臺灣博碩士論文加值系統

摘要
本論文主要針對能夠轉換太陽光能量的再生能源元件作相關研究，利用三五族氮化鎵/氮化鎵銦(GaN/InGaN)材料製作光伏(photovoltaic, PV)元件與光電化學(photo-electro-chemical, PEC)水解出氫氣之元件。首先在PV元件的研究上，我們改變n型高摻雜層(n+-layer)的有效深度(teffn)與金屬電極分佈來縮短受光激發的載子在元件中的傳輸距離，藉此降低材料缺陷對元件特性的影響。轉換效率上，teffn為40 nm比起teffn 740 nm之元件減少了35%的光電流損耗；指叉狀電極分佈的光電流比起網狀電極高出30%。在SiO2光學薄膜的應用上，適當選擇的光學薄膜除了減少光反射(Fresnel reflection loss)外，元件表面形成的鈍化層亦減少半導體材料的表面復合速率，當元件本身表面缺陷較少的情況下對元件的開路電壓(VOC)有明顯提升，並且在轉換效率上有高達22%的提升。
PEC水解氫氣元件的研究上，我們設計不同金屬電極密度，改變電場在半導體內的延伸，降低受光激發載子在傳輸過程被復合的比例，且為了避免金屬電極參與光電化學反應而剝落，以SiO2薄膜做為金屬的保護層，使用的光源為300 W的氙燈、電解液為一個莫耳濃度之氯化鈉(NaCl : 1 mol/L)。比較光電化學反應的產氣速率，網狀金屬電極分佈比起直接藉由n+-GaN傳輸載子的元件高出72%，而且在外加1V參考偏壓時氣體反應速率更有161%的提升效果。

Abstract
InGaN-based photovoltaic (PV) devices with GaN/InGaN superlattice absorption layers epitaxially grown on sapphire substrates by metal-organic vapor phase epitaxy techniques are performed to reach band edge absorption at around 445 nm. The stacked superlattice structures with barrier and well layers form a miniband with lower bandgap energy instead of thick InGaN junctions with high indium compositions. PV devices designed with different structures and post-treatment are performed to alleviate the loss in photovoltaic effects of the InGaN-based absorption layers. In this study, shorter effective thickness of n+-layer (teffn ~ 40 nm) for PV-A reduces 35% in photo-generated current loss as compared with that of PV-B (teffn ~ 740 nm). On the other hand, the conversion efficiency of the devices with electrodes in digitated arrangement is improved by around 30% as compared to that of PV devices with electrodes in grid arrangement. In addition, SiO2 antireflection layers applied to the PV devices could effectively reduce the reflection of incident light and reduce surface recombination of surface states. As a result, the overall conversion efficiency is enhanced by approximately 22%.
Hydrogen generation by direct photoelectrolysis of aqueous solutions was also studied by using n+-GaN films to serve as working electrodes. To enhance the photocurrent, i.e., gas generation rate, meshed Cr/Au contacts on the n+-type GaN films with SiO2 protection layers were immersed in the NaCl electrolyte. The meshed Cr/Au contacts could effectively reduce the transit time of photogenerated electrons before they reach the Cr/Au Ohmic contacts while the SiO2 protection layers could isolate the Ohmic contacts from electrolyte. We designed two different n+-type GaN photoelectrodes. One is the n+-type GaN photoelectrode with Ohmic contacts in grid arrangement and SiO2 protection layers deposited on the Ohmic contacts (labeled as PEC2). For comparison, the carrier collection was directly extracted to the external circuit by working n+-GaN electrodes without the grid Ohmic contacts (labeled as PEC1). Under zero bias, the gas generation rate of PEC2 is enhanced by approximately 72% as compared to PEC1. The high generation rate could be attributed to the fact that the electrons generated by the light irradiation on the n-GaN working electrodes might recombine with holes or other material defects before they reach to the electrodes (i.e., external circuits) if the diffusion length of the electrons is shorter than the distance from the the n+-type GaN photoelectrode to the Ohmic contact. When a reference bias of 1V (compared with Pt electrodes) was applied to the n+-GaN working electrodes (PEC1 and PEC2), the generation rate was increased to 161% .

目錄
摘要 I
Abstract II
誌謝 IV
目錄 V
表目錄 IX
圖目錄 X
第一章 序論 1
1.1前言 1
1.2 研究動機與目的 3
參考資料 8
第二章 原理及量測方法 10
2.1 太陽能電池原理(Solar Cell Principles) 10
2.1.2太陽光頻譜 10
2.1.3太陽能電池等效電路模型(effective circuit model) 11
2.2太陽能電池效率相關參數與量測 14
2.2.1短路電流(Short Current，ISC) 14
2.2.2開路電壓(Open-circuit Voltage，VOC) 14
2.2.3最大輸出功率(Maximum Output Power，PMAX) 15
2.2.4最大輸出電流、最大輸出電壓 15
2.2.5填充因子(Fill Factor，FF) 15
2.2.6能量轉換效率(Energy Conversion Efficiency，η) 16
2.2.7串聯電阻與量測 16
2.2.8外部量子效率(external quantum efficiency, EQE) 17
2.3太陽能電池的材料與設計 18
2.3.1材料吸收與光電流產生 18
2.3.2 p-n接面與p-i-n接面 20
2.3.3 光學薄膜 22
2.3.4 超晶格 23
2.4 光電化學原理(PEC theorem) 24
2.4.1 光電化學轉換太陽能的基礎理論 24
2.4.2 半導體光電化學電池工作原理 25
2.4.3 影響光電化學反應速率之因素 26
2.5 光電化學反應實驗的量測方法 28
2.5.1穩態電流的量測 28
2.5.2氣體收集與定性及定量上的量測 28
參考文獻 40
第三章 實驗方法與製程步驟 42
3.1儀器設備 42
3.2氮化鎵銦太陽能電池元件製作 46
3.2.1氮化鎵銦太陽能電池元件結構設計 46
3.2.2超晶格藍光氮化鎵銦太陽能電池結構 47
3.2.3試片清潔 49
3.2.4製程步驟 50
3.3光電化學元件製作 53
3.3.1光電化學元件結構 53
3.3.2製程步驟 54
參考資料 59
第四章 實驗結果與分析討論 60
4.1氮化鎵銦太陽能電池製程優化 62
4.1.1平台蝕刻深度(Mesa)研究 62
4.1.2電極分佈研究 65
4.2光學薄膜對氮化鎵銦太陽能電池優化之研究 68
4.2.1光學薄膜的穿透與反射 68
4.2.2光學薄膜之於元件運用 69
4.2.3元件特性提升之分析 70
4.3金屬電極分佈對光電化學製備氫氣優化之研究 73
4.3.1 光能與外加偏壓對光電化學反應影響之分析 73
4.3.2 金屬電極分佈對光電化學反應影響之分析 76
4.3.3 氣體生成速率與成分分析 78
參考資料 97
第五章　結論與未來展望 98

表目錄
表4-1 mesa研究典型量測資料 82
表4-2 電極研究典型量測資料 84
表4-3 PV-D與PV-F典型量測資料 87
表4-4 PV-E與PV-G典型量測資料 88
表4-5 PEC1與PEC2光電流密度比較 95
表4-6 PEC1與PEC2在Pt電極的氣體生成速率比較 96

圖目錄
圖1.1(a) 氮化鎵材料光吸收係數與波長對應圖【4】 6
圖1.1(b) 半導體材料光吸收係數與波長對應圖【10】 6
圖1.2氮化鎵銦材料之合金系統能帶示意圖【1】 7
圖2.1 p-n接面太陽能電池能帶示意圖 29
圖2.2(a) 空氣質量示意圖 29
圖2.2(b) 太陽頻譜照度 30
圖2.3 理想太陽電池等效電路圖 30
圖2.4 非理想太陽能電池等效電路圖 31
圖2.5 漏電流的路徑分析 31
圖2.6 太陽能電池照光之電流電壓圖 32
圖2.7 多重光強度法 32
圖2.8 光子在半導體內部產生電子電洞對 33
圖2.9 光子被半導體材料吸收示意圖 33
圖2.10(a) p、本質和n的半導體能帶圖 34
圖2.10(b) p-n接面半導體能帶圖 34
圖2.10(c) p-i-n接面半導體能帶圖 35
圖2.11 半導體表面的缺陷 35
圖2.12 光學薄膜示意圖 36
圖2.13(a) 多重量子井能帶示意圖 36
圖2.13(b) 超晶格形成miniband能帶示意圖 37
圖2.14 半導體與電解異的異質接面【15】 37
圖2.15 水的氧化還原電位【12】 38
圖2.16 不同電解液對應時間的光電化學反應電流變化【13】 38
圖2.17 光電化學反應實驗架構 39
圖3.1 結構一 iBSL1 55
圖3.2 結構一iBSL1的微光激螢光光譜 55
圖3.3 結構二iBSL2 56
圖3.4 結構二-iBSL2的微光激螢光光譜 56
圖3.5 結構三BPIN 57
圖3.6 太陽能電池製程元件示意圖 57
圖3.7 PEC-1元件示意圖 58
圖3.8 PEC-2元件示意圖 58
圖4.1 超晶格結構iBSL1與多重量子井結構BLED的外部量子效率 80
圖4.2 蝕刻平台深度示意圖 80
圖4.3 PV-A與PV-B外部量子效率量測 81
圖4.4 PV-A與PV-B元件電流密度與電壓的特性曲線圖 81
圖4.5(a) 網狀金屬電極分佈 82
圖4.5(b) 指叉狀金屬電極分佈 83
圖4.6 PV-A與PV-C外部量子效率量測 83
圖4.7 PV-A與PV-C元件電流密度與電壓的特性曲線圖 84
圖4.8(a) ITO與ITO-SiO2穿透率量測 85
圖4.8(b) ITO與ITO-SiO2反射率量測 85
圖4.9(a) 入射太陽能電池元件主動層的光強度 86
圖4.9(b) 入射太陽能電池元件主動層的光子數 86
圖4.10 PV-D與PV-F元件電流密度與電壓的特性曲線圖 87
圖4.11 PV-E與PV-G元件電流密度與電壓的特性曲線圖 88
圖4.12 PV-D的電流電壓特性圖 89
圖4.13 PV-F的電流電壓特性圖 89
圖4.14 PV-E的電流電壓特性圖 90
圖4.15 PV-G的電流電壓特性圖 90
圖4.16 iBSL1的SEM圖 91
圖4.17 iBSL2的SEM圖 91
圖4.18 PEC1光電化學反應的穩態光暗電流密度與電壓特性曲線 92
圖4.19 PEC2光電化學反應的穩態光暗電流密度與電壓特性曲線 92
圖4.20(a) 光電化學反應能帶示意圖：未照光 93
圖4.20(b) 光電化學反應能帶示意圖：n-GaN陽極照光 93
圖4.20(c) 光電化學反應能帶示意圖：n-GaN陽極照光、正偏壓 94
圖4.21光電化學反應的穩態光暗電流密度與電壓特性log曲線 94
圖4.22 PEC1與PEC2光電流密度與電壓特性曲線 95

第一章 參考資料
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第二章 參考文獻
【1】楊智喬, “三五族太陽能電池製作與分析Fabrications and Characteristics of Group III/V Solar Cells”, 國立成功大學光電科學與工程研究所碩士論文, 2007.
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第五章 參考資料
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