高效率氮化銦鎵發光二極體之主動區結構設計

Abstract

近年來，發光二極體由於其擁有極高的效率而成為最重要的固態光源，具有十足的潛力取代傳統光源。但在發展過程中，仍存在兩項最主要的問題，第一便是由於氮化鎵與藍寶石基板間存在很大的晶格常數差異，進而導致大量的差排缺陷出現，另一項則是在高電流注入下產生之效率下降(efficiency droop)的問題。 本研究的第一部分將要研究隨超晶格結構層數而改變的V型缺陷與元件發光效率的關係，此章分別製作10、15、30、60層超晶格之結構作為分析樣品，並從實驗的結過中證實V型缺陷的產生確實能夠有屏蔽載子進入差排缺陷的能力，而使效率提升，透過優化超晶格結構層數，在15層超晶格結構樣品中找到最好的屏蔽能力及內部量子效率。 第二部分，本研究展示了高效率的非對稱三角多重量子井結構發光二極體，非對稱結構能夠有效使載子分布更加平均並抑制歐傑非輻射複合，除此之外，鎵面方向的非對稱三角量子井結構還可降低內建極化效應對樣品的影響。從實驗結果鎵面方向的非對稱三角量子井結構在100mA的電流注入下僅有27%的效率下降，且相較於傳統對稱的垂直量子井結構在效率上及降低效率下降的表現分別有11.7%及31.1%的提升。

Recently, InGaN/GaN light emitting diodes (LEDs) have become the major elements in solid-state lighting, and because of their high luminescence efficiency, these LEDs are potential replacements for traditional lighting sources. However, there are two major problems limiting the performance of LEDs. First, due to the mismatch in the lattice constant between the GaN and sapphire substrate, high threading dislocation densities will occur during the epitaxial process. Second, as injection current increases, the quantum efficiency of InGaN/GaN LEDs decreases; this is the so-called ”efficiency droop” phenomenon that has become crucial in high-power operations. On the first part of this study, we investigated the relationship between the light emission efficiency of InGaN/GaN MQWs and V-shaped pits with varying superlattice(SL) layers. Then, InGaN/GaN SL layers with different periods ranging from 0, 10, 15, 30 and 60 were grown on the n-GaN layer. The experimental result show the formation of V-shaped defect can assist the InGaN MQWs to resist the carriers into the nonradiative recombination centers, lending to the enhancement of the emission efficiency. By properly controlling the V-shape defect formation can facilitate to achieve high efficiency LEDs on sapphire substrates. For the optimal LED structure with 15 pairs SLS, it has largest energy barrier high and the internal quantum efficiency On the second part, we demonstrated high efficiency InGaN/GaN light emitting diodes (LEDs) with asymmetric triangular multiple quantum wells (MQWs). Asymmetric triangular MQWs not only contribute to uniform carrier distribution in InGaN/GaN MQWs but also yield a low Auger recombination rate. In addition, asymmetric triangular MQWs with gallium face-oriented inclination band profiles can be immune from the polarization charge originating from typical c-plane InGaN/GaN quantum well structures. In the experiment, the gallium face-oriented asymmetric triangular MQWs structure exhibited a 27.0% efficiency droop at 100 mA, which accounted for an 11.7% efficiency improvement and a 31.1% droop reduction compared with symmetric square quantum well structure LEDs.