單量子點與單量子點分子在磁場下的光譜研究

Abstract

本論文中探討單一量子點及單一量子點分子中載子受侷限的機制。我們以顯微光激螢光光譜技術偵測單一量子點螢光光譜，並藉由改變雷射激發功率、激發能量，及螢光偏振分析，辨別激子的種類及帶電態。單一InAs量子點光譜可以清楚的觀察到不同的激子態，其復合能量除了由量子點尺寸決定，還受到了各個激子態不同的庫侖作用力影響。為了探討庫侖作用力與激子受侷限程度的關係，我們進一步利用顯微磁光技術，藉激子在外加磁場下的反磁能移估計載子波函數分佈，觀察到激子在InAs單一量子點中所受強侷限影響有些微的降低，因此必須將庫侖作用對激子侷限的影響加以考慮。 相同的技術也用在單一InGaA量子點分子的分析。我們觀察到電子容易被侷限在同一量子點中，而電洞則分別被侷限於不同量子點中。藉由觀察直接激子及間接激子的顯微磁光光譜及TEM影像，可證實電子及電洞分別受到不同的侷限。在水平磁場作用下，直接激子與單量子點中的單激子具有相同的特性。明激子與暗激子在外加水平磁場下形成混態，暗激子由不可與光耦合變成可以與光耦合。間接激子則因波函數重疊降低，電子─電洞交互作用也因而降低，因而無法 觀察到間接激子訊號。

We discuss the confined mechanism of different exciton complexes in single quantum dots and quantum dot molecules. With varying laser excitation power and energy, we can identify the different exciton complexes luminescence and model the Coulomb interaction of each exciton complexes. As measuring diamagnetic shifts for different exciton complexes confined in single InAs/GaAs quantum dots, biexcitons and charged excitons were found to exhibit a weaker diamagnetic shift due to the Coulomb interactions among the constituent carriers. In the magneto-photoluminescence, we deduce exciton g factor of the single InGaAs/GaAs quantum dots to be -0.67. This value is significantly smaller than the reported values ranging from -1.5 to -3. We presumed that such a small g factor might come from the band mixing of light hole and heave hole. Finally, with comparing the single InGaAs/GaAs quantum dot molecules transmission electron microscopy (TEM) image to the spectrum, the direct exciton and indirect exciton was observed due to the electrons had been confined in the same quantum dot.