探究V型缺陷與隨機合金擾動對於紅光氮化銦鎵發光二極體的影響

Abstract

隨著微發光二極體的尺寸不斷微縮，研究發現紅光磷化鋁鎵銦發光二極體的側壁表面複合效應加劇，由於載子遷移率高和等效質量輕，因此載子擴散得很快至側壁的缺陷進行複合，元件性能逐漸趨於劣勢；氮化鎵材料相對不易受尺寸、溫度變化限制，然而紅光氮化銦鎵發光二極體存在著晶格不匹配的問題，導致元件形成V型缺陷，以及產生不容忽視的量子侷限斯塔克效應，強大的壓電場引發更高的能障，使載子難以流入量子井進行複合。雖然V型缺陷包含非輻射中心，但載子可藉由V型缺陷傾斜面上的側壁量子井流進量子井，載子注入受限的狀況得以改善，啟動電壓也大幅下降。目前紅光氮化銦鎵發光二極體的效率約15∼25%，現今許多學者致力於找出提升效率的方法。

本篇論文除了探討V型缺陷，還有紅光量子井的數量和位置對於紅光氮化銦鎵發光二極體的影響，其中氮化銦鎵量子井有考慮現實情況中的隨機合金擾動。我們的模擬結果顯示：(1)若V型缺陷上的量子井的銦濃度較小，載子特別是電洞容易通過多重量子井，抵達底層的量子井，這代表載子主要從V型缺陷的側壁注入。(2)若以橘光量子井上下包夾紅光量子井，載子傾向流進量子井深度較深的紅光量子井，這將有助於工程師設計讓載子複合在品質更好的量子井來提高效率，實驗部份[1]也有相關的研究證實此趨勢。

With the chip size continuing to shrink for micro-LED applications, the sidewall surface recombination effect has been shown to be more severe in red AlGaInP LEDs. Since the carriers have higher mobility and lighter effective mass, they quickly diffuse into the sidewall and recombine at the defects. The device performance gets worse. On the other hand, indium gallium nitride (InGaN) material is now less dependent on the chip size and temperature. However, the red InGaN LEDs suffer from the lattice mismatch problem, which generates the V-defect in the device and the substantial Quantum Confined Stark Effect (QCSE). The piezoelectric polarization field induces more considerable barriers, which makes the carriers hard to flow into the quantum well (QWs) to recombine. Though V-defect includes a non-radiative recombination center, the carriers can inject into the QWs through the sidewall QW in the V-defects tilted plane. The current injection is improved, and the turn-on voltage drops significantly. To date, the efficiency of the red InGaN LEDs is around 15~25%. Many researchers are dedicated to increasing efficiency.

In addition to V-defects, the number and the position of red QWs are discussed about their influence on the red InGaN LEDs, considering the random alloy fluctuation that exists in reality. Our simulation results show that (1) if the indium composition of the V-defect sidewall QWs is more minor, The carrier, especially for the hole, is easier to cross the multiple QW and reach the bottom QW. This shows that carriers injected are mainly from the sidewall of the V-defect center. (2) If orange QWs sandwich the red QWs, the carrier tends to flow into red QWs since they are deeper. This help engineers to design carrier to recombine at better quality QW layers and improve efficiency. The result was reported experimentally in Ref. [1].