Structural, Electrical, and Optical Characterizations of Undoped and Impurity-doped ZnO
- 주제(키워드) ZnO , Electrical , Structural , Optical , Impurity-doped ZnO
- 발행기관 고려대학교 대학원
- 지도교수 성태연, 안재평
- 발행년도 2011
- 학위수여년월 2011. 8
- 학위구분 박사
- 학과 일반대학원 신소재공학과
- 세부전공 신소재공학 전공
- 원문페이지 194 p
- 실제URI http://www.dcollection.net/handler/korea/000000026102
- 본문언어 영어
- 제출원본 000045670642
초록/요약
In this thesis, correlation between microstructures of undoped and impurity-doped ZnO for transparent conductive oxide (TCO) applications and the characteristics of electrical conductivity are discussed. This thesis is comprised of four chapters. In the first chapter, we describe the general characteristics such as crystal structures, optical properties, and ZnO nanostructures, and issues such as contacts in ZnO device and ZnO for TCO applications. In the second chapter, we introduce the methodology for determining the structural and electrical properties of ZnO. Continuously, in the third chapter, we manufacture individual undoped ZnO nanowire (NW) devices with Ohmic contacts using focused ion beam for exploring the relation between electrical transport phenomena and rapid thermal annealing (RTA). The resistivity and microstructural characterization has been studied by nanoprobe and transmission electron microscopy (TEM) observation. The resistivity was 0.2 ~ 0.4 Ωcm. With increasing the RTA temperature, the resistivity began to be decreased. The Pt junction of as-manufactured device consisted of Pt nanoparticles of 5 nm and amorphous carbon of 9.1 wt.%. After RTA, the size of Pt nanoparticles grew up to 100 nm, and the content of carbon was decreased within the Pt junction. It was strongly suggested that the content of carbon is the most important factor for the electrical enhancement. The electrical transport of individual undoped ZnO NW devices was investigated by the direct measurement of the electrical resistance at electrode junctions of cross-sectioned devices using two nanoprobes. Cathodoluminescence (CL) measurements were also performed to evaluate the crystallinity at the center and edge of the cross-sectioned undoped ZnO NWs. The electrical transport of individual undoped ZnO NW devices depends strongly on the crystallinity of ZnO NW itself and the carbon content at Pt junctions. The ZnO-Au junction of the device acted as the fastest path for electrical transport. Finally, in the fourth chapter, we have investigated the Ga-ordering controlled by the structural changes from nanotwin to superlattice in Ga-doped ZnO (GZO) targets for TCO using X-ray diffraction (XRD) and TEM, and discussed the distribution effect of Ga atoms on the electrical conductivities of GZOs. The nanotwin formed at low sintering temperature (1200℃) transformed to superlattice at a high sintering temperature up to 1400℃. However the Ga concentration above Ga solubility in the superlattice prohibited the structural change from nanotwin to superlattice, and increased the twin-to-superlattice ratio in GZO grains. On the position and distribution of Ga atoms, we found that Ga atoms are distributed as clusters at twin boundary and as disorder states at twin matrix, while they are completely ordered in superlattice. The structural change and Ga-ordered states of GZOs led to the variation of electrical conductivity, showing the conflicting behavior of conductivity below and above a Ga transition concentration (TC≒5.6%Ga). Ultimately, the electrical conductivity is highly enhanced when the GZOs consists of superlattice-structured grains, where Ga atoms are ideally ordered in the atomic level. This study has demonstrated a close relationship of structural change and electrical properties in GZO for TCO applications.
more목차
Chapter 1: Introduction
1. General introduction about ZnO
2. Crystal structure & Lattice properties
2.1. Crystal structure
2.2. Lattice parameters
3. Optical property
3.1. Absorption and emission processes
3.2. Band-to-band transitions (Near band-edge (NBE))
3.3. Deep-level defect
4. ZnO nanostructures
4.1.General introduction of ZnO nanostructure
4.2. Synthesis of ZnO nanostructure using VLS process
4.3. Applications of ZnO nanostructure
5.Contacts
5.1. Semiconductor-Metal contacts
5.2. Ohmic contacts
5.3. Schottky contacts
6. Application of ZnO for TCO
6.1. Transparent conducting oxide and thin films transistor
6.2. Meta-insulator transition (MIT)
Chapter 2: Methodology
1. Electrical property measurement
1.1. 2-point probe
1.2. Kelvin probe (4-point probe)
1.3. Van der Pauw
2.Lithography
3. FIB applications for TEM works
3.1. History of FIB development in semiconductor and materials analysis
3.2. TEM sample preparation
3.3. Surface artifacts after FIB milling
3.4. Recent FIB applications
Chapter 3: Electrical transport property of undoped ZnO NW
1. Current Issues on undoped ZnO NW (Motivation)
2. Experimental
2.1. Synthesis of ZnO NWs
2.2. Fabrication of a ZnO NW device using FIB
2.3. Electrical activation of ZnO NW device using RTA
2.4. Preparation of cross-section samples of electrical and optical properties measurements
3. Possible electrical transport mechanisms
3.1. Microstructural analysis of Au contacts on ZnO NW
3.2. Electrical and optical properties of cross-section ZnO NW device
4. Conclusion
Chapter 4: Ga ordering and electrical conductivity in sintered Ga-doped ZnO (GZO)
1. Introduction: Current issues on GZO
2. Experimental: Preparation of GZO
3. Results and discussion
3.1. Structural and electrical characterization
3.2. Orientation dependent of Optical properties
3.3. Relationship between Ga distribution and electrical properties
4. Conclusion
Chapter 5: General conclusion
