Quantum electrical transport in semiconductor nanowire devices
- 주제(키워드) Quantum transport , Semiconductor nanowire
- 발행기관 고려대학교 대학원
- 지도교수 이긍원
- 지도교수 도용주
- 발행년도 2016
- 학위수여년월 2016. 2
- 학위구분 박사
- 학과 대학원 응용물리학과
- 세부전공 디스플레이·반도체소자전공
- 원문페이지 129 p
- 실제URI http://www.dcollection.net/handler/korea/000000064695
- 본문언어 영어
- 제출원본 000045867352
초록/요약
Recent advancements in bottom-up growth technique for single-crystalline semiconductor nanostructures enable us to explore the low-dimensional quantum electronic transport phenomena in various material systems. One-dimensional semiconductor nanowires (NWs), which are the primary interests in this thesis, provide a useful platform for developing quantum electronic devices in nanoscale, where quantum confinement and interference effects are revealed at low temperatures. Furthermore, the semiconductor NWs can be a building block to constitute a new class of gate-tunable quantum information devices incorporating superconductivity and spintronics into the nano-hybrid quantum devices, in which the NWs are contacted with superconducting or ferromagnetic electrodes. For a semiconductor NW with a direct band gap, it could be possible to assemble photonics with the nano-hybrid devices to convert the charge or spin information into the optical one. In the first part of this thesis, we investigate the quantum transport properties of surface electrons on a topological insulator Bi2Te3 nanowire in a magnetotransport study. Although the nanowires are synthesized by using a relatively coarse method of electrochemical deposition, clear Aharonov-Bohm oscillations of phases 0 and π are observed, owing to the highly coherent surface electron channel. The oscillation amplitude exhibits exponential temperature dependence, suggesting that the phase coherence length Lφ is inversely proportional to the temperature, as in quasi-ballistic systems. In addition, a weak antilocalization analysis on the surface channel by using a one-dimensional localization theory, enabled by successful extraction of the surface contribution from the magnetoconductance data, is provided in support of the temperature dependence of Lφ. In the second part, we report on the fabrication and electrical transport properties of gate-tunable superconducting quantum interference devices (SQUIDs), made of semiconducting PbS nanowire contacted with PbIn superconducting electrodes. Applied with a magnetic field perpendicular to the plane of the nano-hybrid SQUID, periodic oscillations of the critical current due to the flux quantization in SQUID are observed up to T = 4.0 K. Nonsinusoidal current-phase relationship is obtained as a function of temperature and gate voltage, which is consistent with a short and diffusive junction model. In the third part, we report a novel negative photoconductivity (NPC) mechanism in n-type indium arsenide nanowires (NWs). Photoexcitation significantly suppresses the conductivity with a gain up to 10^5. The origin of NPC is attributed to the depletion of conduction channels by light assisted hot electron trapping, supported by gate voltage threshold shift and wavelength-dependent photoconductance measurements. Scanning photocurrent microscopy excludes the possibility that NPC originates from the NW/metal contacts and reveals a competing positive photoconductivity. The conductivity recovery after illumination substantially slows down at low temperature, indicating a thermally activated detrapping mechanism. At 78 K, the spontaneous recovery of the conductance is completely quenched, resulting in a reversible memory device, which can be switched by light and gate voltage pulses. The novel NPC based optoelectronics may find exciting applications in photodetection and nonvolatile memory with low power consumption.
more목차
1 Theoretical background 1
1.1 Topological insulator 1
1.1.1 Weak localization and Weak anti-localization 3
1.1.2 Aharonov-Bohm oscillations in Topological insulators 6
1.2 Josephson junctions in superconducting loops 9
1.2.1 Josephson junction 9
1.2.2 Superconducting quantum interference devices 10
1.2.3 Current phase relation in short diffusive junction 14
2 Fabrication and measurement 17
2.1 Device fabrication 17
2.2 Measurement 22
3 Part I : Quantum electrical transport properties of topological insulator Bi2Te3 nanowires 26
3.1 Introduction 26
3.2 Fabrication and measurement 28
3.3 Results and discussion 32
3.3.1 Aharonov-Bohm oscillations in Bi2Te3 nanowire 32
3.3.2 Extraction of the surface electron contribution 40
3.3.3 Weak anti-localization in Bi2Te3 nanowire 43
3.3.4 General electrical transport characteristics of the Bi2Te3 nanowires 47
3.3.5 Conclusion 49
4 Part II : Gate-tunable superconducting quantum interference devices of PbS nanowires. 50
4.1 Introduction 50
4.2 Fabrication and measurement 53
4.3 Results and discussion 56
4.3.1 Magnetic field modulation 56
4.3.2 Current bias dependence 59
4.3.3 Characteristics of PbS nanowires 61
4.3.4 Temperature dependence 63
4.3.5 Gate-voltage dependence 67
4.3.6 Conclusion 69
5 Part III : Hot carrier trapping induced negative photoconductance in InAs nanowires towards novel nonvolatile memory 70
5.1 Introduction 70
5.2 Fabrication and measurement 73
5.3 Results and discussion 76
5.3.1 Negative photoconductance behaviors of InAs nanowire FETs 76
5.3.2 Intensity dependence of photoconductance 81
5.3.3 Wavelength dependence of photoconductance 87
5.3.4 Negative photoconductance mechanism 89
5.3.5 Optical memory effect at low temperature 98
5.3.6 Conclusion 102
6 References 103
