Growth and Characterization of InxAl1-xN Epilayers Using MOCVD

In this study, the InxAl1-xN epilayers have been grown on GaN templates by metalorganic chemical vapor deposition (MOCVD). Several growth conditions consisting of the deposition pressure, the amount of superlattice pairs, and the TMIn flow rate were modified to investigate their effects on the characteristics of InxAl1-xN epilayer. To eliminate the compressive strain generated in the InxGa1-xN multiple quantum well, the InxAl1-xN was used as a quantum barrier. As the composition of InxAl1-xN was varied, the band gap and the lattice constant of this material both were changed in a large range. Therefore, by adjusting the In content of InxAl1-xN, the lattice constant of InxAl1-xN could be the same with that of InxGa1-xN. In this research, the In0.15Ga0.85N was used as a quantum well, while the In0.3Al0.7N was employed as a quantum barrier. This is attributed to the same lattice constant of these two materials. With increasing the deposition pressure from 100 to 500 mbar, the growth rate of InxAl1-xN epilayer was decreased from 0.402 to 0.094 μm/hr. Meanwhile, the In content of InxAl1-xN was increased from 6.1% to 25%. To improve the quality of InxAl1-xN epilayer, the InGaN/GaN superlattice was inserted between the GaN template and the InxAl1-xN epilayer. It was found that the In content of InxAl1-xN was increased from 22.3% to 43.7% with increasing the InGaN/GaN superlattice from 0 to 20 pairs, and the quality of InxAl1-xN epilayer was also enhanced. However, when the insertion of InGaN/GaN superlattice was more than 5 pairs, the quality of InxAl1-xN epilayer became worse. On the other hand, the reduction in TMIn flow rate can lead to the decreases both in the In content and the growth rate of InxAl1-xN. With decreasing the TMIn flow rate from 220 to 100 sccm, the growth rate of InxAl1-xN was reduced from 0.246 to 0.095 μm/hr. Additionally, as the TMIn flow rates were kept at 220, 180, 140, and 100 sccm, the root-mean-square roughness values of InxAl1-xN surface were measured to be 5.70, 8.11, 7.73, and 5.57 nm, respectively. Furthermore, the APSYS software was used to simulate the performance of blue LED with the In0.3Al0.7N quantum barrier. The lattice match between the In0.3Al0.7N quantum barrier and the In0.15Ga0.85N well can reduce the piezoelectricity of In0.15Ga0.85N well due to the reduction of residual strain in the multiple quantum well. Thus, the emission wavelength of LED device can be predicted to blue shift as the In0.3Al0.7N quantum barrier was inserted. Finally, the simulated LED structure was prepared by MOCVD. Based on the result of photoluminescence spectrum, it can be observed that the LED without inserting the In0.15Ga0.85N/In0.3Al0.7N superlattice possessed two emission peaks at 380 and 460 nm, and the intensities of these two peaks were both weak. However, the LED with the In0.15Ga0.85N/In0.3Al0.7N superlattice had only one emission peak at 400 nm, and its intensity was much higher than that without this superlattice. It can be confirmed that the InxAl1-xN with an improved quality can be useful in the LED epitaxial structure, causing an efficient enhancement in the emission property.本研究利用有機金屬化學氣相沉積系統在氮化鎵模板上成長氮化銦鋁磊晶膜。探討不同的成長壓力、插入的超晶格對數及三甲基銦流量對氮化銦鋁薄膜結晶特性之影響及其相關性。最後，由於氮化銦鋁的晶格常數與能隙可調變範圍很大，本論文將氮化銦鋁做為量子障壁並調整氮化銦鋁的銦含量，使氮化銦鋁的晶格常數與作為藍光發光波段量子井的氮化銦鎵晶格常數匹配，以達到消除量子井內的殘留壓應力的目的。 在固定其他磊晶參數的情況下，成長壓力由100升至500 mbar，氮化銦鋁的成長速率由0.402降至0.094 μm/hr且銦含量由6.1%升至25%。為了改善相分離而導致柱狀成長的現象，我們在氮化鎵模板與氮化銦鋁磊晶膜之間插入氮化銦鋁/氮化鎵超晶格對氮化銦鋁進行品質改善的動作，並發現由插入0對超晶格提高至插入20對超晶格，氮化銦鋁的In含量從22.3%升至43.7%，氮化銦鋁的磊晶品質在插入5對超晶格時達到最好，而一旦插入超過5對超晶格時，氮化銦鋁的磊晶品質卻會下降。 降低三甲基銦流量除了降低氮化銦鋁的銦含量外，氮化銦鋁的成長速率也會下降。當三甲基銦流量由220降至100 sccm，氮化銦鋁的生長速率從0.246降到0.095 μm/hr。當三甲基銦的流量依序為220、180、140、100 sccm，氮化銦鋁的均方根粗糙度為5.70、8.11、7.73和5.57 nm。 本論文使用APSYS模擬軟體模擬氮化銦鋁應用於藍光發光二極體的量子障壁，發現與量子井晶格匹配之氮化銦鋁可以減緩多層量子井內部的殘留壓應力，因此減緩量子井所受的壓電效應，並可以預期此LED結構的發光波段將藍移。最後利用MOCVD成長此種氮化銦鎵/氮化銦鋁發光二極體結構。在光激發螢光光譜可以發現沒有超晶格結構的氮化銦鎵/氮化銦鋁發光二極體有380、460 nm兩個不同的發光波段，並且發光強度很低，而超晶格結構的氮化銦鎵/氮化銦鋁發光二極體則只有400 nm一個發光波段。證實在足夠品質改善的情況下，氮化銦鋁可以應用於LED的磊晶結構。誌謝 I 摘要 II ABSTRACT IV 目錄 VI 表目錄 IX 圖目錄 X 第一章 緒論 1 1-1 前言 1 1-2 三元氮化物的發展趨勢 3 1-2-1 AlGaN的發展及應用 3 1-2-2 InGaN的發展及應用 3 1-2-3 InAlN的發展及應用 3 1-3 研究動機 4 1-4 論文架構 5 第二章 理論基礎與文獻回顧 7 2-1 有機金屬化學氣相沉積 7 2-1-1 有機金屬化學氣相沉積之流程 7 2-1-2 有機金屬化學氣相沉積生長模式 9 2-1-3 三族氮化物反應氣體 10 2-2 三族氮化物材料 10 2-2-1 三族氮化物材料結構特性簡介 10 2-2-2 基板與三族氮化物結構之差異 11 2-3 應變與應力的產生 12 2-4 三元氮化物的晶格與能隙 14 2-5 InxGa1-xN磊晶膜特性簡介 15 2-6 極化效應 16 2-6-1 自發極化 16 2-6-2 壓電極化 17 2-7 InxAl1-xN磊晶膜特性簡介 18 第三章 實驗方法 20 3-1 前言 20 3-2 實驗流程 20 3-2-1 GaN模板磊晶流程 20 3-2-2 測試成長壓力對InxAl1-xN磊晶膜的影響 21 3-2-3 測試應力釋放層對InxAl1-xN磊晶膜的影響 22 3-2-4 測試TMIn流量對InxAl1-xN磊晶膜的影響 22 3-2-5 將InxAl1-xN應用於藍光LED元件中 22 3-3 儀器介紹 23 3-3-1 有機金屬化學氣相磊晶 23 3-3-2 X光繞射分析儀 24 3-3-3 顯微光激發螢光頻譜分析儀 25 3-3-4 掃描試電子顯微鏡 25 3-3-5 穿透式電子顯微鏡 26 3-3-6 APSYS模擬軟體 27 3-3-7 原子力顯微鏡 28 第四章 實驗結果與討論 29 4-1 前言 29 4-2 不同成長壓力對InxAl1-xN磊晶膜的影響 29 4-2-1 不同成長壓力對InxAl1-xN磊晶膜的晶相分析 29 4-2-2 不同成長壓力對InxAl1-xN磊晶膜的剖面和表面形貌分析 30 4-2-3 不同成長壓力對InxAl1-xN磊晶膜的TEM分析 31 4-3 應力釋放對InxAl1-xN磊晶膜的影響 32 4-3-1 應力釋放對InxAl1-xN磊晶膜的晶相分析 32 4-3-2 應力釋放對InxAl1-xN磊晶膜的SEM分析 33 4-3-3 超晶格結構之TEM分析 34 4-4 TMIn流量與InxAl1-xN磊晶膜的關係 34 4-4-1 TMIn流量對InxAl1-xN磊晶膜的晶相分析 34 4-4-2 TMIn流量對InxAl1-xN磊晶膜的剖面和表面形貌分析 35 4-5 InxAl1-xN磊晶膜應用於LED發光二極體元件 36 4-5-1 InxAl1-xN磊晶膜應用於量子障壁的優點 36 4-5-2 InxAl1-xN磊晶膜應用於量子障壁的難點與解決方式 37 4-5-3 InxAl1-xN磊晶膜應用於量子障壁的變溫光激發光譜量測 39 第五章 結論與未來展望 40 5-1 結論 40 5-2 未來展望 41 參考文獻 4