以穿透式電子顯微術研究生長於矽基板上之氮化銦鎵/氮化鎵量子井結構

Abstract

熱膨脹係數的不同讓在矽基板上高溫成長完成之氮化鎵磊晶層在降溫過程中產生很強的伸張應力，使得氮化鎵層龜裂。為解決此問題，我們利用溫度漸變過程成長氮化鋁緩衝層以產生收縮應力來補償上述降溫過程產生的伸張應力，我們發現使用最多變溫成長階段之量子井樣品有最弱的殘留伸長應力、最短的發光波長以及最高的發光內部量子效率。本研究中，我們使用應變分析軟體(SSA)計算矽基板和藍寶石基板上不同變溫生長氮化鋁緩衝層條件下成長之氮化銦鎵/氮化鎵的量子井樣品內銦成分，得到和X光繞射分析相同的變化趨勢。然而使用應變分析軟體得到的銦含量變化幅度較大。再者，我們由穿透式電子顯微術的研究發現，隨著殘留應力下降，樣品內有較低的線性狀差排密度。另外也觀察到在氮化鎵/氮化鋁超晶格結構上方比其下方有較低的線性差排密度，這指出氮化鎵/氮化鋁超晶格結構可以阻擋線性差排往上延伸。

The difference of thermal expansion coefficient between GaN and Si results in a strong tensile stress on the GaN epitaxial layer during the cooling process. In our study, we create a compressive thermal stress by using an AlN buffer layer grown with graded temperatures to compensate the tensile thermal stress. The InGaN/Gan quantum well (QW) sample with the largest number of graded-temperature growth stages has the weakest residual tensile stress, shortest emission wavelength, and highest emission internal quantum efficiency. In this study, the variation trend of indium composition of the QW samples grown on Si and the control sample grown on sapphire based on strain state analysis is shown to be the same as that based on the X-ray diffraction measurement and fitting. However, the variation range becomes larger. Also, from the cross-sectional transmission electron microscopy study, it is found that the threading dislocation (TD) density decreases with decreasing residual stress. The TD density above the GaN/AlN superlattice inter-layer is lower than that below the inter-layer, indicating that the inter-layer can block the TDs.