Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: William. Alan Doolittle; Committee Member: Jeffrey Nause; Committee Member: Linda S. Milor; Committee Member: Shyh-Chiang Shen; Committee Member: Stephen E. Ralph.

Thesis (M.S.)--California Polytechnic State University, 2009. / Mode of access: Internet. Title from PDF title page; viewed on May 21, 2009. Major professor: Xiaomin Jin. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Electrical Engineering." "March 2009." Includes bibliographical references (p. 80-84). Also available on microfiche.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains viii, 77 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 66-68).

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Samuel Graham; Committee Member: Donald Dorsey; Committee Member: Douglas Yoder; Committee Member: Michael Leamy; Committee Member: Sankar Nair; Committee Member: Zhuomin Zhang. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph.D.(Physics))--University of Pretoria, 2009. / Includes abstract in English. Includes bibliographical references. Also available online.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

Thesis (Ph.D.)--Ohio University, March, 2003. / Title from PDF t.p. Includes bibliographical references (leaves 147-151)

We report on the characteristics of a ZnO based metal insulator semiconductor (MIS) diode comprised of a heterostructure of n-ZnO nanorods/n-GaN. The MIS structure consisted of unintentional - doped n type ZnO nanorods grown on n-GaN sample using hydrothermal synthesis at low temperature (100°). The ZnO nanorod layer was vertically grown from the GaN sample, having the diameter 100nm and length 2µm. Then, an insulator layer for electrical isolation was deposited on the top of ZnO nanorod layer by using spin coating method. A metal layer (gold) was finally deposited on the top. The I-V dependences show a rectifying diode like behavior with a leakage current of 2.10⁻⁵ A and a threshold voltage of about 3V. Depend on the thickness of the insulator, the I-V dependences of the n-ZnO/n-GaN heterostructure was varied from rectifying behavior to Ohmic and nearly linear. / Singapore-MIT Alliance (SMA)

Optoelectronic devices fabricated from nitride semiconductors include blue and green light emitting diodes (LEDs) and laser diodes (LDs). To design efficient devices, the structure and composition of the constituent materials must be well-characterised. Traditional microscopy techniques used to examine nitride semiconductors include transmission electron microscopy (TEM), and atomic force microscopy (AFM). This thesis describes the study of nitride semiconductor materials using these traditional methods, as well as atom probe tomography (APT), a technique more usually applied to metals that provides three-dimensional (3D) compositional information at the atomic scale. By using both APT and correlative microscopy techniques, a more complete understanding of the material can be gained, which can potentially lead to higher-efficiency, longer-lasting devices. Defects, such as threading dislocations (TDs), can harm device performance. An AFM-based technique was used to show that TDs affect the local electrical properties of nitride materials. To investigate any compositional changes around the TD, APT studies of TDs were attempted, and evidence for oxygen enrichment near the TD was observed. The dopant level in nitride devices also affects their optoelectronic properties, and the combination of APT and TEM was used to show that Mg dopants were preferentially incorporated into pyramidal inversion domains, with a Mg content two orders of magnitude above the background level. Much debate has been focused on the microstructural origin of charge carrier localisation in InGaN. Alloy inhomogeneities have often been suggested to provide this localisation, yet APT has revealed InGaN quantum wells to be a statistically random alloy. Electron beam irradiation in the TEM caused damage to the InGaN, however, and a statistically significant deviation from a random alloy distribution was then observed by APT. The alloy homogeneity of InAlN was also studied, and this alloy system provided a unique opportunity to study gallium implantation damage to the APT sample caused during sample preparation by the focused ion beam (FIB). The combination of APT with traditional microscopy techniques made it possible to achieve a thorough understanding of a wide variety of nitride semiconductor materials.

abstract: This dissertation covers my doctoral research on the cathodoluminescence (CL) study of the optical properties of III-niride semiconductors. The first part of this thesis focuses on the optical properties of Mg-doped gallium nitride (GaN:Mg) epitaxial films. GaN is an emerging material for power electronics, especially for high power and high frequency applications. Compared to traditional Si-based devices, GaN-based devices offer superior breakdown properties, faster switching speed, and reduced system size. Some of the current device designs involve lateral p-n junctions which require selective-area doping. Dopant distribution in the selectively-doped regions is a critical issue that can impact the device performance. While most studies on Mg doping in GaN have been reported for epitaxial grown on flat c-plane substrates, questions arise regarding the Mg doping efficiency and uniformity in selectively-doped regions, where growth on surfaces etched away from the exact c-plane orientation is involved. Characterization of doping concentration distribution in lateral structures using secondary ion mass spectroscopy lacks the required spatial resolution. In this work, visualization of acceptor distribution in GaN:Mg epilayers grown by metalorganic chemical vapor deposition (MOCVD) was achieved at sub-micron scale using CL imaging. This was enabled by establishing a correlation among the luminescence characteristics, acceptor concentration, and electrical conductivity of GaN:Mg epilayers. Non-uniformity in acceptor distribution has been observed in epilayers grown on mesa structures and on miscut substrates. It is shown that non-basal-plane surfaces, such as mesa sidewalls and surface step clusters, promotes lateral growth along the GaN basal planes with a reduced Mg doping efficiency. The influence of surface morphology on the Mg doping efficiency in GaN has been studied. The second part of this thesis focuses on the optical properties of InGaN for photovoltaic applications. The effects of thermal annealing and low energy electron beam irradiation (LEEBI) on the optical properties of MOCVD-grown In0.14Ga0.86N films were studied. A multi-fold increase in luminescence intensity was observed after 800 °C thermal annealing or LEEBI treatment. The mechanism leading to the luminescence intensity increase has been discussed. This study shows procedures that significantly improve the luminescence efficiency of InGaN, which is important for InGaN-based optoelectronic devices. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020