Magnetic nano-clusters in silicon involving iron and cobalt were synthesized using low energy (50 keV) ion implantation technique and post-implantation thermal annealing. Before the irradiation, multiple ion-solid interaction simulations were carried out to estimate optimal ion energy and fluence for each experiment. For high-fluence low-energy irradiation of heavy ions in a relatively lighter substrate, modeling the ion irradiation process using dynamic code SDTrimSP showed better agreement with the experimental results compared to the widely used static simulation code TRIM. A saturation in concentration (~ 48%) profile of the 50 keV Fe or Co implants in Si was seen at a fluence of ~ 2 × 1017 ions/cm2. Further study showed that for structures with a curved surface, particularly for nanowires, better simulation results could be extracted using a code "Iradina" as the curve geometry of the target surface can be directly defined in the input file. The compositional, structural, and magnetic properties were studied using Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction, atom probe tomography, and vibrating sample magnetometry. Irradiation of high-current (~ 2 μA/cm2) 50 keV Fe ions into Si at a fluence of 2 × 1017 ions/cm2 showed the formation of Fe5Si3 nano structures in the near-surface region of the substrate. Post-implantation thermal annealing in vacuum at 500 οC for one hour showed a significant enhancement in structural and magnetic properties. Similar high-current irradiation of 50 keV Co with a fluence of 3.2 × 1016 ions/cm2 into Si substrate showed the formation of superparamagnetic structure even at room temperature in the as-implanted samples. The simulation results for irradiation of Co and Fe on the curved surface were validated by ion irradiation on pre-fabricated Si nano tip followed by atom probe tomography analysis.

Gallium antimonide (GaSb) is a promising low-bandgap binary substrate for the fabrication of various infrared-based optoelectronic devices, particularly thermophotovoltaics (TPV). In order to make GaSb-based technologies like TPV more widely available, non-epitaxial dop- ing methods for GaSb must be pursued. Ion implantation is relatively unexplored for GaSb, and can offer advantages over the more common method of zinc diffusion, including higher flexibility with regards to substrate type and control over the resulting doping profile. Pre- vious work has shown beryllium (Be+) implantation to be a suitable method for fabricating a diode in an n-type GaSb substrate, opening the possibility for other ions to be considered for implanting into both n-type and p-type substrates. This work identifies sulfur (S+) as another species to investigate for this purpose. To do so, material and electrical characterization was done on S+ and beryllium implanted GaSb films grown onto a semi-insulating gallium arsenide (GaAs) substrate. X-ray Diffraction spectroscopy (XRD) and Atomic Force Microscopy (AFM) indicate that the post-implant anneal of 600 for 10 s repaired the implant damage in the bulk material, but left behind a damaged surface layer composed of coalesced vacancies. While the beryllium implant resulted in moderate doping concentrations corresponding to an activation percentage near 15 %, Hall Effect data showed that implanting S+ ions induced a strongly p-type behavior, with hole concentrations above 1 × 19 cm^3 and sheet hole densities 3.5 times higher than the total implanted dose. This strong p-type behavior is attributed to the remaining lattice damage caused by the implant, which induces a large density of acceptor-like defect states near the valence band edge. This technique was used on an unintentionally-doped p-type GaSb substrate to create a + /p junction. The implant process succeeded in producing a potential barrier similar to that of a hole-majority camel diode with a thin delta-doped region suitable for collecting diffused carriers from the p-type substrate. A post-fabrication etching process had the effect of strongly increasing the short circuit current density to as high as 41.8 mA/cm^2 and the open circuit voltage as high as 0.21 V by simultaneously removing a high carrier recombination surface layer. This etching process resulted in a broadband spectral response, giving internal quantum efficiencies greater than 90 %. / Doctor of Philosophy / Thermophotovoltaics (TPV) is a technology that converts light and other forms of electromagnetic energy into electrical power, much like a typical solar panel. However, instead of sunlight, the energy source used in a TPV system is a terrestrial heat source at a temperature range of 1250–1750 ◦C, whose radiation is primarily infrared (IR). The IR-absorbing qualities and commercial availability of the compound semiconductor gallium antimonide (GaSb) have made it a key component in the development of absorber devices for TPV-related systems. GaSb-based devices have most often been fabricated using epitaxy, a method in which layer(s) of material are ‘grown’ in a layer-by-layer fashion atop a substrate GaSb wafer to induce an interface between negatively-charged (n-type) and positively-charged (p-type) regions. In order to improve upon the scalability of TPV production, device fabrication methods for GaSb that avoid the use of epitaxy are sought after as a lower-cost alternative. In this work, sulfur ion implantation is examined as one of these methods, in which elemental sulfur ions are injected at a high energy into a p-type GaSb substrate. The implanted ions then alter the charge characteristics at the surface of the material, producing an electric field from which a photovoltaic (PV) device can be fabricated. The results of this study showed that by implanting sulfur ions, an extremely p-type (p++) layer was formed at the surface of the GaSb substrate, which was attributed to residual damage induced by the implant process. The resulting interface between the p++ surface and the moderately p-type GaSb substrate was found to induce an electric field suitable for a PV device. Removing the excess surface damage away from the device’s metal contacts resulted in an improvement in the output electrical currents, with measured values being significantly higher than that of other devices made using more common non-epitaxial fabrication methods. The success of this work demonstrates the advantages of using a p-type GaSb substrate in place of an n-type substrate, and could help diversify the types of TPV-related devices that can be produced.

Malgré son grand potentiel, l’énergie photovoltaïque n’arrive pas encore à trouver une grande place dans le paysage énergétique mondial. Elle se heurte à deux problèmes de taille : le coût et le rendement. Les cellules solaires à base du silicium multicristallin (mc-Si) perdent beaucoup de leur rendement à cause de la présence des impuretés métalliques. Plusieurs recherches ont montré que les cavités induites par implantation ionique sont efficaces dans le piégeage des impuretés. Mais les techniques utilisées dans l’implantation n’ont pas permis à ce procédé de se développer dans l’industrie à cause de leur coût élevé. Le plasma immersion ion implantation (PIII) est une technique bas coût qui permet d’implanter de grandes surfaces. Elle est utilisée dans le traitement de surface à l’échelle industrielle, mais à ce jour aucune étude n’a montré son utilisation dans le piégeage des impuretés dans le silicium. Dans cette thèse nous avons créé des cavités dans le mc-Si par implantation d’hydrogène par PIII. Plusieurs techniques de caractérisation ont été utilisées afin d’étudier le mécanisme de formation de ces cavités. La MET, la photoluminescence et les positons ont été utilisées pour avoir un maximum d’informations sur la nature et l’évolution des défauts créés par implantation d’hydrogène. Nous avons également étudié la différence entre les cavités formées par PIII et celles formées par implantation classique. Les cavités formées ont été utilisées, par la suite, pour le piégeage des impuretés métalliques présentes dans le mc-Si (Cu, Fe, Cr et Ni). Les résultats obtenus par SIMS ont monté l’efficacité de notre procédé dans le piégeage des impuretés métalliques. / Extraction of silicon metal impurities to be used for photovoltaic by plasma immersion ion implantation (PII)

Opto-electronic semiconductor technology continues to grow at an accelerated pace, as the industry seeks to perfect devices such as light emitting diodes for purposes of optical processing and communication. A strive for greater efficiency with shrinking device dimensions, continually pushes the technology from both a design and materials aspect. Nanosystems such a quantum dots, also face new material engineering challenges as they enter the realm of quantum mechanics, with each system and material having markedly different electronic properties. Traditionally, the semiconductor industry has focused on materials such Group II-VI and III-V compounds as the basis material for future opto-electronic needs. Unfortunately, these material systems can be expensive and have difficulties integrating into current Si-based technology. The industry is reluctant to leave silicon due in part to silicon's high quality oxide, and the enormous amount of research invested into silicon based circuit fabrication. Although recently materials such as GaN are starting to dominate the electro-optical industry since a Si-based substitute has not been found. The purpose of the dissertation was to examine several promising systems that could be easily integrated into current Si-based technology and also be produced using simple inexpensive fabrication techniques such ion implantation. The development of optically active nano-sized precipitates in silica to form the active layer of an opto-electronic device was achieved with ion implantation and thermal annealing. Three material systems were investigated. These systems consisted of carbon, silicon and metal silicide based nanocrystals. The physical morphology and electronic properties were monitored using a variety of material characterization techniques. Rutherford backscattering/channeling were used to monitor elemental concentrations, photoluminescence was used to monitor the opto-electronic properties and transmission electron microscopy was used to study the intricate morphology of individual precipitates. The electronic properties and the morphology were studied as a function of implant dose, anneal times and anneal temperatures.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22442号 / 工博第4703号 / 新制||工||1734(附属図書館) / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 斉藤 学, 教授 神野 郁夫, 准教授 松尾 二郎 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1978 / Vita. / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

The aim of this work is to analytically treat the dynamic ion behavior during the evolution of the ion matrix sheath, considering the industrial application plasma source ion implantation for both planar and cylindrical targets, and then to de-velop a code that simulates this dynamic ion behavior numerically. If the sepa-ration between the electrodes in a discharge tube is small, upon the application of a large potential between the electrodes, an ion matrix sheath is formed, which fills the whole inter-electrode space. After a short time, the ion matrix sheath starts moving towards the cathode and disappears there. Two regions are formed as the matrix sheath evolves. The potential profiles of these two regions are derived and the ion flux on the cathode is estimated. Then, by us-ing the finite-differences method, the problem is simulated numerically. It has been seen that the results of both analytical calculations and numerical simula-tions are in a good agreement.

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SiC has become an attractive wide bandgap semiconductor due to its unique physical and electronic properties and is widely used in high temperature, high frequency, high power and radiation resistant applications. SiC has been used as an alternative to Si in harsh environments such as in the oil industry, nuclear power systems, aeronautical, and space applications. SiC is also known for its polytypism and among them 3C-SiC, 4H-SiC and 6H-SiC are the most common polytypes used for research purposes. Among these polytypes 4H-SiC is gaining importance due to its easy commercial availability with a large bandgap of 3.26 eV at room temperature. Controlled creation of defects in materials is an approach to modify the electronic properties in a way that new functionality may result. SiC is a promising candidate for defect-induced magnetism on which spintronic devices could be developed. The defects considered are of room temperature stable vacancy types, eliminating the need for magnetic impurities, which easily diffuse at room temperature. Impurity free vacancy type defects can be created by implanting the host atoms of silicon or carbon. The implantation fluence determines the defect density, which is a critical parameter for defect induced magnetism. Therefore, we have studied the influence of low fluence low energy silicon and carbon implantation on the creation of defects in n-type 4H-SiC. The characterization of the defects in these implanted samples was performed using the techniques, RBS-channeling and Raman spectroscopy. We have also utilized these characterization techniques to analyze defects created in much deeper layers of the SiC due to implantation of high energy nitrogen ions. The experimentally determined depths of the Si damage peaks due to low energy (60 keV) Si and C ions with low fluences (< 1015 cm-2) are consistent with the SRIM-2011 simulations. From RBS-C Si sub-lattice measurements for different fluences (1.1×1014 cm-2 to 3.2×1014 cm-2) of Si implantation in 4H-SiC, the Si vacancy density is estimated to range from 1.29×1022 cm-3 to 4.57×1022 cm-2, corresponding to average vacancy distances of 4.26 Å to 2.79 Å at the damage peak (50±5 nm). Similarly, for C implanted fluences (1.85×1014 cm-2 to 1×1015 cm-2), the Si vacancy density varies from 1.37×1022 cm-3 to 4.22×1022 cm-3 with the average vacancy distances from 4.17 Å to 2.87 Å at the damage peak (110±10 nm). From the Raman spectroscopy, the implantation-induced lattice disorders calculated along the c-axis (LO mode) and perpendicular to c-axis (TO mode) in 4H-SiC are found to be similar. Furthermore, the results obtained from SQUID measurements in C implanted n-type 4H-SiC sample with fluences ranging from 1×1012 to 1.7×1016 ions/cm2 have been discussed. The implanted samples showed diamagnetism similar to the unimplanted sample. To date, to our best of knowledge, no experimental work has been reported on investigating defect induced magnetism for self-ion implantation in n-type 4H-SiC. These first reports of experimental results can provide useful information in future studies for a better understanding of self-ion implantation in SiC-based DMS.