氮化鎵薄膜表面V 型缺陷結構之微拉曼光譜研究

Abstract

在本論文中，我們利用原子力顯微鏡(AFM)、微拉曼光譜(micro-Raman)等方法研究利用金屬有機化學氣相磊晶系統(MOCVD)所成長的氮化鎵薄膜表面上的V型缺陷。在微拉曼光譜分析中，發現在不同摻雜濃度n型氮化鎵薄膜上直徑3.3微米的V型缺陷內，其LO相關的模態相對於平坦處都有明顯的藍移情形。而在同樣摻雜濃度下、不同大小的V型缺陷中，隨著V型缺陷的直徑增加，禁止模態(forbidden modes) A1(TO)、E1(TO)強度增加，而LO相關的模態則有明顯的藍移行為。我們將禁止模態的出現歸因於表面形貌的改變而提供了側向散射，而LO相關模態的藍移則是由於V型缺陷下方較高的線差排密度(dislocation density)提供了許多的電子。經由LO聲子-電漿的耦合模型(LO phonon-plasmon coupling)以及有效電子濃度(effective electron density)計算，我們推測在V型缺陷中心下方的線差排密度數量級在1010cm-2以上。

The optical properties of V-defects on GaN films were characterized by using atomic force microscopy and micro-Raman spectroscopy. Raman LO related modes of 3.3□m V-defects show noticeable blue shifts from different doping concentration samples. For V-defects of different size, the appearance of forbidden Raman modes A1(TO) and E1(TO) inside V-defects is due to the right angle scattering from morphology variation. Distinct blue shift of LO related modes was also observed inside V-defects compare to the plain region, especially in large V-defects. Simulation results obtained from the phonon-plasmon interaction model suggest a higher carrier density inside V-defects than that on the plain region. Thus, we deduced a higher dislocation density (~1010cm-2) inside V-defects than that (108~109cm-2) on the plain by considering effective electron density.