極化感應形成p-型氮化鋁鎵的穿透電子顯微研究

Abstract

基於穿透電子顯微術觀察中的能量色散X-光能譜（EDX）和d-spacing晶格分析方法，我們研究用分子束磊晶生長的六個鋁含量梯度的氮化鋁鎵樣品和三個鋁含量固定的氮化鋁鎵樣品中的鋁含量變化。生長鋁梯度氮化鋁鎵樣品可以產生極化感應的p-型行為，而固定的鋁含量樣品可當作參考來比較鋁含量變化。從能量色散X-光能譜數據，我們可以估算這些樣品中鋁含量的變化趨勢。數據可以線性擬合，但我們也觀察到鋁含量些許偏離目標值。基於局部區域繞射圖的d-spacing晶格分析，我們可以精確地計算沿c軸，a軸或m軸的局部晶格常數。 從計算的晶格常數，在氮化鋁鎵未受應變影響的假設下可以估算鋁含量。但由於獲得繞射圖案以實現高精度晶格常數需要相當大的晶體區域，因此在厚度為100-200奈米的氮化鋁鎵層內只能獲得有限的數據點。

Based on the energy-dispersive X-ray spectroscopy (EDX) and d-spacing crystal lattice analysis methods in transmission electron microscopy observation, we study the Al content variations in six Al-gradient AlGaN samples and three fixed Al-content AlGaN samples, all grown with molecular beam epitaxy. The Al-gradient AlGaN samples are grown for producing polarization induced p-type behaviors. The fixed Al-content samples are used as the references for comparing the Al-content variations. From the EDX data, we can estimate the variation trends of Al content in those samples. The data are well fitted with linear variation lines. However, deviations of Al content from the targeted values are observed. Based on the d-spacing crystal lattice analysis from the diffraction pattern of a local region, we can precisely evaluate the local lattice constants along the c-, a-, or m-axis. From the evaluated lattice constants, we can estimate the Al content assuming that AlGaN is un-strained. Because quite a large crystal region is required for obtaining the diffraction pattern to achieve a high-precision lattice constant, only limited data points can be obtained across an AlGaN layer of 100-200 nm in thickness.