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Research on Surface Passivation of Ⅲ-Ⅴ Quantum Dots with Organic and Inorganic materials for Their Application to Display and IR photodetector.

  • 서해운 (Haewoon Seo, 아주대학교 일반대학원)

초록/요약

The main contents of this paper are to investigate the properties of Ⅲ-Ⅴ quantum dots, develop higher optical properties through the improvement of synthesis methods and surface treatment processes, and apply them to LEDs and photoelectric devices. Ⅲ-Ⅴ quantum dots are attracting attention as toxic metal-free quantum dots to replace conventional Cd, Pb-chalcogenide quantum dots used in the visible light region and NIR-SWIR region. Despite extensive research, their performance still little poor compared to Cd, Pb-chalcogenide quantum dots due to their own weaknesses. In this paper, we tried to improve the performance of III-V quantum dots by introducing a new core/shell structure and surface treatment. Modification of synthesis method and shell coating materials of InP quantum dots led to improvement of luminous efficiency and reduction of FWHM (full width at half maximum) in the visible light region, which was applied to PL-type LED device, and increased device stability through Dithiol ligand substitution process. We improved the synthesis method of InSb quantum dots to ameliorate and expand their range of the absorption of quantum dots. We coated the synthesized core with a type-I shell to induce emission in the SWIR region and enhance the optical stability of the quantum dots. Furthermore, applied to a photodetector, and its potential as a SWIR region photodetector was confirmed. In Chapter 1, we introduced ZnSe inner shell from the InP/ZnS QD, synthesized InP/ZnSe/ZnS core/shell/shell type QDs. We proceeded ZnSe shell coating step with a heating-up method in which ZnSe precursors were added to a low-temperature InP core solution and then rapidly raised to a temperature of 270-320 °C. Interestingly, when reacting at high temperature, the shape of the QD changes to tetrahedron, and FWHM of PL spectrum becomes narrower than low temperature. We have applied InP quantum dots to on-chip-based light emitting devices to fabricate highly efficient white LEDs. In Chapter 2, we synthesized 1,2-hexadecanedithiol ligands, which are thiol ligands in the bidentate form, and proceeded with ligand exchange in InP quantum dots. The presented ligands are attached strongly to the QD surface via the chelate effect, that induced higher surface stabilization of InP QDs. As a result, stability of the dithiol exchanged InP QDs are greatly increased than pristine InP QDs, and the effect can be confirmed even when the ligand exchanged QDs are applied to the device. In Chapter 3, we synthesized InSb core quantum dots with absorption in the NIR-SWIR region by utilizing InCl3 during the quantum dot synthesis process, and InSb/InAs core/shell quantum dots and InSb/InAs/ZnSe core/shell/shell quantum dots were synthesized by coating the core with InAs and ZnSe shells, and the optical performance and stability of InSb quantum dots were improved. In addition, the InSb core and InSb/InAs core/shell quantum dots having light absorption in the SWIR region were applied to photodetectors to confirm their potential as SWIR region photoelectric devices.

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초록/요약

이 논문에서 말하고자 하는 주제로서는 Ⅲ-Ⅴ족 기반의 양자점에 대하여 그 특성을 알아보고 이를 바탕으로 합성법의 개량 및 표면 처리과정을 통하여 더 높은 광학 특성을 개발해 LED 및 광전 소자에 응용하는 것이다. Ⅲ-Ⅴ족 양자점은 기존의 가시광 영역과 NIR-SWIR 영역에서 사용되어 지고 있는 Ⅱ- Ⅵ, Ⅳ-Ⅵ 기반의 Cd,Pb-chalcogenide 양자점을 대체할 수 있는 toxic metal free 양자점으로서 주목을 받고 있으며, 이에 많은 연구가 진행되어져 왔으나, 자체적인 약점들로 인하여 그 성능이 Cd,Pb-chalcogenide 양자점에 비해 부족하다. 이에 본 논문에서는 새로운 코어/쉘 구조의 도입과 표면 처리등을 통하여 Ⅲ-Ⅴ양자점의 성능 향상을 시도하였다. InP 기반의 양자점을 개량하여 가시광 영역의 발광 효율 향상 및 반치폭 감소를 유도하고 이를 PL type LED 소자에 적용하였으며, Dithiol 리간드 치환 과정을 통해 소자에서의 안정성을 높였다. InSb 양자점의 합성법을 개량하여 양자점의 흡광을 개선하고 그 영역을 확장하였다. 합성된 코어에 type-Ⅰ 의 쉘을 코팅하여 SWIR 영역에서 발광을 유도하였고 양자점의 광학 안정성을 증가시켰다. 추가로 광 검출 소자에 적용하여 SWIR 영역 광 검출 소자로서의 가능성을 확인하였다. 1 장에선 기존의 InP/ZnS 의 QD 구조에서 inter shell 로 ZnSe 를 도입, InP/ZnSe/ZnS 의 core/shell/shell type 의 QD 를 합성하였다. InP core 용액에 ZnSe 전구체를 저온에서 주입 후 heating-up 방법을 통해 270 - 320 ℃로 빠르게 승온하여 코팅을 진행하였다. 온도가 높아질수록 정사면체의 QD 가 늘어나고, 동시에 양자점의 PL spectrum 에서 FWHM 이 줄어드는 것을 확인하였다. 위의 결과를 토대로 합성 온도가 높아지면서 나타나는 물리적, 화학적 변화를 측정, 결과에 대한 분석을 하였으며 합성된 양자점을 onchip 기반의 발광 소자에 적용, 높은 효율의 백색 LED 를 제작하였다. 109 2 장에서는 bidentate form 의 thiol 리간드인 1,2-Hexadecanedithiol 리간드를 합성하여 InP 양자점에 리간드 치환을 진행하였다. 제시된 리간드는 1 개의 리간드가 chelate effect 를 통해 양자점 표면에 강하게 달라붙는데, 이를 통하여 InP 양자점의 더욱 높은 표면 안정화를 유도하였다. Dithiol ligand 를 양자점 표면에 치환하였을 경우 InP 기반 양자점의 전반적인 안정성이 크게 증가하였으며, 소자로 적용했을 경우에도 그 효과를 확인할 수 있었다. 3 장에선 양자점 합성 과정에서 InCl3를 활용하여 NIR-SWIR 영역에서 흡광을 가지는 InSb 코어 양자점을 합성하였고, 이 코어에 InAs, ZnSe 쉘을 코팅하여 InSb/InAs core/shell 양자점과 InSb/InAs/ZnSe core/shell/shell 구조의 양자점을 합성해 InSb 양자점의 광학 성능 및 안정성을 개선하였다. 추가로 SWIR 영역의 흡광을 가지는 InSb 코어와 InSb/InAs 코어/쉘 양자점을 광 검출 소자에 적용하여 SWIR 영역 광전소자로서의 가능성을 확인하였다.

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목차

PART 1. Introduction 1
1. Quantum dots (Nanocrystals) 2
1.1 What is the quantum dots? 2
1.2 Classify of Quantum Dots with consistence elements 7
1.3. Surfactant for quantum dots 7
1.4. Classify of core/shell structure 9
2. Ⅲ-Ⅴ quantum dots 11
2.1. Introduction of Ⅲ-Ⅴ quantum dots 11
2.2. Problem of Ⅲ-Ⅴ quantum dots 12
2.3. Recently work of Ⅲ-Ⅴ quantum dots 12
3. References 17

 
PART 2. Improvement of InP quantum dots optical performance by adjustment of synthesis method and ligand exchange process. 20

Chapter 1. Highly Qualified InP Based QDs through Temperature Controlled ZnSe Shell Coating Process 21

1. Introduction 22
2. Experiment section. 24
2.1. Materials 24
2.2. Characterizations 24
2.3. Synthesis of Green-light-emitting InP QD 24
2.4. Synthesis of Red-light-emitting InP QD 25
2.5. On-chip LED fabrication with InGaP/ZnSe/ZnS QD 26
2.6. Computational details 26
3. Results and discussion 29
3.1. Effect of ZnSe inner shell and analysis thereof 29
3.2. DFT calculation for determine shape of QDs 39
3.3. On-Chip WLED fabrication 48
4. Conclusions 51
5. References 52

Chapter 2. Unprecedented surface stabilized InP quantum dots with bidentate ligands 54

1. Introduction 55
2. Experiment section 57
2.1. Materials 57
2.2. Characterization 57
2.3. Synthesis of 1,2-hexadecanedithiol. 57
2.4. Synthesis of blue-light-emitting ZnSe/ZnS QDs 58
2.5. Ligand exchange process 59
3. Results and discussion 60
3.1. Property of dithiol exchanged QDs 60
3.2. Dithiol-exchanged QDs to a LED as a solid-state light device 71
4. Conclusions 74
5. References 75


 
PART 3. InSb quantum dots : Ⅲ-Ⅴ quantum dots for NIR-SWIR region 77

Chapter 3. Performance improvement of InSb QDs via modified method and core-shell structure 78
1. Introduction 79
2. Experiment section 82
2.1. Materials 82
2.2. Characterization 82
2.3. Electrical characterization of the OPDs 82
2.4. Synthesis of InSb QDs. 83
2.5. Synthesis of InSb/InAs QDs. 83
2.6. Synthesis of InSb/InAs/ZnSe QDs 83
2.7. Materials and device fabrication on glass 84
3. Results and discussion 85
3.1. Characterization of InSb core QDs 85
3.2. InSb/InAs core/shell and InSb/InAs/ZnSe core/shell/shell QDs 91
3.3. Fabrication of InSb QD based photodetector device 99
4. Conclusions 103
5. References 104



PART 4. Conclusions 106
1. Conclusions 107

Abstract in Korean 108

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