Hydride Vapor Phase Epitaxy of Freestanding GaN Films

본 논문에서는 III-V족 화합물 반도체인 GaN 물질을 ZnO를 template 층을 이용하여 Sapphire 기판 위에 성장하였고 구조적, 광학적 조사를 통하여 고품질의 Freestanding(FS)-GaN 기판의 제작에 대한 가능성을 고찰하였다. 이 논문의 목적은 종래에 사용해 오던 기판 제거 방법의 문제점들에 의해 고품질의 성장이 제한이 되어온 것에 대하여 GaN 기판을 ZnO를 sacrificial 층으로 사용, 성장 조건의 최적화에 따른 FS-GaN 기판의 새로운 성장 가능성을 보여줌에 있다. 본 논문은 총 6 장으로 구성되어 있으며 각 장의 내용은 다음과 같다. 제 1장에서는 기본적인 GaN 물성과 종래의 FS-GaN 기판제작이 가지고 있는 문제점, 그리고 다양한 응용분야에 대하여 설명을 하였다. 제 2장에서는 제작된 자립형 GaN 기판을 성장, 평가하기 위해 본 연구에서 사용한 방법인 HVPE, SEM, HRXRD 그리고 PL 측정에 대하여 정리를 하였다. 제 3장은 GaN의 성장을 위한 ZnO template 층의 적합한 polarity의 확인에 있다. 다른 polarity를 가지는 ZnO 위에 성장된 GaN의 구조적 및 광학적 특성에 대해 고찰 하였다. 제 4장에서는 성장온도 및 가스 flow (V/III)의 변화를 통하여 GaN 성장에 적합한 성장조건을 구조적 및 광학적 특성 평가를 통하여 확인하였다. 그리고 제 5장에서 3장과 4장에서 확인 된 ZnO의 polarity와 GaN의 성장조건을 통하여 자립형 GaN 기판을 화학적 etching 방법을 통하여 제작 하였으며 마지막으로 제 6장에서는 본 논문에서 얻은 결과를 정리하여 결론 및 향후 과제에 대해 기술하였다.In this thesis, the growth structural and optical properties of FS-GaN with ZnO template buffer layer have been investigated. The objective of this thesis is to fabricate the high quality FS-GaN substrate by using ZnO sacrificial layer. In the chapter 1, the fundamental GaN properties, problems in the fabrication of FS-GaN substrate, and many application of the GaN are introduced. In the chapter 2, the principles of hydride vapor phase Epitaxy (HVPE), scanning electron microscopy (SEM), high resolution X-ray diffraction (HR-XRD), and photoluminescence (PL) are explained. In the chapter 3, ZnO polarity was determined for the growth of GaN on ZnO. In the chapter 4, the high quality GaN film growth was achieved by using ZnO sacrificial layer and optimization of growth condition. And in the chapter 5, a new self-separation method by using chemical etching of ZnO template was developed. And the quality of GaN was characterized in terms of structural and luminescence properties. Finally, the results found from this thesis are summarized and concluded in the chapter 6.논 문 요 약 1 Abstract 3 Figure list 4 Table list 8 Chapter 1. Introduction 1.1) Introduction to III-Nitrides semiconductors 1.1.1) Application of GaN 9 1.1.2) Physical properties of GaN 12 1.1.3) Problems in GaN epitaxy 13 1.1.4) Piezoelectric polarization in GaN 17 1.2) Necessity of Free-standing GaN substrate 1.2.1) History of GaN substrates and problems in fabrication 19 1.2.2) Difficulty in substrate removal techniques by HVPE 22 1.3) Proposal and purpose of this study 28 Reference 31 Chapter 2. Experimental 2.1) growth method 2.1.1) Hydride Vapor Phase Epitaxy 35 2.2) Characterization of measurement method 2.2.1) Scanning Electron Microscopy (SEM) 37 2.2.2) High Resolution X-ray Diffraction (HRXRD) 2.2.2.1) Conventional high resolution X-ray 40 2.2.2.2) &#61559scan 42 2.2.3) Photoluminescence (PL) 45 References 50 Chapter 3. Comparison of GaN on Zn-polar/O-polar ZnO 3.1) Introduction 51 3.2) Experimental details 53 3.3) ZnO etching rate of GaN after growth 53 3.4) Surface morphology and Photoluminescence (PL) intensity 54 3.5) Conclusion 55 Reference 56 Chapter 4. Optimization of growth condition for high quality GaN grown on ZnO template 4.1) Introduction 57 4.2) Experiment details 57 4.3) Effect of the growth temperature for GaN on ZnO growth 4.31) ZnO etching rate after GaN growth 58 4.3.2) Surface morphology 59 4.3.3) Evaluation of structural property by HRXRD 60 4.3.4) Room temperature (RT) of PL spectrum 61 4.4) Effect of the V/III ratio for GaN on ZnO growth 4.4.1) ZnO etching rate after GaN growth 62 4.4.2) Surface morphology 63 4.4.3) Evaluation by HRXRD 64 4.4.4) Room temperature (RT) of PL spectrum 65 4.5) Conclusion 66 Reference 67 Chapter 5. Fabrication of Freestanding GaN substrate 5.1) Introduction 68 5.2) Experimental details 69 5.3) Fabrication sequence of the self-separated FS-GaN substrate 69 5.4) Evaluation by HRXRD 70 5.5) Low temperature Photoluminescence (PL) properties 71 5.6) Temperature dependence Photoluminescence (PL) properties 72 5.7) Conclusion 73 References 74 Chapter 6. Summary and conclusion 75 Appendix A 77 감사의 글 79 Curriculum vitae 80-2&#61553scan (rocking curve) and &#6155

Diamond semiconductor technology for RF device applications

This paper presents a comprehensive review of diamond electronics from the RF perspective. Our aim was to find and present the potential, limitations and current status of diamond semiconductor devices as well as to investigate its suitability for RF device applications. While doing this, we briefly analysed the physics and chemistry of CVD diamond process for a better understanding of the reasons for the technological challenges of diamond material. This leads to Figure of Merit definitions which forms the basis for a technology choice in an RF device/system (such as transceiver or receiver) structure. Based on our literature survey, we concluded that, despite the technological challenges and few mentioned examples, diamond can seriously be considered as a base material for RF electronics, especially RF power circuits, where the important parameters are high speed, high power density, efficient thermal management and low signal loss in high power/frequencies. Simulation and experimental results are highly regarded for the surface acoustic wave (SAW) and field emission (FE) devices which already occupies space in the RF market and are likely to replace their conventional counterparts. Field effect transistors (FETs) are the most promising active devices and extremely high power densities are extracted (up to 30 W/mm). By the surface channel FET approach 81 GHz operation is developed. Bipolar devices are also promising if the deep doping problem can be solved for operation at room temperature. Pressure, thermal, chemical and acceleration sensors have already been demonstrated using micromachining/MEMS approach, but need more experimental results to better exploit thermal, physical/chemical and electronic properties of diamond

Theory of Optical Nonlocality in Polar Dielectrics

Sub-wavelength confinement of mid-infrared light can be achieved exploiting the metal-like optical response of polar dielectric crystals in their Reststrahlen spectral region, where they support evanescent modes termed surface phonon polaritons. In the past few years the investigation of phonon polaritons localised in nanoresonators and layered heterostructures has enjoyed remarkable success, highlighting them as a promising platform for mid-infrared nanophotonic applications. Here we prove that the standard local dielectric description of phonon polaritons in nanometric objects fails due to the nonlocal nature of the phonon response and we develop the corresponding nonlocal theory. Application of our general theory to both dielectric nanospheres and thin films demonstrates that polar dielectrics exhibit a rich nonlocal phenomenology, qualitatively different from the one of plasmonic systems, due to the negative dispersion of phononic optical modes.Comment: 13 pages, 6 figure

Development, Properties, and Applications of CVD Diamond-Based Heat Sinks

Heat sink is an essential component to nanoelectronics, microelectronics, and optoelectronics applications because it allows the thermal management of devices such as integrated circuits (ICs), microelectromechanical systems (MEMSs), and graphic unit processing. There are different materials being employed for heat sink production. Among them, diamond has stood out due to its excellent chemical and physical properties. This book chapter focuses on the development, properties, and applications of CVD diamond heat sinks. It covers the basic concepts of heat conduction applied to CVD diamond as a heat sink material and its production as freestanding CVD wafers of polycrystalline CVD diamond, since the literature about this topic is extensive, giving the reader a comprehensive overview. We will comprise the use and potential widening of applications of in CVD diamond heat sink technology, providing the reader with a substantial background at the current development of solutions and new frontiers in the practical use of CVD diamond thermal management devices

The Boston University Photonics Center annual report 2005-2006

This repository item contains an annual report that summarizes activities of the Boston University Photonics Center in the 2005-2006 academic year. The report provides quantitative and descriptive information regarding photonics programs in education, interdisciplinary research, business innovation, and technology development. The Boston University Photonics Center (BUPC) is an interdisciplinary hub for education, research, scholarship, innovation, and technology development associated with practical uses of light.This Annual Report is intended to serve as a synopsis of the Boston University Photonics Center’s wide-ranging activities for the period from July 2005 through June 2006, corresponding to the University’s fiscal year. It is my hope that the document is reflective of the Center’s core values in innovation, entrepreneurship, and education, and that it projects our shared vision, and our dedication to excellence in this exciting field. For further information, you may visit our new website at www.bu.edu/photonics. Though only recently appointed as Director, my involvement in Center activities dates back to the Center’s formation more than ten years ago. In the early years, I worked with a team of faculty and staff colleagues to design and construct the shared laboratories that now provide every Center member extraordinary capabilities for fabrication and testing of advanced photonic devices and systems. I helped launch the business incubator by forming a company around an idea that emerged from my research laboratory. While that company failed to realize its vision of transforming the compact disc industry, it did help us form a unique vision for our program of academically engaged business acceleration. I co-developed a course in optical microsystems for telecommunications that I taught to advanced undergraduates and graduate students in the new M.S. degree program in Photonics offered through the Electrical and Computer Engineering Department. And since the Center’s inception, I have contributed to its scholarly mission through my work in optical microsystem design and precision manufacturing at the Center’s core Precision Engineering Research Laboratory. Recently, I had the opportunity to lead the Provost’s Faculty Advisory Committee on Photonics, charged with broadening the Center’s mission to better integrate academic and educational programs with its more established programs for business incubation and prototype development. [TRUNCATED

First-Principles Calculations on the Electronic and Optical Properties of Polar Functional Materials

Advanced computational methods are continually pushing the boundary of modern materials science. They can guide experimental inquiry by surveying a large number of materials for functional properties as well as guide the design and synthesis of new materials with targeted properties, at a much faster speed than experimental approaches. This rise in predictive insight has helped foster the semiconductor revolution, and in turn, created technologies which make a direct impact on global challenges such as the energy crisis and global warming. However, even with this success, there are a wide variety of materials left to be examined in detail. In this work two-dimensional (2D), hydrogen-passivated III-nitrides are examined. Density functional theory and many-body perturbation theory are applied to produce accurate band structures and use the Bethe-Salpeter Equation to predict exciton binding energies. The strong polarization in III-nitride monolayers results in a significant quantum-confined Stark effect (QCSE), reducing the large band gaps caused by quantum confinement. Using the polarization as a degree of freedom in constructing bilayer heterostructures, it is shown that aligned orientations yield relatively small band gaps (1.9 eV - 3.2 eV), whereas in anti-aligned orientations there is no QCSE and the gap remains large (>4.4 eV). Exciton binding energies are on the order of 1 eV. These results show that UV emission from 2D GaN is possible andthat the optical gaps of 2D III-nitrides span the visible and UV spectra. The second portion of this work is dedicated to examining the carrier mobilities of various semiconductors using density functional theory, many-body perturbation theory, and the electron-phonon Wannier method. The phonon-limited hole mobility of Cu2O is determined and it is shown that at room temperature it is polar optical modes which are predominantly responsible for carrier scattering. Four ultra-wide-band-gap(UWBG) materials, rs-BeO, wz-BeO, zb-BeO, and MgO, are then examined. Their ultra-wide band gaps (>6 eV) highlight their promise in high-power electronics, and their electron carrier mobilities are high as well (>107cm2/Vs at room temperature). Finally, the carrier mobility of cubic BN and diamond are examined since experimen-tal results on cBN hole mobility span two orders of magnitude. Electron-phonon coupling matrix elements are evaluated to show that acoustic mode coupling is lower in diamond than in cBN. It is also shown that the room temperature scattering rate of holes is much faster in cBN than diamond. Overall, electron mobilities are comparable while cBN hole mobility (80.4 cm2/Vs) is lower than that of diamond (1970 cm2/Vs). These computational results emphasize the applicability of 2D and UWBG materials to optoelectronic devices and suggest that polar materials provide a wide degree of useful functional properties.PHDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169996/1/nocona_1.pd

Deposição de filmes do diamante para dispositivos electrónicos

This PhD thesis presents details about the usage of diamond in electronics. It presents a review of the properties of diamond and the mechanisms of its growth using hot filament chemical vapour deposition (HFCVD). Presented in the thesis are the experimental details and discussions that follow from it about the optimization of the deposition technique and the growth of diamond on various electronically relevant substrates. The discussions present an analysis of the parameters typically involved in the HFCVD, particularly the pre-treatment that the substrates receive- namely, the novel nucleation procedure (NNP), as well as growth temperatures and plasma chemistry and how they affect the characteristics of the thus-grown films. Extensive morphological and spectroscopic analysis has been made in order to characterise these films.Este trabalho discute a utilização de diamante em aplicações electrónicas. É apresentada uma revisão detalhada das propriedades de diamante e dos respectivos mecanismos de crescimento utilizando deposição química a partir da fase vapor com filament quente (hot filament chemical vapour deposition - HFCVD). Os detalhes experimentais relativos à otimização desta técnica tendo em vista o crescimento de diamante em vários substratos com relevância em eletrónica são apresentados e discutidos com detalhe. A discussão inclui a análise dos parâmetros tipicamente envolvidos em HFCVD, em particular do pré-tratamento que o substrato recebe e que é conhecido na literatura como "novel nucleation procedure" (NNP), assim como das temperaturas de crescimento e da química do plasma, bem como a influência de todos estes parâmetros nas características finais dos filmes. A caracterização morfológica dos filmes envolveu técnicas de microscopia e espetroscopia.Programa Doutoral em Engenharia Eletrotécnic

Chemical vapour deposition synthetic diamond: materials, technology and applications

Substantial developments have been achieved in the synthesis of chemical vapour deposition (CVD) diamond in recent years, providing engineers and designers with access to a large range of new diamond materials. CVD diamond has a number of outstanding material properties that can enable exceptional performance in applications as diverse as medical diagnostics, water treatment, radiation detection, high power electronics, consumer audio, magnetometry and novel lasers. Often the material is synthesized in planar form, however non-planar geometries are also possible and enable a number of key applications. This article reviews the material properties and characteristics of single crystal and polycrystalline CVD diamond, and how these can be utilized, focusing particularly on optics, electronics and electrochemistry. It also summarizes how CVD diamond can be tailored for specific applications, based on the ability to synthesize a consistent and engineered high performance product.Comment: 51 pages, 16 figure