研究動機

在前面的章節，我們已回顧了 InAs/GaAs 量子點的相關文獻，從這些文獻中可以了 解目前研究內層量子點的結構性質仍有大部分是藉由量測成長相同條件的表面量子點 來表示，而這量測的結果仍存在很多的疑慮，所以本論文中有關結構的研究均是使用 TEM 直接量測[010]GaAs方向的內層 InAs/GaAs 量子點尺寸，避免結構與光學結果的差異 性。

InAs/GaAs 量子點在光學元件的應用上，目前有三個光學性質的產業需求：發光強 度的增加、較低的發光能量與好的能量同調性(Energy coherence)。本論文中所研究的量 子點超晶格與緩衝層結構正是目前普遍被認為解決發光強度的方法，就先前發表的文獻 對於這兩個結構的光學性質均有詳細地研究，然而內層量子點結構與光學結果關聯性的 研究卻是很有限。因此，在本論文中，我們將使用 TEM 相關技術藉由直接量測內層量 子點的形貌與尺寸，來討論與光學量測出的結果。

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分子束磊晶(Molecular beam expitaxy, MBE)是一種有效成長高品質單晶結構的製程 技術。在 1960 年代由貝爾實驗室的 J. R. Arthur 和 卓以和開發出。一般來說，以往傳統 系統必須在 UHV 下磊晶，因為該環境擁有較大的平均自由徑(Mean free path)，這會讓 分子束有效的噴在基材上。在圖 3-2 中，MBE 使用真空大都在 10^-9~10^-10torr 左右，這使 得分子束在 10⁷cm 的距離內幾乎都不會碰撞到其他氣體分子，而磊晶腔體一般都是小於 10²cm。

本研究的試片成長是使用工研院光電中心 Riber 系統的 MBE 機台，如圖 3-3。圖 3-3(a) 為 MBE 系統腔體主要部分，(b)為控制系統，(c)為試片輸送腔，(d)為反射高能電子散射 儀(Reflection high-energy electron diffraction, RHEED)是用來了解磊晶狀況的臨場分析儀