in silicon. EDMR was used to investigate the properties of P donors in isotopically purified 28Si . The material had a background doping level too high to detect small numbers of spins, however, the narrow linewidth of the phosphorus resonance confirm that the isotopic purity is greater than 0.999. A proof-of-principle demonstration of pulsed EDMR of ion-implanted donors in silicon is presented. The spin dependent transient that results from manipulating the donor spins via pulsed ESR is sensitive to as few as 104 donors, and is a required component for observation of spin Rabi oscillations by this technique.

We investigate the newly discovered, superconducting metal-mixed polymers made by embedding a surface layer of metal (a tin-antimony alloy) into a plastic substrate (polyetheretherketone - PEEK). Focusing initially on pre-implanted systems, we show that while the substrate morphology does affect the distribution of metal deposited on the surface, the morphology has no affect on the film's electrical properties. We find that the metal content can be characterised via the film's optical absorption, which along with the conductivity, scales with thickness. By conducting low temperature resistivity measurements we observe that the superconducting critical temperature, $T_c$, remains at that of bulk Sn but the transition broadens with decreasing film thickness. Studying N-implanted metal-mixed polymers, we find that the implant temperature can influence the electrical properties of these systems, as higher implant temperatures result in greater disorder, which in turn causes higher residual resistances and broader superconducting transitions. We observe peaks in the magnetoresistance of superconducting/insulating systems, which we attribute to the competition between superconductivity and weak localisation in a granular network. We determine that the substrate morphology does not influence the electrical properties of implanted systems. We investigate the role sputtering plays by implanting heavier ions (Sn) and show that this technique can be used to overcome the issue of inhomogeneity inherent with using thinner initial films. We study the effect the fabrication parameters of implant dose, beam energy and film thickness have on Sn-implanted metal-mixed polymers and find that with only minor changes in the fabrication conditions, it is possible to tune the conductivities of these materials between a zero-resistance superconducting state, through a metal-insulator transition, to a severely insulating state ($R_s > 10^{10}~\Omega/\Box$). We find that the electrical properties can be further controlled by annealing the samples, and that it is possible to induce optical changes at temperatures approaching the glass transition temperature of PEEK. We demonstrate that metal-mixed polymers are suitable for use in resistance-based temperature sensors by comparing their performance directly against commercially available products and find that the metal-mixed polymers perform at least as well as the commercial models and, indeed, pass the highest industry standards.

We have studied the introduction of defects in silicon wafers with low dose channelling ion implantation. (For complete abstract open document)

Ion Implantation of ruthenium ions into a silicon substrate followed by a high temperature anneal (known as Ion Beam Synthesis) has been used for the first time to fabricate three wafers, under the following conditions. 1. 5.67 X 1016 Ru+ cm-2, beam heated 2. 4.25 X 1016 Ru+ cm-2, heated to ~ 600°C 3. 1.27 X 1017 Ru+ cm-2, heated to ~ 600°C All wafers contained precipitates of the orthorhombic semiconducting silicide of ruthenium, Ru2Si3. No other phase was identified. The samples exhibited a complicated microstructure, with 16 different orientation variants identified, and a high degree of disorder (~ +11% strain). The first optical measurements ever carried out on this material are reported here. Absorption measurements in transmittance yielded a direct band gap, in the region of ~ 0.9eV, 0.87eV, and 0.92eV for wafers 1, 2, and 3 respectively. No discernible variation of band gap magnitude with measurement temperature was found. Upon sequential annealing, the direct band gap magnitude remained constant up to ~ 650°C after which it shifted to above that of silicon, possibly due to a change in microstructural disorder as the precipitates increase in size. This observation was confirmed by several single step anneals at various temperatures above 650°C. No photoluminescence was observed in any of the samples.

Resumo: Filmes finos polimerizados a plasma apresentam várias aplicações nas indústrias óticas, elétrica, mecânica de alimentos, de biomateriais entre outras, devido suas interessantes propriedades químicas e físicas. No entanto, as aplicações para os filmes finos podem ser limitadas em função de algumas de suas características mecânicas e de superfície. Neste trabalho, filmes finos poliméricos foram depositados por radiofrequência a partir de plasmas de hexametildissilazano mantido a baixa pressão. Posteriormente, foram implantados íons de argônio, hélio e nitrogênio nestes filmes através da implantação iônica por imersão a plasma (IIIP). Após os tratamentos, os filmes finos provenientes da polimerização a plasma do hexametildissilazano apresentaram modificações em suas estruturas moleculares e composição química através das análises infravermelha e XPS. O XPS revelou um aumento nas concentrações de oxigênio e decréscimo de carbono e nitrogênio. Este fato indica aumento no nível e entrelaçamento, ramificação e reticulação das cadeias poliméricas para todos os íons implantados. Verificou-se também que a IIIP promoveu mudanças na molhabilidade com variações nos ângulos de contato de 100° para 10°; alterações nos índices de refração entre 1,65 a 2,10; modificações na dureza e módulo elástico de 0,8 a 3,3 GPa e 6,0 a 52,0 GPa respectivamente, assim como redução na taxa etching de 34,0 para 20,0 Å/min. / Abstract: Plasma polymerized thin films have many applications in optical, electrical, mechanical, food, biomaterial industries among others, due to their interesting chemical and physical properties. Polymer thin films applications, however, can be limited because of some mechanical and surface characteristics. In this work, thin polymer films were deposited from radiofrequency plasmas of hexamethyldisilazane at low pressure. Then, these films were implanted with argon, helium and nitrogen ion, by plasma immersion ion implantation (PIII). After the treatments, plasma polymerized hexamethyldisilazane thin films presented modifications in their molecular structure and chemical composition by infrared and XPS analysis. XPS revealed an increase in the oxygen, decrease in nitrogen and carbon concentrations. This fact indicates increased crosslinking of the polymeric chains of all implanted ions. It was also verified that a PIII caused modification in wettability, changing the contacts angles from 100° to 10°. Modifications were also observed in the refractive index from 1,65 to 2,10; in hardness and in the elastic modulus from 0,8 a 3,3 GPa and 6,0 to 52,0 GPa respectively. The study showed a decrease in etching rate from 34,0 to 20,0 Å/min. / Orientador: Rogério Pinto Mota / Coorientador: Deborah Cristina Ribeiro Santos / Banca: Roberto Yzumi Honda / Banca: Elson de Campos / Banca: Emerson Ferreira de Lucena / Banca: José Roberto Ribeiro Bortoletto / Doutor

A unique process of fabricating a strained layer GexSi1-x on insulator is demonstrated. Such strained heterostructures are useful in the fabrication of high-mobility transistors. This technique incorporates well-established silicon processing technology e.g., ion implantation and thermal oxidation. A dilute GeSi layer is initially formed by implanting Ge+ into a silicon-on-insulator (SOI) substrate. Thermal oxidation segregates the Ge at the growing oxide interface to form a distinct GexSi1-x thin-film with a composition that can be tailored by controlling the oxidation parameters (e.g. temperature and oxidation ambient). In addition, the film thickness can be controlled by implantation fluence, which is important since the film forms pseudomorphically below 2×1016 Ge/cm2. Continued oxidation consumes the underlying Si leaving the strained GeSi film encapsulated by the two oxide layers, i.e. the top thermal oxide and the buried oxide. Removal of the thermal oxide by a dilute HF etch completes the process. Strain relaxation can be achieved by either of two methods. One involves vacancy injection by ion implantation to introduce sufficient open-volume within the film to compensate for the compressive strain. The other depends upon the formation of GeO2. If Ge is oxidized in the absence of Si, it evaporates as GeO(g) resulting in spontaneous relaxation within the strained film. Conditions under which this occurs have been discussed along with elaborated results of oxidation kinetics of Ge-ion implanted silicon. Rutherford backscattering spectrometry (RBS), ion channeling, Raman spectroscopy and scanning electron microscopy (SEM) were used as the characterization techniques.