GaAs/In(0.5)Ga(0.5)P 雙接面太陽能電池磊晶與製程的設計

Abstract

近幾年來，由於能源供應日漸缺乏，因此替代性能源的開發則備受重視。而太陽能具備了龐大的能源供給量以及相當低的環境污染，是一種非常好的替代性能源，也因此受到廣泛的研究。本實驗中所研究的多接面 Ⅲ-Ⅴ族太陽能電池具備了相當高的能量轉換效率，是一個很好的研究方向。由於多接面太陽能電池是由不同能隙的半導體材料串接在一起，所以整體元件的電流受到各部電池中最小電流的限制。因此，提升最小電流值並達到電流匹配，對於提升轉換效率而言，是一個很重要的議題。

本實驗中先利用PC1D及APSYS模擬軟體先進行GaAs及InGaP 單接面太陽能電池結構以及 GaAs / InGaP 二接面太陽能電池結構的模擬。藉由模擬過程獲取材料種類、薄膜厚度、掺雜濃度等參數對於轉換效率的影響，藉以達成結構優化的目的。再使用有機金屬化學氣相沉積( MOCVD )來成長Ⅲ-Ⅴ族太陽能電池結構，其中包括了GaAs 及InGaP 單接面太陽能電池結構以及 GaAs / InGaP二接面太陽能電池結構。在此，我們發現薄膜材料形成品質的優良與否有很大的關鍵原因在於反應腔體( reactor chamber )內部流場的穩定性、溫度控制、溫度均勻性以及反應氣體的反應狀況等這幾種重要的因素。因此針對可控制的長晶參數：如溫度、長晶速率( growth rate )、長晶壓力( reactor pressure )、Ⅴ-Ⅲ比( Ⅴ-Ⅲ ratio )、晶格常數( lattice constact )、基板( substrate )的選擇等，即是攸關薄膜品質之探討分析的重點。

在本論文第一章中，將先針對太陽能電池發展歷史做一概述，而後再說明Ⅲ-Ⅴ族太陽能電池發展的優勢以及本實驗研究的方向。

第二章中，將介紹太陽能電池的工作原理、等效電路及常用的基本參數，以及化合物半導體太陽能電池的基本結構介紹。 第三章中將介紹PC1D及APSYS模擬軟體所進行的GaAs、InGaP單接面太陽能電池及GaAs/InGaP二接面太陽能電池的模擬結果。其中包含模擬所需的各種物理參數設定以及太陽能電池結構的規劃。

第四章中將對有機金屬化學氣相沉積法 ( MOCVD )原理及系統做介紹，並且包含了MOCVD反應物的特質、磊晶參數的考量與設定以及磊晶薄膜量測儀器的介紹說明。

最後在第五章中，將延續第三、四章的研究，利用有機金屬化學氣相沉積法 ( MOCVD )來成長GaAa、InGaP單接面太陽能電池及GaAs/InGaP二接面太陽能電池。並對量測結果進行分析與討論，最後在第六章為本論文做一個完整的結論及規劃未來工作重點。

In recent years, due to the shortage in energy supply, the development of alternative energy has caught great attention. Moreover, since solar energy is huge energy supply source and produces very low environmental contamination, it is thus very good alternative energy, and it thus has caught attention and is under wide research. The multi-junction Ⅲ-Ⅴ solar cell studied in this experiment has pretty high energy conversion efficiency, which is a pretty good research direction. Since multi-junction solar cell is serially connected by semiconductor materials of different energy gaps, the current of the entire device is thus limited by the smallest current in each part of the cell. Therefore, the enhancement of smallest current value and the reach of current match is a very important topic for the enhancement of conversion efficiency.

In the experiment, PC1D and APSYS simulation software is used first for the simulation of GaAs and InGaP single junction solar cell structure and GaAs / InGaP double junction solar cell structure. Through the simulation process, the results of the influence of the material type, thin film thickness and doping concentration on conversion efficiency were obtained, and the structure optimization objectives were then obtained. Then Metal organic chemical vapor deposition ( MOCVD ) method is used to grow Ⅲ-Ⅴ solar cell structure, which includes GaAs and InGaP single junction solar cell structure and GaAs / InGaP double junction solar cell structure. Here, we found that the quality of the thin film material formed is mainly due to the internal flow field stability in the reactor chamber, temperature control, temperature uniformity, and the reaction situation of the reaction gas, etc. Therefore, the controllable crystal growth parameters are the key points to be investigated regarding the thin film quality, and the parameter are, for example, temperature, crystal growth rate, reactor pressure, Ⅴ-Ⅲ ratio, lattice constant, and substrate selection, etc.

In the first chapter of this thesis, an overview will first be done on the development history of the solar cell, then the development advantages of Ⅲ-Ⅴ solar cell and the research direction of this experiment will be described.

In chapter 2, we are going to introduce the work principle, equivalent circuit and basic parameters of solar cell, then it will be introduction of the basic structure of compound semiconductor solar cell.

Chapter 3 will be introduction of the simulation result of GaAs, InGaP single junction solar cell and GaAs/InGaP double junction solar cell as performed by PC1D and APSYS simulation software. Wherein it includes the physical parameter setup as needed in the simulation and the planning of solar cell structure.

Chapter 4 will be introduction of the principle and system of MOCVD, which includes MOCVD reactant characteristics, epitaxial parameter consideration and setup, and the introduction and description of the measurement equipment for epitaxial thin film.

Finally, in chapter 5, it will be an extension of the study in chapter 3 and 4. It will use MOCVD to grow GaAs、 InGaP single junction solar cell and GaAs/InGaP double junction solar cell. Moreover, analysis and discussion will be performed on the measurement result, and finally, a complete conclusion and the future work will be presented for chapter 6.