氮化鎵及氧化鋅薄膜之穿透式電子顯微術分析研究

Abstract

在光電材料領域方面，氮化鎵的應用已日漸成熟，但某些電性、光性方面尚待進一步提升。本研究中，前半部分著重於非極性氮化鎵薄膜的晶體品質上的觀察，由於此鍍膜方向存在著不同方向上晶格常數差異性過大的特性，造成非極性氮化鎵薄膜普遍晶體品質不佳，為亟待克服的問題。因此，我們將兩個試片分別鍍上7.5奈米及15奈米厚度的氮化鋁作為緩衝層，看看是否能對於晶體品質上有實質上的幫助。實驗經由電鏡觀察可發現，有較厚的緩衝層差排密度明顯大為減小，晶體品質也較佳。另一方面，我們經由電鏡組織分析，發現許多疊差的存在，也測定出此材料薄膜上的線性差排大部分皆為純螺旋差排的特性。 然而，氧化鋅在物理特性上較氮化鎵更具有發展性。近年來氧化鋅在發光材料上的應用十分熱門，本實驗後半段著重於觀察三個製程上不同形式的氧化鋅試片。第一個試片為在二氧化矽中鑲入許多奈米尺寸的氧化矽顆粒，觀察結果相當令人滿意，相信不久的為來便可投入相當多的應用。而接著兩個試片為分別在兩個不同基材上鍍氧化鋅的比較及觀察。高解析度電鏡影像，X光繞射儀影像，光激發曲線影像…等等，皆為我們比較研究的參考來源。明顯的，在單晶矽上氧化鋅容易形成奈米多晶的形式，且差排、疊差的密度相較於在三氧化二鋁上成長的氧化鋅大上許多。由此歸納出，三氧化二鋁比單晶矽更適合做為氧化鋅的基材。

In the field of optoelectronic materials, the applications of GaN have gotten more and more mature recently. In this study, we focused on the observations for lattice quality of the non-polar GaN in the first part of experimental work. Due to the property of large mismatch anisotropy, the problem of low lattice epitaxy quality usually exists, so that we have to resolve it. Hence, we deposited 7.5nm and 15nm LT-AlN as buffer layers on two samples, trying to make improvement on lattice quality. Via observations of TEM, we can find that thicker buffer layer reduced threading dislocations obviously, and got better lattice quality. In the other hand, from the microstructural analyses of TEM, we observed a lot of stacking-faults, and confirmed that most of the threading dislocations are pure-screw dislocations. Nevertheless, ZnO have some physical properties which make it have more prospective development than GaN. ZnO is quite hot in the field of light-emitting materials in recent years. We focused on the observation of three ZnO samples with different growth conditions in the second half content. The first sample is ZnO nano-dots embedded, and the result is very satisfying. Furthermore, the last two samples are compared as ZnO deposited on different substrates. HR-TEM, XRD spectrum, and PL…etc. are the means we use for studying this samples. It is obvious that ZnO is polycrystalline when grown on silicon, and the density of dislocations and stacking-faults are much higher than the one on sapphire. To conclude, sapphire is better substrate for ZnO film epitaxy.