臺灣博碩士論文加值系統

本論文的主要內容為藉由變溫的PL量測，探討不同氮含量與InAs沉積厚度對InAs/GaAs量子點光性的影響。我們發現摻1%的N在In0.14Ga0.86As 量子井中，可將波長拉至1344nm，但PL強度卻減弱，而直接摻N在量子點中，品質變得更差。對於沉積厚度為1.98ML的樣品，在低溫時即有很大的半高寬，代表這些小size量子點侷限載子的能力較差，一旦溫度上升，明顯的紅移現象與半高寬的減少，起因於載子從小size量子點傳遞至大size量子點。增加沉積厚度至2.34ML和2.7ML，放射波長逐漸拉至1311nm。這些樣品在低溫時的半高寬很小且隨溫度上升並無明顯改變，暗示其侷限載子能力良好。然而，當沉積厚度再繼續增加並超過2.7ML時，量子點的放射波長不但不繼續增加，反而形成兩群不同波長的量子點同時存在，分別在1223nm和1300nm之處，而且這些短波長群量子點在低溫的發光品質與有近似波長的1.98ML樣品相等或甚至更好，但是當溫度增加至200K以上，半高寬劇烈地增加，我們推論是由於載子在高溫時被激發到激發態，此時wave function變寬，再加上受到起因於晶格鬆弛的缺陷影響，經歷非輻射復合所致。最後從PL強度隨溫度變化的曲線中得到每一片樣品的活化能，我們發現活化能與放射波長呈現反比的關係，而且活化能與Grundmann理論中的基態到第一激發態之能量間隔很接近，代表基態放射光隨溫度上升而衰減的主要原因是因為載子受熱從基態跑至第一激發態。

Photoluminescence is used to study the optical properties of self-assembled InAs/GaAs quantum dots (QDs) with different N incorporation and InAs deposition thickness. The emission wavelength can be increased to 1344nm by incorporating 1% N into In0.14Ga0.86As quantum well, but PL intensity becomes weaker. Besides, incorporating N into QDs makes the quality much worse. For small deposition of 1.98ML, a large FWHM at 50K is observed, implying a relatively poor confinement for electrons in such small-size QDs. When temperature increase, we observe a significant red shift and a decrease of FWHM due to the transfer of the electrons from relatively small-size to large-size QDs. By increasing the InAs deposition to 2.34ML and 2.7ML, the emission wavelength increases to 1311nm. The small FWHM at 50K and its temperature insensitivity suggest a good electron confinement. However, when the InAs deposition thickness increases beyond 2.7ML, the QD emission wavelength shows no increase, instead, two groups of different wavelength QDs, one emits at 1223nm and the other at 1300nm, are observed. The quality of the short-wavelength QDs is comparable to the 1.98ML sample in which the QDs emit at a similar wavelength. Nevertheless, when the temperature increases beyond 200K, the FWHM drastically increases. We speculate this abnormal increase of FWHM by that the electrons excitation to first excited state at high temperature and undergo a nonradiative recombination through relaxation-induced defect states. Finally, from the relationship between PL intensity and temperature, we can obtain the activation energy which is found to be inverse proportional the emission wavelength. The obtained activation energy is consistent with the energy separation between the ground state and first excited state according Grundmann’s theory. Hence, we conclude that the decrease in intensity with increasing temperature is due to the carrier excitation from the ground state to first excited state.

目錄
中文摘要 I
英文摘要 III
致謝　　　　　　　　　　　　　　　　　　　　　　　 V
目錄 VI
圖表目錄 VIII
第一章、 緒論 1
1.1 簡介 1
1.2 研究動機 3
1.3 章節概要 4
第二章、 理論 6
2.1 量子點的形成機制 6
2.2 能階密度 7
2.3 半導體的發光現象 9
2.3.1直接半導體與間接半導體 9
2.3.2 直接發光與間接發光 10
2.4 量子點的電子結構理論計算 12
2.4.1激發態只出現在價電帶的理論 12
2.4.2激發態同時在導電帶和價電帶出現的理論 13
第三章、 樣品製備與量測方法 22
3.1樣品的結構與磊晶 22
3.1.1 TR系列樣品的成長 22
3.1.2 MA系列樣品的成長 23
3.2 P L量測系統 23
第四章、 實驗結果與討論 29
4.1 TR系列樣品之比較 29
4.1.1 TR系列樣品在低溫及室溫之PL圖 29
4.1.2 TR系列樣品之放射能量的溫度相依性 30
4.2 MA系列樣品之比較 32
4.2.1 MA系列樣品在低溫及室溫之PL圖 32
4.2.2 MA系列樣品之放射能量的溫度相依性 33
4.3載子在量子點之間的傳遞 34
4.4能量間隔之實驗值與理論值 37
4.5量子點的活化能 42
4.5.1 TR&MA系列樣品之活化能 42
4.5.2活化能與放射波長之關係 44
4.5.3活化能與能量間隔之關係 45
第五章、 結論與未來研究方向 74
5.1結論 74
5.2未來研究方向 75
參考文獻 76
圖表目錄
表3.1 TR系列各樣品之差異 26
表3.2 MA系列各樣品之差異 26
表4.1 TR系列之Varshni擬合參數 47
表4.2 MA系列之Varshni擬合參數 47
圖1.1圖1.1量子結構 (a)量子井(b)量子線(c)量子點 5
圖2.1三種磊晶模式之成長示意圖
(a)Frank-van der Merwe mode
(a) Volmer-weber mode
(b) Stranski-Krastanow mode 15
圖2.2 (a)塊材(b)量子井(c)量子線(d)量子點的能階密度對能量之關係圖 16
圖2.3半導體受光激發後電子轉移情形
(a)直接半導體
(b)間接半導體 17
圖2.4 半導體的發光現象
(a)直接發光過程
(b)間接發光過程
(c)經復合中心的間接復合過程 18
圖2.5基底長度為12 nm量子點之電洞態的機率密度等面圖 19
圖2.6 (a)電子和電洞能階隨量子點大小改變之變化圖
(b)InAs/GaAs QDs的激子束縛能隨基底長度改變之變化圖 20
圖2.7依據兩種不同strain model計算所得電子和電洞能階隨不同大小
量子點的變化關係圖 21
圖3.1 樣品結構圖 27
圖3.2 PL系統架構圖 28
圖4.1 TR系列樣品在(a)300K與(b)50K之PL圖 48
圖4.2 (a)TR502 (b)TR504 (c)TR505之PL隨溫度變化關係圖 49
圖4.3 TR系列樣品之放射能量隨溫度變化關係圖 50
圖4.4 (a)三-五族半導體之晶格常數與Eg的關係
(b)strain reducing layer的作用效應圖 51
圖4.5 (a)InAs/InGaAsN與(b)InAs/InGaAs 量子點的TEM圖 52
圖4.6 MA系列樣品在(a)300K與(b)50K之PL圖 53
圖4.7 (a)MA046 (b)MA045 (c)MA044之PL隨溫度變化關係圖 54
(d)MA047 (e)MA043之PL隨溫度變化關係圖 55
圖4.8 MA系列樣品之放射能量隨溫度變化關係圖 56
圖4.9 TR系列樣品與InAs塊材的放射能量隨溫度變化關係之比較圖 57
圖4.10 TR系列樣品之半高寬隨溫度變化關係圖 58
圖4.11 MA系列樣品與InAs塊材的放射能量隨溫度變化關係之比較圖 59
圖4.12 MA系列樣品之半高寬隨溫度變化關係圖 60
圖4.13載子在不同大小量子點間傳遞的機制
(a)穿遂(b)透過二維量子井的傳遞 61
圖4.14不同大小量子點的能帶示意圖 61
圖4.15 (a)MA043(b)MA047的DLTS圖 62
(c)MA043與MA047相對應之阿瑞尼士圖 63
圖4.16 TR502在300K之變功率圖 64
圖4.17 MA044在300K之變功率圖 65
圖4.18 MA047在300K之變功率圖 66
圖4.19能量間隔與量子點基底長度之實驗和理論關係圖
(a)對照 Grundmann在1998年的假設-CM model
(b)對照 Grundmann在1998年的假設-VFF model 67
圖4.20量子點的size分佈影響載子釋放與再結合之
(a)能帶示意圖(b) PL示意圖 68
圖4.21 TR系列樣品之積分強度對溫度倒數關係圖與擬合活化能 69
圖4.22 MA系列樣品之積分強度對溫度倒數關係圖與擬合活化能 70
圖4.23 TR和MA系列樣品的基態活化能(Ea1)與基態放射光在
(a)300K時(b)50K時波長之關係圖 71
圖4.24活化能與量子點基底長度之實驗和理論關係圖
(a)對照 Grundmann在1998年的假設-CM model
(b)對照 Grundmann在1998年的假設-VFF model 72
圖4.25 InAs/GaAs量子點的能階結構圖 73

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