傳統以來，以氣體□液體□固體三相共存(VLS)方式成長砷化鎵奈米線的製程主要以金當作催化劑，然而金的存在會產生深層能階缺陷，進而影響奈米線的電性及光性質。本研究成功開發出利用矽原生氧化層之孔洞，以分子束磊晶技術在其內形成鎵液滴作為催化劑，再經由VLS過程在矽基板上異質磊晶成長自催化的砷化鎵奈米線。此成長方法可望提昇砷化鎵奈米線之電性及光性質，同時結合高效能的砷化鎵半導體奈米線和矽電晶體工業技術的兩種優點。
本研究依序探討鎵沈積條件、原生氧化層、束流、以及成長溫度等參數對自催化砷化鎵奈米線成長的影響，更進一步地，藉由去除奈米線頂部的鎵液滴及隨後溫度和束流之調控，得以成長徑向核殼結構的砷化鎵/砷化鋁鎵奈米線，並探討砷化鋁鎵殼層的沈積速率以利未來太陽能元件製作。最後，以矽和鈹元素來摻雜砷化鎵奈米線，並對不同濃度摻雜的n-型及p-型砷化鎵奈米線進行電性量測。
本研究藉由掃描式電子顯微鏡來觀察奈米線的表面形貌變化，得知在鎵自催化系統中，鎵沈積的時間及溫度會分別影響奈米線的管徑與密度；另外，在固定砷束流的情況下，奈米線的管徑會隨鎵束流的增加而變粗，而在固定鎵束流的情況下，奈米線的軸向生長速率與砷束流成正比。藉由穿透式電子顯微鏡分析奈米線的微結構，得知奈米線本體在高五/三族束流比的成長條件下為完美的Zinc-Blende結構，然而其頂端及底部容易產生雙晶結構，並且能清楚地看出GaAs/AlGaAs的核□殼界面。此外，拉曼光譜分析亦被運用來探討砷化鎵奈米線的結晶性。

Traditionally, fabrication of GaAs nanowires (NWs) has mainly relied on the use of gold as catalyst through the vapor-liquid-solid (VLS) mechanism. However, the incorporation of gold may generate deep level traps and degrade the electronic and optical property of the nanowires. In this work, we report on a novel method for the growth of vertical GaAs NWs on Si (111) substrates by molecular beam epitaxy without the use of gold. The synthesis is based on gallium-assisted VLS growth, where gallium is selectively pre-deposited in the pinholes in the native oxide prior to the growth of nanowires. This method is expected to grow GaAs nanowires on Si substrates with enhanced electronic and optical property, and hence offer possible integration of high performance GaAs nanoscale devices with the mature Si-based technology. We have systematically studied the influences of Ga pre-deposition condition, native oxide, beam flux, and growth temperature on the growth of GaAs NWs. Furthermore, by eliminating the Ga droplets at the NWs’ tip first and then well controlling the beam fluxes and temperature, we have achieved the growth of GaAs/AlGaAs core-shell nanowires. Besides, we investigated the growth rate of the AlGaAs shell for the benefit of solar cell fabrication in the future. Finally, we studied the incorporation of the commonly dopants Si and Be, and investigated the I-V properties of NWs doped with various Si and Be concentrations. The morphology of nanowires was investigated using scanning electron microscopy. It was found that the Ga pre-deposition time and temperature would control the diameter and density of the nanowires, respectively. On the other hand, the diameter of NWs would increase with increasing Ga flux under constant As flux, while the axial growth rate of NWs is proportional to the As flux under constant Ga flux. Analysis based on the observation of transmission electron microscopy shows that the NWs grown under high V/III flux ratio exhibit a perfect Zinc-Blende structure in the main body region, while twin structure for the tip and bottom. We also observed a clear interface of the GaAs core and AlGaAs shell. The crystal quality of GaAs NWs was also investigated using Raman spectroscopy.

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