- 學位論文
薄膜樣品的高解析度X-光散射研究
Study of thin films using high resolution X-ray diffraction
摘要
本論文是利用X光反射率和高解析X光繞射方法來研究薄膜樣品的界面與表面結構。第一部分觀察藉由有機金屬化學氣相沉積系統所成長於藍寶石基板或矽基板上的AlGaN/GaN多層膜系統。此系統，因為基板的不同，多層膜所排列的方式也會不同。利用這兩種量測法可以清楚地量測到每一層膜的厚度、粗糙度以及密度，並可以確定AlxGa1-xN之中Al的摻雜濃度。利用高解析X光繞射，並可以觀察到成長在藍寶石基板上的凝核層(GaN)受到基板應力的影響，而使得晶格常數產生改變。成長在矽基板的樣品，一樣可以觀察到此現象。從實驗中可得知，由於這些有緩衝作用的凝核層存在，而使得較上層的薄膜品質都變好了。從phi掃描的量測中，也可得知樣品具有六角型對稱的特性結構。 第二部分觀察藉由脈衝雷射沉積系統所成長於鋁酸鑭(LaAlO3)基板上的巨磁阻樣品Nd1-xCaxMnO3。從X光反射率的擬合分析中可以觀察到樣品表面層及介面層的存在。而介面層的產生是受薄膜和基板的晶格不匹配度影響，晶格不匹配度越大，介面層越厚。透過晶格常數的計算，更可以了解基板應力對薄膜晶格常數的影響。
並列摘要
This dissertation presents the study of the surface and interface structures of thin films by means of x-ray reflectivity (XRR) and high resolution x-ray diffraction (HRXRD). One of the systems studied is the AlGaN/GaN multi-layers, which is used for the high electron mobility transistor (HEMT), grown on the Al2O3 and Si substrates by metal-organic chemical vapor deposition (MOCVD). Using XRR, we measured the thickness, roughness, and density of each layer and the concentrations of Al in AlxGa1-xN. From HRXRD measurements, the lattice constants were observed to change because of the lattice mismatch between substrate and nucleation layer (GaN). The second case is the colossal magneto-resistance (CMR), Nd1-xCaxMnO3, thin films grown on LaAlO3 substrate by the pulsed-laser deposition (PLD). From the fitted results of XRR, top and interface layers were observed in all samples. The formation of interface layer is due to the lattice mismatch between the film and substrate, and the thickness of the interface layer becomes thicker as the lattice mismatch increased. From the calculation of the lattice constants, we further understand the strain effect produced by the substrate on the films.