Transmission Electron Microscopy Studies on InGaN/GaN Multiple Quantum-well Structures Grown with Modulation Flow Process and InGaN/GaN Nano-column Structures
Date Issued
2007
Date
2007
Author(s)
Chang, Ming-Hsiu
DOI
en-US
Abstract
在本研究的第一部份中，我們比較兩片分別以不同的長晶方法成長的氮化銦鎵/氮化鎵多重量子井樣品的奈米結構以及光學特性。其中一片樣品在磊晶的過程中間斷地導入銦原子氣體和鎵原子氣體，另外一片樣品則以傳統方法成長。我們利用穿透式電子顯微術及應力分佈分析軟體分析樣本的奈米結構。由穿透式電子顯微術所得之影像，我們可觀察到量子井間不同程度的銦原子聚集現象和成分不均勻的變化以及量子井邊界的清晰度差異。我們發現以流量調變長晶法成長的樣品擁有較為顯著的銦原子聚集現象，並且擁有較好的均勻度和較為清晰的量子井邊界以及較長的衰減時間，但是卻呈現較低的發光效率。
在本研究的第二部分中，我們比較三個不同磊晶條件的氮化銦鎵/氮化鎵奈米結晶柱的奈米結構以及光學特性。在第一個和第二個樣品中，氮化鎵奈米結晶柱分別成長在矽晶圓和藍寶石晶圓上，而第三個樣品則是在藍寶石晶圓上成長氮化鎵奈米結晶柱，並且再成長氮化銦鎵/氮化鎵多重量子井。透過穿透式電子顯微術所得之影像，我們可以瞭解這三個樣品的結晶形狀、密度和結晶品質，並且透過光學儀器的量測，我們可以推論奈米結晶住結構內沒有線性差排的存在。
In this research, we perform the material and optical analyzes of two InGaN/GaN multiple-quantum-well samples to see the effects of the modulation flow growth process. Also, the material and optical properties of three GaN nano-columns samples are studied. The material analysis methods include X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), strain state analysis (SSA), scanning electron microscopy (SEM), and cathodoluminescence (CL). In optical characterization, the fundamental optical properties are obtained with photoluminescence spectroscopy.
In studying the effect of modulation flow growth process for InGaN/GaN quantum wells, from the HRTEM results, we find that the sample grown with the modulation flow process has a clearer interface between a well and a barrier. By analyzing HRTEM images with SSA, we can estimate the indium concentration in a well. Besides, from the line-scan result of the SSA images, we can see that the edge part of the sample wafer with the modulation flow process has a better-defined quantum-well structure than the counter part of the sample without the modulation flow process. From the XRD results, we can confirm that the sample with the modulation flow process has a clearer well boundary.
Then, we compare the nano-structures of three samples of GaN nano-columns. From the HRTEM images, one can see that the grown GaN nano-columns are threading-dislocation free. We compare the results of HRTEM, XRD, SEM, CL and micro PL between three samples, A844, A852 and A855. Sample A844 contains GaN nano-columns growth on sapphire, sample A852 contains fine InGaN/GaN quantum wells on the top of GaN nano-columns, which are grown on sapphire, and sample A855 contains GaN nano-columns grown on silicon. Sample A844 has a higher nano-column density when compared with sample A855. Based on the XRD results, sample A844 has a larger tilt and sample A855 has a larger twist. From the PL and CL results, we can observe that the different emission wavelengths of these three samples.
Subjects
流量調變長晶法
奈米結晶柱
穿透式電子顯微鏡
GaN
nano-column
TEM
modulation flow
threading dislocation free
Type
thesis