Xuan Thang Trinh's Books

Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC

By: Xuan Thang Trinh

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Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC

By: Xuan Thang Trinh

Point defects in semiconductor materials are known to have important influence on the performance of electronic devices. For defect control, knowledge on the model of defects and their properties is required. Information on defects, such as the symmetry and the localization of spins, is essential for identification of defects and understanding their electronic structure. Such information can be obtained from Electron Paramagnetic Resonance (EPR). In many cases, the energy levels of defects can be determined from photoexcitation EPR (photo-EPR) or temperature dependence of the EPR signal. The thesis contains six papers, focusing on the identification and electronic structure investigation of defects and impurities in AlxGa1-xN (x~0.7-1) and silicon carbide (SiC) using EPR in combination with other electrical characterizations and density functional theory calculations. The two first papers concern EPR studies of silicon (Si) in AlGaN alloys. Due to its direct and wide band gap which can be tailored from 3.4 eV for GaN to 6.2 eV for AlN, high-Al-content wurtzite AlxGa1-xN (x?0.7) has been considered as a promising material for fabrication of compact, high-efficiency and non-toxic deep ultraviolet light-emitting diodes (LEDs) and laser diodes (LDs) for replacing low-efficiency and toxic mercury lamps in water/air purification and sterilization. Si is commonly used for n-type doping in AlGaN and AlN, but the conductivity of Si-doped AlxGa1-xN was often reported to drop abruptly at high Al content (x>0.7) and the reason was often speculated to be due to either carrier compensation by other deep levels or Si itself when it transforms from a shallow donor to a DX (or negative-U) center which acts as an acceptor. In paper 1, we showed that Si already forms a stable DX center in AlxGa1-xN with x ~0.77. However, with the Fermi level locating only ~3 meV below the neutral charge state, Ed, Si still behaves as a shallow donor. Negligible carrier compensation by oxygen (O) in Al0.77Ga0.23N:Si layers was observed, suggesting that at such Al content, O does not seem to hinder the n-type doping in the material. In paper 2, we found the coexistence of two Si DX centers, the stable DX1 and the metastable DX2, in AlxGa1-xN for x?0.84. For the stable DX1 center, abrupt deepening of the energy level of the negative charge state DX–, EDX, which determines the ionization energy Ea of the Si donor, with increasing of the Al content for x?0.83 was observed. The dependence of Ea on the Al content in AlxGa1-xN:Si layers (0.79?x?1) was determined. The results explain the drastic decrease of the conductivity as often reported for AlxGa1-xN:Si in previous transport studies. For the metastable DX2 center, we found that the EDX level remains close to Ed for x=0.84÷1. SiC is a wide band-gap semiconductor having high-thermal conductivity, high breakdown field, and large saturated electron drift velocity which are essential properties for high-voltage and high-power devices. In paper 3, the identification of niobium (Nb) in 4Hand 6H-SiC grown by high-temperature chemical vapor deposition (CVD) by EPR and theoretical calculations is presented. We showed that the incorporated Nb formed asymmetric split-vacancy defect (NbSiVC) in which Nb locates in a divacancy, closer to the Si vacancy, and prefers only the hexagonal-hexagonal configuration. In papers 4 and 5, we present the identification and the electronic structure of the negative-U Z1/Z2 center in 4HSiC. The Z1/Z2 defect is known to be the most common deep level revealed by Deep Level Transient Spectroscopy (DLTS) in 4H-SiC epitaxial layers grown by CVD. The center is also known to be the lifetime killer in as-grown CVD material and, therefore, attracts much attention. Using high-doped n-type free-standing 4H-SiC layers irradiated with low-energy (250 keV) electrons, which mainly displace carbon atoms creating C vacancies (VC), C interstitials and their associated defects, it was possible to increase the irradiation dose and, hence, the defect concentration, allowing the application of EPR and DLTS on the same samples. In paper 4, using EPR, photo-EPR, DLTS and capacitance-voltage measurements, we showed that the Z1/Z2 center is related to the (2-|0) level of VC and its higher-lying levels Z1 and Z2 are related to the (-|0) levels of VC at the hexagonal (h) and quasi-cubic (k) sites, respectively. In paper 5, combining EPR and supercell calculations, the negatively charged VC at the k-site was identified. We obtained the excellent agreement in the energy levels of Z1/Z2 determined by DLTS and energy levels of VC calculated by supercell calculations and observed clear negative-U behaviors of the negatively charged VC at both k and h-sites by EPR measurements, consolidating our assignment of the Z1/Z2 levels to the negatively charged states of VC. In paper 6, we studied a defect related to displaced C atoms in n-type 4H-SiC irradiated by low-energy electrons. In irradiated layers, we observed an EPR center at room temperature. After annealing at temperatures in the range of 300-500 °C, this center transforms to a second configuration which is observed in darkness and can be changed back to the first configuration under illumination. Based on the observed 29Si and 13C hyperfine structures, two observed configurations of the EPR center were suggested to be related to different configurations of a carbon interstitial cluster. The annealing, bistable behaviors and energy levels of this EPR center are discussed.

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Linköping University Electronic Press

Published Date

ISBN 10

9175190648

ISBN 13

9789175190648

Hope and Vanquished Reality

By: Nguyen Xuan Phong

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Hope and Vanquished Reality

By: Nguyen Xuan Phong

The author writes that from his personal perspective this book is about hope. But it is also about a complex of historical, tumultuous, tragic and hopeful events that were not only played out in Viet-Nam but also on the world stage, in which he became a participant, from the time of the 1960s. The book is organized into Prologue, eleven chapters, and an Epilogue that relate historical events after which the author then forms conceptions related to hope. At the end of each chapter are "codas" which emerged as reflections-even meditations-on hope as the author was in the process of writing the book. At the end of the book are sections with a glossary of abbreviations, biographical data on both Vietnamese and foreign persons referred to in the book, and an annotated history of Viet-Nam from the time of 2879 B.C. to the present.

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388

Publisher

Xlibris Corporation

Published Date

ISBN 10

1453565612

ISBN 13

9781453565612

Information Technology in Vietnam (and Southeast Asia): Discussion Cases

By: Mathews Zanda Nkhoma,Narumon Sriratanaviriyakul,Hiep Pham ,Vo Thi Trung Trinh ,Huan Khoa Le,Hung Xuan Vo

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Information Technology in Vietnam (and Southeast Asia): Discussion Cases

By: Mathews Zanda Nkhoma,Narumon Sriratanaviriyakul,Hiep Pham ,Vo Thi Trung Trinh ,Huan Khoa Le,Hung Xuan Vo

Over the past decade, Vietnam has become a major player in the rapidly growing region of Southeast Asia. Anyone who has visited the country has sensed the extraordinary energy of its commercial activities. Few outsiders, however, have been granted access to the individual decision making processes that have driven this rapid development. With the publication of this book, that situation has changed. The ten discussion cases included in the collection examine important choices facing Vietnamese decision-makers in a broad range of contexts. Examples of these contexts include: a locally developed ERP considers how to compete with much larger international players, a coffee shop examines how IT might be harnessed to address employee theft, a burgeoning eCommerce site that leads in book sales wonders what it should sell next, an IT manager tries to decide whether or not to risk failure by accepting a promotion to a new level, a textile manufacturer seeks to use IT to more effectively manage production, a local investment company attempts to redesign its portal, and the list goes on--and even includes one entry from Vietnam's neighbor, Thailand. The ten case studies provided in this book are all open, authentic, discussion cases. What makes them open is that none of them have a "right" answer--although each has strong and weak responses to the situation described. They are authentic because each has been meticulously researched by its authors and, with the exception of some of the names (which have been disguised), they describe an actual situation faced by the key decision-maker. Most importantly, what makes them discussion cases is the fact that they are specifically optimized for use as a basis for discussion in the classroom, the teaching technique known as the case method.

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244

Publisher

Informing Science

Published Date

ISBN 10

1932886850

ISBN 13

9781932886856

Forest Property in the Vietnamese Uplands

An Ethnography of Forest Relations in Three Dao Villages

By: Phuc Xuan To,Solvay Gerke,Hans-Dieter Evers

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Forest Property in the Vietnamese Uplands

An Ethnography of Forest Relations in Three Dao Villages

By: Phuc Xuan To,Solvay Gerke,Hans-Dieter Evers

The Center for Development Research (ZEF) is an international and interdisciplinary academic research institute of the Rheinische-Friedrich-Wilhelms University of Bonn, Germany, EU. ZEF's research aims at finding solutions to global development issues. A 10 years strategy plan outlines land- and water use, biodiversity, public health and renewable energies as priority transdisciplinary research areas.

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290

Publisher

LIT Verlag Münster

Published Date

ISBN 10

3825807738

ISBN 13

9783825807733

Book's by Xuan Thang Trinh

Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC

Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC

Hope and Vanquished Reality

Hope and Vanquished Reality

Information Technology in Vietnam (and Southeast Asia): Discussion Cases

Information Technology in Vietnam (and Southeast Asia): Discussion Cases

Forest Property in the Vietnamese Uplands

Forest Property in the Vietnamese Uplands

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