中斷成長在有機金屬氣相沉積氮化銦鎵量子點時的效應研究

Abstract

由於GaN材料擁有許多其他半導體光電材料所不及的特色，因此得以實現全彩顯示、白光照明及高密度光儲存媒體等生活上的實際應用。目前商業化所製作的GaN光電元件大多為量子井結構，但是由於GaN材料的起始電流遠大於一般半導體光電材料以及與基板晶格不匹配等問題，因此發展低維度的氮化鎵量子侷限結構，也就是所謂的量子點結構是一般認為最有效的解決方式。目前已經發展出許多量子點成長的方式，其中以自我組成為最常用的方式，例如: S–K磊晶模式來成長高密度的量子點，並且藉由成長動力學的成長條件，像是用溫度、壓力等去控制量子點的成長，不過我們發現量子點對於長晶參數的容許度是相當嚴謹的，因此使得量子點的形成並不容易，所以本論文則是提供另一個有別於成長動力學的熱力學平衡方式:即所謂的『成長中斷』來控制量子點的成長並研究這樣的機制對於量子點成長的影響。 在文獻上我們發現，成長中斷在GaN材料方面並沒有像InAs量子點一樣有系統性的研究，因此在本實驗我們利用MOCVD成功的成長出自我組成InGaN量子點結構，並且藉由原子力顯微鏡以及顯微光激發螢光等工具來探討30秒、60秒以及120秒時的不同中斷成長時間對於量子點的表面形貌以及光性的影響，結果發現中斷成長時間60秒為最優化的時間，因為此時的量子點尺寸最小、密度最高且由於活化能為最小，因此光性品質為最好。 最後再經由模擬分析的方式，計算出不同中斷成長時間下InxGa1-xN 量子點中的In含量。從模擬的結果可知，由於In desorption的發生，使得In 含量隨著中斷成長時間的增加而減少，因此不但解釋了PL發光鋒值隨著中斷成長時間而不斷藍移的現象，而且也顯示出In desorption速率大於Ga desorption速率。

Due to GaN material has more excellent characteristics compared to others, we can accomplish some practical application in our life such as full color display、white lighting and high density optical storage media etc…The most commercial GaN optoelectronic devices are quantum well structure. However, GaN material threshold current far larger than typical semiconductor optoelectronic materials and lattice mismatch to substrate issues etc…So, The development of low dimension GaN quantum confined structure i.e., so-called quantum dot (QD) structure is the most effective solution for now. For instance , growing high density QDs with S-K growth mode and controlling these QDs growth by temperature、pressure etc…parameters of Kinetics. However, we find that the window of these growth parameters is very critical for QDs formation. So , we provide an new concept different from Kinetics : so-called 『growth interruption』in this thesis and study its influence on QDs growth. Unlike InAs QDs systematic research, there is few journal study on GaN material with growth interruption. So, We have grown self-assembled InGaN QDs without using any anti-surfactant by MOCVD successfully in this thesis. Then we discuss the influence on QDs morphology and optical property under different growth interruption time at 30s、60s and 120s with AFM and μ-PL etc…We find that QDs with the smallest size and highest density and the best optical property due to the smallest activation energy are achieved at the most optimized growth interruption time of 60s. Finally, we calculate In composition from InxGa1-xN QDs at different interruption growth time with Finite Element Method simulation. In composition has decreased as the increased interruption growth time due to In desorption effect from the simulated result. So, this result not only explains the PL peak blue shit as the increased interruption growth time, but also indicates In desorption rate is larger than Ga desorption rate.