摻氮及氮化鎵族奈米材料之光學特性

Abstract

本論文中, 我們研究兩種以化學氣相沉積法成長之奈米結構樣品。採用光激發螢光光譜及螢光激發光光譜進行一連串的光學特性研究。樣品依材質可區分為兩種類, 一是一組由不同氮含量之氮砷化銦鎵/砷化鎵之單層量子井結構組成, 另一組則是改變長晶條件所成長出一系列的氮化銦鎵量子點結構樣品。 透過不同氮含量之氮砷化銦鎵/砷化鎵之單層量子井樣品之光激發螢光光譜量測, 我們發現氮含量由0%, 0.5%, 增加至2%, 使得其光譜發生了與低氮含量樣本不同的行為, 為了探討這樣差異的來源, 我們量測了變溫時光激發螢光之變化, 並仔細分析能係變化與溫度的關係, 同時並測量出不同激發能量下之行為變化, 進而推論出摻雜之氮含量至2% 時, 此樣品具有類似於量子點之特性, 使得其光譜不像一般量子井結構容易受到溫度的影響, 加上高解析度穿透式電子顯微鏡之影像輔助, 更確認了氮的摻入不但造成空間上分布不均的局化態, 並形成近似於量子點結構之存在。 另外, 我們利用一種新方法成長了高密度之氮化銦鎵量子點樣品。在這個部分, 原子力顯微鏡顯示出當我們改變了SiNx處理之時間, 可成長出一系列由小到大的量子點結構, 其發光能隙具有紅移現象。透過光激發螢光光譜我們比較出不同大小量子點結構發光能隙與溫度間的變化趨勢, 發現其對溫度的敏感度較低, 隨著溫度由10K 增加到300K,能隙變化最多只有40 meV。 為獲得更多資訊, 我們進一步計算出其活化能之變化, 發現較小的量子點樣品相對於大量子點樣品具有較小的活化能, 其值約為只有大量子點結構活化能之二分之一。同時在螢光激發光光譜的實驗中, 我們也觀察到大小量子點間行為的差異。 最後我們選擇了一片氮化銦鎵量子點結構之樣品, 將其做快速熱退火, 觀察在不同之熱退火溫度其發光能隙之變化。隨著退火溫度的增加, 快速熱退火對於我們的樣品產生了影響, 造成波長的藍移現象, 並也使活化能減少, 這主要是由於銦或鎵的原子由於熱而產生相互擴散而改變了樣本的能隙。

In this thesis, two kinds of nanostructure samples grown by metalorganic chemical vapor deposition were studied. We utilized the photoluminescence (PL), photoluminescence excitation (PLE) to investigate the optical properties of our samples. The first series are In0.4Ga0.6As1-xNx/GaAs single quantum well structures with different nitrogen concentrations and the second ones are the InGaN/GaN quantum dots samples with different sizes. InGaAsN SQWs with various nitrogen concentrations, where x=0, 0.5 and 2%, were grown on GaAs substrates. The effects of incorporating nitrogen into the In0.4Ga0.6As1-xNx/GaAs SQW were investigated using photoluminescence (PL) and high resolution transmission electron microscope (HRTEM). In the case of In0.4Ga0.6As1-xNx SQW with 2% nitrogen content, the PL emission from the quantum-dot-like states was observed and confirmed by the temperature- and excitation-dependent PL measurements. Detailed investigations conducted here indicate that the nitrogen not only influences carrier localization, but also is critical in the formation of quantum-dots. In the second part, we investigate the optical properties of ultra-high-density InGaN quantum dots (QDs). Atomic force microscopy revealed that the extremely high density about 3×1011 cm-2 of QDs was obtained and the size of QDs was increased with the duration of SiNx treatment. The PL-peak wavelength at 10K of the InGaN QDs samples is red-shifted as increasing the height of QDs. From the temperature dependence of the photoluminescence, the thermal activation energy (Ea) exhibited different activation energies for large and small QDs. Ea of the smaller QDs samples is about 59meV, much less than that of the largest QDs, 122 meV. In addition, the PLE spectra broadened with increasing the height of QDs. Finally, we study the effects of rapid thermal annealing on optical properties of InGaN QDs with the SiNx treatment time. Their behaviors were investigated through temperature- dependent photoluminescence measurements. The results indicated that emission wavelength of the InGaN QDs shifted toward long wavelength after the post-thermal annealing, which may be due to In/Ga inter- diffusion and variation on the QDs size by post-grown thermal annealing.