플라즈모닉 나노안테나를 탑재한 실리콘 나노선 어레이의 솔라셀 및 포토디렉터 특성에 관한 연구 = Integration of plasmonic nanoantennas on vertically-aligned silicon nanowire arrays for solar cell and photodetector applications

다국어 초록 (Multilingual Abstract)

Group IV semiconductors including Si and Ge are the key materials in current or future nanoelectronic and optoelectronic devices. In particular, one dimensional vertical Si arrays have enormous potential as building blocks for applications such as photodetector and solar cell devices. The vertical wire arrays have the geometrically beneficial effects in these devices due to efficient coupling of incoming photons, wide tolerance of light polarization, and reduced material consumption. In this perspective, we discuss the fabrication of vertically-aligned Si-based wire array for realization of low cost and efficient electric or energy harvesting devices. Integration of Al-doped ZnO (AZO) or plasmonic nanoantenna on this vertical nanowire structure enables photodetection in a certain range of wavelengths from ultraviolet (UV) to near infrared (NIR).
Transparent Al-doped ZnO (AZO) forms Schottky or n+-p heterojunction with p-type Si nanowire array, which allow efficient carrier collection. Conformal coating of AZO films enables us simply to fabricate the radial heterojunction on vertical nanowire array by using co-sputtering method, enhancing the performance of UV photodetector via increase of light active surface area and an antireflection effect.
Resonant plasmonic nanoantennas (NAs) have the potential to significantly modify the optical response via near-field coupling of strongly-enhanced electromagnetic fields. The optical NAs that exhibit a strong resonant interaction with photons concentrate light into a sub-wavelength volume, which makes them appropriate for enhancing the performance of photoactive devices, such as solar cells, light emitting diodes, and photodetectors. A simple nanostructure that optimally integrates the NAs should be effective for converting the concentrated light into a flow of electrons. In particular, high refractive-index silicon nanowire (~100 nm) can exhibit guided mode resonance as a cavity which confine and trap the light. Hence, we suggest a near infrared (NIR) photodetector device consisting of silicon nanowires and Au NAs. Especially, hemispherical Au NA can remarkably amplify the intensity of the near-infrared optical field, while suppressing visible-range guided mode excitation of Si nanowire. The Au NA also can form Schottky contacts with Si nanowires and increase efficient carrier collection. All these traits enable our photodetector to possess an NIR-selective enhanced response, thereby overcoming the inherent poor optical absorption of Si in the NIR wavelengths.

목차 (Table of Contents)

• Table of contents ------------------------------------- iv
• Table of figures ------------------------------------- viii
• Abstract ---------------------------------------------- 1
• Chapter 1. Introduction --------------------------------- 3
• 1.1 Energy issue of the 21st century -------------------- 3
• 1.2 Cost reduction strategies in solar cell --------------- 5
• 1.3 Fundamentals of energy conversion ---------------- 9
• 1.3.1 Principles of solar cell ------------------------ 9
• 1.3.2 Principles of photodetector -------------------- 11
• 1.4 Alternative designs for solar cell and photodetector -- 13
• 1.4.1 Silicon (Si) nanowire solar cell --------------- 14
• 1.4.2 Plasmonic solar cell ------------------------- 16
• 1.4.3 Integration of metallic transparent conductors
• on Si nanowires for solar cell and photodetector applications 17
• Chapter 2. Group IV semiconductor nanowire arrays ---- 19
• 2.1 Vapor-liquid-solid (VLS) growth ------------------- 19
• 2.1.1 Conditions for stable VLS growth -------------- 21
• 2.1.2 Catalyst selection for VLS growth ------------- 21
• 2.2 Ni-catalyzed growth of Si and Si1-xGex nanowires - 24
• 2.2.1 Growth of Si nanowires with SiCl4 ------------ 24
• 2.2.2 Growth of Si1-xGex nanowires with SiCl4 and GeCl4 - 30
• 2.2.3 Control of growth rate and Ge concentration --- 30
• 2.2.4 Ge segregation effect ------------------------ 35
• Chapter 3. Nanowire Schottky diode ------------------ 38
• 3.1 Metal-semiconductor contact --------------------- 38
• 3.1.1 Operation of Schottky diode under dark ------- 39
• 3.1.2 Operation of Schottky diode under illumination - 39
• 3.2 Schottky diode properties of Ni-catalyzed Si wire --- 40
• 3.2.1 Patterned VLS growth ------------------------ 40
• 3.2.2 Fabrication of Schottky diode ----------------- 42
• 3.2.3 Measurement of conductive atomic force microscopy - 44
• 3.3 Schottky diode properties of Si1-xGex wire arrays -- 47
• 3.3.1 Fabrication of large area Schottky diode ------- 47
• 3.3.2 J-V measurement --------------------------- 48
• Chapter 4. Ultraviolet (UV) photodetector --------------- 51
• 4.1 Introduction -------------------------------------- 51
• 4.2 Al doped ZnO (AZO) films and their properties ----- 52
• 4.2.1 DC and RF sputtering ------------------------ 52
• 4.2.2 Optical and electrical characteristics of AZO film on glass - 53
• 4.3 Fabrication of radial heterojunction of AZO/p-Si nanowire - 57
• 4.3.1 Lithography-free patterned p-Si nanowires ----- 57
• 4.3.2 Conformal coating of AZO film on p-Si nanowire -58
• 4.3.3 Antireflection effect of AZO coated p-Si nanowire - 60
• 4.4 Performances of UV photodetector ----------------- 62
• 4.4.1 J-V characteristics -------------------------- 62
• 4.4.2 UV photodetection --------------------------- 64
• Chapter 5. Near-infrared (NIR) photodetector ----------- 67
• 5.1 Optical antenna effects for solar cell ---------------- 68
• 5.2 Localized surface plasmon (LSP) ------------------ 71
• 5.3 Geometric effects: shape and substrate ------------ 73
• 5.4 Substrate effects: ultrathin Si ----------------------- 76
• 5.5 Optical properties of Au NPs coated Si nanowires --- 79
• 5.5.1 Morphologies and optical absorption properties -79
• 5.5.2 Electron energy loss spectroscopy analysis --- 83
• 5.5.3 Simulation: Absorption enhancement in Si nanowire - 85
• 5.5.4 Simulation: Optical mode resonance in Si nanowire - 90
• 5.6 Performances of NIR photodetector ----------------- 92
• 5.6.1 J-V characteristics --------------------------- 94
• 5.6.2 NIR photodetection --------------------------- 95
• Chapter 6. Conclusion and outlook -------------------- 98
• Chapter 7. References ------------------------------- 100
• Acknowledgements --------------------------------- 105