Collective Magneto-Optical Properties of Artificial Composite Materials Made From Semiconductor Nano-Objects
Le Minh Thu
|關鍵字:||磁光特性;半導體奈米物質;magneto-optical properties;semiconductor nano objects|
我們設計複合的分裂-連續模型去普遍性的模擬任意形態的半導體奈米物質的磁光響應，我們的普遍複合模型模擬被奈米物質侷限的電子與電洞的量子能階的同調操作，並且用實驗上全體磁光響應分析量測印證(包含反射、穿透、吸收)，這個操作是在外加磁場的情況下，我們的三維模型使我們可以施加任意方向的磁場模擬，這個技術的最大突破是可以建構任意形狀與尺寸的奈米物質並施加任意方向外加磁場。只要我們知道個別單一奈米物質的磁光響應，我們就可以使用此模型進行群體奈米物質的磁光響應模擬。我們藉由添加極化率參數來特徵化奈米物質的磁光響應，這個極化率包含穩態與動態部分，因此我們同時需要一個多階電動態與量子機制描述。穩態部分利用波松等式計算，動態部分(包含物質發光的能量與機率)利用量子機制計算，我們使用 K•P近似數值計算(包含 2+2 與 2+4非線性迴圈法的能帶模型)計算被奈米物質侷限的電子與電洞的能量與波函數。為了實現模型，我們考慮了非對稱量子點分子(包含兩個或者三個量子點)的電子能階的同相操作和一層分子結構的全體磁光特性，我們的模擬結果顯示了量子點分子的量子機制組態可以藉由監控橢圓儀結果觀察到，這個磁場橢圓儀資料清楚的展現量子點分子的量子機制資訊。
In this dissertation, we theoretically studied the collective magneto-optical properties of artiﬁcial composite materials made from semiconductor nano-objects such as quantum dot molecules and nano-rings. We present results of simulations on relations between quantum mechanical states in semiconductor quantum dot molecules and the magneto-optical response of embedded layers of these nano-objects. We also study the eﬀect of the inhomogeneous broadening on the magnetic response of ensembles of asymmetrical nano-rings and excitonic peaks in triple concentric nano-rings ensembles. We have generalized hybrid discrete-continuum model to simulate magneto-optical response of systems of embedded semiconductor nano-objects with arbitrary shapes. Our generalized hybrid model allows us to simulate the coherent manipulation of quantum states of electrons and holes conﬁned in nano-objects and monitor that by means of analysis of the collective magneto-optical response (reﬂectance, transmittance, absorbance) from the systems. The manipulation is performed by an external magnetic ﬁeld applied upon the systems. Our description is done in three-dimensions which allows us to consider arbitrary directions of the external magnetic ﬁeld. The great advantage of our approach is flexibility in modeling of systems with arbitrary shapes, sizes and directions of the external ﬁeld in contrast to most of the calculations done before. Using the generalized hybrid model the magneto-optical response of layers of semiconductor nano-objects can be found once we know the responses of individual nano-objects. In the hybrid description the response of a nano-object is characterized by the excess polarizability. This polarizability includes a static part and dynamic part. Therefore, our approach requires for a simultaneous multi-scale electrodynamic and quantum mechanical description. The static part is determined electromagnetically by solving the Poison’s equation. The dynamic part (requiring for energies and probabilities of the optical transitions in the object) is determined quantum mechanically. To calculate this part the energies and wave functions of electrons and holes conﬁned in the semiconductor nano-objects are obtained numerically within the k.p approximation including 2+2, and 2+4 band models by the nonlinear iterative method. To demonstrate our model we consider the coherent manipulation of the electronic states of asymmetrical quantum dot molecules (triple and double quantum dot molecules) and the collective magneto-optical properties of a layer of the molecules. Our simulation results show that changes in the quantum mechanical configuration of the quantum dot molecules can be observable by monitoring changes in the ellipsometric data obtained for layers made from them. The magnetoellipsometric data can reproduce an important and clear information on the quantum mechanics of the molecules. We proposed mapping method which allows us to eﬃciently simulate quantum mechanical properties of semiconductor nano-objects with variations of their sizes and shapes. Using our mapping method we have investigated the inhomogeneous broadening of magnetic response and optical properties of ensembles of nano-rings due to size and shape dispersion. In our method three-dimensional confinement potential is mapping the actual geometrical, structural, and material composition of nano-objects. Using this potential, we find energy states of electrons and holes confined in the nano-objects. Then we simulate the inhomogeneous broadening of the magnetic response and excitonic peaks of ensembles of nano-objects. Generally, our method can be applied to simulate the inhomogeneous broadening effect in ensembles of nano-objects with arbitrary shapes. However, in this dissertation, to implement our method, we perform simulations to explain in detail the temperature stability of magnetic response of asymmetrical nano-rings and the appearance of wide asymmetrical excitonic peaks in ensembles of concentric triple nano-rings. Our simulation results show that the amplitude of the differential magnetic susceptibility is sensitive to geometry and composition of semiconductor nano-rings. Because of the inhomogeneous broadening eﬀect the differential magnetic susceptibility of the ensembles of wobbled nano-rings demonstrates the temperature stable behavior. We also investigated the inhomogeneous broadening eﬀect on excitonic peak in triple concentric nano-rings ensembles. It has been shown that the broadening is preferably caused by variation of the inner height of the ring. The simulation results have reproduced and explained the appearance of the wide and asymmetrical excitonic peak in the experimental photoluminescence spectra. The calculated position of the excitonic peak in the optical spectrum is in good agreement with the experimental observation as well. We have managed to demonstrate that our mapping method is very efficient for simulation and modeling of magnetic and optical properties of ensembles of nano-rings with sophisticated shape. The calculation results for ensembles of nano-rings help us to explain and understand clearly experimental data.
|Appears in Collections:||Thesis|