原子層沉積法成長之氮化鎵/鋁氮化鎵量子井結構之光學與物理特性研究

Abstract

在本論文中我們對於氮化鎵/鋁氮化鎵量子井結構進行光學與物理特性的研究，此量子井的屏障層是以原子層沉積法成長之鋁化鎵/氮化鎵超級晶格層所建構而成，首先藉由光激發螢光頻譜 (PL) 與穿透式電子顯微鏡的圖像分析，圖像顯示出氮化鎵/鋁氮化鎵量子井在 沉積過程中晶格得到對稱性的成長並擁有良好的品質，另外在原子力顯微鏡實驗中告訴我們在原子層沉積法成長之屏障層，比起一般的合金沉積法擁有更好的表面特性。

在第二部分中，我們藉著時間解析光激發螢光 (TRPL) 分析樣品光學特性，在能量相關的時間解析光激發螢光分析 (TRPL) 結果顯示氮化鎵/鋁氮化鎵量子井中輕微的局化態激子主宰了低溫的發光，接下來我們更進一步探討輻射複合與非輻射複合在變溫過程中的動態特性，結果反應出螢光強度的衰減受非輻射複合在室溫下影響明顯，為了更了解與激發載子密度相關的螢光衰減表現以及其背後的物理意義，我們透過理論以及變載子密度光激發螢光實驗來歸納出光激發螢光在不同載子密度的動態行為與伴隨的效應。

最後為了要得知樣品的內部量子效率，我們進行不同的載子密度來激發螢光的實驗，以此來推估材料真正的內部量子效率，相較於現今的期刊報告，實驗所得到結果顯示出我們成長出的奈米結構材料對於更效率的UV發光元件製作是具有淺力的。

In this thesis, we report the optical and material analysis of GaN/AlGaN quantum well using quasi AlGaN as a barrier layer, which is formed by AlN/GaN super-lattice layers grown with the technique of atomic layer deposition (ALD). In first part, the crystal quality were demonstrated by using PL spectra and HRTEM images which indicate the symmetry properties and good crystalline quality of the GaN/ALD-AlGaN QWs. Additionally, images of atomic force microscopy (AFM) revealed that the surface morphology of ALD-AlGaN are superior to those using conventional alloy AlGaN barrier.

In second part, we investigate the optical properties by means of time-resolved photoluminescence system. According to energy dependence time-resolved PL measurement, we found slight localization in our ALD-QWs at low temperature. Detailed investigations of dynamical behaviors of Non-radiative and radiative recombination processes had been study through temperature dependent time-resolved photoluminescence (TRPL). It shows that quenched intensity of PL is significantly affected by non-radiative recombination at room temperature. Additionally, to investigate the physics behind quenched intensity, we performed the study of rate equation model and power dependent TRPL spectra of each sample at 15K. We concluded different effects which in turn dominate the mechanisms and carrier recombination in different excitation conditions.

Finally, to check the internal quantum efficacy of our ALD-QWs, power dependent PL was experimentally used to estimate value of IQE. Compare to recent reports, the result appeals that our nanostructure has potential to fabricate high efficiency UV-emitting devices.