Electrical Properties of Semiconducting Nanostructures : Influence of Nanoscale Contact, Junction and Surface reactions
- 주제(키워드) Nanowire , Semiconducting nanostructure , ZnO , SnO2 , Schottky contact , Junction property , Surface reaction , Electrochemical impedance spectroscopy , Equivalent circuit , Gas sensor , Hydrogen detection
- 발행기관 고려대학교 대학원
- 지도교수 김규태
- 발행년도 2011
- 학위수여년월 2011. 2
- 학위구분 박사
- 학과 일반대학원 전기공학과
- 원문페이지 124 p
- 실제URI http://www.dcollection.net/handler/korea/000000024644
- 본문언어 영어
- 제출원본 000045641262
초록/요약
In this dissertation, electrical properties of semiconducting nanostructure devices are investigated for the case of ZnO and SnO2. This dissertation deals with a study on effects of semiconductor-metal contacts (e.g. Schottky contact), structural junctions, nanowire-nanowire junctions and surface reactions in the nanostructure device. We first demonstrate that the structural junction plays a decisive role on the overall electrical property of the nanodevice. Due to the structural difference (wurzite and zinc-blende) in a ZnO-tetrapod (ZnO-T), it is expected that the local electrical property in those regions may differ from one another. However, conventional dc-characterization methods previously employed to explore the electrical property of the ZnO-T can not measure such local electrical properties separately so that the role of the junction in the overall electrical property was unknown. We have measured the local resistances in the arms (wurzite) and at the junction (zinc-blende) in a ZnO-T separately using the electrochemical impedance spectroscopy (EIS). The resistance at the junction is found to be even greater than that in the arms although a volume fraction of the junction is negligibly small compared with that of the arms. The Schottky contact can determine the electrical characteristics of the asymmetric contact device for applying a photovoltaic device and nanowire sensors with high performances. It is thus critically important to understand the nature of the contact and the electrical behavior associated with it at a fundamental level to better understand actual device performances and thus to eventually develop nano-scale devices reliable for practical use. Individual SnO2 nanowire devices with asymmetric contacts have been thoroughly studied through dc measurements and EIS analyses. We found that the relevant equivalent circuit in terms of dc analysis is a back-to-back diode model connected with a series resistance. The impedance spectra of the device were measured at various temperatures and atmospheres (N2 and 1%-O2), and were analyzed to be equivalent to two sets of parallel R//C circuits. Multiply-connected ZnO nanorods are very attractive chemical-sensing materials and deserve to be studied in terms of the hydrogen reaction and kinetics on the ZnO surface and inter-rod junctions. We have successfully demonstrated a ZnO nanorod-based 3-dimensional (3-D) nanostructure to show a high sensitivity and very fast response/recovery to hydrgogen gas. Its superior performance can be explained from the point of its porous structure in a 3-D network and the enhanced surface reaction of the hydrogen molecules with the oxygen defects owing to a high surface-to-volume ratio. We have studied the temperature- and the concentration-dependence of the hydrogen sensing characteristics in the multiple ZnO nanorod network. A Langmuir-Isotherm following the ideal power-law and cross-over behavior of the activation energy with respect to hydrogen concentration were found. The results of this dissertation show that the influences of the nanoscale contact, the structural junction, the nanowire-nanowire junction, and the surface reaction can detmerine the electrical properties of the semiconducting nanodevice. The experimental achievements and understanding will be very helpful to the intense related research of nanodevice technologies, in addition to a fundamental study of the electrical tansport and the surface reaction within the nanostructures.
more목차
Abstract i
1 Introduction 1
2 Theoretical and experimental backgrounds 6
2.1 Semiconducting nanomaterials 6
2.1.1 The characteristics of ZnO nanostructure 7
2.1.2 The characteristics of SnO2 nanostructure 9
2.2 Transport mechanism at Semiconductor-metal contact 10
2.3 Chemical interaction on semiconducting metal oxides 16
2.3.1 Chemical interaction on surface 16
2.3.2 Electron transport and chemical interaction at interface 20
3 Electrical properties of junction in nanostructure 26
3.1 Introduction 27
3.2 Experiment 29
3.3 Nanostructure analysis of ZnO-T 31
3.4 Current-voltage characteristics of ZnO-T 34
3.5 Impedance properties of ZnO-T 37
3.6 Electrical properties of junction in ZnO-T 40
3.7 Summary 42
4 Electrical properties of semiconductor-metal contact in nanodevice 45
4.1 Introduction 46
4.2 Fabrication of asymmetric contact devices 48
4.3 Asymmetric contact Properties: dc Analysis 51
4.4 Asymmetric contact Properties: ac Analysis 59
4.5 Summary 71
5 Electrical properties of nanostructure surface 75
5.1 Introduction 76
5.2 Experiment 78
5.3 Nanostructure analysis of ZnO nanorod 81
5.4 Current-voltage characteristics of ZnO nanorod 84
5.5 Gas sensing reaction on surface of ZnO nanorod 86
5.6 Surface reaction between ZnO and molecules 95
5.7 Summary 103
6 Conclusions 107
