GaN/AlGaN和InGaN/AlInGaN多量子井雷射二極體之模擬最佳化主動層研究

Abstract

本論文中，我們以理論模擬的方式探討紫外光氮化鎵/氮化鋁鎵半導體雷射的多重量子井主動層結構最佳設計分析以得到較小的臨界電流，並且討論其內部的元件物理機制。在模擬中，我們使用由加拿大Crosslight公司所發表的Lastip商用模擬軟體進行探討。模擬結果發現，當量子井個數是兩個或三個時且位障層使用鋁含量約在10~12%左右可以得到較小的臨界電流。形成最佳化結構的物理機制主要歸因於幾個不同的因素，包括電子溢流、載子分布不均、極化電荷造成的內建電場、以及光場侷限能力。我們研究量子井個數以及在位障層中不同的鋁含量對雷射特性的影響，這些元件內部的物理機制是需要被研究及了解，才能進一步設計出最佳化元件結構。 再者，我們也利用此模擬軟體來探究在氮化銦鎵雷射中氮化鋁鎵銦使用於位障層來消除 quantum-confined Stark effect (QCSE)。模擬結果發現，此四元材料的使用可以消除QCSE並且改善雷射的特性。由於四元材料可以經由不同鋁和銦的含量而具有不同組成。因此，我們也針對不同組成的氮化鋁鎵銦材料做最佳化理論分析並且討論其內部的物理機制。模擬結果顯示，氮化銦鎵/氮化鋁鎵銦雷射在位障層的鋁含量是15%及銦含量是18.8%時，會有最佳的主動層結構。同時，我們也討論了影響此元件效能的機制，分別是電子溢流、載子侷限、以及光場侷限的問題。

In this thesis, theoretical analysis for different active layer structures is performed to minimize the laser threshold current of the ultraviolet GaN/AlGaN multiple-quantum-well laser diodes by using the LASTIP simulation program developed by Crosslight. The simulation results show that the lower threshold current can be obtained when the number of quantum wells is two or three and the aluminum compositions in barrier layer is about 10~12%. This optimal structure is attributed to several different effects including electron leakage current, non-uniform carrier distribution, interface charge density induced by spontaneous and piezoelectric polarization, and optical confinement factor. These internal physical mechanisms are investigated by theoretical calculation to analyze the effects of quantum-well number and different aluminum compositions in barrier layer on laser threshold properties. These internal physical mechanisms should be investigated and understood to obtain the optimal device structure. Furthermore, we also perform the theoretical simulation to study the elimination of quantum-confined Stark effect (QCSE) on the InGaN/InGaN and InGaN/AlInGaN multiple-quantum-well (MQW) laser performance. The simulation results illustrate that the quaternary alloys used in the quantum-barrier layer can eliminate the QCSE indeed and also improve the performance of the laser diodes. Since different quaternary alloys can be obtained by varying aluminum and indium compositions, we optimize the quaternary AlInGaN barrier layer and investigate the internal physical mechanisms in this study. The InGaN/AlInGaN laser diodes with an active layer of x = 0.15 and y = 0.188 in the AlxInyGa1-x-yN barrier layer will be the optimized active layer structure due to the competition between three internal physical mechanisms, including the severe electron leakage current, carrier confinement in the quantum well, and optical confinement factor.