Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

In this project, nano-sized gallium oxide and indium oxide produced by ion implantation of nitrogen/carbon and subsequent rapid thermal annealing (RTA) have been investigated. The material synthesis technique is based on using implantation of different species, which include nitrogen, carbon, oxygen and argon, with variable implant dosage to form an amorphous surface layer on GaAs or InP substrates. RTA then provides the required thermal energy for the amorphous material to re-crystallize. We found that the type of implanted species play an important role in controlling the material for nation during the RTA stage. Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were conducted to provide detailed characterization on the samples. For the nitrogen/carbon implanted samples, RTA at 950°C resulted in the formation of single crystalline Ga2O3 nano-ribbons on the sample surface. These Ga2O3 ribbons possess strong visible photoluminescence and cathodoluminescence. For the carbon implanted InP samples, In2O3 nanowires were found on the InP sample surface when RTA was performed at 750°C. However, In2O 3 nanowires only occurred when gold was present. On the other hand, when the nitrogen implanted samples were annealed in pure nitrogen ambient, a Raman peak at 577cm-1 associated with GaN was observed. Cross-sectional TEM showed that the thickness of the region containing GaN was about 40nm. We also used the synthesized GaN as a buffer layer to grow ZnO film by using MOCVD. The possible formation mechanisms of these nanomaterials and the role of the implanted species are discussed. For the nanowires with gold nano-particles at the free end, we believe that they are synthesized by vapour-liquid-solid (VLS) mechanism. On the other hand, the growth of nano-wires in the cases where no gold nano-particles on the free end may be explained on the basis of a vapour-solid (VS) mechanism. For the case of carbon or nitrogen implantation, carbon works as a reduction agent and nitrogen favours the formation of group III nitride template, which may lead of the growth of nano-wires. / Lo, Kwong Chun. / "March 2008." / Adviser: Aaron H. P. Ho. / Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1887. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 112-119). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 116-126).

Tin-doped indium oxide (ITO) has been widely used for various optoelectronic devices such as display panels, light-emitting diodes and solar cells due to its unique optical and electrical properties. Thin ITO films can be fabricated by a number of methods such as molecular beam epitaxy (MBE), laser ablation, dc sputtering, e-beam deposition, vapor phase deposition, electrochemical deposition and hydrothermal method. Apart from the conventional thin film form, one dimensional ITO nanorods or nanowires are attracting much research interest due to their high aspect ratio and large surface to volume ratio. For instance, a network made of ITO nanowires can exhibit high transparency (over 95 %) and high flexibility without losing its conducting property as reported recently. This network can be potentially used for flexible photovoltaic devices. In this study, ITO nanorods or nanowires were fabricated using the vapor deposition, dc sputtering and e-beam deposition. The use of short ITO nanorods (100 nm) on glass and commercial ITO substrates as bottom electrodes improving the charge collection of bulk heterojunction organic solar cells had been demonstrated. The morphology of the ITO nanostructures was studied by scanning electron microscope (SEM) and transmission electron microscope (TEM). The crystal structure and growth direction were studied by x-ray diffraction (XRD) and selected area electron diffraction (SAED), respectively. Optical properties were examined using transmission and photoluminescence measurements. The performance of the organic solar cells was examined using the I-V characteristics and external quantum efficiency (EQE) measurements. The growth mechanism of the ITO nanowires using different fabrication methods was discussed. The effects of the substrate temperature, oxygen content, choice of substrate and evaporation rate on the morphology, transmittance and sheet resistivity were investigated. When short ITO nanorods were incorporated into the bulk heterojunction organic solar cells, a significant improvement of the power conversion efficiency (PCE) was observed. The higher efficiency of the studied solar cells was attributed to the improved charge collection. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

The conduction band of InAs lies lower in energy than the GaSb valence band. In order to preserve continuity of the Fermi level across the interface, charge transfer takes place resulting in a confined quasi two dimensional electron gas (2DEG) in the InAs and a confined quasi two dimensional hole gas (2DHG) in the GaSb. This study is an investigation into the vertical transport in an n-InAs/p-GaSb single heterojunction (SHET). Application of a forward bias (InAs negative with respect to GaSb) increases the 2DEG and 2DHG concentrations and, therefore, their confinement energies. Eventually a critical bias is reached where the electron confinement energy moves above the hole confinement energy (the theoretical voltage induced semimetal/semiconductor transition V_c). Any subsequent increase in voltage is expected to result in a current decrease, and a region of negative differential resistance (NDR) should occur. The SHET can be grown with two distinct interface types, 'InSb-like' and 'GaAs-like'. This in turn affects the vertical transport characteristics of each type. Experimental IV traces at various pressures are compared with the corresponding results from sophisticated self-consistent band profile calculations taking into account band mixing effects for the first time through a k.p theory framework. Experimental IV traces of the SHETs under a magnetic field parallel to the interface are also compared with results from calculations that take into account the coupling of the growth and in-plane electron and heavy hole motions. Both sets of analysis support earlier conclusions that NDR occurs after V_c for both interfaces, and that each interface supports a different conduction mechanism. Evidence of multiple phonon processes occurring in both sample types is observed for the first time and is proposed to reconcile the above experimental observations with theory. This data is found to offer explanations for a number of other observations. Field perpendicular to the interface leads to the observation of features beyond the NDR region in both sample types. In samples with an 'InSb-like' interface, applying additional hydrostatic pressure leads to very strong features beyond the main NDR. Through a complex self-consistent decoupled model taking into account electrons and heavy holes, all these features are proposed to be due to a filling of an integer number of Landau levels. The band profile is predicted to alter dramatically at this point. The same model explains the observation of weaker features at 1 bar at high fields (~ 40T). A variation of NDR position is found with a rotation of an-plane field.

Thesis (M.S.)--Ohio University, August, 2000. / Title from PDF t.p.

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Gerhardt, Rosario; Engineering: Dr. Arun M. Gokhale; Engineering: Dr. Preet Singh; Engineering: Dr. Mohan Srinivasarao; Engineering: Dr. Meisha Shofner.