InGaN/GaN多層量子井半導體材料之電子顯微鏡觀察與分析

TEM Observation and Analysis of InGaN/GaN multiple quantum wells

蔡鴻麟(Hung-Ling Tsai)

指導教授 ： 楊哲人

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.01901

摘要

在論文中成功地利用TEM使得我們可以更加瞭解Ⅲ-族氮化物。我們成功地利用金屬有機化學沈積法(MOCVD)及脈衝雷射蒸鍍(PLD)將GaN及InGaN/GaN多層量子井沈積於氧化鋁基材上。由於氧化鋁基材與磊晶薄膜間晶格常數差異很大導致在靠近界面的區域有許多的疊差及錯位差排，磊晶薄膜中也有很高密度的線形差排存在。我們也成功地將GaN沈積於矽及氧化鋅基材上。雖然它們是很有希望的基材，但是仍然有許多問題亟待解決。矽基材與磊晶薄膜層間過大的熱膨脹係數與晶格常數差異導致高缺陷密度的產生甚至有裂痕形成。另一方面，較差的表面處理及使用金屬有機化學沈積法時較高之沈積溫度都會使沈積於氧化鋅之GaN薄膜品質變差。在4-3章節中我們使用HAADF-STEM及HRTEM來觀察在一綠光發光二極體中之InGaN/GaN多層量子井。HAADF-STEM提供了一個確實的證據證實在多層量子井中所形成之V形缺陷為具有InGaN/GaN{10 1}側面的六角錐。V形缺陷之詳細結構是根據GaN晶體的成長動力學及在線形差排附近銦原子偏析所造成的覆蓋效應來加以討論。在4-4章節中，我們則是對於GaN-基紫光雷射二極體與AlInGaN-基紫外光發光二極體中所使用之AlGaN/GaN應變超晶格作觀察。在GaN-基紫光雷射二極體中P-型應變超晶格包含了34對p-Al0.1Ga0.9N/p-GaN:Mg層，其中Al0.1Ga0.9N與GaN在HAADF-STEM影像中可以清楚區分為黑色及白色條紋，厚度也都約為6nm。同樣地在試片中也觀察到許多線形差排。在這些線形差排中有些會向上穿過應變超晶格，但是也有許多線形差排會消失於應變超晶格中，這顯示出應變超晶格可以減少到達多層量子井區域的線形差排密度。在線形差排的HAADF-STEM影像中觀察到在沿著較亮的條紋中心有條黑線，這可能是因為在差排核附近原子量較小之原子(鎂或鋁)局部偏析所造成。在紫外光發光二極體的HAADF-STEM影像中，位於多層量子區域中之AlInGaN及AlInGaN:Si可以清楚地分辨，分別為黑色及白色條紋，同樣也可以清楚觀察到此結構中所使用之應變超晶格。在結果與討論的最後一章節是觀察利用於GaN上部分覆蓋SiNx所成長之高密度InGaN量子點。SiNx覆蓋層於HAADF-STEM影像中為黑色條紋，厚度估計約小於2nm。InGaN量子點在HAADF-STEM影像中可觀察到是呈現出白色三角形狀，我們將其視為奈米島狀晶體，側面為{10 1}平面，高度約有數個奈米大小。在HRTEM影像中量子點區域的晶格與磊晶下方之GaN或覆蓋層部分之GaN相比會受到更大之應變。

關鍵字

氮化鎵 ； 穿透式電子顯微鏡 ； LED ； STEM

並列摘要

In the thesis, TEM has successfully been applied leading to a better understanding of the Ⅲ-nitride material system and devices. We successfully deposit GaN layers and InGaN/GaN multiple quantum wells(MQWs) on sapphire by metalorganic chemical vapor deposition(MOCVD) and pulsed laser deposition(PLD). There are many stacking faults and mismatch dislocations exiting near the interface to release the strain originated from lattice mismatch between sapphire and epitaxial layers. These samples have high defects density. We also successfully deposit GaN layers on Si substrate and ZnO substrate. Although they are promising substrate, there are still many problems need to be addressed. The large thermal expansion and lattice mismatch between Si-substrate and epilayers cause cracks on the growth surface and lead to high defects density. Poor surface preparation and severe issues associated with high temperature growth by MOCVD degrade the GaN film quality on ZnO substrate. In chapter 4-3, Multiple In0.18Ga0.82N/GaN MOWs layers in a green LED were observed by high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and high resolution TEM (HRTEM). HAADF-STEM provided undoubted evidence that V defects in the multiple QWs have the thin six-walled structure with InGaN/GaN {10 1} layers. The detailed structure of the observed V defects is discussed on the basis of the formation mechanism of V defects which was proposed taking into account the growth kinetics of the GaN crystal and a masking effect of In atoms segregated around the threading dislocation. In chapter 4-4, we investigated the nanostructure of AlGaN/GaN strained-layer superlattice (SLS) cladding in the GaN-based violet LD and the AlInGaN-based ultraviolet (UV) LED with a STEM. In the p-SLS cladding, comprising thirty four pairs of p-Al0.1Ga0.9N/p-GaN:Mg layers in the GaN-based LD, the Al0.1Ga0.9N and GaN layers were distinguished as dark and bright bands ~6 nm wide in the HAADF-STEM images. Threading dislocations (TDs) were observed. Among of TDs that came from the underlying layer, some run outside through the SLS, and the others disappeared within the SLS, which discloses a role of the SLS in suppressing defect propagation. A HAADF-STEM image of the TD with a dark line along the center of a bright contour was found. One of probable explanations for the dark line is local segregation of light atoms (Mg or Al) in Cottrell atmosphere around the dislocation core. In the HAADF-STEM image of the UV LED wafer, the AlInGaN and AlInGaN:Si layers in the MQW were definitely resolved, appearing as dark and bright bands. HAADF-STEM also distinguished between the AlGaN and GaN layers in the p-SLS cladding in the UV LED wafer. In the last chapter, high density InGaN quantum dots (QDs), grown on the GaN underlying layer which was partially masked with SiNx nano-crystals, were investigated by HAADF-STEM, HRTEM and energy dispersive X-ray spectroscopy. The layer of SiNx masks appeared as a dark line in HAADF-STEM images and the height of the masks was roughly estimated to be less than 2 nm from the thickness of the dark line. The InGaN QDs were observed as bright triangles in the HAADF-STEM images. The QDs can be regarded as nano island crystals with the {10 1} side walls and a height of several nanometers. The lattices in the InGaN crystals were strained compared with the underlying and the capping GaN lattices, contacting in the coherent lattice relation with them.

並列關鍵字

InGaN ； TEM ； STEM ； LED

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