利用三維等效侷域量子位能模型分析合金擾動和應力對深紫外光發光二極體的影響

Abstract

此研究使用了包含應力變形的等效侷域量子位能模型。此模型是藉由省略k·p方法中的非矩陣對角位置貢獻，來減少計算所需時間，並達到在等效侷域量子位能模型中，考慮k·p方法中應力對不同價帶造成的影響之目的，因此可分別解出不同價帶的位能。此模型藉由價帶與不同導帶間的自發放光來算出橫向電場極化光、橫向磁場極化光及其極化比。本文藉由比較極化比之結果及趨勢說明:在使用應力變形的等效侷域量子位能模型後，由於多能帶位置已取得，且模擬上的極化比趨勢相近。因此，傳統上拿來計算多能帶位置及波函數的k·p方法可以被省略。包含應力變形的等效侷域量子位能模型在省略k·p方法之下計算出的極化比可被快速估計且模擬結果具有可信度。所以，本研究在優化結構時是在省略k·p方法計算下，使用包含應力變形的等效侷域量子位能模型。此外，在此研究的模擬結構下每步疊代可以省略大約47小時的時間。

在多量子井結構之深紫外線發光二極體的模擬上，由於高鋁情況下，氮化鋁鎵的電洞活化能高，在深紫外線發光波段，高鋁材料摻雜後的低電洞注入和高阻抗下注入的電洞流低，都將是導致內部量子效率下降的重要因素。此外，在低電洞注入下的高電子溢流情況也將使得內部量子效率進一步下降，因此本研究藉由3D模擬來優化量子能障結構及p型氮化鋁鎵來改善電洞注入以期達到降低電子溢流情形，並分析隨機合金擾動及應力造成的能帶變形如何對載子阻擋能力造成影響。

This study uses the strain-induced deform potential localization landscape(LL) model to do the simulation. To consider the strain effects, we applied the stain-induced deformation potential shift from the k·p equations into the LL model and solved different valence band states separately. It ignores the influences of the off-diagonal term in the k·p model and tries to accelerate the calculation of device results. With the model, the multi-band position corresponding to the different states will be obtained. According to the spontaneous light emission from the electron and the hole in different states, the transverse electronic (TM) polarized light, transverse magnetic (TE) polarized light, and the polarization ratio (PR) will be calculated. The comparison of the polarization ratio between the modified LL model and the k·p model shows a similar trend, which can be used to estimate the polarization ratio quickly. We only need to use the modified LL model for the optimized structures to obtain the final results. In addition, after removing the k·p method calculation, the calculation time will save around 47 hours per iteration under the simulation structure of this work.

For the UVC multiple quantum well simulation, due to the high activation energy in AlGaN with high Al, the low activated hole density and high resistance of hole current in the p-type AlGaN layer is a critical reason for the low internal quantum efficiency in UVC-LEDs. The severe electron carrier overflow under the low hole injection will further reduce the internal quantum efficiency. Hence, this study tries to reduce the electron carrier overflow by optimizing the structure of quantum barriers and the p-AlGaN layer with the 3D simulation method considering Al random alloy fluctuation. Then, the influence of random alloy fluctuation and the strain-induced band structure deformation will be analyzed and the optimized structure to improve the carrier-blocking ability will be discussed in this paper.