臺灣博碩士論文加值系統

本篇論文主要是研究三元量子點ZnS1-xTex的成長方法，及光學分析的實驗結果與討論。
　我們利用有機金屬化學氣相沉積(Metal-Organic Chemical Vapor Deposition,MOCVD)系統，以Volmer-Weber mode直接島嶼式成長量子點的方法，先長出一層較不平整的ZnS 磊晶表面，將ZnSTe嵌入能隙較寬的的ZnS材料中，在其他的長晶條件相同下，直接利用不同的ZnSTe量子點成長時間，以得到不同尺寸大小的量子點。
　我們經由X-Ray 繞射實驗結果得到，在相同的長晶條件下，不同ZnSTe量子點成長時間的樣品，並沒有因為量子點成長時間的不同，而改變了ZnSTe量子點的成分。ZnSTe量子點中的成分確定後，在光致激發螢光譜(Photoluminescence,PL)的實驗中，比較不同量子點成長時間的樣品在10K下的PL光譜，結果發現，PL光譜峰值位置，隨著量子點成長時間的減少，而有能量藍移(blue shift)的趨勢，由此證明，我們的量子點成長方法，的確能夠直接控制量子點成長時間，而得到不同尺寸的量子點。在PL隨溫度變化的實驗中，我們討論在高溫時候PL發光強度熱淬滅現象(thermal quenching)，結果發現，越小的量子點具有越大的活化能(activation energy)，且活化能與理論計算的ZnSTe/ZnS量子點的激子束縛能非常接近，因我們實驗得到的活化能就是激子束縛能，從各種實驗結果的分析，與理論計算的結果，顯示PL的發光機制主要是來自於激子的輻射復合(exciton radiation)。

　　In this thesis, we present our investigation on the Volmer-Weber mode growth and characterization of ternary ZnSTe/ZnS quantum dots (QDs) have been studied.
The ZnSTe quantum dots were grown by MOCVD (Metal-Organic Chemical Vapor Deposition). The basic idea of our deposition method is to embed small island directly in another material with wider band gap. Based on this concept, a rough layer was first prepared as a starting surface. In this study, we choose ZnS was chosen as the rough layer. ZnSTe quantum dots were then grown on this rough surface. After that, the quantum dots were covered by ZnS barrier layer. Dot size can be controlled by growth duration.
The obtained samples of the ZnSTe/ZnS QDs were characterized by X-Ray diffraction and the photoluminescence(PL)measurements. In the X-Ray diffraction measurement, it is shown that the composition of the ternary ZnSTe QDs is independent of the growth duration. From the PL measurement, a strong quantum confinement effect was observed in the spectra. The emission can persist up to room temperature, which is an indication of the strong exciton effect in the quantum dot structure. In the temperature dependence of the PL measurement, the activation energy was found to increase with decreasing dot size. This exciton binding energy in the ZnSTe/ZnS QDs structure, we obtain that the value of the exciton binding energy is in the result implies that the activation energy giving rise to the thermal quench effect is dominated by the exciton binding energy. According to the theoretical calculation of the order of 100meV, which is consistent with our experimental results. We therefore conclude that ternary ZnSTe quantum dots can be successfully grown by our simple method.

第一章導論
1.1 量子點介紹
1.1.1量子點的應用及優點………………………………1
1.1.2量子點的狀態密度函數……………………………3
1.1.3量子井能帶理論……………………………………5
1.1.4量子點成長機制……………………………………8
1.2 ZnS1-xTex /ZnS 量子點介紹
1.2.1 ZnSTe 半導體材料介紹…………………………... 11
1.2.2 ZnS1-xTex /ZnS 量子點的激子束縛能計算………...17
1.2.3 ZnS1-xTex /ZnS 應力效應……………………………25
1.2.4 量子點尺寸估計……………………………………28
第二章 實驗系統及實驗方法
2.1 有機金屬化學氣相沉積法(MOCVD)簡介…………….34
2.1.1 MOCVD 系統設備………………………………..38
2.1.2量子點樣品設計………………………………….. 46
2.1.3 ZnSTe 量子點實驗步驟………………………….. 48
2.2 光激發螢光譜量測實驗系統介紹………………………51
2.3　X-Ray 繞射實驗系統……………………………….…53
第三章 實驗結果與討論
3.1 X-Ray 繞射樣品成分分析實驗………………………….55
3.2 低溫下的光激發光譜
3.2.1 溫度10 K下的光譜峰值…………………………..59
3.2.2 溫度10 K下不同ZnSTe 量子點成長時間的光激發螢光譜....62
3.3 隨溫度變化的PL光譜
3.3.1 峰值對溫度變化的關係…………………………….65
3.3.2 線寬隨溫度變化的關係……………………………..71
3.3.3 PL光譜熱淬滅現象………………………………….75
第四章 結論………………………………………………….80
參考文獻………………………………………………..81

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