利用液滴狀磊晶成長方式在矽(111)基板上成長氮化鎵量子點

Abstract

本研究使用電漿輔助式分子束磊晶系統﹙PA-MBE﹚，以液滴磊晶成長方式在矽基板上成長氮化鎵量子點，在超高真空環境下，先成長島狀鎵金屬接著進行氮化處理，以形成氮化鎵量子點，氮化鎵量子點的密度控制可以藉由改變成長基板溫度﹙475-550 °C﹚、氮化處理時間﹙5-10分鐘﹚以及矽基板有無預先氮化處理60分鐘去控制，利用場效發射式掃描電子顯微鏡觀察氮化鎵量子點的密度與表面形貌，當成長基板溫度降低或是氮化處理時間增加，氮化鎵量子點的密度都增加，且矽基板有預先氮化處理60分鐘也會增加氮化鎵量子點的密度。氮化鎵量子點表面成分分析，以X射線光電子能譜學的結果證實，液滴狀的鎵在氮化處理過程轉變成氮化鎵量子點，此外更使用穿透式電子顯微鏡觀察氮化鎵量子點在矽表面的分佈與其結晶結構。除了實驗結果證明以氮化鎵量子點的成長，我們更提出氮化鎵量子點利用液滴磊晶之成長機制，藉由成長機制說明基板溫度、氮化處理時間以及矽基板有預先氮化處理60分鐘，對氮化鎵量子點密度之影響。

GaN nanodots（NDs）were fabricated on Si（111）substrates by droplet epitaxy using Plasma-Assisted Molecular Beam Epitaxy (PA-MBE) system. In ultra-high vacuum condition, Ga metallic droplets formed, and then became GaN NDs by nitridation process. The density of GaN NDs can be controlled by the growth temperatures between 475 and 550°C, the nitridation time within the range 5-10 minutes, and the Si（111）substrates with and without pre-nitridation 60 minutes. Field emission scanning electron microscopy（FESEM）was used for the investigation of density and surface morphology of GaN NDs on Si （111）. We can find the density of GaN NDs increases as the growth temperature decreases. By increasing the nitridation time, we observed GaN NDs density increase. The pre-nitridation treatment for 60 minutes of Si（111）substrates can also increase GaN NDs density. The results of X-ray photoelectron spectroscopy（XPS）confirm that Ga droplets that transformed into GaN NDs and self-assembled over the sample surface during nitridation. Transmission Electron Microscopy（TEM）was used for the investigation of surface distribution, crystalline quality and shape of GaN NDs. From the results of experiments, we demonstrated that density of GaN NDs grown by droplet epitaxy strongly affected by growth temperature, nitridation time and pre-nitridation treatment of the Si（111）substrates. Meanwhile, the growth mechanism of GaN NDs was proposed in this study.