- 學位論文
矽鍺半導體奈米線的成長與分析
Growth and Analysis of Group IV Semiconductor Nanowires
摘要
將四族半導體材料成長為奈米線(Nanowire)結構，可應用於製作效能更高的電子元件，並克服矽鍺異質介面結構因晶格常數差異而產生缺陷的難題。為了達到這些目的，半導體奈米線的形貌以及成份分佈必須能精準的控制。在本篇論文研究中，奈米線成長是以化學氣相沉積(CVD)的製程方法，藉由氣相液相固相(Vapor-Liquid-Solid, VLS)機制成長出矽奈米線以及矽鍺合金奈米線，另外並藉由氣相固相固相(Vapor-Solid-Solid, VSS)機制成長具有矽鍺異質介面的奈米線結構。研究中對各種影響奈米線成長的要素包含催化劑的成份、氣體選擇、溫度壓力、試片表面乾淨度進行研究與探討。而在矽鍺合金奈米線中，鍺元素會改變奈米線的傳導性質，因此控制矽鍺合金奈米線中鍺含量的多寡、以及鍺含量的準確量測即成為重要的問題。由於奈米線的直徑小於一百奈米，常見的表面分析成份量測工具不易得到準確的結果，因此我們藉由掃描穿透式電子顯微鏡的能量分散光譜技術，利用已知成份組成的矽鍺薄膜做為標準試片，定量分析奈米線中鍺的含量多寡。實驗結果顯示，矽鍺合金奈米線中矽鍺含量的比例與CVD中反應氣體的成份比呈現非線性的關係，進料氣體先驅物的化學活性差異是控制矽鍺含量比的最重要因素。在矽鍺異質介面的成長中，有效控制介面處的成份變化，將有助於達成理想的電子元件結構。針對這個目的，改採以VSS的成長機制，利用金銀合金(成份比1:1)作為成長用的催化劑，製作出寬度僅數奈米的矽鍺異質介面。
並列摘要
Group IV semiconductor materials such as silicon and germanium are potential candidates for future applications in high performance semiconductor devices by means of nanowire structure. Defects due to lattice mismatch between Si and Ge at Si-Ge heterojunction interface can be avoided as well when the heterojunction is made into nanowire structure. In order to realize these applications, the morphology and interior composition distribution must be controlled precisely. In this study, we grew Si nanowires and SiGe alloy nanowires via vapor-liquid-solid (VLS) mechanism and grew heterojunction structure nanowires via vapor-solid-solid (VSS) mechanism in a chemical vapor deposition (CVD) reactor. The correlation between nanowire growth and growth factors such as catalysts, gas precursors, temperature, pressure, and cleanness was discussed based on our experimental results. In SiGe alloy nanowires, the amount of Ge would affect the transport properties of nanowires, so it is important to control and measure the Ge content in nanowires. Common surface analysis techniques are difficult to get accurate composition due to the small diameter of nanowires. Thus, we performed quantitative analysis of SiGe alloy nanowires by using energy dispersive spectroscopy (EDS) in scanning transmission electron microscopy (STEM). Four SiGe films with different compositions were served as standards in EDS analysis. The results of quantitative analysis showed that the amount of Ge increases as a nonlinear function of partial pressure of gas precursors, and the chemical reactivity of gas precursors is the key to control the nanowire interior composition. In Si-Ge heterojunction growth, controlling the composition distribution at interface precisely is helpful for fabricating desired electronic devices. For this purpose, we grew nanowires via VSS mechanism and finally fabricated heterojunction nanowires by using a mixture of Ag and Au as catalysts (AgAu). The interface width of Si-Ge heterojunction is only few nanometers.