單一砷化銦量子點之磁光特性及其與光子晶體共振腔之耦合

Abstract

此篇論文主要在研究單一量子點的螢光特性。我們報告單一自組式砷化銦/砷化鎵量子點內中性激子(X)、雙激子(XX)和帶電激子(X+/X-)對磁場的響應。與中性激子傳統上二次方相關的反磁性位移不同，我們觀察到的負帶電激子其反磁性位移較小而且與磁場呈現非二次方相關。更特別地的是，我們也觀察到一個負號的反磁性位移。經過理論的分析，說明了負帶電激子這樣的異常行為是由於其在複合發光後，剩餘電子失去了未複合前電洞的強庫倫吸引力，而導致波函數在空間的分布劇烈地改變。對於小尺寸的量子點而言，這樣的效應非常明顯，因為其侷限電子的能力較弱，電子波函數延伸到周圍較高能障的砷化鎵。當電子逐漸地失去侷限性，負帶電激子的磁響應也將從對磁場二次相關的反磁性位移，逐漸變為四次方相關，最後變成一個順磁性的行為，也就是說隨著磁場強度的增加，負帶電激子的發光能量會變低。另一方面，我們研究單一量子點與光子晶體共振腔的耦合行為，為了達到高品質因子的H1型光子晶體共振腔，我們提出一個設計的方法，其在計算上可以達到最高的品質因子大約120,000。空間中共振模態電場分布的傅立葉轉換形式說明了品質因子的提升是因為有效地抑制了漏光模態。在實驗上，也展示了品質因子的提升，量測到的最高品質因子大約為11,700。我們的設計在提升品質因子的同時並不會造成模態體積太大的提高，因此可以應用在量子點與H1型共振腔耦合的研究。最後我們成功地展示砷化銦量子點與H1型共振腔的強耦合效應。此時，量子點與共振腔混合成兩個新的polariton量子態造成螢光特性的改變。量測溫度大約在37.75 K時，有最強的耦合效應。經分析，其Rabi分裂大約是156.7μeV。

This dissertation mainly researches the photoluminescence characteristics of single quantum dot. We report on the magnetic responses of neutral exciton (X), biexcitons (XX) and positive/negative trions (X+/X-) in single self-assembled InAs/GaAs quantum dots. Unlike the conventional quadratic diamagnetic shift for neutral excitons, the observed X- diamagnetic shifts are small and nonquadratic. In particular, we also observed a reversal in sign of the conventional diamagnetic shift. A theoretical analysis indicates that such anomalous behaviors for X- arise from an apparent change in the electron wave function extent after photon emission due to the strong Coulomb attraction induced by the hole in its initial state. This effect can be very pronounced in small quantum dots, where the electron wave function becomes weakly confined and extended much into the barrier region. When the electrons gradually lose confinement, the magnetic response of X- will transit gradually from the usual quadratic diamagnetic shift to a quartic dependence, and finally into a special paramagnetic regime with an overall negative energy shift. On the other hand, we purpose to study the coupling effect between single quantum dot and photonic crystal cavity, a method for designing H1 photonic crystal cavity is introduced to enhance its quality factor (Q factor). The highest theoretical Q factor of 120,000 is obtained. The Fourier transformation of field distribution shows that the enhancement arises from the component reduction of leaky mode. The Q-factor improvement has also been demonstrated experimentally with the highest value of 11700. Our design could be useful for studying light-matter interaction in H1 cavity as the mode volume only increases slightly. Finally, we successfully demonstrated the strong coupling effect in the H1 photonic crystal cavity embedded single InAs/GaAs quantum dot. Two polariton states arise from the hybridization of the cavity mode and quantum dot, which reflect in the alterations of observed emission characteristics, such as emission wavelength, full width half maximum and intensity. Via analysis, the strongest coupling effect occurs at about 37.75 K, while Rabi splitting is equal to 156.7 μeV.