No description available.

The use of SiGe/Si heterostructures in the fabrication of electronic devices results in an improvement of the device performances with respect to bulk silicon. Ion implantation has been proposed as one of the possible technologies to produce these structures and, thus, the aim of this work is to develop an ion beam technology to fabricate strained SiGe heterostructures. The formation of extended defects in SiGe alloy layers formed by high dose Ge+ ion implantation followed by Solid Phase Epitaxial Growth (SPEG) has been investigated by transmission electron microscopy. Rutherford backscattering spectroscopy has also been used to determine the chemical composition and the crystalline quality of the synthesised structures. In addition, X-ray diffraction has been used to evaluate the strain level in selected samples. Two different structures have been studied in this project. The first consisted of "all-implanted" layers, where the Ge+ implants were followed in some cases by additional implants of Si+ and/or C+ ions, prior to SPEG, to investigate methods to inhibit defect formation. The second was achieved by capping the ion beam synthesised SiGe alloy layer by the deposition of a thin film of silicon, in order to realise structures compatible with device dimensions. Single crystal device worthy SiGe alloy layers have been achieved by implantation of Ge+ ions at energies ranging from 70 keV to 400 keV, where the only extended defects observed are EOR defects at a depth correspondent to the a/c interface formed during the Ge+ implant. In some cases, "hairpin" dislocations have also been observed in the vicinity of the EOR defects and extending up to the surface. Both types of defects are annihilated after post-amorphisation with 500 keV Si+ and replaced with dislocation loops at a depth of about 1 fj,m. For each Ge+ implantation energy a critical value of the peak germanium concentration exists above which the structures relax through the formation of stacking faults or "hairpin" dislocations nucleated in the vicinity of the peak of the germanium concentration depth profile and extending up to the surface. A critical value of the elastic energy stored in the structures (~300 mJ/m2) has been determined above which ion beam synthesised SiGe alloys relax, independently of the implantation energy. This empirical approach has been found to successfully account for the results obtained in this work as well as in many other studies reported in the literature. "Hairpin" dislocations formed under different experimental conditions have been investigated by plan view TEM and have been found to have the same crystallographic orientation () and Burgers vector (b= a ). Their formation has been explained within a "strain relaxation model". For a regrowth temperature of 700° C, all samples investigated by XRD have been found to be almost fully strained, including samples containing relaxation-induced defects, indicating that, under these conditions, the energy transferred to the defects is very low. C+ co-implantation has been successfully used to reduce both relaxation-induced defects and EOR dislocation loops. It is noted that a mixed technology entailing both layer deposition and ion implantation to produce the Si/SiGe/Si device structures requires extra process steps to control surface contaminations, pre cleaning and/or native oxide formation, resulting in increased fabrication costs. In this work an " all-implanted" route to the synthesis of Si/SiGe/Si device structures is therefore described, which exploits all of the advantages given by ion implantation.

No description available.

Superior properties of Silicon Carbide (SiC), such as wide bandgap, high breakdown field and high thermal conductivity, have made it the frontrunner to replace Silicon for applications requiring high breakdown strength, mechanical and radiation hardness. Commercial SiC devices are already available, although their expected performance has not yet been realized due to a few problems related to device fabrication technologies, such as selective doping. This work explores non-traditional techniques for SiC doping (and selective doping in particular) based on previously unknown types of defect reactions in SiC and novel epitaxial growth techniques, which offer advantages over currently available technologies. Recent developments in SiC epitaxial growth techniques at MSU have enabled the growth of high quality SiC epitaxial layers at record low temperatures of 1,300°C. Lower growth temperatures have enabled highly doped epilayers for device applications. Prototypes of SiC PiN diodes fabricated, demonstrated low values of the series resistance associated with anodes grown by the low temperature epitaxial growth technique. At room temperature, 100 ìm-diameter diodes with a forward voltage of 3.75 V and 3.23V at 1,000 A/cm2 before and after annealing were achieved. The reverse breakdown voltage was more than 680 V on average, even without surface passivation or edge termination. Reduced growth temperatures also enabled the possibility of selective epitaxial growth (SEG) of SiC with traditional masks used in the SEG in Si technology. Previously, SEG of SiC was impossible without high temperature masks. Good quality, defect free, selectively grown 4H-SiC epilayers were obtained using SiO2 mask. Nitrogen doped selectively grown epilayers were also obtained, which were almost completely ohmic, indicating doping exceeding 1x1019 cm-3. Moreover, conductivity modulation via defect reactions in SiC has been reported as a part of this work for the first time. The approach is based on a new phenomenon in SiC, named Recombination Induced Passivation (RIP), which was observed when hydrogenated SiC epilayers were subjected to above bandgap optical excitation. Additional acceptor passivation, and thereby modification of the conductivity of the epilayer, was observed. Results of investigations of the RIP process are presented, and conductivity modulation techniques based on the RIP process are proposed.

Neste trabalho, estudamos o crescimento de camadas semicondutoras de compostos III-V pela técnica de epitaxia por feixe molecular (MBE). Um grande esforço foi inicialmente realizado para entender o funcionamento do sistema inteiro e otimizar o uso de cada instrumento disponível para a caracterização in situ. Demos uma ênfase particular ao estudo da dopagem homogênea de camadas do tipo p usando duas novas técnicas e, pela primeira vez, obtivemos com sucesso camadas do tipo p crescidas pela co-evaporação de átomos de Si sobre susbtratos de GaAs (001). Finalmente, camadas de alta mobilidade eletrônica foram conseguidas, assim como espelhos de Bragg (DBRs) de alta refletividade. Estes dois tipos de estrutura possuem numerosas aplicações na indústria de microeletrônica e optoeletrônica / In this work, we studied the growth o f III-V semiconductor compounds by molecular beam cpitaxy (MBE). Much efTort was initially spem to understand the functioning of the whole system and optimize the use o f some specific instruments available for m si tu characterization. We gave some emphasis to the homogeneous doping o f p-type layers using two new techniques and, for the fírst time, a thick p-type GaAs layer was successfully grown using co-evaporation o f Si atoms on top o f (00 I) GaAs substrates. Finally, layers with high electron mobility were obtained, as well as distributed Bragg reflectors (DBRs) showing high retlectivity. These two types of structures have many applications in microelectronics and optoelectronics industry.

Neste trabalho, estudamos o crescimento de camadas semicondutoras de compostos III-V pela técnica de epitaxia por feixe molecular (MBE). Um grande esforço foi inicialmente realizado para entender o funcionamento do sistema inteiro e otimizar o uso de cada instrumento disponível para a caracterização in situ. Demos uma ênfase particular ao estudo da dopagem homogênea de camadas do tipo p usando duas novas técnicas e, pela primeira vez, obtivemos com sucesso camadas do tipo p crescidas pela co-evaporação de átomos de Si sobre susbtratos de GaAs (001). Finalmente, camadas de alta mobilidade eletrônica foram conseguidas, assim como espelhos de Bragg (DBRs) de alta refletividade. Estes dois tipos de estrutura possuem numerosas aplicações na indústria de microeletrônica e optoeletrônica / In this work, we studied the growth o f III-V semiconductor compounds by molecular beam cpitaxy (MBE). Much efTort was initially spem to understand the functioning of the whole system and optimize the use o f some specific instruments available for m si tu characterization. We gave some emphasis to the homogeneous doping o f p-type layers using two new techniques and, for the fírst time, a thick p-type GaAs layer was successfully grown using co-evaporation o f Si atoms on top o f (00 I) GaAs substrates. Finally, layers with high electron mobility were obtained, as well as distributed Bragg reflectors (DBRs) showing high retlectivity. These two types of structures have many applications in microelectronics and optoelectronics industry.

Kyoto University (京都大学) / 0048 / 新制・論文博士 / 博士(工学) / 乙第12695号 / 論工博第4084号 / 新制||工||1555(附属図書館) / 29947 / (主査）教授 平尾 一之, 教授 田中 勝久, 教授 三浦 清貴 / 学位規則第4条第2項該当

Avec les besoins croissants en enregistrement magnétique à haute densité, un effort important a été apporté à la fabrication et au contrôle des nanoalliages magnétiques. En effet les alliages magnétiques possèdent des propriétés beaucoup plus intéressantes que les métaux purs, en particulier les alliages chimiquement ordonnés (par exemple une forte anisotropie magnétique). Quand ces alliages se retrouvent à l'échelle du nanomètre, leurs propriétés peuvent de plus être exaltées ou fortement modifiées. Ces dix dernières années, une grande attention s'est tournée sur les remarquables propriétés magnétiques de l'alliage ordonné FeRh, d'un point de vue tant fondamental que technologique. En effet l'alliage FeRh présente, dans une étroite gamme de composition proche de l'équiatomique, une transition magnétique d'un état antiferromagnétique (AFM) vers un état ferromagnétique (FM). Cette transition est observée, dans l'alliage massif, à une température proche de 370K, soit au-dessus de la température ambiante. Cet alliage est de ce fait un excellent candidat pour l'enregistrement magnétique assisté thermiquement ainsi que pour la microélectronique. Le travail présenté est centré sur l'élaboration et l'étude de nanostructures de FeRh de différentes morphologies. Toutes les nanostructures ont été élaborées par voie physique dans un bâti ultra-vide de pulvérisation cathodique. Une attention particulière s'est portée sur l'évolution des caractéristiques structurales, et dans certains cas magnétiques, des nanostructures, en fonction de leur taille et des paramètres d'élaboration. Deux types de nanostructures ont été étudiés : des films minces épitaxiés sur un substrat cristallin de MgO (001) et des nanoparticules élaborées dans une matrice d'alumine amorphe. L'évolution des caractéristiques morphologique, chimique et structurale a été analysée par diffraction des rayons X et par microscopie électronique en transmission et spectroscopies associées. Les propriétés magnétiques ont été étudiées macroscopiquement par magnétométrie à échantillon vibrant (VSM) et in-situ dans un microscope par holographie électronique. / With the increasing demand for ultra-high density magnetic recording, an important effort was put on fabrication and control of magnetic nanoalloys. Indeed, magnetic alloys possess much more interesting properties than magnetic pure metals in particular chemically ordered alloys (higher magnetic anisotropy). When these alloys have a nanometer size, their properties may change significantly. In the last decade, much attention has been paid to the remarkable magnetic properties of the FeRh ordered alloy, for both fundamental and technological issues. Indeed, the FeRh alloy presents, in a very narrow range of composition close to the equiatomic one, a magnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) state. This transition takes place at a temperature close to 370K in the bulk, i.e. slightly higher than room temperature, which make with alloy particularly attractive for applications as heat-assisted magnetic recording or for microelectronics. The present work focuses on the fabrication and study of FeRh nanostructures with different morphologies. All the nanostructures were grown by dc magnetron sputtering in an ultra-high vacuum chamber. Particular attention was paid to the evolution of the structural, and eventually magnetic, characteristics of the nanostructures as the function of their size and the growth conditions. Two types of nanostructures were studied: thin films epitaxially grown on MgO (001) and nanoparticles embedded in an amorphous alumina matrix. The evolution of the morphological chemical and structural characteristics was analyzed by high-angle X-ray diffraction (XRD) and by transmission electron microscopy (TEM) and associated spectroscopies. Magnetic properties were studied by vibrating sample magnetometer and in-situ in a microscope by electronic holography.

With the low-temperature halo-carbon epitaxial growth technique developed at MSU prior to this work, use of a halo-carbon growth precursor enabled low-temperature homoepitaxial process for 4H-SiC at temperatures below 1300 °C with good quality. Investigations of the nitrogen doping dependence are reported. It has been demonstrated that the efficiency of the nitrogen incorporation may be different for different substrate orientations, with the Cace showing the higher value of doping. The Si/C ratio is known to influence the doping during the epitaxial growth due to the site-competition mechanism. The doping on the Cace showed weak dependence on the Si/C ratio. On the Siace, the doping dependence follows the site-competition trend. At high Si/C ratio, the doping trend on Siace shows strong deviation. Both of the investigated trends are suggested for use as the main process dependencies for achieving a wide range of n type doping of SiC during the low-temperature halo-carbon homoepitaxial process.

Die vorliegende Arbeit befasst sich mit dem Einfluss einer hyperthermischen Stickstoffionenbestrahlung (Ekin < 25 eV) auf das Galliumnitrid-Schichtwachstum. Dabei wird insbesondere der Einfluss einer Oberflächenrekonstruktion, einer Strukturierung der Oberfläche, einer Zwischenschicht (Pufferschicht) und der Einfluss verschiedener Siliziumsubstratorientierungen auf das epitaktische Wachstum von dünnen Galliumnitrid-Schichten nach einer hyperthermischen Stickstoffionenbestrahlung diskutiert. Ziel war es, möglichst dünne, epitaktische und defektarme Galliumnitrid-Schichten zu erhalten. Für die Charakterisierung der Galliumnitrid-Schichten und der Siliziumsubstrate standen diverse Analysemethoden zur Verfügung. Die kristalline Oberflächenstruktur konnte während des Wachstums mittels Reflexionsbeugung hochenergetischer Elektronen beobachtet werden. Nachfolgend wurde die Oberflächentopografie, die kristalline Struktur und Textur, sowie die optischen Eigenschaften der Galliumnitrid-Schichten mittels Rasterkraftmikroskopie, Röntgenstrahl-Diffraktometrie, hochauflösender Transmissionselektronenmikroskopie und Photolumineszenzspektroskopie untersucht.