氮化銦鎵/氮化鎵多重量子井結構於不同預施應力條 件之穿透式電子顯微術硏究

Abstract

在本研究中，我們比較四片具有不同結構的氮化銦鎵/氮化鎵多 重量子井樣品的奈米結構及光學特性。其中三個樣品在成長與控制樣品相同的高濃度量子井結構之前，先成長一低濃度之量子井，同時，低濃度量子井上分別成長不同的厚度之氮化鎵阻障層。我們利用穿透式電子顯微術及應力分布分析軟體分析這四片樣本的奈米結構，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以及成分不均勻的變化。經由應力分佈分析計算其各個量子井的平均濃度，在與控制樣品的結果比較之下，我們發現愈接近低濃度量子井的高濃度量子井具有越高的銦含量。這樣的銦濃度增加現象應歸因於低濃度量子井的應力對於上層產生影響。同時，我們發現此種預施應力效應所造成的影響會隨量子井層數的增加而減小。在這四片樣品的光學特性比較中，可發現他們的發光波長雖然大致都位於500奈米，但從穿透式電子顯微術之影像中，我們發現當預施應力阻障層越薄，在發光二極體中隨著電流注入的增強而產生的波長藍移現象會變的越小。

for growing the five QWs in the control sample. Besides, the GaN barrier layers of different thicknesses right above the low-indium QW are deposited among the three samples. We use the techniques of high-resolution transmission electron microscopy (HRTEM) and strain state analysis (SSA) to analyze the nanostructures of these four samples. From the HRTEM images, one can see different degrees of indium aggregation and composition fluctuation between QWs are observed. From the calibrations of the average indium contents of those QWs based on the SSA images, it is found that the QWs closer to the low-indium one have higher indium contents. Such an increase of indium incorporation is attributed to the pre-strain effect of the low-indium QW on the barrier layer right above it. Also, we found that the pre-strain effect diminishes along the growth of more QWs. In the comparison of optical property in these four samples, one can see that the light-emitting wavelengths in each sample are all around 500nm. Also, we find that the smaller the thickness of the pre-strained layer in the LED is, the smaller the blue shift in wavelength induced by the increase of current injection becomes.