非極性"a"面氮化銦鎵多重量子井成長在奈米圖樣基板之光學特性研究

Abstract

在本論文中，我們利用有機金屬化學氣相沉積法成長非極性”a”平面氮化銦鎵/氮化鎵多重量子井的結構，樣品的差異為氮化鎵基板中不同的奈米柱(Nanorod)深度。在特性分析中，包含了光學與結構特性上的相關研究；在發光特性方面，所利用的是光激發螢光光譜(PL)進行樣品的光學特性分析，結構及相關成分的研究包含了掃描式和穿透式電子顯微鏡圖像、原子力顯微鏡、X射線繞射…。 由AFM、TEM可知，奈米柱深度越深再成長的氮化鎵基板，表面的質地越好，藉由變溫PL的量測，可以得到室低溫強度比隨著奈米柱深度越深值越大，活化能也提升，意味著減少樣板的缺陷，多重量子井的侷限能力會提升；在變功率的PL實驗中，樣品的發光波長不隨者雷射功率增加而改變，得知非極性面成長的氮化銦鎵多重量子井能確實抑制QCSE的效應。在非極性結構的極化發光特性量測中，我們發現發光極化率、能量差會隨著奈米柱深度越深而降低，顯示了應力的改變，再經由模擬得到驗證。 接著，我們量測變溫變功率PL的內部量子效率，得到經由奈米柱深度1.7微米（最深）成長的樣品是39％，而直接成長的樣品是13％，再透過實驗數據的分析，得到非輻射係數（A），隨著奈米柱深度越深而降低，與TEM估算出來的錯位密度缺限變化相吻合，所以在奈米柱深度1.7微米有最佳的載子捕捉及放光效率。

In this thesis, we investigated a-plane InGaN/GaN multiple quantum wells were grown on r-plane sapphire by metal organic chemical vapor deposition, and the difference of samples is nanorod depth of a-plane GaN templates. We utilized several methods including photoluminescence（PL）, atomic force microscopy（AFM）, and transmission electron microscopy（TEM）to investigate the optical characteristics and material structures of our samples. We have known that the crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on a nanorod GaN template by AFM and TEM. And from the temperature dependent PL measurement, we get the result which the value of IQEPL and activation energy is higher when the etching depth of nanorods is deeper. It means carries confinement in MQWs was enhanced by lowering defects of a-plane GaN templates. Moreover, the un-shift emission peak from the power-dependent PL measurement indicated the absence of QCSE within our samples. The polarization-dependent PL shows that the degree of polarization and peak energy shift decreased with increasing nanorods depth, which can be attributed to stain relaxed , injection carrier density and scattering. In the second part, we measure the internal quantum efficiency（IQE）of the MQWs, and the IQE of a-plane InGaN/GaN MQWs are approximately 39%(1.7um) more than 13%(as-grown). Next, using the measured data and knowing the B value, one can obtain nonradiative coefficient A. The measured nonradiative recombination coefficient A decreased one order as the etching depth increases from 0 to 1.7 um. It matched the variation of threading dislocation density and we could observe the best luminescence efficiency and quality with 1.7um nanorod sample.