Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 125-132). Available also in a digital version from Dissertation Abstracts.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 69-70). Also available in electronic version.

Thesis (Ph. D.)--Oregon Graduate Center, 1987.

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xvi, 217, 2 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 198-207).

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 87-91). Also available on the Internet.

Submitted by Gustavo Caixeta (gucaixeta@gmail.com) on 2017-02-16T10:41:56Z No. of bitstreams: 1 texto compĺeto.pdf: 927308 bytes, checksum: 87f5c56a4b88cc4b7ab4bed346550ec1 (MD5) / Made available in DSpace on 2017-02-16T10:41:56Z (GMT). No. of bitstreams: 1 texto compĺeto.pdf: 927308 bytes, checksum: 87f5c56a4b88cc4b7ab4bed346550ec1 (MD5) Previous issue date: 2003-12-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES, Brasil / Este trabalho faz uma breve revisão das técnicas de crescimento de cristais, tanto volumétricas, quanto em camadas. São abordadas as técnicas Czocrhalski, Bridgman, Epitaxia por Fase Líquida, por Fluxo Molecular e de Paredes Quentes. Esta última técnica é utilizada no crescimento de filmes de CdTe sobre substratos de Si. A caracterização das amostras produzidas é feita por microscopia de força atômica, técnica que é descrita em detalhes. Finalmente são apresentados os resultados do estudo sobre o processo de nucleação do CdTe sobre Si e discutida a possibilidade de utilização deste processo na fabricação de pontos quânticos auto-formados. / This work makes a brief revision of crystal growth techniques. It describes the techniques Czocrhalski and Bridgman, used for bulk crystal growth, and also Liquid Phase Epitaxy, Molecular Beam Epitaxy and Hot Wall Epitaxy, which are used for the growth of thin layers. The last technique (HWE) is used in the experimental part of this work for the growth of CdTe films on Si(111) substrates. The characterization of the produced samples is done by Atomic Force Microscopy. The results obtained about the nucleation process of CdTe on Si(111) are presented and the possibility of the use of this technique in the production of self-assembled quantum dots is discussed.

This thesis mainly aims at application of principles of engineering technology in the field of molecular beam epitaxy (MBE). MBE is a versatile technique for growing epitaxial thin films of semiconductors and metals by impinging molecular beams of atoms onto a heated substrate under ultra-high vacuum (UHV) conditions. Here, a LabVIEW® (laboratory virtual instrument engineering workbench) software (National Instruments Corp., http://www.ni.com/legal/termsofuse/unitedstates/usH) program is developed that would form the basis of a real-time control system that would transform MBE into a true-production technology. Growth conditions can be monitored in real-time with the help of reflection high energy electron diffraction (RHEED) technique. The period of one RHEED oscillation corresponds exactly to the growth of one monolayer of atoms of the semiconductor material. The PCI-1409 frame grabber card supplied by National Instruments is used in conjunction with the LabVIEW software to capture the RHEED images and capture the intensity of RHEED oscillations. The intensity values are written to a text file and plotted in the form of a graph. A fast Fourier transform of these oscillations gives the growth rate of the epi-wafer being grown. All the data being captured by the LabVIEW program can be saved to file forming a growth pedigree for future use. Unattended automation can be achieved by designing a control system that monitors the growth in real-time and compares it with the data recorded from the LabVIEW program from the previous growth and adjusts the growth parameters automatically thereby growing accurate device structures.

InAs/GaSb superlattices are a material system well suited to growth via molecular beam epitaxy. The ability to tune the band gap over the entire mid and long wave infrared spectrum gives a large number of applications for devices made from InAs/GaSb superlattice material. The growth of high quality InAs/GaSb superlattice material requires a careful study of the parameters used during epitaxial growth. This work investigates the growth of tunnel junctions for InAs/GaSb based superlattice light emitting diodes, the presence of defects in GaSb homoepitaxial layers, and variations in the growth rate of InAs/GaSb superlattice samples. Tunnel junctions in cascaded structures must provide adequate barriers to prevent carriers from leaking from one emission region to the next without first recombining radiatively, while at the same time remain low in tunneling resistance for current recycling. A variety of tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice light emitting diodes, which past studies have found hole confinement to be problematic. GaSb was used on the p-side of the junction, while various materials were used on the n-side. Al0.20In0.80As0.73Sb0.27 tunnel junctions function best due to the combination of favorable band alignment and ease of growth. Pyramidal defects have been observed in layers of GaSb grown by molecular beam epitaxy on GaSb substrates. These defects are typically 3-8 nanometers high, 1-3 microns in diameter, and shaped like pyramids. Their occurrence in the growth of GaSb buffer layers can propagate into subsequent layers. Defects are nucleated during the early stages of growth after the thermal desorption of native oxide from the GaSb substrate. These defects grow into pyramids due to a repulsive Ehrlich-Schwoebel potential on atomic step edges leading to an upward adatom current. The defects reduce in density with growth of GaSb. The insertion of a thin AlAsSb layer into the early stages of the GaSb buffer increases the rate of elimination of the defects, resulting in a smooth surface within 500nm. The acceleration of defect reduction is due to the temporary interruption of step-flow growth induced by the AlAsSb layer. This leads to a reduced isolation of the pyramids from the GaSb epitaxial layer, and allows the pyramidal defects to smooth out. Investigations into varying the superlattice growth rate have not been reported widely in the literature. Due to the frequent use of soaks, growth interrupts, and other interface structuring steps the superlattice growth rate and the interface layer sequence are linked. In order to properly study the effects of growth rate variations and interface design changes it is necessary to account for the effect on growth rate due to the interfaces. To this end it is useful to think of the effective growth rate of the superlattice, which is the total layer thickness divided by the total time, per superlattice period. Varying the effective growth rate of superlattice photoluminescence samples shows a peak in output at ˜ 0.5 monolayers per second. Investigations into the structural properties of the superlattices show no decrease in structural uniformity for effective growth rates up to ˜ 1.4 monolayers per second.

Semi-conductor industry relies heavily on silicon (Si). However, Si is not a direct-band gap semi-conductor. Consequently, Si does not possess great versatility for multi-functional applications in comparison with the direct band-gap III-V semi-conductors such as GaAs. To bridge this gap, what is ideally required is a semi-conductor material system that is based on silicon, but has significantly greater versatility. While sparsely studied, the semi-conducting silicides material systems offer great potential. Thus, I focused on the growth and structural characterization of ruthenium silicide and osmium silicide material systems. I also characterized iron silicon germanide films using extended x-ray absorption fine structure (EXAFS) to reveal phase, semi-conducting behavior, and to calculate nearest neighbor distances. The choice of these silicides material systems was due to their theoretically predicted and/or experimentally reported direct band gaps. However, the challenge was the existence of more than one stable phase/stoichiometric ratio of these materials. In order to possess the greatest control over the growth process, molecular beam epitaxy (MBE) has been employed. Structural and film quality comparisons of as-grown versus annealed films of ruthenium silicide are presented. Structural characterization and film quality of MBE grown ruthenium silicide and osmium silicide films via in situ and ex situ techniques have been done using reflection high energy electron diffraction, scanning tunneling microscopy, atomic force microscopy, cross-sectional scanning electron microscopy, x-ray photoelectron spectroscopy, and micro Raman spectroscopy. This is the first attempt, to the best of our knowledge, to grow osmium silicide thin films on Si(100) via the template method and compare it with the regular MBE growth method. The pros and cons of using the MBE template method for osmium silicide growth are discussed, as well as the structural differences of the as-grown versus annealed films. Future perspectives include further studies on other semi-conducting silicides material systems in terms of growth optimization and characterization.

III-Nitride materials, which consist of AlN, GaN, InN, and their alloys have become the cornerstone of the third generation compound semiconductor. Planar IIINitride materials are commonly grown on sapphire substrates which impose several limitations such as challenging scalability, rigid substrate, and thermal and lattice mismatch between substrate and material. Semiconductor nanowires can help circumvent this problem because of their inherent capability to relieve strain and grow threading dislocation-free without strict lattice matching requirements, enabling growth on unconventional substrates. This thesis aims to investigate the microscopic characteristics of the nanowires and expand on the possibility of using transparent amorphous substrate for III-nitride nanowire devices. In this work, we performed material growth, characterization, and device fabrication of III-nitride nanowires grown using molecular beam epitaxy on unconventional substrates. We first studied the structural imperfections within quantum-disks-in-nanowire structure grown on silicon and discovered how growth condition could affect the macroscopic photoluminescence behavior of nanowires ensemble. To expand our work on unconventional substrates, we also used an amorphous silica-based substrate as a more economical substrate for our nanowire growth. One of the limitations of growing nanowires on an insulating substrate is the added fabrication complexity required to fabricate a working device. Therefore, we attempted to overcome this limitation by 5 investigating various possible GaN nanowire nucleation layers, which exhibits both transparency and conductivity. We employed various nucleation layers, including a thin TiN/Ti layer, indium tin oxide (ITO), and Ti3C2 MXene. The structural, electrical, and optical characterizations of nanowires grown on different nucleation layers are discussed. From our work, we have established several key processes for transparent nanowire device applications. A nanowire LED emitting at ∼590 nm utilizing TiN/Ti interlayer is presented. We have also established the growth process for n-doped GaN nanowires grown on ITO and Ti3C2 MXene with transmittance above 40 % in the visible wavelength, which is useful for practical applications. This work paves the way for future devices utilizing low-cost substrates, enabling further cost reduction in III-nitride device fabrication.