臺灣博碩士論文加值系統

為了發展新一代的結晶矽太陽能電池並持續利用矽材料，許多有機會能改善電池轉換效率的新型矽奈米材料、結構或製程技術陸續被提出，其中，應用寬能隙矽基材料作為異質接面太陽能電池的射極藉以增加入射光的穿透率便是選項之一。在介電質基材中(如氧化矽、氮化矽或碳化矽)嵌入矽奈米晶粒可形成一種能隙略大於塊材隙的矽基複合薄膜結構，然而，若要將此新薄膜材料應用於太陽能電池的射極，仍必須克服矽奈米晶粒的摻雜製程以增加此薄膜材料的導電性。目前為止，在氧化矽或碳化矽基材中嵌入摻雜矽奈米晶粒之結構已開始陸續被探討與利用，然而，以氮化矽為基材嵌入摻雜矽奈米晶粒的材料開發與相關性質研究卻進展有限。
在本論文中，我們首次利用電子迴旋共振化學氣相沉積系統成長含有磷原子的富含矽氮化矽薄膜，並調整磷化氫對矽甲烷的氣體流量比例改變薄膜中磷原子的濃度。含有磷原子的富含矽氮化矽薄膜經過高溫退火後，便可形成在氮化矽基材中嵌入磷摻雜矽奈米晶粒的複合結構。本研究首先探討成長時所加入的磷原子濃度對退火時矽奈米晶粒結晶行為的影響，從實驗結果可知，磷原子的存在可加強富含矽氮化矽薄膜的相分離行為並加速矽奈米晶粒的結晶速率，固定退火條件下，相較於未含有磷原子之富含矽氮化矽薄膜，在含有磷原子的對照組薄膜中可形成尺寸較大的矽奈米晶粒。此外，在相分離與析出矽奈米晶粒的過程中，磷原子所佔據的位置也同時重新分佈，我們也對此鍵結結構的變化進行分析，並發現磷原子確實與矽奈米晶粒中的矽原子產生鍵結而可能位於取代位置。隨後，我們也發現隨著磷原子濃度的增加，磷摻雜矽奈米晶粒嵌入於氮化矽基材薄膜將會出現Fano干涉效應，同時其薄膜導電率亦出現變化，這兩項實驗結果可證實磷原子佔據在矽奈米晶粒中的取代位置且形成被活化之摻雜元素。最後，由於成功在氮化矽基材中形成n型摻雜的矽奈米晶粒，我們利用此薄膜製作矽基異質接面太陽能電池並獲得轉換效率8.6%。

For development of next generation crystalline Si solar cells, one of the new concepts for heterojunction solar cells is using wide bandgap materials as emitter layers due to the higher light transmittance. Silicon nanocrystals (Si-NCs) embedded in a wide bandgap dielectric matrix, such as SiOx, SiNx, and SiCx could be used for this purpose. Moreover, for increasing the conductivity of Si-NCs, incorporating the dopants into Si-NCs has also been demonstrated. So far, the doped Si-NCs in SiOx or SiCx matrix have been used for device fabrication. However, there are few studies for discovering the properties of the doped Si-NCs embedded in SiNx, even if SiNx has a higher bandgap than SiCx and better conductivity than SiOx theoretically.
In this dissertation, we first utilized electron cyclotron resonance chemical vapor deposition (ECRCVD) rather than sputtering or inhomogeneous implantation process to grow homogeneous Si-rich SiNx films doped with phosphorus atoms. The initial doping concentration was controlled by changing the introduced [PH3]/[SiH4] gas flow ratio. The as-grown phosphorus doped Si-rich SiNx thin films were then annealed for the formation of phosphorus doped Si-NCs. The effects of phosphorus additives on the Si crystallization behavior in Si-rich SiNx films were investigated. From the experimental results, existence of phosphorus enhances phase separation of Si-rich SiNx and Si crystallization rate. As the phosphorus content within the as-grown Si-rich SiNx thin film increases, the Si-NC size in the Si-NCs/SiNx film increases under the same annealing conditions. In addition, the bonding configurations of phosphorus atoms have been investigated and we could speculate that the phosphorus atoms would probably position at three regions according to the analysis results, including Si-NCs, boundaries between Si-NCs and SiNx, or SiNx matrix. Furthermore, observation of the Fano interference and improvement in conductivity of Si-NCs/SiNx films as a function of the phosphorus content within the as-grown Si-rich SiNx thin film provide evidences for the phosphorus activation, that is, the phosphorus atoms could position at the substitutional sites within Si-NCs. Owing to the achievement of Si-NCs n-type doping, Si-NCs/c-Si heterojunction solar cells have also been realized with a best power conversion efficiency of 8.6%.

中文摘要 I
Abstract II
Acknowledgement IV
Table of Contents V
List of Figures VII
List of Tables X

Chapter 1 Introduction 1
1.1 Silicon Technology 1
1.2 Role of Silicon in Solar Cells 2
1.3 Overview of Dissertation 6
1.4 References 8

Chapter 2 Fundamentals of Silicon Nanocrystals 9
2.1 Introduction of Si-NCs 9
2.2 Phase Separation 11
2.3 Effect of the Dielectric Matrix on the Wide Bandgap Si-NCs/dielectric Films 15
2.4 Issue of Doped Si-NCs for the Realization of Electrical Devices 16
2.5 References 18

Chapter 3 Experimental Procedures 22
3.1 Instrumentation 22
3.2 Substrate Cleaning Procedures 25
3.3 Preparation of Undoped and Phosphorus-doped SRN Films 26
3.4 Annealing for the Segregation of Undoped and Phosphorus-doped Si-NCs 27
3.5 Fabrication of Photovoltaic Devices 27
3.6 Characterization methods 28

Chapter 4 Results and Discussions 31
4.1 Fundamental Characterizations of As-grown SiNx Films and Si-NCs embedded in SiNx matrix 31
4.1.1 Analysis of As-grown SiNx Films 31
4.1.2 Analysis of Si-NCs embedded in SiNx matrix 36
4.1.3 Summary 40
4.1.4 References 41
4.2 Influence of Phosphorous Doping on Si-NC Formation in SRN films 42
4.2.1 Results and Discussion 42
4.2.2 Summary 53
4.2.3 References 53
4.3 Phosphorus Content Dependent Microstructure and Carrier Transport Variations of Phosphorus-doped Si-NCs Embedded in SiNx Matrix 56
4.3.1 Results and Discussion 56
4.3.2 Summary 64
4.3.3 References 65
4.4 Fabrication of Si Heterojunction Solar Cells Using Phosphorus-doped Si-NCs embedded in SiNx Films as Emitters 66
4.4.1 Results and Discussion 66
4.4.2 Summary 77
4.4.3 References78

Chapter 5 Conclusions and Future Works 79

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